A comparison of gingival marginal adaptation and surface ...

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Theses and Dissertations

2014

A comparison of gingival marginal adaptation andsurface microhardness of class II resin basedcomposites (conventional and bulk fill) placed inlayering versus bulk fill techniquesMohamed Ahmed Anis AbouelnagaUniversity of Iowa

Copyright 2014 Mohamed Ahmed Abouelnaga

This dissertation is available at Iowa Research Online: http://ir.uiowa.edu/etd/1281

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Recommended CitationAbouelnaga, Mohamed Ahmed Anis. "A comparison of gingival marginal adaptation and surface microhardness of class II resin basedcomposites (conventional and bulk fill) placed in layering versus bulk fill techniques." MS (Master of Science) thesis, University ofIowa, 2014.http://ir.uiowa.edu/etd/1281.

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A COMPARISON OF GINGIVAL MARGINAL ADAPTATION AND SURFACE

MICROHARDNESS OF CLASS II RESIN BASED COMPOSITES

(CONVENTIONAL AND BULK FILL) PLACED IN LAYERING VERSUS BULK

FILL TECHNIQUES

by

Mohamed Ahmed Anis Abouelnaga

A thesis submitted in partial fulfillment

of the requirements for the Master of

Science degree in Operative Dentistry

in the Graduate College of

The University of Iowa

August 2014

Thesis Supervisors: Professor Gerald Denehy Professor Steven Armstrong

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Copyright by

MOHAMED AHMED ANIS ABOUELNAGA

2014

All Rights Reserved

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Graduate College

The University of Iowa

Iowa City, Iowa

CERTIFICATE OF APPROVAL

_______________________

MASTER'S THESIS

_______________

This is to certify that the Master's thesis of

Mohamed Ahmed Anis Abouelnaga

has been approved by the Examining Committee

for the thesis requirement for the Master of Science

degree in Operative Dentistry at the August 2014 graduation.

Thesis Committee: ___________________________________ Gerald Denehy, Thesis Supervisor

___________________________________ Steven Armstrong, Thesis Supervisor

___________________________________ Deborah S Cobb

___________________________________ Rodrigo Maia

___________________________________ Fang Qian

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To my parents, for their unconditional love and encouragement.

To all my family and friends, who in one way or another participated on this journey.

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ACKNOWLEDGMENTS

I would like to express my deepest gratitude to my mentor, Dr. Gerald Denehy, an

example of a person and a professional, who I had great pleasure to work with. Throughout

my thesis project he guided me and helped me make the most appropriate decisions. My

sincere thankfulness also goes to my thesis committee, who’s support, encouragement and

insightful comments were fundamental for the completion of my work. I would like to

deeply thank Dr. Steven Armstrong, my co-mentor in this project, for sharing his

phenomenal knowledge in the field of adhesion and marginal adaptation field of resin based

composites. Thanks for helping me to develop the methodology for my research project

and my critical thinking throughout these years. Thanks also to Dr. Deborah Cobb, who as

program director was always supportive and willing to help not only in my thesis project

but also in the entire master program. Special thanks goes to Dr. Fang Qian for providing

excellent and detailed statistical analysis. I also want to thank Dr. Rodrigo Maia for his

friendship and suggestions in my thesis project. Thanks to all my committee members for

the significant guidance on how to report the results in my thesis and continuous

suggestions to improve the quality of my research project and thesis.

I would like to acknowledge the manufacturers for their donation of materials:

Ivoclar Vivadent, Dr. Shashikant Singhal who was always there to help me with the

materials support and even to develop some steps of my methodology.

My gratitude is also due to all members of the Operative Dentistry Department,

faculty, staff and graduate students, who directly or indirectly helped me going through my

master program and in finishing my thesis. Thanks for making my life easier and my time

in Iowa enjoyable.

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TABLE OF CONTENTS

LIST OF TABLES ................................................................................................... vii

LIST OF FIGURES ................................................................................................ viii

LIST OF ABBREVIATIONS ................................................................................... xi

CHAPTER I INTRODUCTION ........................................................................... 1

Purpose of the study ................................................................................ 3

Research Hypotheses .............................................................................. 3

CHAPTER II LITERATURE REVIEW ............................................................... 5

Tooth Composition ................................................................................. 5

Enamel and Dentin Composition ........................................................ 5

History and Evolution ............................................................................ 8

Chemical Composition ......................................................................... 10

Classifications ................................................................................... 11

Posterior Restorations ........................................................................ 13

Adhesion and Bonding ......................................................................... 13

Polymerization Reaction ...................................................................... 20

Dental Photopolymerization .............................................................. 21

Polymerization Shrinkage ................................................................. 23

Mechanical and Physical Properties ..................................................... 24

Surface Micro-hardness ..................................................................... 25

Cavity Designs for Class II Resin Based Composites .......................... 29

Resin Based Composite Failures Related to the Class II Cavity

Design ................................................................................................... 31

Polymerization Shrinkage and C-factor ............................................ 31

Marginal Adaptation of Resin Based Composites (Marginal Gaps) . 33

Methods Introduced to Overcome Resin Based Composite Failures

with

Class II Restorations ............................................................................. 36

Different Techniques of Placement ................................................... 37

Incremental Placement Technique ................................................ 37

Bulk Placement Technique ............................................................ 39

Tetric EvoCeram and Tetric EvoCeram Bulk Fill Resin Based

Composites .................................................................................... 41

Comparing the Degree of Polymerization Shrinkage and

Marginal Adaptation using One Type of Resin Based

Composite Placed with Different Techniques (Layering versus

Bulk) ............................................................................................. 42

Comparing the Degree of Polymerization Shrinkage and

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Marginal Adaptation using Different Types of Resin Based

Composites Placed with Different Techniques (Layering versus

Bulk) ............................................................................................. 43

Degree of Polymerization Shrinkage and Cuspal Deflection of

Teeth using Different Placement Techniques (Layering versus

Bulk) in Class II Posterior Cavities .............................................. 49

Resistance to Fracture ................................................................... 56

Creep Tendency ............................................................................ 57

Cavity Liners ....................................................................................... 59

Snowplow Technique.......................................................................... 60

Pre-heated Resin Based Composites ................................................... 60

Summary ............................................................................................... 62

CHAPTER III MATERIALS AND METHODS ................................................ 64

Overview ............................................................................................... 64

Research Question ............................................................................ 66

Methodology ......................................................................................... 66

Independent Variables ..................................................................... 66

Standardized Criteria ....................................................................... 66

Dependent Variables ........................................................................ 67

Experimental Groups ............................................................................ 67

Teeth Preparation .................................................................................. 68

Cavity Design................................................................................... 69

Restorative Procedure ........................................................................... 71

Matrixing of the Preparation ............................................................ 71

Adhesion Procedures ....................................................................... 73

Restorative Material Placement ....................................................... 76

SEM Sample Preparation and Image Capture ...................................... 79

Randomization and Blinding ................................................................ 83

Gingival Margins Evaluation ................................................................ 83

Scoring Criteria ................................................................................ 86

Surface Micro-hardness Testing ........................................................... 87

Pilot Study ............................................................................................ 89

Power Analysis ................................................................................ 90

Statistical Analysis ................................................................................ 90

Variables .......................................................................................... 91

Overall Statistical Methods ................................................................... 91

CHAPTER IV RESULTS .................................................................................... 93

Difference in Gingival Marginal Gap Scores between the Four

Tested Groups at the Distal and Mesial Surfaces ................................ 93

Difference in Gingival Marginal Gap Scores between the Mesial and

Distal Surfaces of Each Group of the Four Groups .............................. 95

Difference in the Internal Surface Micro-hardness (KHN) Scores

between the Three Different Layers (Depths) Tested of Each Group

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of the Four Tested Groups at the Distal and Mesial Surfaces ............. 97

Group 1 (bulk fill RBC, placed in bulk) ............................................ 97

Group 2 (bulk fill RBC, placed in layers) ........................................ 100

Group 3 (conventional RBC, placed in layers) ................................ 102

Group 4 (conventional RBC, placed in bulk) .................................. 105


between the Four Tested Groups at the Distal and Mesial Surfaces .. 107


between the Mesial and Distal Surfaces of Each Group of the Four

Tested Groups ..................................................................................... 110

Statements on Research Hypotheses .................................................. 112

Typical SEM Images of Tested Groups .............................................. 113

CHAPTER V DISCUSSION ......................................................................................... 117

Light Curing Source and Radiant Energy Exposure ........................... 117

Radiant Energy Exposure Standardization in Air ............................ 118

Radiant Energy Exposure Measurement in Resin Based

Composites ..................................................................................... 119

Polymerization Reaction and Depth of Cure ..................................... 121

Quantitative Marginal Analysis ......................................................... 122

Experimental Procedures .................................................................... 124

Replica Technique .......................................................................... 124

SEM Data Interpretation ................................................................. 124

Internal Surface Micro-hardness ..................................................... 125

Limiting Psychomotor Skills Variability ............................................ 126

Effect of Resin Based Composite Type and Placement Technique

on the Gingival Marginal Adaptation ................................................. 127

Effect of Resin Based Composite Type and Placement Technique

on the Internal Surface Micro-hardness .............................................. 130

Standardization of Procedures ........................................................... 133

Limitations of the Study ..................................................................... 134

Strengths of the Study ......................................................................... 135

Clinical Significance .......................................................................... 135

Future Research Suggestions .............................................................. 135

CHAPTER VI CONCLUSION ......................................................................... 137

APPENDIX ………………………………………………………………………………...…………….138

Descriptive Statistics for External Marginal Gap and Internal

Surface Micro-hardness by RBC Groups………...………...……..…138

Gingival Marginal Gaps of Each Image of the Seven Images Taken

For the Margins tested on the Mesial and Distal of Each Tooth ..…..141

REFERENCES ...................................................................................................... 142

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LIST OF TABLES

Table

1. Composition of resin based composites (Tetric EvoCeram system) ................... 65

2. Syntac bonding system composition (Ivoclar Vivadent) .................................... 73

3. The light curing time for each group ................................................................... 77

4. Scoring criteria illustrated with SEM images. ..................................................... 84

5. Results of one-way ANOVA for external marginal gap at distal surface. ........... 93

6. Results of one-way ANOVA for external marginal gap at mesial surface. ......... 94

7. Comparisons of External marginal gap among four resin composite restorative groups. .................................................................................................................. 95

8. Number of gap free margins and voids in the different restorative groups ......... 97

9. Comparisons of internal surface micro-hardness among three surface levels

within Bulk RBC placed in bulk technique (BB) group ......................................98


within Bulk RBC placed in two layers (BL) group ...................................... ...101


within conventional RBC placed in two layers (CL) group ............................103


within conventional RBC placed in bulk technique (CB) group .....................106

13. Results of one-way ANOVA for internal surface micro-hardness at distal

surface. .......................................................................................................... ...108

14. Results of one-way ANOVA for internal surface micro-hardness at Mesial Surface. ............................................................................................................ 109

15. Comparisons of internal surface micro-hardness among four resin composite

restorative groups .............................................................................................111

16. Radiant energy exposure standardization in air…………………...……….…119

17. Radiant energy exposure measurement in resin based composites…..….……120

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LIST OF FIGURES

Figure

1. A flow chart of the step by step protocol of the study ......................................... 68

2. Flattened teeth on the occlusal, mesial and distal surfaces. ................................. 69

3. CNC Specimen Former machine used for standardizing cavity preparations.

b) mounted teeth for the CNC machine. c) standardized cavity preparations on

the mesial and distal of each tooth. ...................................................................... 70 4. a) teeth placed in putty for restorative procedures. b) placement of a tofflemire matrix band between both teeth. c) pushing teeth tight with a C-clamp.............. 72

5. a) Tetric EvoCeram Bulk Fill, b) Tetric EvoCeram filling material .................... 74

6. Ultra etch (UltraDent Products, Inc) .................................................................... 75

7. Syntac bonding system ........................................................................................ 75

8. Accurate measurement of the resin based composite increments ........................ 76

9. Restored tooth on the mesial and distal ............................................................... 78

10. a) impression of the margins b) Tooth out of the impression material.

c) replica after complete setting from the impression ........................................ 80

11. Gold sputter coating the replica for SEM examination. .................................... 81

12. The epoxy resin replica after gold sputtering .................................................... 81

13. a) The whole margins showing under magnification of 30X. b) the seven

images stitched together at 200 X using computer software. ............................ 82

14. a) Measuring the width of the restoration Buccolingually and marking with

Pencil at point of 1.99mm to section in this area. b) re-assuring

measurements and sectioning of teeth using the Isomet machine. .................... 87

15. a) teeth sectioned (occlusal view), b) teeth sectioned (Proximal view). ............ 88

16. Comparison of external marginal gaps between the four groups

(distal surface) .................................................................................................... 94

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17. Comparison of external marginal gaps between the four groups (mesial

surface).........................................................................................................…..94

18. Comparison of external marginal gaps between the mesial and distal surfaces of the four groups ............................................................................................... 96

19. Comparison between the three surface levels of internal surface

micro-hardness in the BB group (distal surface)…....……….……………......99


micro-hardness in the BB group (mesial surface) .............................................. 99


micro-hardness in the BL group (distal surface) .............................................. 101


micro-hardness in the BL group (mesial surface)……..………...……………102


micro-hardness in the CL group (distal surface)……………………………..104


micro-hardness in the CL group (mesial surface)...………..…………..……104


micro-hardness in the CB group (distal surface) ............................................. 106


micro-hardness in the CB group (mesial surface)………………………...….107

27. Comparison of the internal surface micro-hardness between the four groups

tested (distal surface).………….......................................................................109

28. Comparison of the internal surface micro-hardness between the four groups

tested (mesial surface)……………………………………………...….…..…109

29. Comparison of internal surface micro-hardness between the mesial and distal

surfaces of the four groups…………………..…………...…...…………..….111

30. Typical SEM picture of group 1 (bulk RBC placed in bulk, BB) gingival

Marginal interface under magnification of 200X.............................................113

31. Typical SEM picture of group 2 (bulk RBC placed in layers, BL) gingival

Marginal interface under magnification of 200X……………………………114

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32. Typical SEM picture of group 3 (conventional RBC placed in layers, CL)

Gingival marginal interface under magnification of 200X………..…………115

33. Typical SEM picture of group 4 (conventional RBC placed in bulk, CB)

Gingival marginal interface under magnification of 200X…………..…..…..116

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LIST OF ABBREVIATIONS

RBC: Resin based composite

BB: Bulk Fill RBC, placed in bulk technique

BL: Bulk Fill RBC, placed in layering technique

CL: Conventional RBC, placed in layering technique

CB: Conventional RBC, placed in bulk technique

CNC Specimen Former: Computer numerically controlled specimen former

SEM: Scanning electron microscope

LED: Light emitting diode

QTH: Quartz tungsten halogen

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CHAPTER I

INTRODUCTION

In recent years, major advancements in restorative materials have been made in the

field of dentistry. These innovations have included changes in restorative materials,

instruments utilized in their manipulation and placement and, more importantly, the

methods of diagnosing, treatment planning, and preparing and restoring teeth. A material

that has played a very important role in these changes is resin based composite.

Advances in RBC materials and bonding systems have effectively changed many

of the principles for cavity preparation; from that of extension for prevention to preserving

tooth structure and using a minimally invasive technique according to the caries extension

(Summitt 2006), In addition to conservation, RBC’s have other provided advantages

including reinforcement of tooth structure and patient esthetics. Although originally used

primarily in the anterior teeth, improved physical properties and patient demand for

esthetics have greatly increased their uses in Class I and Class II restorations. RBC

restorations have now become the most commonly used direct restorative material placed

by dentists.

Along with their positive properties, RBC’s also exhibit certain disadvantages.

Marginal leakage is a major concern and cause of many of failures. A major reason for

marginal leakage is polymerization shrinkage (Hickel and Manhart 2001) which is present

in all RBC’s. Current RBC’s including flowable types exhibit a volumetric polymerization

shrinkage ranging from less than one to six percent (Kleverlaan and Feilzer 2005). Potential

for the effect of shrinkage can be determined by the C- Factor, the ratio is of bonded to

unbonded tooth surfaces. As the C-Factor increases, stresses on RBC’s and the probability

of marginal leakage also increased (Feilzer, De Gee et al. 1987). The C-Factor is considered

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to be higher in posterior cavity preparations because their design often results in an increase

in the ratio of bonded to unbonded walls, (Davidson and Feilzer 1997).

Gingival cavo-surface margins of Class II restorations can be an early area of failure

(Moffa 1989). Possible causes include limited access of proximal boxes making the

placement of the material more challenging, insufficient polymerization of the RBC at the

gingival wall, and the high C-Factor characteristic of the box shape and the adhesive

bonding to the cervical tooth structure. This contribute to the increase in polymerization

shrinkage stresses during the setting reaction of the material (Sabatini 2007).

Many studies have looked at methods to improve marginal adaptation and reduce

the rate of polymerization shrinkage. These include layering techniques (Feilzer, De Gee

et al. 1987, Usha, Kumari et al. 2011), placement of liners (Chuang, Jin et al. 2004), heating

the RBC and pressure with two different RBC’s (Snow-plow technique) (Opdam, Roeters

et al. 2003, Chuang, Jin et al. 2004). Most of these studies have been done with

conventional RBC’s.

Although conventional RBC’s have typically been placed in layers not exceeding

2mm thick, the advent of newer high intensity lights, and the recent introduction by

manufacturers of modified resin systems which claim bulk cure up to 4 mm may offer

advantages to dentists in terms of simplicity and speed of Class II RBC placement. It is

important however with these new bulk fill systems, that the physical properties, marginal

adaptation and degree of conversion of the RBC restoration are not negatively affected.

More research is needed in this area before the products can be fully endorsed.

Studies have shown that the depth of cure and the degree of hardness was a direct

indication of the degree of polymerization of the RBC systems (Ferracane and Greener

1984, Ferracane 1985, DeWald and Ferracane 1987). Many of these studies accepted the

method of knoop hardness number (KHN) testing as an accurate indirect measurement of

the hardness of the RBC’s (Ferracane 1985).

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Purpose of the Study

The purpose of this study was to compare the techniques of layering versus bulk

placement with a conventional RBC and a bulk fill RBC. Two areas were to be examined.

The first area was polymerization shrinkage as exhibited by the marginal adaptation of the

RBC to the gingival cavo-surface margin of the restorations. The second area was

determination of the degree of conversion measured by Knoop hardness numbers (KHN)

at different levels (depths) of the restoration.

Research Hypotheses

The five main null hypotheses proposed in this study were:

1) There is no difference in gingival marginal adaptation among different groups

restored with RBC (bulk fill and conventional types) placed in bulk or in

layering technique at the mesial and distal surfaces

2) There is no difference in gingival marginal adaptation between the mesial and

distal surfaces within each group restored with RBC (bulk fill and conventional

types) placed in bulk or in layering technique

3) There is no difference in the internal surface micro-hardness (KHN) among the

three different levels of measurements within each group restored in RBC (bulk

fill and conventional types) placed in bulk or in layering technique on the mesial

and distal surfaces

4) There is no difference in the internal surface micro-hardness (KHN) among

different groups restored with RBC (bulk fill and conventional types) placed in

bulk or in layering technique at the mesial and distal surfaces

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5) There is no difference in the internal surface micro-hardness (KHN) between

the mesial and distal surfaces within each group restored with RBC (bulk fill

and conventional types) placed in bulk or in layering technique

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CHAPTER II

REVIEW OF LITERATURE

Tooth Composition

Enamel and Dentin Composition

Enamel is the hardest and most mineralized tissue found in humans (AR 1985). Its

main component is inorganic (96% by weight and 86% by volume) composed of

hydroxyapatite crystals. Enamel also has a small volume of organic matrix in addition to

4% to 12% water which can be found intercrystalline and in the micropores of enamel rods.

These channels form some sort of communication with the pulpal tissue and the dentinal

tubules (Summitt 2006). Enamel has the property of brittleness due to the fact that its

inorganic content is high. Enamel is non vital and insensitive, therefore regeneration is

impossible after structure loss (AR 1985). Enamel is arranged in prisms or rods which are

parallel to each other but perpendicular to the tooth surface (Summitt 2006). The

interprismatic substance is found between these rods. Maturation of enamel and its

components results in increased mineral content which leads to high resistance against

demineralization (Lopes, Thys et al. 2007). Enamel surface acts as a semi-permeable

membrane where it has the ability to exchange substances and components with the outer

environment. Therefore fluoride containing water and tooth pastes result in the diffusion

of fluorides into the enamel structure to form fluoroapatite crystals which are more resistant

to demineralization. When teeth become dehydrated during mouth breathing or rubber dam

isolation, the color becomes whiter as the micropores lose water, however the condition is

reversible once the teeth are rehydrated. Teeth discoloration and darkness with aging may

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be attributed to increased translucency of enamel or accumulation of trace elements in the

enamel structure or even the sclerosis of the dentin structure (Summitt 2006).

Normally the outer surface of the enamel layer is hyper-mineralized (Albers 2002).

The Striae of Retzius are found also in the enamel where they run perpendicular from the

dentino-enamel junction to the outer surface of enamel creating a parallel pattern of lines

which appear over the surface of these striae called perikymata. These striae result from

the formation of enamel and may represent growth lines (Heymann, Swift et al. 2012).

Caries in enamel is initiated by bacterial degradation of carbohydrates in the mouth where

the PH of the oral cavity is decreased and acidity is increased. Caries is caused as result of

a demineralization process of enamel due to the under-saturation of minerals and their

diffusion out of the enamel and insufficient remineralization (Featherstone 2008). Five

different zones can be seen in enamel lesions which are; 1) surface zone (less than 5%

mineral loss), 2) body of the lesion (5%-30% mineral loss), 3) dark zone (2%-4% mineral

loss), 4) translucent zone (1% mineral loss) and normal enamel (Hiremath 2011).

Dentin is the structure underlying the enamel which acts as a cushion for the brittle

enamel. It is more elastic as its inorganic content is less than (50% by volume) and its

organic content is 30% by volume. The organic phase in dentin is composed of around 90%

type one collagen and 10% non-collagen protein. Dentin consists primarily of dentinal

tubules extending from the pulp to the dentino-enamel junction (Heymann, Swift et al.

2012). These tubules are more dense and wider towards the pulp (45,000/mm and 2- 2.8

um wide) and less dense (20,000/mm2) and narrower (0.8 um) closer to the dentino-enamel

junction (Summit third edition Quintessence, 2006). The dentinal tubules contain the

dentinal fluids and odontoblasts which help in formation of dentin and pulp and are

considered an extension of the pulp morphology. The dentin is heterogeneous unlike

enamel (homogenous) and is composed of peritubular and intertubular dentin. Peritubular

dentin is hypermineralized whereas the intertubular dentin is less mineralized and contains

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higher collagen content (Summitt 2006). The permeability of the dentin varies depending

on the area of the tooth surface. The coronal dentin is much more permeable compared

with the root dentin; also there are some differences in permeability within the coronal root

dentin. The permeability of dentin mainly depends on the diameter and thickness of the

remaining dentin. Dentinal tubules near the pulp are numerous, short and have large

diameters making deep dentin a less effective pulpal barrier compared with the superficial

dentin (Heymann, Swift et al. 2012). This difference in permeability makes bonding of

RBC’s different than enamel (Pashley 1989). The smear layer is a layer created during

preparation of a cavity using hand or rotary instruments. The thickness of this layer can

range from 1um-2um (Pashley 1992). Adhesion to enamel is much easier than adhesion to

the dentin substrate as enamel is made primarily from hydroxyapatite crystals with high

surface energy where dentin is composed of two different substrates, hydroxyapatite and

collagen, with low surface energy (Heymann, Swift et al. 2012). When teeth are prepared,

cutting debris is deposited on the surface of the prepared cavity forming what is known as

the smear layer. Removal of this layer is recommended to achieve a good bond between

the RBC and dentin. The removal of the smear layer is mainly done by etching of the dentin

with phosphoric acid (Summitt 2006). The process in the formation of a carious lesion in

dentin is not different than enamel as the demineralization process occurs in the presence

of bacteria and fermentable carbohydrates. The layers of carious lesions in dentine are; 1)

outer infected dentine (cavitated, irreversible) 2) turbid layer (affected dentine, reversible)

3) transparent layer (affected dentine, reversible) and 4) sub-transparent (affected dentine,

reversible) (Hiremath 2011).

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History and Evolution

Dental materials have undergone major changes in properties and characteristics.

(Buonocore 1955) greatly enhanced the development of RBC’s by recommending acid

etching of enamel prior to placement of adhesive and RBC restorative material (Bowen

1982). These new techniques changed a key principle of G.V Black which was extension

for prevention (Black 1917). In addition these advancements in adhesive dentistry made

dentists depend more on adhesion rather than the mechanical means for retention. Cavity

preparation became more conservative and defect specific, preserving more tooth structure

(Bowen 1982).

Silicates were invented in 1878 and these materials are considered to be the first

tooth colored restorative materials invented for esthetic dentistry (Heymann, Swift et al.

2012). This material had many disadvantages such as, high coefficient expansion and

contraction, low color stability and weak adhesion to tooth structure. Thus researchers

sought a better material with greater physical and mechanical properties (Bowen 1956).

RBC’s were developed in the 1960's and offered a large esthetic advancement (Schulein

2005). RBC’s later became known as reinforced polymers. Early RBC’s were introduced

as a base and catalyst which were mixed together to start a chemical reaction and were

called self-cured RBC’s. These early types also had limitations such as incorporation of

voids and air bubbles while mixing, which directly affected the esthetic and the mechanical

outcome of the restorations. In the 1970's, new RBC’s were developed that became

activated by ultraviolet wavelengths (UV). Subsequent improvements and developments

led to curing RBC’s using visible light. This curing method is now used widely in dental

practices (Kwon, Bagheri et al. 2012)

Early RBC’s were used primarily for restoring anterior restorations because of their

large filler particles and resin content which had significant wear in the oral cavity. These

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properties contraindicated them for use in high stress bearing areas such as posterior Class

I or II cavities (NJM 1997). Researchers worked to enhance the filler particle size and

volume of RBC’s to improve their functional and chemical properties. Developments were

made in the filler particle size, volume, shape and distribution which resulted in improved

physical, mechanical and functional properties (Moszner 2007). Dentists increasingly used

these new types with modified filler structure in high stress bearing areas such as posterior

teeth after many articles and studies were published testing those materials under different

stress and load conditions and confirming the success of these restorations (Letzel 1989,

Rowe 1989, Qvist, Johannessen et al. 1992).

Fillers added to dental RBC’s improve the translucency, reduce the coefficient of

thermal expansion and polymerization shrinkage of the RBC; and make the material harder,

denser, and more resistant to wear. The addition of fillers has a maximum limit where by

adding more than these limits the material may become too viscous for clinical use

(Summitt 2006). RBC may exhibit a wide range of filler particle size which affects the

properties of these restorations and indications for their use. This broad spectrum of

properties and clinical application gives versatility to the material. Current RBC restorative

materials provide patients with improved physical properties as well many options in shade

and opacity, providing highly esthetic and functional restorations.

Bonding to tooth structure not only allowed cavity preparations to become defect

specific, but also enhanced the mechanical properties of the restoration and tooth structure.

Bonded RBC’s reduce the chance of cuspal fracture compared to other restorations such as

amalgam (Roeters, Shortall et al. 2005). Retention of restorations also was improved by

bonding (Hinoura, Setcos et al. 1988). RBC’s have low thermal conductivity and electrical

conductivity decreasing sensitivity and post-operative pain. The majority of the

restorations are radiopaque making it easier to differentiate them from tooth structure in

radiographs.

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RBC development has greatly affected the field of dentistry. Many problems and

limitations were overcome, but some limitations still remain that pose problems for

clinicians and patients. In order to better understand these problems and the methods

proposed to overcome them, we must first understand the chemistry and the basic

composition of these tooth colored restorations and the mechanism of bonding to tooth

structure.

Chemical Composition

RBC’s are made up of four main components; the polymer organic matrix, filler

particles, coupling agents and the initiator. The polymer matrix is the main component of

RBC’s to which the other components are added. Inorganic filler particles increase the

mechanical and physical properties of the RBC. RBC’s have high mechanical properties

and stability because of the good bond formed between resin matrix and the inorganic filler

particles using a silane coupling agent (Heymann, Swift et al. 2012). Filler particles are

coated with silane before mixing them to the unreacted organic matrix. The purpose of the

coupling agent is to transfer stresses to the particles in order to improve strength and

mechanical properties of RBC’s (Pierre 2011). RBC’s are supplied in many consistencies

and viscosities. The degree of viscosity is directly affected by the shape, content and size

of the resin matrix and filler particles (Lee, Um et al. 2006).

Most RBC’s have matrices based on the bis-GMA (bisphenol-A-glycidyl

methacrylate) resin while some others use UDMA (urethane dimethacrylate) and still

others use a combination of these two monomers. Generally bis-GMA is highly viscous,

so in order to increase the handling properties in clinical practice, lower molecular weight

diluents are added called TEGDMA (triethylene dimethacrylate). Other materials are also

used as diluents such as the EGDMA ethylene glycol dimethacrylate to decrease viscosity

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(Peutzfeldt, 1997). Usually 75% bis-GMA is used in combination with 25% TEGDMA in

order to get a good consistency of the material for application.

The origin of fillers can be from triflouride, ytterbium, aluminum oxide, silicon

dioxide, quartz and glass and colloidal silica. The microfine particles are derived from the

colloidal silica where the fine particles are driven from glass and quartz. The smaller sized

filler particles have shown better polishing properties than the large sized irregular filler

particles (Marghalani 2010).

Classifications

RBC’s have been classified in a variety of methods to include by filler content and

particle size. Five main groups have been classified as macrofill, microfill, fine particle,

nanofill and hybrid RBC’s. Differences in the filler content and resin matrix affect the

viscosity of the material and make possible the flowable and packable RBC’s (Heymann,

Swift et al. 2012).

The first RBC type was introduced in the 1960's and was known as, traditional or

macrofill RBC. These RBC’s had large filler particles with average size of 8 um and high

filler loading (75%-80% by weight) which produced high amounts of wear and a rough

surface. In the 70's, microfill RBC’s (microfine) were introduced with very small particle

size of 0.04-0.01um resulting in smoother surfaces and better polishing properties, Fillers

were 35%- 60% by weight. However the microfill RBC’s exhibited lower mechanical and

physical properties and more of a tendency for chipping. Hybrid RBC’s were introduced

to try to combine the high mechanical properties of the macrofill RBC’s and the smooth

surface of the microfills and have replaced the macrofill RBC’s. These materials have high

filler content (75%-85% by weight) and an average filler size of (0.4-1um) that provide

good mechanical and physical properties. The latest generation of RBC’s developed was

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the nanofill RBC’s. Nanofills contain extremely small sized fillers (0.005um-0.01um). It

is common for hybrid RBC’s to incorporate some nano sized filler particles into their

composition to optimize the material further. High filler content can be incorporated in the

nanofills which results in good physical properties and improved esthetics. These nanofills

and nanohybrids have become the most commonly used RBC’s in dentistry due to their

enhanced mechanical and esthetic properties (Heymann, Swift et al. 2012).

More recently two types of RBC’s have been introduced into the market, the

packable and flowable RBC’s. Packable RBC’s were introduced as having similar

condensing capabilities to amalgam. Methods were used to increase the viscosity of these

RBC’s by increasing the filler content and size, adding glass fibers or modifying the matrix.

The aim of these materials was to have similar packing properties as amalgams providing

greater ease in restoring proximal contacts compared to other RBC material. Packable

RBC’s failed to accomplish this goal because of the increased viscosity of the material

(Heymann, Swift et al. 2012).

Flowable RBC’s have less filler content (44% to 54% by weight) and are less

viscous than regular RBC’s. Flowable RBC’s exhibited lower mechanical properties due

to the reduced filler content. Flowable RBC’s are mainly used as sealants or cavity liners

and also to seal gingival margins in deep Class II proximal boxes under conventional

RBC’s. Recently new types of flowable RBC’s have been advocated for use with a bulk

filling technique to fill the entire cavity with a 4mm thick increment. The manufacturers

claim decreased polymerization shrinkage due to the low elastic modulus of these materials

(Heymann, Swift et al. 2012).

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Posterior Restorations

Although in the past there has been controversy regarding the use of RBC’s in

posterior teeth, studies have shown that the longevity of posterior RBC’s is acceptable. A

study reported that the failure of amalgam annually was 0 % to 7% and 0% to 9% for

RBC’s (Hickel and Manhart 2001). (Roeters, Shortall et al. 2005) also reported that the

failure rates of RBC’s were similar to or less than amalgam. On the other hand, a

retrospective study by (Opdam, Bronkhorst et al. 2010)comparing the longevity of

amalgam and RBC restorations after 12 years showed that the RBC restorations had less

failure rates in the low caries risk group, but increased failure with the high caries risk

group. There was not enough evidence to predict the high failure rates of RBC’s compared

to the amalgam restorations. Authors also stated that there was not enough evidence of the

adverse toxic effects of mercury on the amalgam patients (Rasines Alcaraz, Veitz-Keenan

et al. 2014).

Adhesion and Bonding

Bonding of RBC’s depends on the chemical structure of both enamel and dentin.

As mentioned before enamel is more mineralized having higher inorganic content than

dentin. Dentin is less mineralized having more organic content and fluid compared to

enamel. As a result, bonding to enamel is stronger and more durable than bonding to dentin.

Dentin is unlike enamel in that its structure is heterogeneous having different dentinal

components throughout the whole crown. Many developments in adhesive systems were

made to overcome the problems of dentin bonding and to have more durable and

predictable restorations (Liu, Tjaderhane et al. 2011). The main two approaches used for

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bonding are etch and rinse and self-etching systems. Both of these systems can come in

different forms and combinations (Heymann, Swift et al. 2012).

Michael Buonocore in 1955 discovered a way to create micropores in enamel and

dentine for bonding (acid etching). By using phosphoric acid on an in-vitro tooth he greatly

increased the bond between acrylic restoration and enamel, Dr. Buonocore concluded that

the high bond strength was due to the increased surface area and wettability of enamel

surface. In Buonocore’s study, the phosphoric acid concentration used was 85 % for 30

seconds (Buonocore 1955). It was later shown that decreasing the etching time of enamel

and dentine from 60 seconds to 15 seconds using the 37% phosphoric acid gave adequate

for shear bond strength of RBC’s (Fejerskov, Johnson et al. 1974).

Acid etching removes about 10 um of the top surface of enamel and leaves an

irregular surface with micropores of 5-50 um deep (Gwinnett 1971, Summitt 2006). Acid

etching increases the infiltration of the adhesive system of RBC’s into the micropores

formed by acid etching, as well as increasing the wettability and surface energy. After

polymerization the infiltrated resin, forms retentive resin tags which produce a strong long-

lasting bond (Buonocore, Matsui et al. 1968). Etching mainly appears as keyholes when

scanned under scanning electron microscope because of the dissolution of the

interprismatic substance (Summitt 2006).

Many dental adhesive systems were introduced in the field of dentistry (Summitt

2006). Classifications were made to differentiate between these systems. One of the

classifications was based on the conditioning mechanism and the number of steps included

in the bonding protocol. This classification was made to describe the self-etch and the total

etch (etch and rinse) bonding mechanisms.

Total etch and self-etch systems were further classified according to the number of

steps. Total etch systems depend mainly on removing the outer layer of enamel and the

smear layer produced as a result of instrumentation to ensure high bonding properties,

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whereas the self-etching adhesives only partially dissolves those components (Summitt

2006). The gold standard system used among the different adhesive systems is currently

considered the three-step total-etch system.

Bonding to dentin is less reliable than bonding to enamel because of the high

organic and fluid content of the dentin and the flexible surface of dentin. The dentinal

tubules are wider close to the pulp and narrower and less close to the external enamel

surface, Dentin is also a vital tissue which undergoes structural changes with time (sclerotic

dentin, dead tracts, secondary dentin and tertiary dentin) (Perdigao 2010). Thus, adhesion

to dentin is less predictable and more variable dependent than bonding to enamel. When

bonding to dentin, the smear layer may be completely removed (total etch) or partially

dissolved (mild-etch). Past studies have shown total etch have shown the best results in the

longevity and strength of bond between the RBC’s and the tooth although the self-etch two

step adhesive systems are showing promising results (Casselli, Faria-e-Silva et al. 2013).

The development of adhesive systems that can enhance the bond strength of the RBC

restorations has gone through many steps and much research. Enhancements made to

bonding systems were as follows:

1) First generation, in 1956 Buonocore and colleagues suggested the use of

glycerophosphoric acid dimethacrylate resin to bond to dentin structure (Bowen 1956).

Later Bowen tried to modify in the chemical formula of the adhesive system by

incorporating N-phenylglycine, glycidyl methacrylate or NPG-GMA as a bifunctional

molecule or a coupling agent (Bowen 1965).

2) Second generation, in the late 1970's, the second generation came out with some

improvements and changes. The majority of these systems incorporated halophosphorous

esters of unfilled resins bisphenol A glycidyl methacrylate or bisGMA or Hydroxyethyl

methacrylate or HEMA. These systems bonded to dentin by forming ionic bonds to calcium

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which was a stronger bond than the first generation. In this generation dentin wasn’t etched

and the bonding was applied over the smear layer.

3) Third generation, this group recommended the etching of dentin and modifying

the smear layer to let the primer adhere and penetrate (Kato and Nakabayashi 1998). The

primer presented contained hydrophilic resin monomers which included trihydroxyethyl

trimellitate anhydride, 4-META and biphenyl dimethacrylate. Following the primer

application, an unfilled resin was placed over enamel and dentin. This generation had better

results than the first and second generations.

4) Fourth generation, this was the start of the total etch or etch and rinse system. In

this system, the smear layer was totally removed to facilitate bonding to dentin, enamel

and dentin was etched with 40% phosphoric acid. The higher concentrations, however,

caused dentin to be over etched and the collagen fibers collapsed (Fusayama and Kohno

1989). In 1982 the formation of the hybrid layer was reported. The hybrid layer is defined

as "the structure formed in the dentin due to demineralization of the surface and subsurface

followed by infiltration of monomers and subsequent polymerization”. (Nakabayashi,

Kojima et al. 1982). The fourth generation used the total etch technique where enamel and

dentin were etched 15 to 20 seconds. The surface was left slightly wet for application of

the hydrophilic monomer followed by the unfilled resin for the dentinal tubules to be totally

sealed with the resin tags (Kanca 1991, Gwinnett 1993, Kanca 1996, Tay, Gwinnett et al.

1996)

5) Fifth generation, this generation involved the introduction of the self-etch system

as well as combination of the primer and adhesive with the total etch system. The concept

was to provide a faster and an easier way for bonding to enamel and dentin. With the self-

etch system, the primer and the conditioner were combined with the adhesive separate.

With the total etch system, the primer and adhesive were combined in one bottle to be

applied after etching of enamel and dentin (Tay, Gwinnett et al. 1994). The self-etching

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primer developed was an aqueous solution of 20% phenyl P in 30% HEMA (Watanabe and

Nakabayashi 1993). The combination of the etching and priming step together was

advantageous in that less time was needed for the procedure, but the drawback was that the

smear layer partially remained between the bonded layers and the overall strengths with

the systems were less effective than the phosphoric acid etching (Kato and Nakabayashi

1998). The total removal of the smear layer was suggested to enhance the durability and

reliability of bonding to dentin (Toida 1995). However (Carvalho, Yoshiyama et al. 1996)

suggested that bond strength tests did not show statistical differences in bond strength

between the one bottle system and the self-etching primer bonding systems.

6) Sixth generation, these self-etch systems involved a one-step procedure for

bonding where the conditioner, primer and adhesive were combined into one bottle. Initial

products in this category had stability problems. Typically the bond to dentin was good but

enamel bond strengths were low since the solution has ph which is typically too high to

properly etch enamel. (Gerald Kugel, 2000)

A study by (Roggendorf, Kramer et al. 2011) was done to compare the marginal

integrity and the bonding of the bulk fill RBC’s and the conventional RBC’s when using a

self-etch adhesive versus etch and rinse adhesive. Five types of RBC’s were used (SDR,

Ceram X mono, Tetric EvoCeram, Filtek Supreme and Venus Diamond). These RBC’s

were bonded by using their respective adhesives, XP bond, Xeno V, Syntac, Adper Prompt

L-pop and iBond self-etch. Eighty MOD cavities were prepared in extracted human third

molars with gingival margins just below the DEJ. Teeth were divided into eight groups (10

teeth per group) where four groups had bulk Fill SDR placed and over it the conventional

RBC’s where the other four groups had only the conventional RBC’s placed. Teeth were

restored with different RBC types and were examined under a SEM at a magnification of

200X using epoxy resin replicas.

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The results showed that all adhesive systems used showed high percentages of gap

free margins in enamel. Etch and rinse adhesives performed better (87.4%-91.5% gap free

margins) compared to the self-etch adhesives (42.1%-64.1% gap free margins). In dentin,

a high percentage of gap free margins was found with etch and rinse adhesives again

performing better (63.2%-66.6% gap free margins) than self-etch adhesives (38.5%- 56.2%

gap free). Internal adaptation to dentin was found to be better in etch and rinse adhesives

(66.3%-70.1% gap free) compared to self-etch adhesives (31%- 57% gap free). Generally

there was no difference in the marginal adaptation between the bulk Fill and conventional

RBC’s.

(Casselli, Faria-e-Silva et al. 2012) evaluated different adhesive systems and their

effect on the marginal adaptation of RBC’s. Forty bovine incisors were selected for testing.

Class V cavities were prepared with a 3mm height, 3mm width and 2mm depth and a C-

factor of 3.7. Four adhesive systems were evaluated, a two-step self-etching adhesive

(Clearfil SE Bond, Kuraray), a single step self-etching adhesive (Xeno IV, Dentsply), and

two different two-step etch and rinse adhesives (Single bond 2, 3M ESPE and Prime and

Bond NT, Dentsply). Cavities were restored with Filtek Z250, (3M ESPE) and filled in one

increment of 2mm thickness and cured for 20 seconds. The curing procedures were done

either by QTH light (Optilux 501, Kerr) or an LED light (Radii-Cal, SDI) without

mentioning the irradiance produced. Results of the study indicated no significant difference

in enamel margins in all cavities restored and cured either with the QTH or LED light.

However in dentin margins, Clearfil SE Bond demonstrated the lowest amount of gaps

regardless of the light cure used. The type of curing light used only affected results in the

enamel margins of Xeno IV, where larger gaps were formed when cured with Optilux 501

QTH light than those cured with Radii-Cal LED.

Another study conducted by (Casselli, Faria-e-Silva et al. 2013) tested the margin

location and type of adhesive system used on the marginal adaptation on the RBC’s used.

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Forty bovine incisors were examined for marginal adaptation. Class V cavities were

prepared with dimensions of 3mm by 3mm and 2mm depth with a C-factor of 3.7. Adhesive

systems used were two-step etch and rinse (Single bond 2, 3M ESPE) and two-step self-

etch (Clearfil SE Bond, Kuraray). The cavities were all restored with Filtek Z250 (3M

ESPE) in one increment of 2mm and cured for 20 seconds. The procedure of light curing

was done by a LED Radii-Cal (SDI) producing irradiance of 600 mW/cm2. Results of this

study were similar to the previous study done by the same author where on the enamel

margins Single Bond 2 exhibited less marginal gaps compared to Clearfil SE, However in

dentin the opposite was true where Clearfil SE showed less gaps than Single Bond 2. In

dentin the Clearfil showed better marginal adaption however in enamel the Single Bond

was better. A study by (Casselli, Faria-e-Silva et al. 2012) compared bonding of RBC’s to

enamel and dentin using different adhesive systems showed that in dentin the best bond

with the lowest marginal gaps was demonstrated with the Clearfil SE bond however in

enamel margins there was no any difference between different adhesive systems.

(Blunck and Zaslansky 2011) evaluated the margins in enamel of Class I

restorations using a one bottle all in one adhesive systems. Ninety-six human molars were

selected for testing. Class I cavities were prepared 3mm deep, 6mm wide mesio-distally

and 4mm wide bucco-lingually. All teeth were divided into 12 groups of eight teeth each.

Each group was assigned to one adhesive system. Twelve adhesive systems were used with

three control groups as: 1) Optibond FL, 2) Clearfil SE Bond, 3) Adper Prompt L-Pop, and

nine one bottle one step self-etching adhesives (OBOSSEA) products : 4) Adhese one, 5)

Adper Easy Bond, 6) Bond Force, 7) G-Bond, 8) I-Bond Self Etch, 9) One Coat 7, 10)

Optibond All In One, 11) Tri-S-Bond and 12) Xeno V. All teeth were restored with Z250

RBC in three increments (one horizontal and two oblique layer) which were cured for 40

seconds using the Astralis 10 (Ivoclar). Results of the study indicated that all in one

adhesives exhibited significantly lower marginal integrity compared with etch and rinse

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system (Optibond FL) and the two step self-etch system CSE. Comparing the nine all in

one groups, the best marginal adaptation was found in the groups of Bond Force, G-Bond

and Optibond All in One.

The bonding system used for the current investigation Syntac bonding system

(Ivoclar Vivadent) was from the same manufacturer as the RBC and light curing unit to get

the most accurate results. This bonding system is a three-step (sometimes referred as a

four step) total etch system. It is composed of an etchant, Syntac primer, Syntac adhesive

and the Heliobond.

Studies such as (Kanemura, Sano et al. 1999, Hannig and Fu 2001, Pashley and Tay

2001, Deliperi, Bardwell et al. 2006) stated that the use of self-etch adhesive systems

especially the mild etching systems produced a reduced bonding effectiveness to enamel

when compared to the total-etch systems. Generally the total etch systems and 2 step self-

etch systems have better bonding qualities compared to the one bottle all in one bonding

systems as stated by (Blunck and Zaslansky 2011).

Polymerization Reaction

The process of polymerization is a continuous process where at a certain stage the

monomers start forming a solid mass which is called the gel point. At this point, the RBC

starts losing its elasticity and becomes stiffer. Any contraction beyond this stage can form

direct stresses in the RBC, and if the RBC is bonded to the cavity walls shrinkage may

occur (Braga and Ferracane 2004). In the process of polymerization small molecules are

turned into large chains of polymers. The normal spaces between monomers before curing

is 3-4A whereas after polymerization it becomes 1.5A which can result in shrinkage of

1.5%-5%. The amount of shrinkage is dictated by the amount of covalent bonds formed

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and the amount of double carbon bonds of the monomer conversion (Alvarez-Gayosso,

Barcelo-Santana et al. 2004).

A study done (Bouschlicher and Rueggeberg 2000) tested the rate of

polymerization shrinkage after light curing with different light intensities in a hybrid RBC.

They concluded that slower conversion rates resulting from the gradual increase in light

intensity resulted in lower the polymerization stress which was produced without affecting

the physical property of the restoration since the maximum degree of conversion occurred.

(Yoshikawa, Burrow et al. 2001) tested the effect of light curing intensity on the

marginal adaptation and contraction rate of the Conventional RBC (Clearfil Bright hybrid

RBC). RBC’s were cured with different light intensities of 600 and 270 mW/cm2 with

various curing times. The conclusion was that using a low light intensity of 270 mW/cm2

for 20 seconds yielded the lowest polymerization shrinkage rate and the best marginal

adaptation results compared with all other curing intensities.

Dental Photopolymerization

Most of the procedures nowadays done in the dental field needs a photocuring step.

The light curing systems are used mainly to initiate the polymerization reaction of the

dental materials. The type of light curing unit used has a direct effect on the polymerization

shrinkage and rate of cuspal deflection (Fleming, Khan et al. 2007). The light curing

systems went through a lot of advancements until getting to use the newer LED light curing

systems available today. The first light curing systems were developed in the early 1970’s

utilizing the ultra-violet light (365 nm) through a quartz rod from a high pressure source of

mercury (Lienhard O 1973). The typical exposure durations were 20 seconds to 60 seconds

(Murray, Yates et al. 1981). These light curing systems had many disadvantages such as,

the limited ability of light to penetrate deep within the material and the harmful effects of

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the light when exposed to human eyes and the possible adverse effects on the oral

microflora (Craig 1981). A new light technology was then developed using a visible light

radiation in 1976 where the first dentist Dr. Mohamed Bassoiouny placed the first visible

light cures RBC as a restorative material. The light curing units were designed to activate

a photo-initiator camphorquinone and a tertiary amine co-initiator to increase success rates

in the RBC systems used (Stansbury 2000). The usage of visible light had some advantages

such as: curing RBC’s in 2mm increments for 40 or 60 seconds, the cataract and eye side

effects were minimized. However, still the retinal burning and macular degeneration were

still a probability of ocular damage.

The Quartz tungsten halogen lights (QTH) were then developed; it utilized a

halogen cycle to remain clear from the tungsten contamination around the quartz used.

Some advantages of these newer systems were: availability, easy installation, being

inexpensive. These lights had to be fan cooled to allow proper working mode of the halogen

cycle. Light systems then started developing by introduction of an argon ion laser with an

output wavelength of 514nm, then the Plasma arc lights were introduced being developed

in the mid 1960’s where the typical output for these systems was near 2000mW/cm2 with

a broad band of 380 to 500 nm wavelength.

The newest and the last generation introduced were the LED’s where these lights

depended mainly on the energy difference obtained from two dissimilar semiconductor

substrates (Rueggeberg 1999). The manufacturers supplied LED chips sets that had a

variety of emitting wavelengths which were suitable for the photo-initiators available in

the RBC systems. Many manufacturers nowadays recommend a curing time of 10 seconds

using a high intensity curing light delivering an irradiance of at least 1000 mW/cm2.

Manufactures have made a wide range of claims concerning the usage and qualities

of different light curing systems. Thus it becomes important to discover the true operating

characteristics of the curing lights. It was stated that the measurement of the light curing

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output using the hand held dental curing radiometers resulted in inaccurate data in showing

the different depths of cure among lights (Hansen and Asmussen 1993). The total power

output (not differentiating between different frequencies) of the light curing systems should

be determined using a well calibrated thermopile, where black body absorbing plates with

layers of thermocouples are used to respond to the absorption of energy (Rueggeberg

2011). It was always known that the light cures have major differences in the light diversion

which required holding the tip of the light as close as possible to the detector plane however

the ISO 106500-1 testing standard for determining the exitance radiation, the tip ends are

held at a distance from the detector plate and thus may give inaccurate results of power

emission. The spectro-radiometers were used to evaluate the dental curing radiometers and

measure the power at the visible spectrum. These instruments used were referred as hand

held spectro-radiometers.

The light beam homogeneity (intensity contour generation) is very important in

detecting the different intensity patterns found in a specific light source and to know if the

beam power is higher in the core or in the periphery. The basic setup of the machine is

utilizing a charged coupled device (CCD) camera where the beam is targeted. The beam

power maybe measured by a thermopile and then the camera side image can be analyzed

using a software that shows on a screen. A color coded image is then generated of the beam

irradiance. It’s very important to mention that the light curing tip movement when tested

resulted in lower overall hardness at both the top and bottom (2mm) (Rueggeberg F 2010).

Polymerization Shrinkage

Light cured RBC’s harden after curing by a polymerization reaction changing the

viscous phase into a more hard or rigid phase. During this polymerization reaction

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shrinkage occurs which can have direct effect on the cuspal stresses (Davidson, de Gee et

al. 1984).

The polymerization reaction that occurs in RBC’s is mandatory as these materials

proceed in their setting reactions. Cross linking of all monomers occurs thus decreasing

spaces between them and causing a reduction in the general volume of a restoration which

may result in marginal gaps at the tooth interface. No RBC is totally free from

polymerization shrinkage. Polymerization shrinkage mainly depends on the oligomers and

diluents which are main components of RBC’s, and shrinkage increases with increased

diluents present. During setting, the material pulls away from the surface with the weakest

link and creates space defects at the tooth interface (Lutz, Krejci et al. 1991). The

microhybrid and nanohybrid RBC’s are more highly filled compared to microfills

(Heymann, Swift et al. 2012). The amount of filler is critical as the increase in filler content

decreases the amount of polymerization shrinkage (Li, Li et al. 2012). Results of

polymerization shrinkage and gap formation can increase marginal leakage, discoloration,

sensitivity and increased stresses at tooth-restoration interface (Park, Chang et al. 2008)

Mechanical and Physical Properties

The type of RBC directly affects the rate of polymerization shrinkage, gap

formation and surface hardness of the restoration. The physical and mechanical properties

of the RBC’s depend mainly on the filler content, matrix system and their coupling

(Heymann, Swift et al. 2012). Polymerization shrinkage can be directly affected by filler

particle morphology and size. The surface hardness, stiffness and resistance to abrasion

and fracture toughness can be affected by the filler content, particle size and shape

(Summitt 2006). The amount of fillers incorporated in RBC’s are directly affected by the

shape of the particles, so spherical (round) shaped RBC particles can be more heavily filled

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compared to the lathe cut irregular and Pre-polymerized type of particles (Kim, Ong et al.

2002). All properties of RBC’s such as resistance to abrasion, fracture toughness, surface

hardness and polymerization shrinkage are improved with higher filler content except for

the surface roughness and polishing. However, the increase in the filler content must not

surpass a certain limit or else the RBC will become too viscous for clinical handling

(Summitt 2006).

Surface Micro-hardness

The polymerization reaction leads to the hardening of RBC’s. The degree of

polymerization can be measured directly or indirectly. Many laboratory tests have been

used to measure the degree of conversion of RBC systems including infrared spectrometry

(Ferracane and Greener 1986, Moore, Platt et al. 2008), resonance imaging for direct

measuring, Knoop hardness testing and Vickers hardness testing for indirect

measurements. The standard most commonly used method was the scraping method ISO

4049 which has been shown to overestimate the depth of cure values (DeWald and

Ferracane 1987, Price, Felix et al. 2005). Hardness has been well correlated with the degree

of polymerization and depth of cure (Ferracane and Greener 1984, Ferracane 1985,

DeWald and Ferracane 1987). Hardness values are usually obtained at different points from

top to bottom and the mean values are calculated to get the depth of cure. This determines

the relative extent of conversion at different levels within a RBC restoration. Many

researchers have accepted that a percent depth of cure at the bottom of the restoration

compared to the maximum top hardness of 0.80 is clinically acceptable (Rueggeberg and

Craig 1988, Bouschlicher and Rueggeberg 2000, Bouschlicher, Rueggeberg et al. 2004,

Price, Felix et al. 2005). The fillers content and size play an important role in the surface

hardness of the RBC’s (Bouschlicher, Rueggeberg et al. 2004)

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(Garcia, Yaman et al. 2013) compared the depth of cure and the surface micro-

hardness (KHN) between different types of bulk and conventional RBC’s Four types of

RBC’s were used: 1) SureFil SDR Flow (Dentsply), 2) Venus Bulk Fill (Heraeus Kulzer),

3) Sonic Fill (Kerr), 4) Filtek Supreme Ultra Flowable (3M ESPE). The hardness testing

procedures were done on ten specimens for each group (40 specimen's total) in a 10x10

mm mold and cured for 20 seconds using the Smart Lite iQ2. Specimens were tested at the

top surface (2mm, 3mm, 4mm and 5mm sections) and bottom surface (2mm, 3mm, 4mm

and 5mm sections) by using 100 gm load in 11 seconds. Results of the study revealed no

significant differences in hardness numbers between the different sections tested at the top

surface between different restorative materials. SureFil SDR Flow was the only material

of the bulk fills that showed lower values of Bottom to top KHN numbers of 70% where

Venus Bulk Fill and SonicFill both had an 80% acceptable B/T KHN. Filtek Supreme Ultra

Flowable was too soft to test at thickness of 4 and 5mm. The study was comparing also

between two methods of hardness testing the ISO 4049 and the knop hardness testing where

results showed that the Knoop hardness number testing (KHN) was more accurate

compared to the ISO 4049 which always overestimated the hardness numbers.

In the study done (El-Safty, Akhtar et al. 2012), the surface nano-hardness was

compared between different types of RBC’s to test the nano-mechanical properties of the

dental RBC’s. Ten different RBC materials were used including three flowable RBC’s

(GrandioSo Flow, GrandioSo Heavy flow and Estellite flow quick) and three bulk fill

materials (x-tra base, Tetric EvoCeram and SureFil SDR) and four conventional RBC’s (

GrandioSo, Venus Diamond, Filtek Supreme XTE and Spectrum TPH3). Disc specimens

(15mm X 2mm) were prepared and filled with the different types of RBC’s and cured in

multiple overlapping points for forty seconds each. Authors used a halogen light curing

unit (Optilux 501, Kerr, USA) with light irradiance of 650 mW/cm2. After restoration all

specimens were mounted in phenolic ring forms and embedded in a self-curing resin

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(Polyestyrene). Specimens were ground and polished and stored in distilled water at 37

Celsius for 7 days. The specimens were loaded with one loading rate and three unloading

rates using Agilent Technology XP nano-indentor with 30 indentations for the unloading

rate at a load of 10 mN. Results of this study showed that the surface micro-hardness mean

values of the different RBC’s tested were between 0.73 GPa to 1.60 Gpa. The study also

showed a positive correlation between the amount of filler loading and the surface micro-

hardness numbers. Final results showed that the surface micro-hardness and modulus of

elasticity for bulk fills and flowable RBC’s were lower than those for conventional

nanohybrid RBC’s.

A study conducted by (Alrahlah, Silikas et al. 2014) compared the different surface

micro-harness numbers (VHN) using different bulk fill dental RBC’s. Five different bulk

fill RBC’s were tested (Tetric EvoCeram, x-tra base, Venus Bulk Fill, Filtek Bulk Fill and

Sonic Fill). Stainless steel molds were prepared and were restored with the different types

of RBC’s with dimensions of (15mm X 4mm X 2mm). Specimens were cured for 20

seconds each using a light curing device (Elipar S10, 3M ESPE, USA) with an irradiance

of 1200 mW/cm2. All specimens were stored at 37 Celsius for 24 hours. The Vickers

hardness number was measured in the materials at 0.3 mm intervals of depth to the

maximum depth of 4mm. The specimens were tested with a micro-hardness instrument

(FM-700, Future Tech Corp, Japan). The load applied was 300gm for 15 seconds. Authors

tested the maximum VHN, the 80% VHN and the depth of the 80% VHN in the different

RBC’s. Results of this study showed maximum VHN numbers ranging from 37.8 to 77.4.

Sonic fill and Tetric EvoCeram Bulk Fill showed highest VHN numbers (P less than

0.0001) while lowest numbers were for Venus Bulk Fill RBC (P less than 0.0001). Sonic

Fill and Tetric EvoCeram Bulk Fill materials had the best depth of cure and hardness

numbers compared to the x-tra base, Venus and Filtek Bulk Fill. All bulk Fill RBC’s tested

showed acceptable hardness numbers of 80% of the top layer hardness at depths of 4mm.

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A study conducted by (Felix, Price et al. 2006) compared the surface micro-

hardness (KHN) of different RBC’s cured with two different light systems (LED light

emitting diode, QTH quartz-tungsten halogen in high and medium power). Two lights were

used for the study. An LED light (Free Light 2, 3M ESPE) used to cure at three levels

including 0mm (mean irradiance of 1300), 2mm (mean irradiance 400) and 9mm (mean

irradiance 140). A QTH curing light (Trilight 3M ESPE) used to cure at three different

levels including 0mm (mean irradiance 900 mW/cm2 in high power and 500 mW/cm2 in

medium power), 2mm (mean irradiance 700 mW/cm2 in high power and 400 mW/cm2 in

medium power) and 9mm (mean irradiance 200 mW/cm2 in high power and 100 mW/cm2

in medium power). Ten different available RBC brands were used for testing the surface

micro-hardness including : 1)Z250 (3M ESPE) shades A2 and B0.5, 2) Supreme (3M

ESPE) shades A2D and A2B, 3) Esthet X (Dentsply) shades A2B and A2O, 4) Heliomolar

(Ivoclar Vivadent) shades A2 and 110T and 5) Tetric EvoCeram (Ivoclar Vivadent) shades

A2 and bleach XL. Each tooth was sectioned into a mesial and distal half and placed in a

mold. Class I preparations were made with dimensions of 1.5 mm wide and 4mm deep

surrounded by dentin. RBC was placed and a Mylar strip was placed in the middle of the

two molds where the molds were closed for curing. After curing molds were opened for

Hardness testing. A good correlation between the Knoop hardness testing and the degree

of conversion has been shown. The Knoop diamond indentor was applied for 15 seconds

with 100 g weight measured at 0.5, 1, 1.5, 2, 2.5, 3 and 3.5mm from the top surface. The

mean of all hardness points was calculated for comparison between different groups.

Results showed that at a distance of 2mm with all RBC types the LED light produced

greater hardness than the QTH curing lights, however in distance of 9mm from the surface

of the RBC the QTH light delivered higher irradiance and produced harder RBC’s at depths

below 1.5mm.

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A study done by Price et al (Price, Felix et al. 2005) was similar to the study by

Corey A. et al (Corey A. Felix et al, 2006) where the aim was to compare micro-hardness

(KHN) of different RBC’s cured with two different light systems (LED light emitting

diode, Free light 2, 3M ESPE; QTH quartz-tungsten halogen, Trilight, 3M ESPE). All

methods followed were the same as the other study however the distance from the tooth

surface in this study was standardized at 2mm. Results showed that using the LED curing

light at a distance of 2mm in all RBC’s produced significantly harder RBC’s at depth of

3mm compared to QTH lights on high power mode (P<0.01). All three RBC’s (Z250 A2,

Tetric EvoCeram A2 and Tetric EvoCeram Bleach XL) maintained a high Knoop hardness

number at depths of 3.5mm.

Cavity Designs for Class II Resin Based Composites

The cavity preparation for RBC’s is different from that of the G.V Black

preparation. Preparations are more conservative and defect specific preserving more tooth

structure. The preparation finish line (cavo-surface angle) is the line at the junction between

the prepared cavity surface and the unprepared surface (Summitt 2006). There are different

types of finish lines that can be prepared including 90 degree angle (butt joint), beveled,

chamfer and shoulder finish lines. These different types of finish lines are used depending

on the type of restoration used and the esthetic and retentive needs of the dentist. The 90

degree margin means that the junction between the prepared cavity and outer tooth surface

is 90 degrees (Heymann, Swift et al. 2012). These margins are prepared for amalgam as

these materials are brittle and need support at the cavo-surface margins to increase the

fracture resistance. A beveled cavo-surface angle is usually prepared for the RBC materials

to expose more ends of enamel rods and increase the bonding capacity of the RBC’s

adhesive systems. Studies have compared the marginal leakage between restorations with

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beveled and unbeveled margins with the beveled margins showing less marginal leakage

(Crim, Swartz et al. 1984, Porte, Lutz et al. 1984, Coelho-De-Souza, Camargo et al. 2012).

It was shown that beveled cavities restored with RBC’s showed higher resistance to

fracture and better bonding of the restoration (Coelho-De-Souza, Camacho et al. 2008).

Restorations bonded to beveled margins also had better esthetic results due to the gradual

transition of color between the tooth and restoration (Albers 2002). However on the other

hand it has been suggested that bonding to beveled margins did not produce a better

marginal seal than the unbeveled margins but only improves esthetics (Baratieri and Ritter

2005, Bagheri and Ghavamnasiri 2008). Microleakage is defined as the infiltration of

bacteria, fluids and oral debris at the restoration and tooth interface (Papacchini, Monticelli

et al. 2007). Opinions differ whether or not to bevel the margins when bonding to RBC’s,

and the debate of which margins should be beveled still exists.

The gingival margin of cavity preparation in this investigation was placed below

the cemento-enamel junction at the dentin level as to provide more challenge in bonding

and adaptation to dentin and increase the possibility of detection of differences in marginal

adaptation. Bonding to dentin has been shown to be less predictable than bonding to enamel

leading to a weaker bond in resisting polymerization shrinkage (Manhart, Chen et al. 2001).

The cavity preparations were all standardized to the dimensions of 4mm occluso-

gingivally, 4mm bucco-lingially and 2mm mesio-distally. A study done by Sabatini et al

(Sabatini et al, 2010) used the same cavity dimensions to test different conventional RBC’s,

however the investigators in this study used the conventional burs to standardize the

preparations.

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Resin Based Composite Failures Related to the Class II Cavity Design

Polymerization Shrinkage and C-Factor

Polymerization shrinkage of RBC’s is affected by the shape and depth of the cavity

and the degree of flow of the material (Taylor and Lynch 1993). The rate of polymerization

shrinkage is directly related to the configuration factor of the cavity preparation known as

the c-factor. The c-factor can be defined as the ratio of the bonded surfaces to the unbonded

surfaces (Feilzer, De Gee et al. 1987, Summitt 2006). An increased C-factor leads to

increased shrinkage stresses. Generally Class I and II posterior cavities possess a higher C-

Factor due to the walls of bonded restoration which increases the shrinkage stresses and

affects bonding (Cakir 2007, Karthick 2011).

Exact relation between the c-factor and its effect on bonding of RBC is unclear,

however it's well known that increased C-factor causes higher polymerization shrinkage

rates. Polymerization shrinkage increases in cavity designs with high c-factors. This is

because of the inability of RBC’s to reduce the extra stress by the flow through unbonded

surfaces of high C-factor preparations as the unbonded , the only surface that can act as a

reservoir for the plastic deformation that happens during polymerization shrinkage

(Karthick 2011).

An article by (Van Ende, De Munck et al. 2013) evaluated the influence of the high

c-factor when bonding of different types of RBC’s to cavity bottom dentine. Three types

of RBC’s were used in the study including a flowable RBC (Geanial Universal flow, GC),

a bulk fill RBC (SDR, Dentsply) and a hybrid type RBC (Z100, 3M ESPE). Different

cavity preparations were done with different c-factor numbers including C=3.86 (class I

cavity 2.5 mm deep, bulk filled), C=5.57 (Class I cavity of 4mm depth, bulk filled), C=

1.95 (Class I cavity of 2.5mm depth, filled into three equal layers) and C=0.26 (flat

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surface). After being stored for one week in water, the specimens were sectioned into 4

rectangular parts for the micro-tensile bond strength test. Results of the study showed that

the micro-tensile values ranged from 0 MPa to 70.1 MPa. The RBC when filled in

increments or when it was built upon a flat surface didn’t have any significant differences

in bonding (P > 0.05), however for the flowable RBC and the conventional types, bulk

filling of the cavity resulted in a decrease in bond strength where the P value was less than

0.001. The authors concluded that satisfactory bond strengths were obtained when an

incremental filling technique or bulk was done in a low c-factor flat surface for all RBC’s

used, however the bulk fills showed significant lowered bond strengths in class I cavities

irrespective to the depth.

Another article (Boroujeni, Mousavinasab et al. 2014) compared the effect of the

c-factor on gap formation on three different restorative materials including a hybrid RBC,

a low shrinkage RBC and a resin modified glass ionomer restorative material. Cylindrical

5mm diameter cavities in dentin were prepared with three different depths (1mm, 2mm and

3mm). Ninety-nine human molars were selected for the cavities and were separated into 3

groups with 33 teeth in each. , Each group had three subgroups depending on the three

prepared depths. The three restorative materials used were a resin modified glass ionomer

(Fuji II LC) and two RBC materials (Filtek P90 and Filtek Z250). Teeth were then

sectioned mesio-distally, and gaps were measured under the stereomicroscope. The results

did not show any significant differences in the amount of gingival gaps between the two

RBC’s, regardless of C factor change (1.8-3.4), however the group restored with the resin

modified glass ionomer showed more gaps when the c-factor increased from 1.8 to 3.4.

The least gaps were found with Filtek P90 followed by Filtek Z250 and the majority of the

gaps were found in the group restored with resin modified glass ionomer (Fuji II LC). As

a conclusion, authors concluded higher c-factors resulted in more gap formation only with

the RMGI. This study may have got these results because of using a glass ionomer which

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is less filled and weaker and may have had more gingival gaps because of its own inherent

properties not because of the difference in the c-factor.

Marginal Adaptation of Resin Based Composites (Marginal Gaps)

The marginal integrity is defined as the degree of proximity of a restoration to a

tooth surface. This property influences the longevity, esthetics and mechanical properties

of RBC’s (Schmidt and Ilie 2013). The marginal gap can start forming from a space created

between the restoration and tooth, 0.5 to 1 um wide, where bacteria, oral fluids and debris

may enter and destroy the bond decreasing the longevity of the restoration and speeding up

its functional and mechanical failure (Taylor and Lynch 1992). The association between

recurrent caries and gap formation was and still is a controversial topic, with some studies

stating a direct cause and effect while others state that no relation is found between both

phenomena. A study done by (Totiam, Gonzalez-Cabezas et al. 2007)studied the

relationship between the gap size and the extent of recurrent caries. Many gap sizes were

tested ranging from 0 to 1 um. Results showed that with increased gap size, the amount

of recurrent caries increased also. All gaps studied developed recurrent carries. An in-situ

study (Cenci, Tenuta et al. 2008), tested the gap formation while using fluoride from tooth

paste or glass ionomer. Results showed no association between gap formation and recurrent

carries. In another study done also by (Cenci, Pereira-Cenci et al. 2009) different sizes of

gaps were compared to their effect on recurrent carries. The authors concluded that gap

size directly influenced the recurrent carries but not when using fluoride in conjunction. In

another study (Hodges, Mangum et al. 1995) tested marginal gaps for recurrent decay, the

authors concluded that there was a direct relation between the gap width and the formation

of recurrent decay. However (Mjor 2000) stated that recurrent decay didn’t form from mild

micro leakage and minor marginal cracks but rather occurred with wide marginal voids.

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Factors that directly affect the gap formation are the degree of polymerization shrinkage,

finishing, polishing and expansion of RBC’s.

Successful adhesion to enamel and dentin is the main goal when restoring using

adhesive resins. Although high quality adhesive systems have been recently introduced,

they cannot guarantee perfect adhesion to tooth structure. Despite all developments in

adhesive systems, polymerization shrinkage and marginal leakage remain the main cause

of RBC failures (Cakir 2007). Restorations are affected directly by many factors such as

cavity design, placement technique (layering versus bulk), curing mode and wavelength,

the adhesive system used, water sorption of the RBC and shade and opacity of RBC (Cakir

2007).

It is impossible to totally avoid marginal gaps and leakage between tooth interface

and RBC’s (Papacchini, Monticelli et al. 2007). It also has been stated (Samet, Kwon et al.

2006) that it is impossible to totally eliminate voids formed between the different layers of

RBC’s. Many factors will be introduced in this literature review to overcome or at least

decrease the amount of marginal gap formation such as using cavity liners, incremental

RBC placement, modifying the time and intensity of curing lights. Step or ramp cure light

cures that start with low intensity then switches to high intensity and the pulse delay cure

which is a discontinuous curing procedure may help decrease the polymerization shrinkage

and marginal leakage (Cakir 2007).

(Roeters, Shortall et al. 2005) summarized the main requirements for a posterior

RBC restoration as providing high strength against fracture, high marginal integrity, high

wear resistance and high radio-opacity. The main advantages also of RBC’s have been

described (Cenci, Demarco et al. 2005, Coelho-De-Souza, Camacho et al. 2008) as their

high esthetics, adhesion properties and the reinforcement of the remaining tooth structure.

Major problems of failure in RBC’s can be due to the degree of polymerization shrinkage.

Posterior fillings such as Class I and Class II restorations have higher C-factor compared

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to anterior restorations which increases the amount of shrinkage (Deliperi and Bardwell

2002).

The increased degree of conversion of monomers to polymers increases mechanical

properties but at the same time increases shrinkage (Venhoven, de Gee et al. 1993, Roeters,

Shortall et al. 2005) concluded that the marginal gap was due mainly to the filler particles

size and content and type of degradation. Other opinions have suggested that marginal gap

is mainly formed due to the polymerization shrinkage and contraction stresses of RBC’s.

In the same study the authors discussed the white lines that may appear in enamel surface

adjacent to the restoration. These white lines were suggested to be craze lines or micro

fractures due to polymerization shrinkage (Olmez, Oztas et al. 2004, Cakir 2007).

Differences in the coefficient of thermal expansion and contraction between the restoration

and tooth play an important role in considering the amount of marginal leakage. This

difference causes the restoration and tooth to expand and contract differently at varying

temperatures creating gaps and leakage tendencies (Heymann, Swift et al. 2012).

Some reasons for the early failure of RBC’s are dependent on the operator and not

a deficiency of the material itself. Proper packing of RBC’s and elimination of all air voids

between restoration and tooth structure is crucial. The presence of voids at margins due to

improper adaptation can lead to marginal leakage, gap formation and subsequent failure.

These leakage sites can allow the ingress of bacteria, saliva and enzymes which can lead

to recurrent decay and post-operative sensitivity (Lutz and Kull 1980, Dietschi, De

Siebenthal et al. 1995, Dietschi, Scampa et al. 1995, NJM 1997). Gaps may form in the

internal line angles and can be altered and increased by forces of occlusal loading which in

time can lead to the percolation of fluids in dentinal tubules which may lead to fracture of

the restoration under recurrent heavy loads. Gaps formed at the external cavo-surface

margins can open a pathway for penetration of oral fluids and bi-products. Sometimes gaps

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can appear as radiolucent areas in radiographs which can produce a dilemma in the

diagnostic phases (NJM 1997).

Methods Introduced to Overcome Resin Based Composite Failures with Class

II Restorations

Many approaches have been used in an attempt to decrease the amount of

polymerization shrinkage in restoring Class II RBC’s. These approaches have included an

incremental technique when applying RBC’s which decreases the bulk of RBC cured at

one time and helps in decreasing the polymerization shrinkage and gap formation (Lutz,

Krejci et al. 1991). Another approach is the use of bulk fill materials which manufacturers

claim have very good marginal adaptation and low polymerization shrinkage (Jackson

2011). Another method introduced to decrease the amount of shrinkage of RBC’s was the

use of different light curing units with increasing light irradiance or pulsed emission. Some

studies have shown that when light curing intensity was used at 150 mW/cm2 followed by

light curing at 650 mW/cm2, the curing reaction slowed down and enhanced the marginal

adaptation of the RBC’s without affecting the properties (Uno and Asmussen 1991, Feilzer,

Dooren et al. 1995, Mehl, Hickel et al. 1997). Also the use of liners before applying

conventional RBC’s and the use of low elasticity layers has been also shown to enhance

marginal integrity (Braga and Ferracane 2004)

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Different Techniques of Placement

Incremental Placement Technique

The incremental technique is widely used in placing RBC’s in Class II cavities to

reduce the adverse effects of polymerization shrinkage and marginal gap formation. The

incremental technique reduces the bonded to unbonded surfaces thus reducing the C-factor

and stresses on the RBC restoration (Feilzer, 1987).

The study done by (Frankenberger, Kramer et al. 2007) using different adhesive

systems and layering techniques found that the horizontal layering technique had the best

bond quality compared to the vertical and oblique layering techniques. On the contrary, a

study done by (Versluis, Douglas et al. 1996) showed that the layering technique increased

the deformation of the restored tooth and caused higher polymerization shrinkage and

marginal gap formation.

In a study done by (Usha, Kumari et al. 2011), one type of RBC, a silorane low

shrinkage RBC (Filtek P90) was used to restore the teeth. The silorane self-etch primer and

adhesive were used. The cavity dimensions were 1.5 mm in depth, 3mm in length and 2mm

in width. The sample size was 40 premolar teeth which were extracted due to orthodontic

treatment. The Class V cavities were prepared and the teeth divided into two groups of 20

teeth: 1) Group 1 was restored by a horizontal split incremental technique in two steps.

The preparation was first filled using a 1.5 mm thick RBC increment where a diagonal cut

was made in this increment and the preparation was filled with both diagonal increments

and cured for 20 seconds each (total of 40 seconds). 2) Group 2 was restored by an oblique

layering technique where two layers were inserted obliquely and each one was cured for

20 seconds (total 40 second cure for 2 oblique increments). Restorations were tested for

the degree of shrinkage and marginal adaptation. Teeth were sectioned bucco-lingually

through the center of the restoration and a digital scale (Snagit digital scale) was used to

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calculate the width of interface between the restoration and tooth. The split incremental

technique had a mean score marginal opening between restoration and tooth of 3.98

microns compared to 8.27 microns in the oblique layering technique. Authors concluded

that using a split layering technique produced less marginal gap than using an oblique

layering technique.

A study conducted by (Kramer, Reinelt et al. 2009) tested the marginal adaptation

of different RBC’s in Class II cavities over a four years period of time using the USPH

criteria. The study was a prospective split mouth study. Thirty-six Grandio restorations

were bonded using the Solobond M bonding system (Voco) and thirty-two teeth were

restored with Tetric EvoCeram bonded by Syntac bonding system (Ivoclar Vivadent). All

cavities were Class II MO, OD or MOD. The restorations were placed by incremental

technique with no mention of number of layers and cured for 40 seconds using Elipar

Trilight (3m ESPE) with irradiance of 650 mW/cm2. Restorations were examined at

baseline, one year and four years. Authors had many criteria of testing including surface

roughness, color change, marginal integrity, tooth integrity, proximal contact, sensitivity

and restoration integrity. Results showed no significant differences in the amount of gap

formation between the two restorative materials after four years of follow-up (P>0.05).

Authors concluded that Grandio and Tetric EvoCeram had satisfactory performance in

Class II cavities after four years. Significant changes over time were observed for all

criteria tested including tooth integrity which deteriorated due to enamel cracks (P<0.05).

A continuation of the previous study (Kramer, Garcia-Godoy et al. 2011) evaluated the

RBC’s after six years. Results didn’t differ from the previous study with a 100 % success

rate. Neither the material nor the restoration location affected the clinical outcome after

the six years testing period (P>0.05). Molar restorations performed the worst in marginal

integrity, filling integrity and tooth integrity. Significant changes were found for all criteria

recorded (P<0.05). Negative step formation due to wear was observed more in molars (87%

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after 4 years) (P<0.05). Tooth integrity was found deteriorating due to cracks (P<0.05).

Restorations generally had more wear and roughness with 28% after one year, 75% after

two years, 84 % after four years and 91% after six years.

Another study (Sabatini, Blunck et al. 2010) evaluated the effect of preheating

RBC’s and using flowable liners on the gingival margin gap formation of Class II cavities.

Forty extracted third molars were prepared as class II cavities either on the mesial or distal

with dimensions of 4mm wide, 4mm high and 2mm deep with the gingival margins located

1mm below the CEJ in dentin. The adhesive system used was standardized for all

restorations (Optibond FL, Kerr). Teeth were divided into 5 groups with 8 specimens in

each group: 1) Preheated RBC at 130F/54.4C, 2) Preheated RBC at 155F/68.3C, 3) A layer

of 0.5 to 1mm of flowable RBC followed by placement of unheated RBC in 2mm thickness,

4) A 0.5 to 1mm thick layer of flowable RBC and placement of unheated RBC directly

over the uncured liner, 5) Room temperature RBC used in 2mm increments. The RBC used

was a microhybrid RBC (Filtek Z250, 3M ESPE) and a flowable RBC (Flow it, Pentron).

Restorations were cured for 40 seconds except for the flowable liner which was cured for

20 seconds, all with a LED light (G-light, GC America) with irradiance of 800 mW/cm2.

Results of marginal adaptation scores were calculated and showed that no significant

difference between the percentages of gap formation at the gingival margins was detected

between groups tested. For all the groups at least one specimen showed perfect marginal

adaptation. Generally the mean gap percentage for the 40 specimens tested were 6.3 with

a median of 1.1 and a SD of 14.8. Therefore the results indicate that the flowable or heated

RBC’s is not superior to conventional RBC’s.

Bulk Placement Technique

Innovations in the types and formulas of RBC’s have recently claimed significant

flow and low polymerization shrinkage values of new bulk fill RBC systems. These

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systems are marketed as RBC’s having greater depth of cure that can be placed in a bulk

fill technique (4mm or 6mm cavity) instead of the standard increments of 2mm. Companies

claim that these RBC systems reduce the amount of polymerization shrinkage and working

time (Burgess and Cakir 2010, Ilie and Hickel 2011, Czasch and Ilie 2013). This new

technology and concept of these newer RBC systems was based on changing the monomer

chemistry to create monomers with lower viscosity. The new changes in RBC systems was

achieved by incorporating hydroxyl free Bis-GMA, aliphatic urethane dimethacrylates or

partially aromatic urethane dimethacrylates or highly branched methacrylates (Moszner,

Fischer et al. 2008). The new changes in the organic matrix of these new bulk fill RBC

systems showed significant reduction in the polymerization shrinkage values and stresses

of 60%-70 % (Giachetti, Bertini et al. 2007, Ilie and Hickel 2011)

A new clinical study conducted (Burgess and Munoz 2014) evaluated the success

of the bulk fill RBC SureFil (Dentsply, Caulk) with capping with a conventional RBC

Esthet X (Dentsply, Caulk). One hundred and seventy class I and class II cavities were

prepared in eighty seven subjects; all restorations were bonded using Prime and Bond

adhesive system (Dentsply, Caulk). The bulk fill RBC was placed in a layer of 4 mm

thickness then capped by the conventional RBC. The restorations were evaluated at

baseline and after six months, twelve months, twenty four months and 36 months. Five

main criteria were tested: 1) fractures and surface defects, 2) proximal contacts, 3) recurrent

caries, 4) sensitivity and 5) gingival index. Results showed: 1) the fracture and surface

defects category showed acceptable results after thirty six month evaluation with only one

restorations which needed replacement and five others that needed repair and the defects

were in the capping material not the bulk fill RBC. 2) proximal contacts were intact where

only six teeth had affected contacts. 3) recurrent decay was only noted in three restorations

at the occlusal surface not the gingival margins indicating the failure of the occlusal

capping restoration not the bulk fill material. 4) sensitivity evaluation was done showing

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absence of sensitivity with the bulk fill RBC’s and as no relation between the sensitivity

and the bulk fill material appeared, sensitivity data were collected only at the twenty four

months recall. 5) no adverse effects on the gingival tissues was shown as all scores were

recorded as no to normal mild gingival inflammation. Authors concluded in this

investigation that the SureFil Bulk Fill RBC showed acceptable performance in three years

evaluation period.

Tetric EvoCeram and Tetric EvoCeram Bulk Fill

Resin Based Composites

The material of RBC used is crucial since the type and percentage of filler particles

and monomers dictate the degree of cure and the time needed for curing as well as the

quality of the polymerization reaction and the amount of polymerization shrinkage

(Amussen and Peutzfeldt, 1988; Amussen and Peutzfeldt, 2002). This study attempted to

use a commercial RBC which is available with quite similar physical composition yet

available in two different versions, that of a conventional fill and that of a bulk filled (Tetric

EvoCeram and Tetric EvoCeram Bulk Fill). The nanohybrid Tetric EvoCeram filling

material contains BIS-GMA, UDMA resins (dimethacrylates) which are all highly

molecular weight monomers. The main components of fillers in both Tetric EvoCeram

RBC systems are Barium glass, ytterbium triflouride, mixed oxide and prepolymers. The

filler content of the Tetric EvoCeram material is 75%-76% by weight and 53%-55% by

volume however the Tetric EvoCeram Bulk fill which has the same resin composition had

differences in the filler content 76%- 80% by weight and 53%-54% by volume. The

manufacturer claim that particles of Ivocerin are added to the resin monomer to act as

highly sensitive photo-initiators and have an important role in increasing the light

activation of the material, increasing the depth of cure and enhancing the polymerization

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reaction, also pre-polymerized particles are added to the Tetric EvoCeram RBC’s to act as

shrinkage stress relievers (Ivoclarvivadent 2014).

Many new bulk fill RBC materials have recently been introduced on the dental

market, The use of one of these other RBC system with different composition may have

caused different results, however EvoCeram Bulk was used because it was indicated for

fully restoring a cavity preparation at a depth of 4mm not just as a base like some other

bulk fills (SureFil SDR). Also Tetric EvoCeram has shown good marginal adaptation and

excellent depth of cure compared to other bulk filling materials (A. Alrahlah et al, 2013).

The last reason for choosing the Tetric EvoCeram Bulk Fill was our need to compare the

two RBC systems which were very similar. The adhesive system was from the same

manufacturer to further standardize the conditions of the study.

Comparing the Degree of Polymerization

Shrinkage and Marginal Adaptation using One

Type of Resin Based Composite Placed with

Different Techniques (Layering versus Bulk)

(Mullejans, Lang et al. 2003) compared the marginal adaptation of RBC’s placed

in bulk or incremental technique. Thirty extracted premolars and molars were prepared as

Class V cavities that were extended past the DEJ. The dimensions were 3 mm mesio-

distally, 5 mm in the occluso-gingival and 2 mm in depth. Teeth were divided into three

groups of ten teeth each. All cavities were restored with Dyract AP (Dentsply detrey) and

the adhesive system Dyract-PSA and cured with spectrum 800 curing light (Dentsply). 1)

1mm thick layer of polyacid modified RBC was applied to the coronal portion and cured

for 40 seconds. The rest of the cavity was filled and cured for 40 seconds (Total of 80

seconds), 2) restored in the same manner of group 1 but the first layer was placed in the

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apical portion instead of the coronal, 3) A single increment technique (bulk technique) was

used without mentioning the curing time.

Results of this study showed the percentage of gap formation at the enamel and

dentin interface were generally higher at the dentin margins. Gap formation for Groups 1-

3 in enamel margins were 28.2%, 30.0% and 26.5% with no statistical difference between

scores (P>0.05). Scores in dentin were 25.7% , 22.8% and 30.6% where Groups 1 and 2

were statistically lower in gap formation than Group 3 (P>0.05). Authors concluded that in

dentin margins of Class V cavities, the percentage of gap formation was less using the

incremental technique compared to a single 2mm increment, however it may take the

operator more time.

Comparing the Degree of Polymerization

Shrinkage and Marginal Adaptation using

Different Types of Resin Based Composites Placed

with Different Techniques (Layering versus Bulk)

(de Wet, Exner et al. 1991) compared the marginal gaps between the layering

technique and the bulk filling technique. Forty five molar teeth were prepared as DO or

MO Class II cavities all having the same dimensions. Three types of RBC’s were used to

restore the teeth to be tested including two microfilled RBC’s, Distalite (Johnson

professional, Inc) and Heliomolar (Ivoclar Vivadent) and one hybrid RBC, P-30 (3M St.

Paul) .The type of bonding system used was not mentioned. Three techniques were used,

two were a variation of layering including horizontal and vertical layering and the other

was a bulk fill technique. Teeth were divided into three groups of 15 teeth with each group

restored with the different techniques: 1) bulk filled and cured for 60 seconds, 2) filled by

using three horizontal layers of RBC, each 2mm in thickness and each individually cured

for 60 seconds (total cure 180 seconds), 3) restored by vertical layering technique by using

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three vertical layers cured for 60 seconds each (total cure 180 seconds). Specimens were

cut longitudinally and examined by the SEM to compare the marginal gaps formed due to

shrinkage. The authors reported that the bulk technique resulted in significantly higher

marginal gaps (P-value less than 0.01) when compared to layering. Scores of the marginal

gap average in the proximal boxes using P-30 was 20 um with bulk technique and 6 um

with both vertical and horizontal layering techniques. Best scores were shown with the P-

30 RBC where the average marginal gaps at the floor of the cavity were 17 um compared

to 61 and 7 um in Heliomolar and Distalite. The authors stated that marginal gap between

the restoration and tooth increased with the bulk technique. They also concluded that the

hybrid P-30 RBC showed better scores (less marginal gaps) than the microfilled RBC’s,

Distalite and Heliomolar.

(Gallo, Bates et al. 2000) compared the marginal adaptation of different

conventional packable RBC’s placed in bulk or incremental technique. Sixty Class II

preparations were prepared on the mesial or distal sides with dimensions of 6 mm deep, 2

mm bucco-lingually and 1.5 mm mesio-distally. Teeth were divided into six groups (10

teeth in each group) with three types of RBC’s placed in incremental technique and with a

bulk fill technique. RBC’s used were: 1) SureFil (Dentsply) bonded with Prime and bond

2, 2) Solitaire bonded with Solid Bond P (Heraeus Kulzer), 3) ALERT Bond -1 Flow It

(Synca). All restorations were cured for 40 seconds from the occlusal and another 40

seconds from the facial and lingual (total cure of 80 seconds) using a XL300 light with

irradiance of 650 mW/cm2. Specimens were submerged in silver nitrate and examined

under a light microscope. Results showed no significant difference in marginal adaptation

between different technique of placement either with bulk or incremental technique

(P>0.05). In comparing different types of RBC, ALERT had the least amount of gaps and

leakage in both technique (bulk and incremental) compared to other restorations (P<0.05).

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Differences in the technique of placement (bulk or layering) using conventional RBC’s

didn’t affect the marginal adaptation of the restorations.

A study done by (Opdam, Roeters et al. 2003) investigated the voids that formed at

the margins of different consistencies of RBC’s placed in different techniques (layering

and bulk technique). Preparations were made in one hundred fifty two Perspex blocks

(Dimensions of 4mm depth, 3mm in diameter). Three different RBC consistencies were

used, 1) High viscous RBC (Packable Prodigy, Kerr), 2) Medium viscosity (Clearfil,

Kuraray) and 3) Low viscosity or flowable RBC (Revolution, Kerr). Restorations were

placed according to one of eight protocols (Each group having nineteen restorations), 1)

bulk filled with packable RBC and cured for 40 seconds, 2) bulk filled with medium

viscosity RBC, 3) bulk filled with the flowable RBC, 4) Snow plow technique where

flowable RBC was placed on the gingival margins, left uncured and placed over it the

medium viscosity RBC and cured for 40 seconds. 5) Same as group 4 but using packable

RBC. 6) Flowable RBC placed in two layers and cured for 40 seconds. 7) Flowable RBC

placed in one layer and cured for 20 seconds followed by a layer of medium consistency

RBC and cured for 20 seconds. 8) Same as previous group but second layer was packable

RBC. Light curing was done from the occlusal surface using a Kulzer Translux CL light

(Irradiance of 700mW/cm2). Adhesive system used was not mentioned. Light microscope

was used for marginal analysis. Authors stated that restoring cavities with absence of voids,

porosities or gaps was very hard to achieve and all restorations had voids except for Group

4 (Snow plow technique where flowable RBC was placed on the gingival margins, left

uncured and placed over it the medium viscosity RBC) where eight restorations were gap

free and Group 2 (bulk filled with medium viscosity RBC) where three restorations were

gap free. The best results were observed in Group 4 where the snow plow technique was

used with medium consistency RBC (11 voids only present, P<0.05).

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(St Georges, Wilder et al. 2002) tested two types of RBC’s including a hybrid RBC,

Z250 (3M ESPE), and a microfill Silux Plus (3M ESPE). Class V cavities with of

dimensions were 1.5 mm in depth, 2mm in height, and 4mm in length were prepared in

100 freshly extracted premolars. The teeth were equally divided into two main groups of

fifty which were each restored with a different type of RBC. Within each group, teeth were

divided into 5 subgroups of ten teeth each where different techniques of RBC placement

were tested: 1) restored by two triangular increments placed obliquely over each other to

fill the entire cavity with both increments individually cured for 40 seconds each from the

facial surface. 2) used the same technique of placement, but the RBC surface was re-bonded

with an adhesive, Singlebond. With both subgroups, the two layers of RBC’s were

individually cured for 40 seconds each as well as an additional10 seconds cure from the

facial. 3) bulk filled in one increment, and cured for 40 seconds. 4) also filled by bulk

technique, but RBC surface was re-bonded with an adhesive, Singlebond, similar to

Subgroup 2. No mention was made of the light curing times for this group. 5) Layered

with the same technique as Subgroup 1, but each layer was cured for 40 seconds (80 total

seconds for both layers) from the lingual (Through the tooth) and an additional 20 seconds

from facial. The teeth were stained with methylene blue dye and then sectioned bucco-

lingually and examined under an optical microscope at 15x magnification to determine the

extent of microleakage in both enamel and dentine. Results of the study stated that in

general the two types of RBC’s placed by layering technique and bulk were successful with

no significant differences between the five techniques of placement in the amount of

marginal leakage. The P-values were p=0.72 for Z250 and P= 0.54 for Silux Plus. The

microleakge scores showed significant differences between enamel and dentin for both

RBC systems. The Silux Plus group had 90% zero leakage scores in enamel and 70% zero

scores in dentin. The P- values were less than 0.005 (P<0.001 for Z250 and P<0.0001 for

Silux Plus). The main conclusion of the study was that the different techniques of layering

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and bulk fill didn’t have any significant differences on marginal leakage. However, the

specific bonded tooth surface had an effect on the leakage with enamel better than dentin.

Two different studies compared the marginal gaps formed with conventional and

bulk RBC’s placed in bulk and layering technique. The first study (Furness, Tadros et al.

2014) compared the internal marginal adaptation of different Class I cavities restored in

bulk or incremental technique at enamel, mid-dentin and pulpal floor areas using different

conventional and bulk fill RBC’s. Class I preparations with dimensions of 4mm diameter,

4mm deep and c-factor of 5 were made in fifty molar teeth. All restorations were bonded

using total etch adhesive systems. Five groups of 10 teeth each were tested. Four bulk

filling materials were used SureFil (Dentsply), Quixx (Dentsply) bonded by Prime and

Bond NT (Dentsply) / Sonic fill (Kerr) bonded with Optibond FL (Kerr) and Tetric

EvoCeram (Ivoclar Vivadent) bonded with Excite F (Ivoclar Vivadent) and one

conventional RBC used as a control Filtek Supreme Ultra (3M ESPE). Teeth were

sectioned and the internal marginal leakage was assessed after applying carries detecting

dye on the internal margins of the restorations and obtaining images of these dyes using a

digital camera and visually examining the samples. Results of the study showed no

significant differences among different restorative procedures or materials at a significance

level (P=0.01) however significant differences were found between different locations of

measurements of internal gaps (enamel, dentin or pulpal) with significance level (P=0.01).

Authors concluded that: 1) Usage of bulk fill or conventional RBC’s resulted in the same

amount of marginal adaptation in the mid-dentin and enamel portion, 2) The amount of gap

formation at the pulpal floor was lower than in enamel and dentin margins for all types

tested except for two, SureFil and the Filtek Supreme Ultra. 3) Gaps in the conventional

group were less in the enamel and mid-dentin portions when it was used as recommended

in 2mm thick layers instead of bulk filling in 4mm layers. Results showed that the

technique of placement and the type of RBC used didn’t have a significant effect on the

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marginal adaptation of the restorations however the location of bonding directly affected

the adaptation of restorations where it was better in enamel than in dentin than in deep

dentin (pulpal walls).

The second study (Campos, Ardu et al. 2014) compared the marginal adaptation in

Class II cavities restored with bulk and layering techniques using bulk fill and conventional

RBC’s. Forty extracted human molars were prepared with large MOD cavities with parallel

walls and beveled margins with the gingival margin 1mm below the enamel-cementum

junction. The dimensions of all cavities were standardized to 5mm wide and 4mm deep in

the occlusal box, 5mm wide and 2mm deep in the proximal box. All bonding procedures

used Optibond FL adhesive system (Ivoclar Vivadent). The teeth were restored with two

horizontal increments of 4mm and 2mm and cured for 40 seconds using a LED light (Demi

plus, Kerr) with irradiance of 1100 mW/cm2. Teeth were divided into five restorative

groups according to first/second increment, Group A: Venus bulk fill/Venus Diamond;

Group B: Tetric EvoCeram bulk fill/Tetric EvoCeram; Group C: SureFil SDR/Ceram X;

Group D: Sonic fill; Group E: Ceram X/ Ceram X (Control group). The results showed that

the differences in percentage of intact margins found between all restorative materials

weren’t significant (P= 0.164). The lowest amount of intact margins were found in Goup

A (Venus bulk fill/Venus Diamond). Scores of intact margins were; Group A: 71.96%,

Group B: 82.45%; Group C: 87.22%; Group D: 82.45% and Group E: 86.14%. The results

for the percentage of intact margins in occlusal enamel margins and proximal enamel

margins showed no statistical differences (P= 0.060 and P= 0.091). Authors concluded that

the margins in dentin showed more discontinuous margins than those located in enamel

and that there was no difference in marginal gaps/adaptation between the bulk and standard

(conventional) RBC’s. Again results showed no differences in marginal adaptation

between different restorations (bulk or conventional) placed either in layering or bulk fill

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technique however the location of bonding differed were more marginal gaps were found

in the dentin margins compared to the enamel margins.

Degree of Polymerization Shrinkage and Cuspal

Deflection of Teeth using Different Placement

Techniques (Layering versus bulk) in Class II

Posterior Cavities

Articles by (Kuijs, Fennis et al. 2003, Park, Chang et al. 2008) compared different

techniques of placement of RBC restorations using layering vs. bulk and evaluated their

effect on polymerization shrinkage and its effect on cuspal deflection in Class II cavities.

In the study done by (Park, Chang et al. 2008), the samples being tested were 15

aluminum molds which were MOD cavities and identical in shape and size with 4mm

depth, 8mm length and 6mm width, to minimize the substrate variation inherent with the

use of natural teeth. Time dependent measurements were performed using linear variable

differential transformers (LVDT).The aluminum molds were divided into three groups: 1)

restored by bulk fill and cured 40 seconds from occlusal and 20 seconds from both mesial

and distal (total 80 seconds cure). 2) layered in three horizontal layers with each layer cured

for 20 seconds and an additional cure of 20 seconds from occlusal (total of 80 seconds

cure). 3) layered in three oblique layers which were individually cured for 20 seconds each

and an additional 20 seconds (total of 80 seconds). All groups were cured using a curing

light with an intensity of 800mW/cm2. The authors didn’t mention the type of RBC used.

The authors had the main purpose of testing the results of polymerization shrinkage when

using the layering technique and bulk fill. The aim was comparing different layering

techniques while standardizing the type of cavities prepared (MOD) and comparing the

effects of polymerization shrinkage on cuspal deflection. Results of the study showed

incremental filling of cavities produced significantly less polymerization shrinkage (p-

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value less than 0.05) compared with the bulk techniques with cuspal pressures recording a

mean value of 21.6 um in the bulk fills, 19.3 um in the horizontal layering and 18.4 um in

the oblique layering. There were no significant differences between either techniques of

layering.

In the study done by (Kuijs, Fennis et al. 2003) RBC was used to restore Class II

cavities and different placement layering techniques were compared to test their effects on

polymerization shrinkage. An FEA (Finite Element Analysis) model was simulated to

mimic an extracted upper premolar tooth with an MOD cavity preparation. The dimensions

of the cavity preparation were not described. The software for the FEA helped observers

to input the properties of the restoration (the compressive, shear and tensile strength and

modulus of elasticity and Poisson's ratio) and calculate the outcome with different designs

on the computer. Techniques of placement of the RBC were by bulk filling and layering

the RBC either from center to periphery or the opposite. The authors didn’t mention the

specific types of RBC used, however they mentioned that one was light cured while the

other was self-cured. The FEA model was tested by one observer only and there were no

control groups.

The authors were testing, the results of polymerization shrinkage when using the

layering technique and bulk fill. The type of RBC used wasn’t mentioned neither was the

sample size nor the light cure unit. Authors were comparing different layering techniques

while standardizing the type of cavities prepared (MOD). The aim was to compare the

effects of polymerization shrinkage on cuspal deflection.

Authors stated that the amount of polymerization shrinkage and stress on cusps was

shown to be less in the self-cured RBC in comparison to the light cured RBC, however in

the higher stress testing (higher than 6 MPa) the differences were small. There were no

significant differences using bulk and different layering techniques with the mean volume

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change in enamel for both techniques were around 25% at 4 MPa stresses. These stresses

were mainly concentrated in the cervical part of the remaining cusps.

A comparison of the results from the two studies mentioned above showed different

results concerning the polymerization shrinkage and the stresses resulting on cusps. (Park,

Chang et al. 2008) concluded that the incremental and layering technique had less

shrinkage and therefore less stresses on the cusps whereas (Kuijs, Fennis et al.

2003)concluded that layering and bulk filling didn’t directly affect the polymerization

shrinkage but that it was affected more by the mode of cure, where chemical cure RBC’s

showed less shrinkage and stresses than light cured RBC’s. (Kuijs, Fennis et al. 2003) also

evaluated the location of stresses and concluded that the greatest forces were found in the

cervical areas and especially high in enamel.

In conclusion both articles considered similar variables of the degree of shrinkage

and its stress effects on the cusps. Results differed between the articles with Park stating

that layering was better than bulk filling but Kujis concluding that both were almost the

same, and that it was the mode of cure that directly affected the shrinkage and stress pattern.

Although self-cured RBC are rarely used today in restoring posterior teeth, these two

articles still reflect the controversy concerning the rate of shrinkage and the stresses on the

remaining tooth structure causes and factors.

Two additional studies (Campodonico, Tantbirojn et al. 2011, Kwon, Ferracane et

al. 2012) compared the degree of polymerization shrinkage and its effect on the cuspal

deflection. In the study done by (Campodonico, Tantbirojn et al. 2011) twenty-five

extracted human teeth including both premolars and molars were selected to be restored

with two different types of RBC’s including x-tra fil bulk fill RBC (Voco America, USA)

and Filtek Supreme Plus (3M ESPE). MOD cavities 4mm deep and 4mm bucco-lingual

were prepared. The prepared teeth were stabilized in a stainless steel ring and digitized

using an optical scanning model (Lava Scan ST, 3M ESPE) on a computer to help in

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showing the high stress areas on cusps. Ten teeth were chosen to be restored with the x-tra

fil RBC in which five were filled with the layering technique and the other five with the

bulk fill technique. The remaining fifteen teeth were restored using Filtek Supreme Plus

with 5 placed in a layering technique, 5 placed in bulk fill and 5 restored in transtooth

illumination bulk fill technique. The layering technique employed the placement of two

layers of 2mm each with curing for 20 seconds (10 from buccal and 10 seconds from

lingual). The bulk fill technique restored the prepared cavity with RBC thickness of 4mm

cured for 40 seconds (20 from occluso-buccal and 20 seconds from occluso-lingual

direction). The transtooth technique placed the RBC in one increment of 4mm and light

cured it for 20 seconds simultaneously with two curing lights through the buccal and

lingual surfaces followed by 20 seconds from the occlusal direction. Authors used two high

intensity curing units (Curemax V LED and Allegro high intensity LED) with intensities

measured around 1300 Mw/cm2. The bonding technique was the same for all cavity

preparations using Prime and Bond NT (Dentsply, Caulk). Cuspal analysis was done by

aligning accurately the digitized images of the tooth before and after the restoration using

the Cumulus Software to calculate the contour changes in the lingual and buccal cusps

perpendicular to the original tooth surfaces. The results of this cuspal defelection study

showed that the teeth restored with both types of fillings had inward movement of their

cusps after the restoration was placed. Filtek Supreme Plus caused more cuspal deflection

compared to x-tra fil. Authors reported no significant difference in cuspal deflection

between the different filling techniques including layering, bulk and transtooth

illumination however the difference was in the type of RBC used only where the bulk fill

RBC showed less cuspal deflection in comparison with the conventional RBC.

A study done by (Kwon, Ferracane et al. 2012) used twenty four aluminum blocks

with MOD cavities prepared to dimensions of 6mm width, 8mm length and 4 mm depth.

Three types of RBC’s were used in restoration including a hybrid RBC (Z250 - 3M ESPE),

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a flowable RBC (Z350 Flowable - 3M ESPE), and a silorane based RBC (P90 - 3M ESPE).

The bonding system, Scotch Bond MP (3M ESPE), was applied before Z250 and Z350

flowable materials and the P90 system utilized its own silane adhesive prior to the

placement. An LED light curing unit (Elipar S10, 3M ESPE) with light intensity of 1160

mW/cm2 was used to polymerize the restorations. The teeth were divided into four different

groups and restored with the following four placement techniques: 1) a bulk filling

technique where Z250 was placed in bulk and light cured for 80 seconds total (20s from

occlusal, 20s mesially, 20s distally and 20s again occlusally), 2) an incremental filling

technique with the Z250 placed in four incremental layers cured for 80 seconds total (first

horizontal layer 1mm in thickness cured from upper side, two oblique layers cured from an

oblique way and the final horizontal layer cured from the upper side), 3) an incremental

flowable liner technique where the first layer was filled with Z350 flowable RBC in 1mm

thickness followed directly with three layers of Z250 cured for 80 seconds total (each

increment was cured for 20 seconds) and 4) an incremental filling with the silorane based

RBC, P90, placed in four incremental layers cured for 80 seconds total (each layer was

cured for 20 seconds). Cuspal deflection was measured using two LVDT probes (Linear

Variable Differential Transformers) placed on the buccal and lingual sides with

measurements starting at 30 second prior curing and continuing for 2000 seconds during

and after curing. A sum of six measurements of cuspal deflection was taken for all teeth.

In this study the cuspal deflection rates showed a rapid increase within the first 500 seconds

and then gradually increased thereafter. In Group 1 (bulk filled group), 50 % of the total

cuspal deflection occurred within the first 40s after initiation of curing, however in Groups

2-4 (incrementally filled) the amount of deflection increased in a stepwise manner in

relationship to light initiation. The incrementally filled groups 2-4 showed less cuspal

deflection compared to the bulk filled Group 1 (P< 0.001). The incremental filled group

with flowable liner showed higher cuspal deflection compared to the group filled

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incrementally without a flowable liner (P= 0.035). Finally, the cuspal deflection rates with

the silorane based RBC P90 showed significant lower values (P< 0.001) than the groups

filled with methacrylate based RBC’s (Z250).

A study comparing the degree of cuspal deflection when restoring teeth with both

the incremental and bulk fill techniques using bulk fill and conventional RB’s was done by

(Moorthy, Hogg et al. 2012). In this study, 24 maxillary premolar teeth containing Class II

preparations (MOD) were utilized. Three types of different RBC’s were used for this study

including two bulk fill flowable RBC’s. x-tra Base (Voco) and SureFil SDR (Caulk) bulk

fills and a conventional RBC (GrandioSO – Voco). A layering technique was used for

GrandioSO RBC and bulk filling in 2mm increment was done with the bulk fills SDR and

x-tra base followed by a surface application of GrandioSO. The restorations were all

bonded in using a three step adhesive (All-Bond 2). The samples were divided into three

groups with 8 teeth in each: 1) restored with GrandioSO RBC only by applying three

oblique increments mesially and three distally and two increments occlusally with each

increment cured for 20 seconds (total of 160 seconds). Groups 2 and 3 were bulk filled by

SDR and x-tra base respectively in a 1.5 mm thick layer at the isthmus portion and cured

for 20 seconds and the last 2 increments in 2mm thickness occlusally were added with

Grandio SO RBC and cured for 20 seconds each (total of 60 seconds curing time). A twin

channel deflection measuring gauge was used to measure the cuspal deflection resulting

from polymerization shrinkage. This study reported that the mean total cuspal deflection

for the oblique incremental restoration was higher than when restored with bulk fill

technique. The mean total cuspal deflection for the oblique incremental technique was

11.26um. Maxillary premolar teeth restored by bulk fill SDR and x-tra base and veneered

by GrandioSO had mean total cuspal deflection of 4.63 and 4.73 respectively. One way

ANOVA showed significant increase in the mean total cuspal deflection for the

incrementally filled GrandioSO compared to the SDR (P=0.007) and x-tra base (P=0.005).

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No significant difference was found between teeth restored with SDR and x-tra base

(P=1.000).

A study by (Kim and Park 2011) compared the degree of cuspal deflection in a

range of conventional RBC restorations placed in either bulk or incremental technique.

One hundred and twenty premolar teeth had MOD cavities prepared (3.5 mm in width and

3mm in depth). Four different RBC systems were used: 1) Heliomolar (Ivoclar Vivadent),

2) Heliomolar HB (Ivoclar Vivadent), 3) Filtek Supreme (3M) and 4) Renew (Bisco). The

four groups was restored using three different techniques: 1) bulk placement, 2) horizontal

placement in two layers and 3) horizontal placement in three layers. Restorations were

bonded using AdheSE (Ivoclar Vivadent). Restorations were cured for a total of 180

seconds total (60 occlusal, 60 mesial and 60 distal) using a Bluephase LED light (Ivoclar

Vivadent) with irradiance of 900 mW/cm2. A cuspal deflection measuring system was in

contacted to the buccal and lingual cusp tips of the teeth. Results of the study showed that

the amount of cuspal deflection with Heliomolar HB was significantly larger than the other

materials (P<0.05). There was no significant difference in cuspal deflection between the

other three RBC systems. Within the different techniques, the highest cuspal deflection

was found in Group 1 (bulk technique) followed by Groups 2 and 3 (P<0.05). The authors

concluded that the layering technique reduced the amount of cuspal deflection where the

three layers had less cuspal deflection than the two layers than the bulk filled restorations.

(Abbas, Fleming et al. 2003) assessed the cuspal deflection in premolar teeth

restored with a packable RBC placed and cured in bulk or in increments. Large MOD

cavities were prepared in forty extracted upper premolars with the isthmus portion

standardized to 3.5mm and to the gingival margin to 1mm above the DEJ. All cavities were

restored with the same packable RBC (SureFil, Dentsply) and it’s associated bonding

system (Prime and Bond NT, Dentsply). Teeth were divided into four groups with 10 teeth

in each one. 1) bulk placed and cured with Plasma Arc (Kent Uk) for 9 seconds. 2) Material

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was placed in bulk and cured with the Optilux 501 light (Kerr) operated at the turbo boost

mode (10 seconds boost + 30 seconds regular). 3) Material placed in eight increments, three

in the mesial box and three in the distal box and two over the occlusal portion and cured

with the plasma arc light for 3 seconds each increment (24 seconds total). 4) Teeth restored

in eight increments using the Optilux 501 light curing unit in turbo boost mode (10 seconds

+ 30 seconds). The degree of cuspal deflection was measured by approximating the buccal

and lingual cusps to the receptors of a deflection measuring gauge. Baseline and each step

of polymerization records were taken for the cuspal deflection. Three measurements for

Groups 1 and 2 and eight measurements for Groups 3 and 4 were taken. Results showed a

significant increase in cuspal deflection with the turbo boosted mode curing light as

compared to the plasma arc light (P<0.05). The total mean of the cuspal deflection with the

incremental cure were significantly increased compared with the bulk cure for both light

sources (P<0.05). The lowest mean cuspal deflection was observed in Group 1 (bulk placed

and cured with Plasma Arc) 4.98; and the highest mean cuspal deflection was found in

Group 4 (Teeth restored in eight increments using the Optilux 501 light curing unit in turbo

boost mode)34.03; the scores of cuspal mean deflection were 19.37 for Group 2 (Material

was placed in bulk and cured with the Optilux 501 light (Kerr) operated at the turbo boost

mode) and 17.75 for Group 3 (Material placed in eight increments, three in the mesial box

and three in the distal box and two over the occlusal portion and cured with the plasma arc

light for 3 seconds each increment ,24 seconds total) .

Resistance to Fracture

A study done by (Wieczkowski, Joynt et al. 1988) presented data for comparing

resistance for cuspal fracture when placement of RBC’s by layering or bulk filling cavities.

Extracted premolar teeth were restored using two different RBC’s Fulfil (Dentsply) and P-

30 (3M/ESPE) with two different placement techniques (bulk versus layering). MOD

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cavities were prepared to 2mm in depth in the isthmus portion and 4mm in the proximal

box. The samples were divided into four groups with Group 1 and Group 2 were restored

by P-30 (3M) RBC by bulk and layering techniques respectively. Groups 3 and 4 were

restored with Fulfil RBC using also the bulk and layering techniques. Force was applied to

the cusps of teeth using the Universal Instron machine and the resistance to fracture was

calculated and compared between the different placement techniques and different RBC’s.

This study reported that layering resisted cuspal fracture better than the bulk

technique. The authors concluded that cuspal stresses increased when bulk technique was

used rather than the layering technique. Authors also stated that P-30 RBC showed better

scores than Fulfil

Creep Tendency

(El-Safty, Silikas et al. 2012) used stainless steel split molds of 4mm in diameter

and 6mm in length to prepare cylindrical specimens for creep testing. Authors used six

types of RBC’s in which four were bulk filled (Venus, SureFil (SDR), Tetric EvoCeram

and x-tra base) and 2 were layered (Beautiful Flow Plus and Filtek Supreme). Sample size

was 60 molds with10 molds each restored by a different type of RBC. The six groups of

the RBC were divided into halves (5 samples in each group) to be tested in a dry or wet

environment. A creep measuring apparatus was used to measure creep values. Results were

different depending on the material used (type of RBC) and the condition (wet or dry).

Within the materials used, Filtek Supreme had the lowest creep values (mean of 0.74%)

compared to Venus Bulk Fill (mean of 1.50%). The dry conditions had better (lower) creep

values compared to wet field. In the cavities filled with Beautiful fill the creep score was

0.90% in the dry field compared to 1.10% in the wet field where the lowest creep values

were exhibited by Filtek Supreme RBC (0.72% and 0.79%). The highest creep values

(strain and permanent set) in dry conditions were recorded for the SureFil Bulk Fill group

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(1.55% and 0.49%), where in the wet conditions it was recorded in the Venus Bulk Fill

group (1.80% and 0.59%). The authors concluded that the conventional RBC’s placed by

the layering technique lowered creep tendency compared with the bulk fill RBC’s placed

in bulk technique yet the bulk RBC’s placed in bulk exhibited acceptable creep which can

be explained as due to the increased filler loading in the recent bulk fill materials.

Another study (Czasch and Ilie 2013) compared the creep deformation as well as

other mechanical properties of bulk fill RBC restorations. Seven bulk fill RBC’s were

tested: 1) Venus Bulk Fill (Heraeus Kulzer), 2) SureFil SDR flow (Dentsply Caulk), 3) x-

tra base (VOCO), 4) x-tra fil (VOCO), 5) Filtek Bulk Fill (3M ESPE), 6) Sonic Fill (Kerr),

7) Tetric EvoCeram Bulk Fill (Ivoclar Vivadent). Five different mechanical properties

were tested including flexural strength, flexural modulus, indentation modulus, Vickers

hardness and creep deformation. The flexural strength and modulus were determined in a

three point bending test. One hundred and forty samples were made in a steel mold having

dimensions of 2x2x16mm. The specimens were cured for 20 seconds for three light

exposures (total of 60 seconds) using an Elipar Freelight 2 (3M ESPE) with irradiance of

1250 mW/cm2. The micromechanical properties were determined by using fragments of

the same specimens used for flexural testing which were larger than 8mm. Results of the

study showed the highest significant flexural strength values for Sonic fill, x-tra Base and

x-tra Fil as 142, 139 and 137 (P<0.05). The differences between materials were more in

the comparison of flexural and indentation modulus where x-tra fil had the highest

significant values (9.5) and Filtek and Venus Bulk Fills achieved the lowest (3.6 and 3.8)

(P<0.05). Authors stated that bulk fills had the same flexural strength when compared to

nanohybrid and micro hybrid RBC’s. Flexural modulus, indentation modulus and Vickers

hardness values for the bulk fills were between the hybrid and flowable RBC’s. In terms

of creep values, bulk fills showed high creep deformation which made them similar to the

flowable RBC’s.

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Cavity Liners

Many materials have been used under posterior RBC’s in order to increase the

wettability and adaptation of RBC’s to gingival margins. These materials include resin

modified glass ionomers (RMGI) and the flowable RBC liners.

Recent research results vary with some studies showing that these liners decreased

the marginal gaps and increased the adaptation (Frankenberger, Kramer et al. 1999,

Peutzfeldt and Asmussen 2002, Opdam, Roeters et al. 2003, Chuang, Jin et al. 2004), some

showed no affect (Chuang, Liu et al. 2001, Haak, Wicht et al. 2003, Sensi, Marson et al.

2004, Lindberg, van Dijken et al. 2005, Ziskind, Adell et al. 2005), and one study showed

that these liners worsened the adaptation and increased the marginal leakage (Chuang, Jin

et al. 2003).

An article (Chuang, Liu et al. 2001) compared the use of a flowable RBC at the

gingival margin below RBC to using only conventional RBC’s and the effect on gap

formation and marginal microleakage. This experiment was done by two dentists; one of

them was experienced while the other was inexperienced. The results measured by dye

penetration showed that operator experience was the only factor that affected the amount

of gingival leakage with the flowable RBC liner best with the experienced dentist.

(Peutzfeldt and Asmussen 2002) compared the use of flowable RBC’s and self-

curing RBC’s in MOD cavities with gingival margins below the CEJ. The RBC used was

a hybrid (Renew). A flowable liner (Aeliteflo) was compared to a self-curing RBC (Bisfil

2B). Dye penetration was used to assess the degree of microleakage. The group that was

restored with flowable RBC’s showed lower marginal gaps compared with the other group

restored with self-curing RBC’s.

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Snowplow Technique

A study (Chuang, Jin et al. 2004) compared the thickness of the RBC liner beneath

the RBC and its effect on the marginal leakage in Class II cavities. Four main groups were

used in this study: 1) RBC only, 2) thin layer of flowable RBC cured simultaneously with

conventional RBC, 3) thin layer of flowable RBC pre-cured, and 4) thicker layer of

flowable RBC pre-cured. Dye penetration was used to assess the amount of microleakage

at the margins. Marginal quality was assessed using SEM. Results showed that the best

margins were found in Group 2 where the RBC was placed and cured at the same time with

the conventional RBC. The worst group was Group 4 with the thick liner.

(Opdam, Roeters et al. 2003) examined the difference in marginal leakage and

marginal adaptation between different techniques of placing RBC’s. The study groups

were; 1) bulk filling technique, 2) Flowable liner pre-cured and then applying over it the

conventional RBC, and 3) Flowable RBC placed and cured simultaneously with the

conventional RBC. All restorations were sectioned and tested under the light microscope

for marginal gaps. The results showed that all three techniques resulted in some sort of

voids, however, the least voids were found in Group 3, the flowable RBC cured with the

conventional RBC.

Pre-heated Resin Based Composites

Higher temperatures may be used to mold and shape plastic materials, which turn

more rigid and attained their form when cooled (Hackman, Pohjola et al. 2002).

Advantages have been mentioned for applying heat to RBC’s (Bagis and Rueggeberg

2000). RBC’s could be heated to temperatures up to 155 degrees F. Studies have tested the

heated RBC’s for their monomer conversion, Kinetics and decrease of viscosity. These

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show that when heated, the degree of monomer conversion increased and the residual

monomers decreased increasing the RBC adaptation to cavity walls (Daronch, Rueggeberg

et al. 2005). Other studies (Trujillo, Newman et al. 2004, D'Alpino, Pereira et al. 2006)

showed that heating RBC’s increased the degree of monomer conversion which minimized

the amount of curing light needed.

Pre-heated RBC’s are characterized to have lower viscosity compared to regular

RBC’s. This property of lower viscosity increases the marginal adaptation and surface

wetting of RBC’s. A study done by (Blalock, Holmes et al. 2006) tested the direct effect

of the heating of RBC’s on the viscosity of different types of RBC’s. Seven different

conventional types of RBC’s were used containing different amount of fillers of different

sizes (packable, hybrid and microfilled) and also five different flowable types. Results from

this studies showed that all conventional RBC’s film thickness decreased from 54% to 77%

of their original film thickness when heated. Different types of RBC’s differed in their

degree of viscosity. Another study (Broome 2006) compared also the film thickness of five

different RBC when heated, and reported a 5%-76% decrease in viscosity.

(Aksu 2004) tested the amount of marginal microleakage with different pre-heated

RBC’s in Class II cavity preparations. Four methods where tested as follows : Group 1)

Esthet X control, Group 2) Flowables esthet X flow with Esthet X, Group 3) preheating of

Esthet X to 130 degrees F, Group 4) Delayed cure for 15 seconds. Ten cavities were

prepared in third molars, then they were restored and after thermocycling they were

sectioned and examined under the microscope for the amount of die penetration. Results

showed that leakage scores were less in the group of pre-heated RBC’s compared with the

control and flowable groups.

Another study (Froes-Salgado, Silva et al. 2010) tested the effect of RBC pre-

polymerization temperature and energy density on the marginal adaptation and the flexural

strength, cross linking and degree of conversion. Class V cavities were prepared in 40

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bovine incisors were all restorations were bonded using the Single Bond 2 system and

restored with Filtek Z350 (3M/ESPE). The RBC was either left at room temperature (25

C) or pre-heated to 60 C in the Calset device. Four groups were tested: 1) room temperature

RBC cured for 40 seconds. 2) preheated RBC cured for 40 seconds. 3) room temperature

cured for 20 seconds. 4) preheated RBC cured for 20 seconds. Results showed that the pre-

heated RBC’s exhibited better marginal adaptation than the room temperature RBC’s

however the degree of conversion, flexural strength and polymer cross-linking was the

same between both groups.

Summary

Different techniques and RBC systems have been developed to improve the

marginal adaptation and mechanical properties of the Class II restoration. Many of these

techniques involve variations of material placement. These have included incremental

placement, usage of cavity liners, Snow plow technique, pre-heating of RBC materials and

bulk filling materials.

The review of the literature targeted articles and studies examining marginal

adaptation and gap formation with different materials and placement techniques. Results

have shown conflicting results. Older studies showed that layering technique and

conventional RBC’s had better marginal adaptation compared to RBC’s restored and cured

in bulk. However newer studies have shown different results where both RBC systems and

techniques (layering versus bulk fills) exhibited similar marginal adaptation scores

(Furness et al, 2014; Campos et al, 2014). This may be the result of the recent development

of newer RBC systems which have specifically recommended for bulk placement.

Many questions still exist about these new bulk fill RBC systems including

marginal adaptation, depth of cure, surface micro-hardness, and the best method of

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placement. These questions and properties need to be evaluated to determine whether the

bulk Fill materials have advantages over the conventional RBC’s in the clinical application.

It is very important to compare between both the type of RBC (bulk fill and conventional)

and the placement technique (bulk and layering) as most literature compared only one

variable either the type of RBC used or the placement technique (bulk and layering) using

one type of RBC. The continuous development of bulk fill RBC’s needs continuous

research and testing to approve these restorations as successful.

Therefore, the objective of this research study was to compare a new bulk fill RBC

Tetric EvoCeram bulk fill to a conventional RBC Tetric EvoCeram filling material by

varying the method of placement (layering versus bulk fill) and evaluating the marginal

adaption and depth of cure through the determination of surface micro-hardness.

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CHAPTER III

MATERIALS AND METHODS

Overview

The purpose of this in-vitro study was to test the effects in a Class II cavity

preparation of layering versus bulk filling of two different types of Tetric EvoCeram RBC’s

as determined by evaluation of the external gingival marginal adaptation and the internal

surface micro-hardness. The types of RBC used in the study were a conventional RBC and

a bulk-fill RBC.

The study utilized Class II proximal boxes prepared on molar teeth. Two different

RBC’s (Ivoclar Vivadent) were used for this study including Tetric EvoCeram

recommended for the layering technique and the Tetric EvoCeram Bulk Fill recommended

for the bulk filling technique. All increments used in the layering technique were placed in

a 2mm thickness while on the bulk fill RBC’s were placed in a 4mm increment following

the manufacturer's instructions (table 1).

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Additional

contents Size

Vol.,

%

Wt.,

% Filler Resin Shade Type

Additives,

catalysts,

stabilizers

and

pigments

Avg.

550

nm

53-

54%

76%-

80%

Barium

glass,

ytterbium

triflouride,

mixed

oxide and

prepolymer

Dimethacrylates A2

Tetric

EvoCeram

Bulk Fill

Material

Additives,

catalysts,

stabilizers

and

pigments

Avg.

550

nm

53%-

55%

75%-

76%

Barium

glass,

ytterbium

triflouride,

mixed

oxide and

prepolymer

Dimethacrylates A2

Tetric

EvoCeram

Filling

Material

Table 1 Composition of resin based composite (Tetric EvoCeram system)

Marginal adaptation between the RBC and tooth structure can be defined as the

degree of integrity or seal that forms at the junction between the restoration and the tooth

cavo-surface and also can be described as the presence or absence of gaps at this junction.

A Scanning Electron Microscope with a final magnification of 200X was used in the study

to evaluate the integrity of the gingival margins of the RBC restorations. The marginal gaps

that formed at the gingival margins were recorded and evaluated along the whole length of

the gingival margins and were measured in microns from the images that resulted from the

SEM images.

The other outcome variable which was evaluated was surface micro-hardness.

Teeth were sectioned in buccal and lingual halves where nine points of hardness testing

were measured on both techniques used.

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Research Question

The research question proposed in this study was to determine which of the two

techniques (the layering or the bulk filling technique) in combination with two materials

(conventional or bulk filled RBC’s) provided better marginal adaptation with less marginal

gaps and had higher surface micro-hardness numbers at different levels of measurements

in a proximal Class II tooth preparation.

Methodology

Independent Variables

The effect of the placement technique and RBC type was evaluated by

standardizing the main factors in the experiment to get accurate and reliable results. The

RBC’s used were the Tetric EvoCeram Bulk Fill and the conventional Tetric EvoCeram

filling material. Two techniques of placements were tested the layering technique (two

increments of 2mm each) and the bulk fill technique (one layer of 4mm increment).

Standardized Criteria

The materials used for each and every step of the investigation was standardized.

These included: A) dimensions of the Class II proximal boxes restored in RBC, B) bulk

filling technique using two nanohybrid filled RBC’s (Tetric EvoCeram Bulk Fill and Tetric

EvoCeram conventional RBC from Ivoclar Vivadent), C) layering technique using both a

conventional RBC (Tetric EvoCeram) and a bulk fill RBC (Tetric EvoCeram Bulk Fill)

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from Ivoclar Vivadent, D) adhesive system used (Syntac three step total etch system from

Ivoclar Vivadent), E) light curing time and intensity using the LED Bluephase 16i light

cure. The LED light which was used produced a narrow spectrum of blue light in the 400-

500 nm range (with a peak wavelength of about 460 nm) and irradiance of around 1200

mW/cm2.

Dependent Variables

The main dependent variables measured in this study were: a) the percentage of intact

gingival margins compared to the non-intact margins to determine amount of gap

formation as determined by SEM, B) Knoop hardness (KHN) testing at different levels to

determine degree of polymerization.

Experimental Groups

The Experimental Groups were: Group 1: Restoration using the bulk fill RBC placed in

bulk (BB), Group 2: Restoration using bulk fill RBC placed in layers (BL) (experimental

group), Group 3: Restoration using Conventional RBC placed in layers (CL) (positive

control), Group 4 – Restoration using Conventional RBC placed in bulk (CB) (negative

control) (Figure 1).

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Figure 1. A flow chart of the step by step protocol of the study

Teeth Preparation

Fully erupted extracted molar teeth were selected for the experiment. Sixty teeth

were chosen (n=15/group). All teeth were checked to insure no presence of caries, defects,

restorations or fractures that might affect the final results. All teeth selected were large

molar teeth to make it easier to flattening and prepping the proximal surfaces. Teeth were

cleaned of soft tissue and debris with a # 12 scalpel blade (Mitex St. Steel, P.A, USA) and

slurry of pumice and water. They were stored in artificial saliva (AS) with 5000 ppm

Chloramine solution at 4 Celsius for 1 week to prevent bacterial growth and then

transferred to AS without Chloramine T.

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The occlusal surfaces and proximal surfaces of the teeth were flattened using a

grinder (Whip Mix Corporation, KY, USA). After flattening, the proximal and occlusal

surfaces were lightly polished using the 600, 1200 and 2000 grit sand paper (Buehler

company, IL, USA). Teeth were stored in AS Chloramine solution 4 Celsius until they

were required for cavity preparation (Figure 2).

Figure 2. Flattened teeth on the occlusal, mesial and distal surfaces

Cavity Design

For the study, Class II slot preparations were prepared on the flattened mesial and

distal parts of each tooth. All occlusal surfaces were flattened to eliminate the cusps. The

proximal box basic outline was prepared using the CNC Specimen Former machine (the

University of Iowa) with a 55 carbide bur (Brasseler, USA) (Figure3). The basic prepared

cavities had dimensions of 4mm length occluso-gingivally, 4mm width bucco-lingually

and 2mm depth mesio-distally. All external margins were ninety degree butt joint margins

without any bevels. All cavity walls were located at least 2mm in dentin gingivally to

provide a 2mm amount of dentin at the ginigival margins of the preparations. Preparations

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were checked for standardization using a digital caliper (Mitutoya, Japan) and were cleaned

using the air water stream.

(a)

(b)

(c)

Figure 3. a) CNC Specimen Former machine used for standardizing cavity preparations.

b) mounted teeth for the CNC machine. c) standardized cavity preparations on the mesial

and distal of each tooth.

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Restorative Procedure

Matrixing of the Preparation

Two teeth were mounted in contact with each other in vinyl polysiloxane putty

material (Exaflex, GC, America, IL, USA) to stimulate a clinical situation. One tooth

proximal contained the preparation while the adjacent tooth was flattened to provide even

contact with the preparation of the other tooth during restoring it. The putty was allowed

to set for 2 minutes. A straight matrix band (WaterPik, USA) was placed between both

teeth to ensure an accurate confinement of restorative material adaptation. A c-clamp was

placed over the putty material on the mesial and distal of both teeth to tighten both teeth

together. The C-clamp was placed on the putty not the tooth as the clamp adapts better on

the putty which in turn pushes the teeth tight (Figure 4).

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(a)

(b)

(c)

Figure 4. a) teeth placed in putty for restorative procedures. b) placement of a tofflemire

matrix band between both teeth. C) pushing teeth tight with a C-clamp

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Adhesion Procedures

Two different RBC’s supplied by Ivoclar Vivadent were used for this study. These

materials included a conventional RBC, Tetric EvoCeram, recommended for placement in

layers of 2mm or less, and the other a bulk fill RBC, Tetric EvoCeram Bulk Fill,

recommended for one increment placement used for the bulk filling (Figure 5). All

preparations were restored with a total-etch bonding system (Syntac, three-step total etch

bonding system, Ivoclar Vivadent, USA. (Table 2)

Heliobond

composition

Adhesive

composition

Primer

composition

Type Name

Bis-GMA,

triethylene

glycol

dimethacrylate

, stabilizers

and catalysts.

Polyethylene

glycol

dimethacrylate,

glutaraldehyde

in an aqueous

solution.

Triethylene

glycol

dimethacrylate,

polyethylene

glycol

dimethacrylate,

maleic acid and

acetone in an

aqueous

solution.

Three step

total etch

system

Syntac

Bonding

System

Table 2. Syntac bonding system composition (Ivoclar Vivadent)

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(a)

(b)

Figure 5. a) Tetric EvoCeram Bulk Fill, b) Tetric EvoCeram filling material

Light energy delivery system was standardized between all the bonding and

restorative procedures to ensure equal degree of cure and polymerization reaction between

the different experimental groups. The manufacturer's recommendations for the light

energy delivery was followed which recommended curing the adhesive system for 10

seconds using a light producing irradiance of 1000 mW/cm2 at least. The energy delivered

for curing of the restorative materials were also standardized using the manufacturer's

instructions to cure the RBC restorations for 10 seconds with a light producing irradiance

of not less than 1000 mW/cm2. The exact mean irradiance of the curing light used

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(Bluephase 16i Ivoclar Vivadent) was measured by the MARC Resin Calibrator (Bluelight

Analytics, Inc) at 2100 mW/cm2 delivering 22.43 J/cm2 at 0mm distance and 1380 mW/cm2

delivering 14 J/cm2 at 4mm. The amount of energy delivered was standardized to 14 J/cm2

to each increment placed which was 11 seconds of cure for the first layer and 7 seconds

of cure for the second layer. The bulk RBC placed in bulk was cured for 11 seconds. The

bulk RBC placed in 2 layers and placed in bulk was cured for 18 seconds.

A step by step procedure was followed with phosphoric acid gel applied first on the

prepared enamel and then to the dentin surfaces. The etchant was left on the teeth for 15

seconds then all etchant gel was removed with vigorous water spray for at least 5 seconds.

Any excess moisture was removed by gently blotting the surface with a piece of cotton

removed leaving the dentin surface with slightly a glossy wet appearance (wet bonding).

Syntac Primer was applied with a brush in the cavity and gently rubbed for a contact time

of 15 seconds on the dentin. Excess Syntac primer was dispersed and dried thoroughly with

air. Syntac adhesive was then applied and left for 10 seconds and then thoroughly dried

with an air syringe. Heliobond then was applied and blown to a thin layer and light cured

for 10 seconds with a curing light (Bluephase 16i Ivoclar Vivadent). The irradiance of the

curing light was monitored throughout the whole study to insure that it was not less than

1000 mW/cm2. (Figure 6, 7).

Figure 6. Ultra etch (UltraDent Products, Inc) Figure 7. Syntac bonding system

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Restorative Material Placement

The RBC material was dispensed out of the RBC compule in a 2mm thickness

measured by the periodontal probe (Premier dental products, USA) (Figure 8). The RBC

was cut from the RBC compule using a Gold Almore Instrument (Swiss Dental Safident)

in order not to incorporate any air bubbles or voids into the RBC material.

Figure 8. Accurate measurement of the resin based composite increments

The RBC was placed using two different techniques. The incremental technique

involved applying two horizontal increments placed in a 2mm thickness increment using a

ball burnisher (Premier dental Products, USA). A curing light (Bluephase 16i, Ivoclar

Vivadent) was used to cure each layer of the sample where the first layer was cured for 11

seconds while the second layer was cured only for 7 seconds. The curing light was tested

on a MARC Resin Calibrator system for consistency in energy delivery. Curing of the first

increment was done with the tip of the light touching the occlusal surface of the tooth while

curing of the second increment was done first at a distance of 0.5-1mm from the occlusal

surface for 2 seconds then the tip was moved to contact the occlusal surface to complete

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curing. The light curing tip was placed in the same orientation, position and distance with

each restoration.

Group

number

Resin based

composite

Technique of

placement

Abbreviation of

group (Composite

type/ technique)

Bonding Curing time

1 Tetric EvoCeram

Bulk Fill bulk technique BB

Syntac

bonding

system

11

Seconds(for

one whole

increment)

2 Tetric EvoCeram

Bulk Fill

Layering

technique BL

Syntac

bonding

system

11 seconds

(first

increment)

7 seconds

(second

increment)

Total of 18

seconds

3 Tetric EvoCeram

Filling Material

Layering

technique CL

Syntac

bonding

system

11 seconds

(first

increment)

7 seconds

(second

increment)

Total of 18

seconds

4 Tetric EvoCeram

Filling Material bulk technique CB

Syntac

bonding

system

11 seconds

(first

increment)

7 seconds

(second

increment)

Total of 18

seconds

Table 3. The light curing time for each group

With the bulk fill technique, the RBC was applied in one increment to fill the entire

proximal box to a thickness of 4mm using the ball burnisher (Premier Dental Products,

USA).The same curing light was used Bluephase 16i (Ivoclar Vivadent) and a curing time

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of 11 seconds only was used for the entire 4mm depth of the RBC according to the

manufacturer’s directions while the bulk RBC placed in layers was cured for 18 seconds.

After placement and curing of the restoration, the matrix band and adjacent tooth

were removed from contact with the restoration (Figure 9). The same adjacent tooth was

reused for all samples. The restored proximal surfaces were lightly polished to remove any

flash using 600, 1200 and 2000 grit sand paper (Buehler Company, IL, USA). All samples

were stored in artificial saliva at 37c for at least 24 hours until evaluated for marginal

analysis and hardness testing. A light microscope (Carl Zeiss, Germany) was used with the

magnification of 10x/23 X 5x to check the initial quality of the RBC placed. Specimens

displaying technique errors such as large single voids more than 250 microns or multiple

voids more than three voids at the margins or the body of the RBC were excluded from the

study and another tooth was added.

Figure 9. Restored tooth on the mesial and distal

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SEM Sample Preparation and Image Capture

All teeth were kept in artificial saliva and a dark medium until the time of testing.

Gingival gaps were analyzed by preparing epoxy resin replicas (Buehler Company, IL,

USA). All teeth were cleaned by placement in a 70% ethanol ultrasonic bath for 2 min

rinsing with water and drying with air. A first impression was taken using Aquasil XLV

Ultrafast Set (Caulk, USA). The impression was left to set for 5 minutes before discarding

it. A second impression was taken with the same material and left to set for 10 minutes.

This impression was stored for 24 hours before pouring the epoxy resin in it. The epoxy

resin (5 parts) with the epoxicure hardener (1 part) was mixed for 2 minutes and placed in

a vacuum for 10 minutes. The resin then was placed inside the impression using a pipette

and was spread uniformly using an air syringe. Once the impression was filled totally with

resin, it was left to set for 24 hours. The replicas were ready after 24 hours to be examined

and studied under the SEM to measure and compare the percentage of intact margins to the

non-intact margins along the gingival margin (Figure 10). The epoxy resin replicas were

sputter coated with gold using the K550 Emitech sputter (Quorum Technologies Ltd, UK)

(Figure11,12).

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(a)

(b)

(c)

Figure 10. a) impression of the margins. b) Tooth out of the impression material. c)

replica after complete setting from the impression

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Figure 11. Gold sputter coating the replica for SEM examination

Figure 12. The epoxy resin replica after gold sputtering

All the external gingival margins were examined under a magnification of 200X by

the same evaluator using the Scanning Electron Microscope (Hitachi S4500). A sequence

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of the gingival margin was captured for all samples. All teeth had eight captured images.

One image was taken at a 30X magnification which showed the entire gingival margin

including at least 2mm up the buccal and lingual margins. This image was taken to evaluate

the cavity form and shape and also to ensure that there wasn’t any RBC flash that may

affect the marginal analysis. Seven images were taken of the gingival margin at a

magnification of 200X. The margins were examined at the along the gingival area and at

least 0.2 mm up the buccal and lingual margins. The images taken for the samples depended

on the landmarks chosen on each image to be the reference for the subsequent image

without overlapping, capturing the gingival floor, corners and line angles (Figure 13).

(a)

(b)

Figure 13. a) The whole margins showing under magnification of 30X. b) the seven

images stitched together at 200 X using computer software

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Randomization and Blinding

All teeth used in the experiment were numbered from 1-60 and each specimen or

restoration (mesial and distal of teeth) was numbered from 1-120, so numerical codes were

assigned for each sample in order to blind the examiner during score recording. Teeth and

surfaces were randomly chosen to be filled with the four different techniques as mentioned

before and were randomly put in a table for measurements of the gingival marginal gaps

and surface micro-hardness. All samples were examined by one operator which was

blinded.

Gingival Margins Evaluation

Once the images of each sample were obtained, the images were examined for

gingival marginal gaps using software Image J (v1.46r, USA). Tracings were performed

on all images for each sample in order to provide an accurate quantitative evaluation of the

margins and to calculate the percentage of gaps formed in respect to all the gingival margin

examined. The gingival margins were assigned scores and were categorized in to different

groups depending on the gap size (Table 4).

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Table 4. Scoring criteria illustrated with SEM images (continued)

SEM Images (200 X) Definition Marg

inal

Quali

ty

Intact

margins

MQ=

1

Severe

irregulariti

es

MQ=

2

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Table 4. Scoring criteria illustrated with SEM images (continued)

Marginal

gap < 2um

MQ=

3

Marginal

gap 2-20

um

MQ=

4

Marginal

gap > 20

um

MQ=

5

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Void less

than 250

um or less

than three

in number

MQ=

6

Table 4. Scoring criteria illustrated with SEM images

The percentage of the marginal gaps in relation to the whole margin examined was

recorded. Training was done on the recording of gaps through meeting with committee

members to define each gap category and to standardize the way of recording gaps between

all samples. Training was done by the same operator on many samples during the pilot

study to standardize the examining criteria and score recording manner.

Scoring Criteria

The gingival marginal morphology was expressed into 5 categories of gap sizes.

All gap measurements were measured using the same technique and software (Image J

v1.46r, USA) where the sum of gap percentages was calculated from the entire margin.

After the preliminary recordings of the gaps at the gingival margin along the entire length,

these data were summarized and separated for statistical purposes into two main nominal

categories “Gap” versus “No Gap”.

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Surface Micro-hardness Testing

Teeth were sectioned (two specimens per tooth) and half of the tooth was used for

the surface micro-hardness testing. Teeth were sectioned in the middle of the preparation

bucco-lingually at the point of 1.9 mm as the full length of the bucco-lingual margin was

4mm (Figure 14, 15).

(a)

(b)

Figure 14. a) Measuring the width of the restoration Buccolingually and marking with

pencil at point of 1.99mm to section in this area. b) re-assuring measurements and

sectioning of teeth using the Isomet machine

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88

(a)

(b)

Figure 15. a) teeth sectioned (occlusal view). b) teeth sectioned (Proximal view)

Measurements of surface mico-hardness were done in three main areas along the

RBC from an occluso-gingival direction. These three points were placed at a parallel line

at the middle of the sample mesio-distally (at 1mm) and the levels were established at

1.8mm, 2.8 and 3.8 mm in distance from the occlusal surface as measured by a digital

caliper (Mitutoyo, Japan) to examine the surface hardness of the different RBC’s. Each one

of these three points had two corresponding points, one on the right and the other on the

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89

left (mesial and distal) with each spaced 0.5mm from the center. A total measurement of

nine points was recorded for each sample. Measurements were taken at least 15 minutes

after exposure to the curing light. The hardness testing was done by the Micromet II

(Buehler, IL, USA) using a100 gm load for 15s.

Pilot Study

A pilot study was conducted to determine the sample size and confirm some major

steps in the design and sequence of specimen’s treatment. In the pilot study the specimens

were prepared using a regular 330 bur (Brasseler) in conjunction with a SONICSYS

APPROX diamond (Kavo) to standardize the shape of the cavities to have the same

dimensions with the gingival outline rounded and not imitating the clinical conditions. The

technique was then modified to include the cavity preparations using a CNC Specimen

Former machine where all teeth were mounted and set to be prepared by the CNC Specimen

Former machine to get more standardized proximal preparations on the mesial and distal

of each tooth in an attempt to standardize the prepared cavities and the stresses applied by

the tooth substrate during restoring the teeth. During the preparation of teeth, pulp

exposures were encountered with some teeth because of the size. Because of this large

molar teeth mesio-distally were selected to avoid such problems in the preparation phase.

Originally, the margins of the preparation were to be all in dentin. However, it was

impossible to place all margins in dentin without excessive flattening of the sides of the

teeth, a design didn’t match the clinical settings. The preparation was changed to include

only the gingival margins in dentin and at least 2mm of the buccal and lingual margins

with the gingival margin at least 1mm below the cement-enamel junction (Wet et al, 1991;

John R. Gallo, 2000; Edson Alves De Campos et al, 2014).

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90

During the pilot study the operator wasn’t blinded to the teeth being tested. To

decrease possible bias during the study testing each tooth was coded by a numerical code

for the purpose of blinding and all codes were tabulated corresponding to their type of RBC

and technique used for future referral whole collecting the results for statistical analysis.

The procedures explained previously were followed to compare between both

techniques of layering versus bulk filling using two different RBC’s which included

conventional and bulk filled.

Power Analysis

To determine the sample size needed for the present study, statistical power analysis

was conducted based on the prior pilot data. In order to achieve significant results, this

analysis suggested that a sample size of at least 15 teeth per group was needed to detect a

significant difference in the external marginal gaps and the internal surface micro-hardness

among the four RBC restorative groups with 80% power and an effect size of 0.895 for the

external marginal gaps and 0.904 for the internal surface micro-hardness at 5 %

significance level, using one-way ANOVA.

Statistical Analysis

Sixty teeth with one hundred and twenty restorations prepared on the mesial and

distal of each tooth were selected and randomly divided into four RBC restorative groups,

including15 teeth per group with thirty (n=2/per tooth) restorations total per group.

External marginal gap and internal surface micro-hardness were measured at both mesial

and distal surfaces of the same tooth, while internal surface micro-hardness scores were

measured at three different hardness levels (depths) within each surface for the same tooth

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91

at levels of 1.8mm, 2.8mm and 3.8mm depth from the top surface. Mean values of hardness

at three levels and mean marginal gaps of the different seven SEM images by each surface

and tooth were used for the statistical comparisons.

Variables

In this study, the independent variables were, the dimensions of the Class II

proximal boxes restored in RBC, the bulk filling technique using two nanohybrid filled

RBC’s (Tetric EvoCeram Bulk Fill and Tetric EvoCeram conventional RBC from Ivoclar

Vivadent), the layering technique using both a conventional RBC (Tetric EvoCeram) and

a bulk fill RBC (Tetric EvoCeram Bulk Fill) from Ivoclar Vivadent. The adhesive system

used (Syntac three step total etch system from Ivoclar Vivadent) and the light curing time

and intensity using the LED Bluephase 16i light cure of 12000 mW/cm2 from Ivoclar

Vivadent. However the dependent variables were the percentage of intact gingival margins

compared to the non-intact margins to determine amount of gap formation as determined

by SEM and the Knoop hardness (KHN) testing at different levels to determine degree of

polymerization.

Overall Statistical Methods

Descriptive statistics were conducted (Refer to appendix A). One-way ANOVA

was performed to evaluate the effect of RBC restorations and placement technique on the

external marginal gap and internal surface micro-hardness. If a significant effect existed,

the post-hoc Tukey’s HSD (Honestly Significant Difference) test was used for the multiple

pairwise comparisons to determine which pairs of groups differed. Within each RBC

restorative group, either a paired-sample t-test or a nonparametric Wilcoxon signed-rank

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92

test, as appropriate, was used to test the difference in external marginal gap and internal

micro-hardness between mesial and distal surfaces.

For assessing the effect of hardness levels on internal surface micro-hardness, when

taking into account the correlated data obtained (i.e. three specimens from the same tooth

for the three hardness levels of internal surface micro-hardness measured on the same

tooth), the random effects in Mixed Models ANOVA (i.e. to allow correlation between

three specimens obtained from the same tooth) was conducted to evaluate the effect of

hardness levels on internal surface micro-hardness within each RBC restorative group.

Additionally, the Shapiro-Wilks’ test was applied to verify the assumption of normality as

nonparametric statistical procedures were carried out.

All tests employed a 0.05 level of statistical significance. SAS for Windows (v9.3,

SAS Institute Inc, Cary, NC, USA) was used for the data analysis.

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CHAPTER IV

RESULTS

Difference in Gingival Marginal Gap Scores between the Four Tested Groups

at the Distal and Mesial Surfaces

The Gingival marginal gap scores were recorded for the four tested groups on the

mesial and distal surfaces. Comparisons were made to evaluate differences in marginal

gaps between the different restorative groups on each tested surface (mesial and distal).

The results of the average marginal gaps of the different seven SEM images for each group

were recorded (Refer to Appendix B).

Data were analyzed using one-way ANOVA. This analysis revealed that there was

no significant effect of RBC restorations on external marginal gap at distal surface (F(3,

56)=1.66; p=0.1870) or at the mesial surface (F(3, 56)=0.97; p=0.4130). That is, no

significant difference in external marginal gap was found among four RBC restorative

groups (Tables 5, 6 and 7) and (Figures 16 and 17).

Source of Variation

Degrees of

Freedom

Sum of

Squares

Mean

Square F

P

value

Type of RBC used and

technique of placement

3 0.28 0.09 1.66 0.1870

Error 56 3.15 0.06

Total 59 3.43

Table 5. Results of one-way ANOVA for external marginal gap at distal surface

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94

Figure 16. Comparison of external marginal gaps between the four groups (distal surface)

Source of Variation

Degrees of

Freedom

Sum of

Squares

Mean

Square F

P

value

Type of RBC used and technique

of placement

3 0.21 0.07 0.97 0.4130

Error 56 4.06 0.07

Total 59 4.27

Table 6. Result of one-way ANOVA for external marginal gap at mesial surface

Figure 17. Comparison of external marginal gaps between the four groups (mesial

surface)

0.452 0.432 0.421

0.28

0

0.1

0.2

0.3

0.4

0.5

CB CL BL BBMEA

N E

XTE

RN

AL

MA

RG

INA

L G

AP

RESTORATIVE GROUPS

MEAN EXTERNAL MARGINAL GAPS

Distal Surface

0.4880.419 0.433

0.323

0

0.1

0.2

0.3

0.4

0.5

0.6

CB CL BL BB

Mea

n E

xter

nal

Mar

gin

al G

ap

Restorative Groups

Mean External Marginal Gaps

Mesial Surface

95

95

Difference in Gingival Marginal Gap Scores between the Mesial and Distal Surfaces of

Each Group of the Four Tested Groups

Based on a paired-sample t-test, no significant difference in external marginal gap

was found between the mesial and distal surfaces within BB group (bulk RBC, placed in

bulk) (p=0.6728), the BL group (bulk RBC, placed in layers) (p=0.8711), the CL group

(conventional RBC, placed in layers) (p=0.8554) and the CB group (conventional RBC,

placed in bulk) (p=0.5883), and mean external marginal gap difference between distal and

mesial (Table7) and (Figure 18).

Resin

Composite

Restorative

Groups

Mean External Marginal Gap

(SD)

Mean External

Marginal Gap

Difference

Between Distal

and Mesial

Surface

(SD)

Distal Surface

Mesial Surface

CB

0.452 (0.229)A,1

0.488 (0.292)A,1

-0.036 (0.247)

CL

0.432 (0.292)A,1

0.419 (0.217)A,1

0.013 (0.256)

BL

0.421 (0.213)A,1

0.433 (0.221)A,1

-0.012 (0.283)

BB

0.280 (0.206)A,1

0.323 (0.329)A,1

-0.043 (0.393)

Table 7. Comparisons of external marginal gap among four resin composite restorative

groups

*Column means with the same letter are not significantly different using the post-hoc

Tukey’s HSD test (P>.05).

**Row means with the same number are not significantly different using a paired-sample

t-test

(p>0.05)

***External marginal gap difference between distal and mesial Surface=external

marginal gap at distal surface minus external marginal gap at mesial surface

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96

Figure 18. Comparison of external marginal gaps between the mesial and distal surfaces

of the four groups

Results showed that there were no any significant differences in the gingival

marginal adaptation between the different restorative groups on the mesial and distal

surfaces, also there was no any significant differences in gingival marginal adaptation

between the mesial and distal restorations within the same group. Results of the mean score

of gaps on the mesial and distal restorations, the number of no gaps and voids scores that

were scored in each restorative group are illustrated (Table 8).

0.4520.432 0.421

0.28

0.488

0.419 0.433

0.323

0

0.1

0.2

0.3

0.4

0.5

0.6

CB CL BL BB

Mea

n E

xter

nal

Mar

gin

al G

ap

Restorative Groups

Mean External Marginal Gaps

Distal Mesial

97

97

Group Mean gap score on the

mesial and distal

surfaces

Number of specimens

with no gaps/ group

Number of samples

with voids/ group

bulk RBC placed

in bulk (BB)

0.302 1 5

bulk RBC placed

in layers (BL)

0.427 0 8

Conventional RBC

placed in layers

(CL)

0.426 1 7

Conventional RBC

placed in bulk

(CB)

0.47 0 7

Table 8. Number of gap free margins and voids in the different restorative groups

Difference in the Internal Surface Micro-hardness (KHN) Scores between the

Three Different Layers (Depths) Tested of Each Group of the Four Tested Groups at

the Distal and Mesial Surfaces

Group 1 (bulk fill RBC, placed in bulk)

Results of internal surface micro-hardness were recorded at three different levels

1.8mm, 2.8mm and 3.8mm. The scores were compared between different levels of hardness

testing in the restorations on the distal and mesial surfaces within the same group.

The data were analyzed using a simple random effect in Mixed Model ANOVA to

allow correlation between three specimens from the same tooth. This analysis revealed

there was a statistically significant effect of hardness level on internal surface micro-

hardness at distal surface within BB (bulk RBC, placed in bulk) group (p<0.0001). It

showed that mean internal surface micro-hardness for KHN 1.8mm below top surface of

RBC was significantly greater than KHN 2.8mm and 3.7mm below top surface of RBC

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98

(p<0.0001 and p<0.0001), while the mean internal surface micro-hardness for KHN 2.8mm

below top surface of RBC was significantly greater than that for KHN 3.8mm below top

surface of RBC (p=0.0010). Using the same analysis model on the mesial surfaces ,

analysis revealed there was a statistically significant effect of hardness level on internal

surface micro-hardness at mesial surface within BB (bulk RBC, placed in bulk) group

(p=0.0040). It showed that mean internal surface micro-hardness for KHN 1.8mm below

top surface of RBC was significantly greater than KHN 2.8mm and 3.7mm below top

surface of RBC (p=0.0077 and p=0.0011), while the mean internal surface micro-hardness

for KHN 2.8mm below top surface of RBC was significantly greater than that for KHN

3.8mm below top surface of RBC (p=0.0169).

Results of multiple pairwise comparisons based on the differences of least squares

means among three surface levels on the mesial and distal can be shown in (Table 9) and

(Figures 19 and 20).

Surface Level (BB)

Mean Internal Surface Micro-Hardness (SD)

Distal Surface Mesial Surface

KHN 1.8mm Below Top Surface of Composite

62.833 (6.951)A

58.853 (6.695)A


55.653 (3.449)B

55.213 (5.079)B


52.427 (4.259)c

52.180 (4.518)C

Table 9. Comparisons of internal surface micro-hardness among three surface levels

within bulk RBC placed in bulk technique (BB) group

*Column means with the same letter are not significantly different (P>0.05).

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99

Figure 19. Comparison between the three surface levels of internal surface micro-

hardness in the BB group (distal surface)


hardness in the BB group (mesial surface)

62.833

55.653

52.427

50

55

60

65

70

KHN 1.8mm

KHN 2.8mm

KHN 3.8mm

INTE

RN

AL

SUR

FAC

E M

ICR

O-H

AR

DN

ESS

THREE SURFACE LEVELS

Mean Internal Surface Micro-hardness (BB)

Distal Surface

50

52

54

56

58

60

62

64

66

68

70

KHN 1.8mm

KHN 2.8mm

KHN 3.8mm

Inte

rnal

Su

rfac

e M

icro

-har

dn

ess

Three Surface Levels

Mean Internal Surface Micro-hardness (BB)

Mesial Surface

100

100

Group 2 (bulk fill RBC, placed in layers)




hardness at distal surface within BL (bulk RBC, placed in layers) group (p=0.0003). It

showed that mean internal surface micro-hardness for KHN 1.8mm below top surface of


(p=0.0005 and p<0.0001), while the mean internal surface micro-hardness for KHN 2.8mm


surface of RBC (p=0.0160). Using the same analysis on the mesial surfaces, This analysis

revealed there was a statistically significant effect of hardness level on internal surface

micro-hardness at mesial surface within BL (bulk RBC, placed in layers) group (p=0.0008).

It showed that mean internal surface micro-hardness for KHN 1.8mm below top surface of


(p=0.0049 and p=0.0004), while the mean internal surface micro-hardness for KHN 2.8mm


surface of RBC (p=0.0107).

The results of multiple pairwise comparisons based on the differences of least

squares means among three surface levels on the mesial and distal surfaces are displayed

in (Table 10) and (Figures 21 and 22).

101

101

Surface Level (BL)




70.573 (8.629)A

66.160 (10.131)A


63.127 (7.492)B

59.840 (8.079)B


59.413 (6.823)c

57.167 (6.952)C


within bulk RBC placed in two layers (BL) group



hardness in the BL group (distal surface)

63.127

59.413

5052545658606264666870

KHN 1.8mm

KHN 2.8mm

KHN 3.8mm

INTE

RN

AL

SUR

FAC

E M

ICR

O-H

AR

DN

ESS


MEAN INTERNAL SURFACE MICRO-HARDNESS (BL)

Distal Surface

102

102


hardness in the BL group (mesial surface)

Group 3 (conventional RBC, placed in layers)




hardness at distal surface within CL (conventional RBC, placed in layers) group





3.8mm below top surface of RBC (p=0.0120). The same analysis was done for the mesial

surface where it revealed a statistically significant effect of hardness level on internal

surface micro-hardness at mesial surface within CL (conventional RBC, placed in layers)

66.16

59.84

57.167

50

55

60

65

70

KHN 1.8 mm KHN 2.8 mm KHN 3.8 mm

Inte

rnal

Su

rfac

e M

icro

-har

dn

ess


Mean Internal Surface Micro-hardness (BL)

Mesial Surface

103

103

group (p=0.0001). It showed that mean internal surface micro-hardness for KHN 1.8mm

below top surface of RBC was significantly greater than KHN 2.8mm and 3.7mm below

top surface of RBC (p=0.0006 and p<0.0001), while the mean internal surface micro-

hardness for KHN 2.8mm below top surface of RBC was significantly greater than that for

KHN 3.8mm below top surface of RBC (p=0.0011).


squares means among three surface levels on the mesial and distal surfaces are displayed

in (Table 11) and (Figures 23 and 24).

Surface Level (CL)




61.607 (7.159)A

62.007 (6.046)A


56.067 (3.411)B

57.427 (4.433)B


53.113 (4.394)c

53.973 (5.034)C


within Conventional RBC Placed in Two Layers (CL) group


104

104


hardness in the CL group (distal surface)


hardness in the CL group (mesial surface)

61.607

56.067

53.113

5052545658606264666870

KHN 1.8mm

KHN 2.8mm

KHN 3.8mm

INTE

RN

AL

SUR

FAC

E M

ICR

O-H

AR

DN

ESS


MEAN INTERNAL SURFACE MICRO-HARDNESS (CL)

Distal Surface

62.007

57.427

53.973

50

55

60

65

70


Inte

rnal

Su

rfac

e M

icro

-har

dn

ess


Mean Internal Surface Micro-hardness (CL)

Mesial Surface

105

105

Group 4 (conventional RBC, placed in bulk)




hardness at distal surface within CB (conventional RBC, placed in bulk) group (p=0.0003).

It showed that mean internal surface micro-hardness for KHN 1.8mm below top surface of


(p=0.0021 and p<0.0001), while the mean internal surface micro-hardness for KHN 2.8mm


surface of RBC (p=0.0012). Same analysis was done the mesial surfaces, This analysis

revealed there was a statistically significant effect of hardness level on internal surface

micro-hardness at mesial surface within CB (conventional RBC, placed in bulk) group





3.8mm below top surface of RBC (p=0.0017).


squares means among three surface levels are displayed (Table 12) and (Figures 25 and

26).

106

106

Surface Level (CB)


Distal Surface

Mesial Surface


64.440 (9.029)A

62.720 (10.061)A


59.467 (6.770)B

55.380 (4.705)B


53.587 (4.685)C

51.840 (5.244)C


within conventional RBC placed in bulk technique (CB) group



hardness in the CB group (distal surface)

64.44

59.467

53.587

5052545658606264666870

KHN 1.8mm

KHN 2.8mm

KHN 3.8mm

INTE

RN

AL

SUR

FAC

E M

ICR

O-H

AR

DN

ESS


MEAN INTERNAL SURFACE MICRO-HARDNESS (CB)

Distal Surface

107

107


hardness in the CB group (mesial surface)

Results showed that the differences between the internal surface micro-hardness were

always significant between the different three layers between all restorative groups within

each and every group tested. Results showed also the biggest change in hardness from the

top layer to the bottom layer to be found in the group restored with conventional RBC

placed and cured in bulk technique (CB) (Figure 21).


Four Tested Groups at the Distal and Mesial Surfaces

The average of three levels of internal surface micro-hardness scores on the distal

surfaces were used in the analyses and comparison between the four tested groups.

62.72

55.38

51.84

50

52

54

56

58

60

62

64

66

68

70


Inte

rnal

Su

rfac

e M

icro

-har

dn

ess


Mean Internal Surface Micro-hardness (CB)

Mesial Surface

108

108


a significant effect of RBC restorations on internal surface micro-hardness at distal surface

(F(3, 56)=6.39; p=0.0008). The post-hoc Tukey’s HSD test indicated that the mean internal

surface micro-hardness observed on the distal surface of the BL group was significantly

greater than the other three groups, while no significant difference was found among BB,

CL, and CB (Table 13).

Source of Variation

Degrees of

Freedom

Sum of

Squares

Mean

Square F

P

value

Type of RBC used and technique

of placement

3 552.10 184.03 6.39 0.0008

Error 56 1614.01 28.82

Total 59 2166.10

Table 13. Results of one-way ANOVA for internal surface micro-hardness at distal

surface

The average of three levels of internal surface micro-hardness scores on the mesial

surfaces were used in the analyses and comparison between the four tested groups.


no significant effect of RBC restorations on internal surface micro-hardness at mesial

surface (F (3, 56) =2.59; p=0.0620). That is, no significant difference in internal surface

micro-hardness was found among four RBC restorative groups (Table14) and (Figures 27

and 28).

109

109

Source of Variation

Degrees of

Freedom

Sum of

Squares Mean Square F

P

value

Type of RBC used and

technique of placement

3 263.05 87.68 2.59 0.0620

Error 56 1897.58 33.89

Total 59 2160.63

Table 14. Results of one-way ANOVA for internal surface micro-hardness at mesial

surface

Figure 27. Comparison of the internal surface micro-hardness between the four groups

tested (distal surface)

Figure 28. Comparison of the internal surface micro-hardness between the four groups

tested (mesial surface)

64.3

59.1

56.9 56.8

50

52

54

56

58

60

62

64

66

BL CB BB CL

INTE

RN

AL

SUR

FAC

E M

ICR

O-H

AR

DN

ESS

RESTORATIVE GROUPS

MEAN INTERNAL SURFACE MICRO-HARDNESS

Distal Surface

60.9

57.6

56.455.3

52

54

56

58

60

62

BL BB CB CL

Inte

rnal

Su

rfac

e M

icro

-h

ard

nes

s

Restorative GroupsMesial surface

Mean Internal Surface Micro-hardness

110

110


Mesial and Distal Surfaces of Each Group of the Four Tested Groups

The average of the three levels of internal surface micro-hardness was used in the

analyses and comparison between the mesial and distal surface of the four groups. (Table

15).

Based on a paired-sample t-test, no significant difference in internal surface micro-

hardness was found between the mesial and distal surfaces within BB (bulk RBC, placed

in bulk) group (p=0.1859). However a significant difference was detected in internal

surface micro-hardness between the mesial and distal surfaces within BL (bulk RBC,

placed in layers) group (p=0.0043). The data showed that mean internal surface micro-

hardness at distal surface was significantly greater than that observed at mesial surface.

Based on a paired-sample t-test, no significant difference in internal surface micro-

hardness was found between the mesial and distal surfaces within CL (conventional RBC,

placed in layers) group (p=0.5268). Due to lack of normality, a nonparametric Wilcoxon

signed-rank test was used to analyze the data. No significant difference in internal surface

micro-hardness was found between the mesial and distal surfaces within CB (conventional

RBC, placed in bulk) group (p=0.3094) (Figure 29).

Results of internal surface micro-hardness showed the group restored with Tetric

EvoCeram Bulk fill RBC and restored in Layers (BL) showed statistical high hardness

numbers (KHN) on the distal compared to the other three groups, where there was no any

statistical differences between the hardness numbers of the other three groups. Comparing

the mesial and distal surfaces the group filled in bulk fill RBC placed in layering technique

was the only group to show statistical significant higher hardness numbers in the distal

compared to the mesial.

111

111

Resin

Composite

Restorative

Groups

Mean Internal Surface Micro-Hardness

(SD)

Mean Internal Surface

Micro-Hardness Difference

Between Distal and Mesial

Surface

(SD) Distal Surface

Mesial Surface

BL

64.340 (6.685)A,1

60.973 (7.604)A,2

3.367 (3.832)

CB

59.093 (6.009)B,1

56.480 (5.860)A,1

2.613 (8.551)

CL

56.880 (3.940)B,1

57.693 (4.676)A,1

-0.813 (4.854)

BB

56.953 (4.356)B,1

55.387 (4.639)A,1

1.566 (4.362)

Table 15. Comparisons of internal surface micro-hardness among

four resin composite restorative groups

*Column means with the same letter are not significantly different using the post-hoc

Tukey’s HSD test (P>.05).

**Row means with the same number are not significantly different using a paired-sample

t-test, (p>0.05)

***Internal surface micro-hardness difference between distal and mesial surface=

Internal surface

Micro-hardness at distal surface minus internal surface micro-hardness at mesial surface.

Figure 29. Comparison of internal surface micro-hardness between the mesial and distal

surfaces of the four groups

64.3

59.1

56.8 56.9

60.9

56.457.6

55.3

50

52

54

56

58

60

62

64

66

BL CB CL BB

Inte

rnal

Su

rfac

e M

icro

-har

dn

ess

Restorative Groups

Mean Internal Surface Micro-hardness

Distal Mesial

112

112

Statements on Research Hypotheses

1) There is no difference in gingival marginal adaptation among different groups

restored with RBC (bulk fill and conventional types) placed in bulk or in

layering technique at the mesial and distal surfaces (Accept)

2) There is no difference in gingival marginal adaptation between the mesial and

distal surfaces within each group restored with RBC (bulk fill and conventional

types) placed in bulk or in layering technique (Accept)

3) There is no difference in the internal surface micro-hardness (KHN) among the

three different levels of measurements within each group restored in RBC (bulk

fill and conventional types) placed in bulk or in layering technique on the mesial

and distal surfaces (Reject)

4) There is no difference in the internal surface micro-hardness (KHN) among

different groups restored with RBC (bulk fill and conventional types) placed in

bulk or in layering technique at the mesial and distal surfaces

- Bulk Fill RBC, placed in bulk (Accept)

- Bulk Fill RBC, placed in layers (Reject on the distal surface only)

- Conventional RBC, placed in layers (Accept)

- Conventional RBC, placed in bulk (Accept)

5) There is no difference in the internal surface micro-hardness (KHN) between

the mesial and distal surfaces within each group restored with RBC (bulk fill

and conventional types) placed in bulk or in layering technique

- Bulk Fill RBC, placed in bulk (Accept)

- Bulk Fill RBC, placed in layers (Reject)

- Conventional RBC, placed in layers (Accept)

- Conventional RBC, placed in bulk (Accept)

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Typical SEM Images of Tested Groups

Figure 30. Typical SEM picture of group 1 (bulk RBC placed in bulk, BB) gingival

marginal interface under magnification of 200X

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Figure 31. Typical SEM picture of group 2 (bulk RBC placed in layers, BL)

gingival marginal interface under magnification of 200X

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Figure 32. Typical SEM picture of group 3 (conventional RBC placed in layers, CL)


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Figure 33. Typical SEM picture of group 4 (conventional RBC placed in bulk, CB)


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CHAPTER V

DISCUSSION

Bulk fill RBC materials have been introduced to help dentists reduce placement

time and work more efficiently. Manufacturers make claims of these products being able

to fill a cavity in a single 4mm-6mm thickness placement instead of 2mm thick increments

with conventional RBC’s. In a study by Alrahlah et al (Alrahlah, Silikas et al. 2014) Tetric

EvoCeram Bulk Fill was shown to have the highest depth of cure and surface micro-

hardness among the tested materials. Therefore, this bulk fill material was selected for the

current study for comparison of the external gingival marginal adaptation and internal

surface micro-hardness to the conventional RBC of the same manufacturer.

This investigation evaluated Class II marginal adaptation and the internal surface

micro-hardness of two different RBC materials (Tetric EvoCeram and Tetric EvoCeram

Bulk Fill) placed in two different techniques (layering versus bulk filling). Four different

groups including two filled by conventional RBC and two filled by bulk fill RBC were

used with both techniques of layering and bulk fill for comparison of marginal gaps and

internal surface micro-hardness. The group of the conventional RBC filled in bulk was

used as a control group for comparison reasons.

Light Curing Source and Radiant Energy Exposure

Our intention was to cure each increment of RBC with an energy delivery of

14J/cm2 based on studies demonstrating that bulk fill RBC’s had acceptable hardness at

4mm if cured by a light cure delivering energy more than 12J/cm2 (Campodonico,

Tantbirojn et al. 2011, Flury, Hayoz et al. 2012, Czasch and Ilie 2013, El-Damanhoury and

Platt 2013, Finan, Palin et al. 2013).

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Radiant Energy Exposure Standardization in Air

A single LED light curing unit was used in an attempt to standardize all the

restorative procedures and ensure equal degree of cure and polymerization reaction

between the different experimental groups. The energy delivered for curing of the

restorative materials were attempted to be standardized using the manufacturer's

instructions to cure the RBC restorations for 10 seconds with a light producing irradiance

of not less than 1000 mW/cm2. The exact mean irradiance of the curing light used

(Bluephase 16i Ivoclar Vivadent) was measured by the MARC Resin Calibrator system.

The light curing unit was delivering 2100 mW/cm2 delivering 21 J/cm2 at 0mm distance

and 1380 mW/cm2 delivering about 14 J/cm2 at 4mm. The amount of energy delivered was

standardized to 14 J/cm2 to all RBC increments that was 11 seconds of cure for the first

layer and 7 seconds of cure for the second layer. The bulk RBC placed in bulk was cured

for 11 seconds. The bulk RBC placed in 2 layers and placed in bulk was cured for 18

seconds (Table 16).

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Depth of measurements of

radiant energy exposure in air

Irradiance

delivered

Radiant energy

delivered in 10 seconds

Time to deliver 14 J/cm2

Radiant energy exposure at

0mm from sensor

2100 mW/cm2 21 J/cm2 7 seconds of cure

Radiant energy exposure at

4mm from sensor

1380 mW/cm2 13.8 J/cm2 11 seconds of cure

Table 16. Radiant energy exposure standardization in air

Radiant Energy Exposure Measurement in Resin Based Composites

The amount of radiant energy exposure was measured on the MARC Resin

Calibrator through the different types of RBC used (the Tetric EvoCeram bulk fill and the

conventional Tetric EvoCeram RBC). The aim of measuring the amount of total irradiance

and the amount of radiant energy exposure was to detect any differences between the

conventional Tetric EvoCeram and the Tetric EvoCeram bulk fill in the degree of

translucency in attenuating the light. It was observed always a higher translucency with the

Tetric EvoCeram bulk fill RBC where more irradiance and radiant energy exposure was

detected by the MARC Resin Calibrator sensor in both the layering and the bulk filling

technique measurements (Table 17).

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Group column 1 column 2 column 3 column 4

First

(bottom)

increment

initial

radiant

exposure

[time in

seconds]

Total radiant

exposure

received by

First (bottom)

increment =

column 1 +

column 4 [time

in seconds]

Second (top)

increment

radiant

exposure

[time in

seconds]

Bulk 4mm RBC

radiant exposure

or

second (top)

increment radiant

exposure with

bottom increment

in place

Total energy

exposure

[total delivery time]

Bulk = column 4

Layered = Column 2

BB NA NA NA 1 J/cm2

[11s]

1 J/cm2

[11s]

BL 3 J/cm2

[11s]

4 J/ cm2

[11s + 7s]

3.6 J/cm2

[7s]

1 J/cm2 4 J/cm2

[18s]

CL 2.34 J/cm2

[11s]

2.74 J/ cm2

[11s + 7s]

2.76 J/cm2

[7s]

0.4J/cm2 2.74 J/cm2

[18s]

CB NA NA NA 0.4 J/cm2

[18s]

0.4 J/cm2

[18s]

Illustr

ation

2 mm of air

above 2 mm

increment of

RBC

Column 1

+

Column 4

2 mm

increment of

RBC and

curing done

in contact to

the surface

2 mm of RBC

below 2 mm

increment of RBC

Table 17. Radiant energy exposure measurement in resin based composites

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Polymerization Reaction and Depth of Cure

Bulk materials can increase depth of cure in a variety of ways including

translucency (Garcia, Yaman et al. 2013) and refractive index by modifying the filler and

matrix components (Lassila, Nagas et al. 2012) Presence of additional co-initiators also

can raise the curing response of the RBC to the intensity of light and increase curing ability

(Fleming G.J, 2008). Tetric EvoCeram Bulk Fill uses both filler modification as well as

the addition of a co-initiator, Ivocerin, to the matrix material in order to achieve a higher

depth of cure and a better degree of polymerization (Ivoclarvivadent 2014). When

compared to other bulk fill RBC’s, Tetric EvoCeram contains a higher percentage of fillers

(76-80% by weight) which has a potential to increase the elastic modulus and hardness of

the restoration (El-Safty, Akhtar et al. 2012).

Adequate depth of cure is very important since insufficiently cured or polymerized

RBC’s have been shown to decrease the quality and longevity of RBC restorations

(Carvalho, Moreira Fdo et al. 2012). It has been reported that the bulk fill RBC’s have

significantly greater flow and lower polymerization shrinkage compared to conventional

RBC’s as their resin matrix is more elastic decreasing the rate of shrinkage (Ilie and Hickel

2011, Czasch and Ilie 2013). These claims were not verified in the current study since no

difference was found in marginal adaptation.

Very minimal differences were found in the current study between Tetric

EvoCeram and Tetric EvoCeram Bulk Fill in both areas tested the external marginal gaps

and the internal surface micro-hardness. If a bulk fill material is to replace a conventional

material, it is important that it be equal or better in all physical properties, Ilie et al (Ilie,

Bucuta et al. 2013) showed that the bulk fill RBC systems had the same flexural strength

when compared to nanohybrid and micro hybrid RBC’s and that flexural modulus,

indentation modulus and Vickers hardness values for the bulk fills were between the hybrid

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and flowable RBC’s. Bulk fills showed higher creep deformation which made them similar

to the flowable RBC’s. Other studies demonstrated similar conclusions where they stated

that the properties of bulk fill RBC’s were equal or slightly lower than the conventional

RBC systems (El-Safty, Akhtar et al. 2012, El-Damanhoury and Platt 2013). These factors

are important when added to the results of our study when deciding whether to use a bulk

fill RBC. Particularly since the current study showed no advantages in the gingival

marginal adaptation or depth of cure (KHN) for the bulk filled RBC’s. Evidence of the

current study didn’t suggest an advantage in the marginal adaptation and surface micro-

hardness when using these materials over conventional RBC’s.

Quantitative Marginal Analysis

The marginal seal of a restoration to the tooth structure can be measured by either

marginal adaptation measurements or micro-leakage measurements. Marginal adaptation

was chosen for this study to provide a quantitative analysis of the amount and width of

gaps formed at the margins and marginal irregularities rather than the qualitative isolated

analysis provided by microleakage.

Quantitative marginal analysis was introduced by (Porte, Lutz et al. 1984)and was

later refined by (Blunck and Roulet 1989). This refined method of recording of marginal

gaps was selected for the current study to decrease subjectivity and to more completely

measure the width and number of gaps for statistical comparisons between different

restorative and placement techniques.

The criteria for scoring marginal gaps in different marginal analysis studies range

from two criteria (Pass or Fail) (Frankenberger, Lohbauer et al. 2008), four in the studies

by (Roulet, Reich et al. 1989, Blunck and Zaslansky 2011) and up to seven criteria

(Gjorgievska, Nicholson et al. 2008, Sabatini, Blunck et al. 2010). The number of criteria

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is crucial to detect differences between tested groups. Too many criteria created to detect

differences in marginal gaps may lead to errors during scoring, and calculating the marginal

data. In addition too many scores could lead to reliability issues and may increase the

subjectivity of different examiners or researchers during marginal analysis. Therefore,

different categories and scores used are often narrowed down and collapsed to the criteria

of gap versus no gap to make statistical analysis and interpretation of results easier. A study

by Sabatini et al. (Sabatini, Blunck et al. 2010) had seven different gap criteria, however

scores and data were reduced to four categories then later reduced again to only two

categories (gap/no gap) for their statistical analysis of results.

In our study, five criteria were used to describe the marginal integrity. A sixth void

formation criteria was added to account for areas on the samples that had void formation

during restoration placement not dependent on the RBC, technique or the polymerization

shrinkage. This sixth criteria of voids was a separate criteria and was not counted as a

marginal gap. The five item scoring system was chosen because the pilot study showed a

good power of differentiating between the different types of gaps and without

overestimating the amount of marginal gaps. The criteria were then collapsed to only two

main criteria which was gap versus no gap as described by Sabatini et al (Sabatini et al,

2010) because the main target of our study was to distinguish between a gap and a gap free

gingival margin. It was stated (Davidson CL, 1988) that the gap formation at the gingival

margins can cause: 1) marginal micro-leakage, 2) debonding of restorations, 3) secondary

decay and 4) teeth sensitivity.

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Experimental Procedures

Replica Technique

Examination of the gingival marginal adaptation between different specimens was

made using the scanning electron microscope. Positive replicas were prepared for the

purpose of this study. The decision to use replicas was made based on several studies. A

study by (Taylor and Lynch 1993) reported that the technique of epoxy resin replicas is

widely used and accepted in the investigation and testing of the marginal adaptation studies

involving SEM. It was also reported that the technique of replicas was more accurate and

precise for detecting marginal gaps than testing the dental tissues directly since this

technique may cause specimen dehydration and shrinkage leading to widening of gaps

(Davila, Gwinnett et al. 1989) Many other studies have successfully incorporated the same

technique of replicas in comparing marginal gaps (Iida, Inokoshi et al. 2003, Heintze,

Cavalleri et al. 2005, Magni, Zhang et al. 2008, Maresca, Pimenta et al. 2010)

Our study showed some disadvantages of the epoxy resin replicas compared to

direct examination of dental structure. These included the fact that it was time consuming

and that some specimens had voids or excess epoxy resin. Specimens were sorted out if the

voids were related to the margins in the replicas and were discarded and the replicas were

remade.

SEM Data Interpretation

The epoxy resin replicas were examined under the SEM at a magnification of 30X

and 200X. In our study, one image was taken at 30X to view the entire cavity margin to

confirm accuracy of preparation and polishing of the restorations. Seven non overlapping

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images were taken for the entire gingival margin extending at least 0.2mm up the buccal

and lingual walls using a magnification of 200X. This magnification was necessary to

discriminate between the different gap criteria, and was chosen based on other studies

which .have examined the external marginal adaptation of different dental restorations

under the same magnification of 200X (Dietrich, Kraemer et al. 2000, Stoll, Remes et al.

2000, Strobel, Petschelt et al. 2005, Sabatini, Blunck et al. 2010, Souza-Junior, Borges et

al. 2012).

The seven images taken for analysis were non-overlapping to try not to replicate

the same gap score of a previous image. The seven images taken were examined for major

defects (voids more than 250um or more than three in number) as agreed upon from the

pilot study and the gingival margins were traced. The six evaluation scores given were

modified from the study done by (Blunck and Zaslansky 2011). All scores were then

tabulated and then were narrowed down to the intact surface (no gap) versus the non-intact

surface (gap). The percentage of the whole gaps in the gingival margins was calculated and

tabulated for statistical comparison between groups.

Calibration of the readings was required for the examiner prior to assignment of

scores. This calibration was done through setting direct meetings with two members of the

committee.

Internal Surface Micro-hardness

Internal surface micro-hardness was measured by using the Micromet II machine

(Buehler) where the Knoop hardness numbers were measured at nine different locations

each having three points at three different depths of 1.8mm, 2.8mm and 3.8mm. Other

studies had different number of testing points to calculate the Knoop hardness number

RBC’s. These include studies done by (Price, Felix et al. 2005, Felix, Price et al. 2006)

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where seven different depths were tested at 0.5mm,1mm, 1.5mm, 2mm, 2.5mm, 3mm and

3.5 mm. Each point of those had three readings were made at each depth making the sum

of all readings 21 points. (Bechtold, Dos Santos et al. 2012) used four levels of hardness

were at 1, 2, 3 and 4mm depth with three readings at each layer (12 readings total). A study

by (Cilli, Pereira et al. 2012) measured the surface micro-hardness of RBC’s with the

Knoop hardness tester using only five points. Different points of depth testing were

considered in our experiment. After testing at different levels and finding minor differences

in the KHN between samples, the decision in the current study was to use three levels with

the bottom level as close as possible to the bottom of the restoration. The 3.8 mm depth

was the deepest that could be tested in the 4mm deep cavity preparation.

Knoop hardness testing was done for all specimens using the Micromet II machine

with a load of 100gm applied for 15 seconds. Although other studies have used different

loads and times (Bechtold, Dos Santos et al. 2012, Garcia, Yaman et al. 2013, Alrahlah,

Silikas et al. 2014) the technique was chosen to compare with other studies using the same

load and time (Price, Felix et al. 2005, Felix, Price et al. 2006).

Limiting Psychomotor Skills Variability

The acquiring of the psychomotor skills specific to the materials used by the

operator was crucial to get reliable and accurate results. This was done through rehearsing

the different experimental procedures several times before the beginning of the actual

study. All test procedures were then replicated with the different specimens with the same

time, sequence and technique.

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Effect of Resin Based Composite Type and Placement Technique on the

Gingival Marginal Adaptation

The first null hypothesis was accepted as results of our study showed no significant

differences in the marginal adaptation between the four different restorative groups when

compared on the mesial surfaces and also when compared on all the distal surfaces

(P>0.05). We compared all mesial surfaces together and the distal surfaces together

between the four different groups to try to standardize the preparations examined, the

orientation of the light curing source, the radiant energy exposure (energy delivery) and

the degree of homogeneity of the curing light. It was also essential to standardize as much

as possible the tooth substrate to which the restoration will bond as studies showed

different bonding results with dentin and enamel where always bonding to enamel was

better (less marginal gaps) compared to dentin and deep dentinal (pulpal floor) bonding

(Campos, Ardu et al. 2014, Furness, Tadros et al. 2014).

Our results are in agreement with other studies comparing the different placement

techniques (layering versus bulk filling) with different RBC systems (conventional versus

bulk) (Roggendorf, Kramer et al. 2011, Campos, Ardu et al. 2014, Furness, Tadros et al.

2014). Other studies also showed similar results where the comparison was made in the

placement technique (layering versus bulk) using only conventional RBC systems (Gallo,

Bates et al. 2000, St Georges, Wilder et al. 2002), and when the comparison was made in

the type of RBC (bulk fill RBC versus conventional RBC) placed in layering technique

(Moorthy, Hogg et al. 2012).

Our results differed from a study done by (de Wet, Exner et al. 1991) and

(Mullejans, Lang et al. 2003) comparing the technique of placement (layering versus bulk)

using one conventional RBC showed that incremental placement decreased the gingival

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gap formation. These results may have differed from our study due to the fact that only

conventional RBC was used and the types of RBC systems used were different.

It was stated that it’s not realistically achievable to get a 100% gap free margins

(Garcia-Godoy F, Kramer N et al 2010, Blunk U 2011). Slight differences in the marginal

gaps between groups (non-significant differences) were observed. Where the group

restored with conventional RBC placed in bulk (CB) had the highest amount of gaps where

the lowest gap amounts were in the bulk RBC placed in bulk. Maybe these slight changes

were due to the slight increase in the filler content in the bulk Fill Tetric Evoceram

enhancing the modulus of elasticity and decreasing the polymerization shrinkage of these

materials (Masouras, Silikas et al. 2008, Moorthy, Hogg et al. 2012, Ilie, Bucuta et al.

2013). Another reason may be due decreased viscosity of the bulk fill materials by

modifying the monomers and adding hydroxyl free BIS-GMA and highly branched

methacrylates which make them adapt well although placed in bulk not in layers (Burgess

2010, Czasch P 2013, Garcia et al 2014). It was suggested (Leung RL, Fan PL, Johnston

WM 1983) that the polymerization reaction continues at a slower rate after the removal of

the light curing system, this reaction may reach a termination point after almost one day

(24 hours). The bulk RBC placed in bulk was cured for the least time (11 seconds only)

compared to the other three groups (18 seconds) which may have decreased the amount of

polymerization reaction decreasing the amount of shrinkage showing this insignificant

better marginal seal. It was stated by the manufacturers (Ivoclar Vivadent) that stress

relievers (special patented filler which is partially functionalized by silanes) were added to

the Tetric Evo-Ceram Bulk Fills which decreased the modulus of elasticity decreasing the

shrinkage stresses which may have led to the decreased marginal gaps in the Tetric

EvoCeram Bulk Fill RBC placed in bulk compared to the other groups (Ivoclarvivadent

2014).

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The type of adhesive system used could directly affect the amount of gap formation

(De campos 2014). The Adhesive system used was the Syntac system (etch and rinse

considered four step) standardized for all restorations. The good bonding properties of this

adhesive system may have masked the differences between groups enhancing the bond

between the restorations placed and the teeth margins resulting in a better gingival marginal

seal (Frankenberger and Tay 2005). All groups showed minimal gap formation with slight

insignificant differences in the number and size of gaps formed.

The second null hypothesis was also accepted as Results comparing the gingival

marginal adaptation between different RBC’s (Tetric EvoCeram filling versus Tetric

EvoCeram Bulk Fill) used in layering and bulk fill technique showed no significant

differences between the mesial and distal restorations (P>0.05). No studies to our

knowledge was done comparing the mesial and distal marginal adaptation using different

types of RBC’s (bulk fill versus conventional RBC’s) placed either in bulk or in layers

however some studies had the same design of two proximal boxes on the mesial and distal

(Zaruba, Wegehaupt et al. 2013).

It is believed that the location of the preparation either on the mesial and distal

specimens should not significantly affect the results because all specimens on the mesial

and distal were similarly prepared on the same tooth with the same type of RBC and

technique of placement, however the tooth substrate to which the restoration bonds to may

have an effect on the shrinkage stresses due to the different substrate compliances to the

applied stresses, which may have affected the amount of gap formation.

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Effect of Resin Based Composite Type and Placement Technique on the

Internal Surface Micro-hardness

The surface micro-hardness was compared between the different specimens at three

different levels of 1.8mm, 2.8mm and 3.8mm. The third null hypothesis was rejected as

Results showed that in all the specimens tested there was a significant difference in the

internal surface micro-hardness (KHN) between each of the three layers from occlusal to

gingival (P<0.05). The gingival surface micro-hardness (3.8mm) was significantly less

than the hardness in the middle layer (2.8mm) which was significantly less than the

hardness in the top surface layer (1.8mm). The hardness was believed to decrease towards

the gingival levels because of the decrease of intensity of light, decrease of depth of cure

and in turn decrease in degree of conversion of the RBC (Bouschlicher, Rueggeberg et al.

2004). The surface micro-hardness numbers were shown to decrease with increased depth

of the restoration (Campodonico, Tantbirojn et al. 2011).

The amount of radiant energy delivery was shown in this study to decrease with

increased depth of the RBC (refer to table 17). Where the bulk fill Tetric EvoCeram RBC’s

still showed a better light propagation manner compared to the conventional Tetric

EvoCeram RBC’s.

The fourth null hypothesis was partially accepted as Results of internal surface

micro-hardness (KHN) testing between the different restorative groups showed a

significant increase in the surface micro-hardness numbers (KHN) on the distal surface of

the group restored with bulk RBC placed and cured in layers compared to the other three

groups (P<0.05). However there were no significant differences in the internal surface

micro-hardness numbers (KHN) in the other three groups on both the mesial and distal

surfaces. It was believed that the KHN in the bulk RBC placed in layers group was higher

since the depth of cure of bulk fills may be greater than the conventional RBC’s due to a

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photo co-initator particle, Ivocerin (Ivoclarvivadent 2014) added to the resin matrix and

the fact that this group was cured in two layers for an increased time, therefore the material

may have undergone a greater polymerization reaction and a higher percentage of cure

(Czasch and Ilie 2013, Ilie, Bucuta et al. 2013).

Our results were not in agreement with a study done by (El-Safty, Akhtar et al.

2012) where the authors concluded that the conventional RBC’s were the hardest followed

by the bulk fill RBC’s followed by the flowable RBC’s being the least hard. The results

were in agreement with a study done by (Garcia, Yaman et al. 2013) which concluded that

there was no difference in the surface micro-hardness of conventional and the bulk fill

RBC’s at the different levels of testing, however the conventional RBC used in this study

was a flowable type. Our results showed acceptable hardness numbers compared to the

conventional RBC’s. Our results also confirmed the fact that bulk filled RBC’s cured well

in 4mm bulk placement which was agreement with other studies (Campodonico, Tantbirojn

et al. 2011, Flury, Hayoz et al. 2012, Czasch and Ilie 2013, El-Damanhoury and Platt 2013,

Finan, Palin et al. 2013) . It was observed in our study that bottom to top surface hardness

scores were higher than 80% in all the tested groups as stated by other authors (Yearn 1985,

Bouschlicher, Rueggeberg et al. 2004).

There was a slight but insignificant increase in hardness in the conventional RBC

group filled in bulk compared to the one filled in layers. It was believed that perhaps the

orientation of the light curing tip may have caused this slight increase and also when

Examining the different levels of surface micro-hardness, the mean hardness of the first

two levels of the conventional RBC placed in bulk were higher than the mean hardness of

the same layers in the conventional RBC placed in layers because the curing time was

almost doubled at these layers in the first group. However, the gingival layer in the

conventional RBC’s placed in bulk still showed good hardness numbers which suggested

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that the depth of cure of the conventional Tetric EvoCeram materials were still good

compared to the Tetric EvoCeram Bulk Fill RBC’s. The lowest group hardness numbers

were found in the bulk RBC’s (non-significant) placed and cured in bulk technique. This

non-significant decrease in hardness may have occurred due to the fact that this group had

the lowest curing time (11 seconds only compared to 18 seconds for all other groups).

Another explanation of the increase in hardness numbers in the bulk fill RBC group placed

in layers is the increased depth of cure and translucency of the Tetric EvoCeram Bulk Fill

RBC compared to the conventional Tetric EvoCeram RBC which increased the hardness

numbers of this specific group, where it was stated (Musanje L and Darvell BW 2006,

Azopardi N and Moharamzadeh K 2009) that for proper polymerization and increased

depth of cure a good match between refractive indices of the resin matrix and silica

particles is required. The manufacturers stated adding a new component in the resin matrix

called Ivocerin which is a Di-benzoyl germanium compound (Al Rahlah 2013) that act as

a photo-initiator booster increasing the depth of cure and degree of polymerization and

hardness. Maybe this component was the cause of increased hardness numbers in the bulk

fill RBC filled in layers group however the hardness of the bulk RBC placed in bulk

remained the lowest compared to other groups which suggested that for increased hardness

of the Tetric EvoCeram bulk fill and for the Ivocerin photo-initiator to have an increased

effect on hardness an increase in curing time was required.

Our results compared the mesial and distal restorations on the same tooth to see if

the tooth surface had an effect on the hardness and depth of cure of RBC’s RBC’s used

with different techniques of placement. The fifth null hypothesis was partially accepted as

No specimens showed any significant differences between the surface micro-hardness

numbers (KHN) of the mesial and distal restorations (P<0.05) except for one group restored

with bulk RBC placed in layers, the distal specimens were significantly harder than the

mesial. It was believed that this change in hardness may have resulted due to improper

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orientation or slight change in orientation between both the mesial and distal restorations.

Another reason for this change may have been due to change in rotational placement of the

light cure where the light homogeneity could have cured one surface more than the other

(Price, Rueggeberg et al. 2010, Rueggeberg F 2010). Again no known studies till now

compared the mesial and distal surface micro-hardness between the restorations (bulk Fill

RBC and conventional RBC) placed either in bulk or in layers.

Standardization of Procedures

Care was taken to control for variability and bias that may occur during the tooth

selection, tooth preparation, tooth restoration, SEM measurements, sectioning and surface

micro-hardness testing. All the steps of the experiment were done by the same operator.

The selection of teeth was done from different sources to ensure that the teeth origins

weren’t biased. Cavity preparations were all standardized by the CNC Specimen Former

machine to the same exact dimensions (Raposo, Armstrong et al. 2012). The restorative

techniques were all practiced to standardize the placement, handling and curing of all

specimens.

Testing specimens under the SEM was done after carefully placing the replicas in

a perpendicular position to the electron beam to ensure proper recording of gap sizes. It has

been reported that a small angulation of the replica under the SEM may change the gap

size to make it appear smaller than it actually is (Taylor and Lynch 1993). Sectioning of

all samples for internal micro-hardness testing was all done by the same manner by

dividing the restoration by half. All specimens were assigned numerical codes for blindness

purposes where the operator measured the gingival marginal adaptation and internal

surface micro-hardness.

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Limitations of the Study

This in vitro study had its own limitations due to techniques done to standardize the

specimens which are not possible in the clinical situation such as: a) The occlusal surface

was flattened to ensure accurate curing of RBC and proximal surfaces were flattened to

ensure perfect adaptation and placement of RBC material in all specimens and to allow

better definition of the margins under the SEM. This may have removed some of the outer

layer of enamel which contains high amount of fluoride and aprismatic hypermineralized

enamel (Whittaker 1982, Albers 2002), b)All specimen preparations were standardized by

the CNC machine which cannot be used in the clinical situation, c) All margins were

polished for accurate testing where in a clinical situation it is impossible to polish.

The present study tested the gingival marginal adaptation where all gingival

margins were bonded to dentin below the level of the cement-enamel junction. However,

in the real clinical setting it is contra-indicated to place RBC restorations below the CEJ.

The light curing unit orientation may have been a possible area for bias as the light

tip was placed over the occlusal surface of all specimens without a definite orientation

guide. Calibration of the SEM data was very difficult as the gaps/ non gap marginal analysis

was a subjective analysis where with different evaluators different scores may have been

given. The sample size may have been relatively small where if a larger sample size was

used the statistical power would have increased substantially.

The present study tested only the Tetric EvoCeram and Tetric EvoCeram Bulk Fill

RBC systems therefore results cannot be extrapolated to other systems.

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Strengths of the Study

The present study had a large sample size of 15 teeth (restored on the mesial and

distal surfaces, a total of 30 restorations) per each group for comparison purposes between

the different restorative materials and techniques. Standardization of the class II Cavity

preparations by the CNC Specimen Former machine where other studies used conventional

burs to prepare the Class II cavities which may have caused some bias in the specimens.

Similar RBC products were used for each step including restorative material, bonding

system and light curing unit was advantageous since the study was able to exactly follow

the manufacturer’s instructions. The light radiant energy exposure was standardized in all

the increments placed to ensure accurate and reliable results.

Clinical Significance

Within the limitations of the current study, Tetric EvoCeram Bulk Fill RBC’s

doesn’t offer any clinical advantages compared to the conventional Tetric EvoCeram

RBC’s in the external marginal adaptation and surface micro-hardness. More studies need

to be done to compare the longevity, the mechanical and physical properties of the different

bulk fill materials in comparison with the conventional RBC’s.

Future Research Suggestions

This study was conducted as an in vitro study where results and conclusions

couldn’t be extended and generalized to different in vivo situations. A similar investigation

conducted in vivo would certainly help confirm the results of the current study. A study

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could be conducted to test the long term durability and longevity of the bulk fill RBC

restorations after thermo-cycling the specimens and testing them aging. More studies

should be done to compare the different mechanical and physical properties of the bulk fill

RBC’s compared to the conventional RBC materials placed in layering technique.

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CHAPTER VI

CONCLUSION

Considering the limitations and disadvantages of this in-vitro study, it was

concluded that there was no significant differences in the gingival marginal adaptation

between all of the tested groups (Bulk Fill Tetric EvoCeram and Tetric EvoCeram) placed

in bulk or layering technique on the mesial and distal surfaces.

Our study also concluded that there was no significant differences in the gingival

marginal adaptation between the mesial and distal surfaces of the same tooth in all the

tested groups when restored with Bulk Fill Tetric EvoCeram and Tetric EvoCeram placed

in bulk or layering technique.

Internal surface micro-hardness measured at three different levels showed

significant differences between the four groups tested on both surfaces mesial and distal.

The first layer tested was always harder than the second layer harder than the third layer.

Bulk Fill RBC placed in layering technique had significant higher internal surface

micro-hardness (KHN) than all the other tested groups where there wasn’t any significant

difference in hardness numbers between the other three groups tested. The surface micro-

hardness numbers were highest in the bulk layered group compared to the other three

groups.

The mesial and distal surfaces surface micro-hardness (KHN) didn’t show any

significant changes except for the group restored in bulk Fill RBC placed in layers, where

the distal surface micro-hardness was higher significantly than the mesial surface.

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APPENDIX

Descriptive Statistics for External Marginal Gap and Internal Surface Micro-hardness by

RBC Groups --------------------------------------------------Group1= bulk RBC placed in bulk tech (BB) ------------------------------------- Standard Lower Upper Quartile Variable N Mean Deviation Minimum Maximum Median Quartile Quartile Range ------------------------------------------------------------------------------------------------------------------------------- MG_M 15 0.323 0.329 0.000 1.000 0.178 0.077 0.571 0.494 MG_D 15 0.280 0.206 0.005 0.677 0.304 0.094 0.470 0.376 Hardness_M1 15 58.853 6.695 48.400 75.000 59.200 52.900 62.700 9.800 Hardness_M2 15 55.213 5.079 46.700 63.200 55.300 51.200 59.900 8.700 Hardness_M3 15 52.180 4.518 44.000 59.700 53.500 48.600 54.700 6.100 Hardness_M 15 55.387 4.639 47.500 64.700 55.700 51.900 59.600 7.700 Hardness_D1 15 62.833 6.951 53.900 75.600 63.900 55.400 67.300 11.900 Hardness_D2 15 55.653 3.449 50.500 63.500 56.300 53.000 57.300 4.300 Hardness_D3 15 52.427 4.259 46.000 60.300 52.100 48.800 56.600 7.800 Hardness_D 15 56.953 4.356 51.200 65.900 57.900 51.900 59.200 7.300 ------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------- Group2= bulk RBC placed in 2 layers (BL) --------------------------------------- Standard Lower Upper Quartile Variable N Mean Deviation Minimum Maximum Median Quartile Quartile Range ------------------------------------------------------------------------------------------------------------------------------- MG_M 15 0.433 0.221 0.037 0.810 0.424 0.267 0.607 0.340 MG_D 15 0.421 0.213 0.162 0.868 0.368 0.254 0.602 0.348 Hardness_M1 15 66.160 10.131 54.300 86.800 64.800 57.400 70.500 13.100 Hardness_M2 15 59.840 8.079 50.200 77.900 58.000 53.600 64.200 10.600 Hardness_M3 15 57.167 6.952 50.000 74.400 55.400 52.900 59.300 6.400 Hardness_M 15 60.973 7.604 52.200 78.000 59.300 55.600 62.000 6.400 Hardness_D1 15 70.573 8.629 58.000 90.600 71.700 63.900 75.600 11.700 Hardness_D2 15 63.127 7.492 52.200 75.800 60.300 56.600 69.000 12.400 Hardness_D3 15 59.413 6.823 49.300 72.000 58.700 54.100 63.000 8.900

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Hardness_D 15 64.340 6.685 55.000 78.300 61.700 58.300 70.000 11.700 ------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------- Group3= Conventional RBC placed in 2 layers (CL) ---------------------------------- Standard Lower Upper Quartile Variable N Mean Deviation Minimum Maximum Median Quartile Quartile Range ------------------------------------------------------------------------------------------------------------------------------- MG_M 15 0.419 0.217 0.000 0.827 0.432 0.267 0.548 0.281 MG_D 15 0.432 0.292 0.041 0.941 0.418 0.127 0.707 0.580 Hardness_M1 15 62.007 6.046 54.000 71.300 60.600 57.000 67.600 10.600 Hardness_M2 15 57.427 4.433 48.300 67.100 56.900 55.600 58.500 2.900 Hardness_M3 15 53.973 5.034 44.100 63.200 53.400 49.500 57.000 7.500 Hardness_M 15 57.693 4.676 49.800 65.800 58.100 54.000 58.800 4.800 Hardness_D1 15 61.607 7.159 52.500 74.900 59.900 54.900 66.800 11.900 Hardness_D2 15 56.067 3.411 50.500 62.300 55.400 54.000 58.500 4.500 Hardness_D3 15 53.113 4.394 44.300 63.000 53.600 49.600 55.800 6.200 Hardness_D 15 56.880 3.940 51.400 63.500 56.200 53.300 60.900 7.600 ------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------- Group4= Conventional RBC placed in bulk (CB) ------------------------------------ Standard Lower Upper Quartile Variable N Mean Deviation Minimum Maximum Median Quartile Quartile Range ------------------------------------------------------------------------------------------------------------------------------- MG_M 15 0.488 0.292 0.120 0.945 0.475 0.224 0.820 0.596 MG_D 15 0.452 0.229 0.031 0.902 0.418 0.320 0.574 0.254 Hardness_M1 15 62.720 10.061 48.400 90.900 61.600 56.300 67.600 11.300 Hardness_M2 15 55.380 4.705 46.600 65.600 55.600 52.900 57.600 4.700 Hardness_M3 15 51.840 5.244 43.100 60.000 51.400 48.200 57.900 9.700 Hardness_M 15 56.480 5.860 45.000 71.200 57.100 52.900 59.300 6.400 Hardness_D1 15 64.440 9.029 50.300 84.600 60.500 58.100 72.200 14.100 Hardness_D2 15 59.467 6.770 50.800 75.000 58.100 53.300 65.000 11.700 Hardness_D3 15 53.587 4.685 46.300 60.800 54.900 49.200 57.500 8.300 Hardness_D 15 59.093 6.009 51.100 72.900 58.500 53.000 62.600 9.600 --------------------------------------------------------------------------------------------------------------------------------

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******************************************************************************

************************************** Low Quartile: 25% of values are lower than this Upper Quartile: 75% of values are lower than this Interquartile range: the difference between the 75th and 25th percentile

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Gingival Marginal Gaps of Each Image of the Seven Images Taken for the Margins

Tested on the Mesial and Distal of Each Tooth

1 = Bulk RBC placed in bulk tech (BB)

2 = Bulk RBC placed in 2 layers tech

(BL)

3=Conventional RBC placed in 2

layers tech (CL)

4=Conventional RBC placed in bulk

tech (CB)

MG (M) =

marginal

gap % of

mesial

restorati

on

1 2 3 4 5 6 7 MG (D)=

marginal

gap % of

Distal

restorati

on

Group # 1 2 3 4 5 6 7 MG (M) Specimen # 1 2 3 4 5 6 7 MG (D) Specimen #

1 27% 0% 0% 29% 0% 0% 70% 18% 1 0% 0% 0% 0% 3% 0% 0% 0.50% 2

1 100% 100% 100% 100% 78% 100% 88% 95% 9 37% 17% 26% 38% 56% 20% 24% 31.10% 10

1 27% 0% 0% 0% 0% 11% 16% 7.70% 17 0% 11% 38% 0% 0% 0% 17% 9.40% 18

1 66% 80% 68% 41% 100% 68% 12% 62.10% 25 14% 65% 100% 15% 18% 46% 31% 40.80% 26

1 0% 26% 0% 0% 0% 0% 29% 7.80% 33 10% 0% 0% 0% 0% 0% 0% 1.40% 34

1 0% 0% 15% 0% 0% 0% 27% 6% 41 28% 27% 83% 74% 36% 62% 36% 49.40% 42

1 100% 100% 100% 100% 100% 100% 100% 100% 49 20% 0% 0% 23% 31% 26% 3% 14.70% 50

1 40% 21% 0% 0% 32% 100% 52% 35% 57 95% 72% 18% 18% 34% 50% 73% 51.40% 58

1 25% 51% 71% 71% 61% 56% 65% 57.10% 65 35% 92% 41% 49% 0% 5% 28% 30.40% 66

1 77% 0% 0% 0% 0% 0% 48% 17.8 73 67% 40% 0% 26% 32% 100% 66% 47% 74

1 20% 11% 0% 18% 0% 11% 32% 13.10% 81 90% 89% 68% 57% 43% 87% 40% 67.70% 82

1 0% 0% 0% 0% 0% 0% 14% 2% 89 97% 32% 19% 15% 11% 18% 38% 32.80% 90

1 57% 54% 0% 0% 0% 0% 0% 15.80% 97 0% 20% 16% 0% 0% 0% 2% 5.40% 98

1 0% 0% 0% 0% 0% 0% 0% 0% 105 65% 45% 10% 20% 13% 18% 10% 25.80% 106

1 61% 43% 32% 44% 34% 54% 65% 47.50% 113 30% 17% 0% 0% 0% 0% 34% 11.50% 114

2 67% 100% 38% 50% 100% 57% 89% 71.50% 3 39% 17% 10% 4% 0% 0% 44% 16.20% 4

2 19% 0% 7% 0% 0% 0% 0% 3.70% 11 0% 0% 0% 62% 18% 84% 15% 25% 12

2 0% 65% 49% 13% 24% 16% 39% 29.40% 19 0% 0% 56% 66% 36% 63% 37% 36.80% 20

2 0% 49% 13% 4% 31% 0% 7% 14.80% 27 23% 8% 3% 0% 27% 68% 51% 25.70% 28

2 0% 100% 100% 100% 100% 25% 0% 60.70% 35 42% 44% 18% 49% 100% 90% 79% 60.20% 36

2 100% 25% 26% 14% 15% 7% 0% 26.70% 43 31% 0% 23% 3% 0% 25% 67% 21.20% 44

2 78% 52% 22% 46% 24% 50% 78% 50% 51 74% 68% 78% 69% 57% 78% 71% 70.70% 52

2 19% 0% 19% 50% 69% 70% 53% 40% 59 35% 0% 27% 34% 24% 47% 56% 31.80% 60

2 24% 49% 12% 45% 42% 47% 53% 38.80% 67 18% 32% 69% 70% 100% 100% 100% 69% 68

2 94% 0% 82% 61% 66% 63% 34% 57.10% 75 17% 30% 65% 26% 30% 5% 14% 26.70% 76

2 17% 46% 4% 37% 66% 72% 55% 42.40% 83 81% 66% 41% 52% 61% 60% 21% 54% 84

2 0% 0% 21% 43% 10% 40% 3% 16.70% 91 51% 4% 16% 16% 45% 62% 100% 42% 92

2 40% 71% 31% 64% 41% 42% 78% 52.40% 99 56% 100% 100% 100% 100% 100% 52% 86.80% 100

2 82% 53% 82% 67% 83% 100% 100% 81% 107 51% 71% 56% 21% 19% 61% 0% 39.80% 108

2 72% 21% 43% 66% 48% 100% 100% 64.20% 115 27% 30% 6% 23% 28% 11% 53% 25.40% 116

3 93% 100% 100% 100% 100% 30% 32% 79.20% 5 92% 67% 100% 100% 100% 100% 100% 94.10% 6

3 32% 9% 9% 0% 64% 50% 78% 34.5 13 30% 37% 18% 0% 0% 0% 0% 12.10% 14

3 87% 71% 30% 20% 26% 30% 45% 44.10% 21 48% 64% 37% 44% 59% 6% 6% 37.70% 22

3 68% 100% 32% 52% 32% 54% 25% 50% 29 0% 0% 0% 41% 19% 32% 34% 12.70% 30

3 38% 20% 0% 0% 14% 33% 79% 26.20% 37 5% 7% 0% 0% 70% 21% 37% 20% 38

3 10% 43% 0% 20% 20% 44% 50% 26.70% 45 54% 63% 42% 34% 7% 38% 65% 43.20% 46

3 39% 24% 40% 0% 100% 100% 17% 45.70% 53 37% 68% 58% 64% 41% 69% 40% 53.80% 54

3 0% 0% 0% 0% 0% 0% 0% 0% 61 11% 0% 0% 0% 0% 0% 18% 4.10% 62

3 0% 0% 24% 74% 91% 55% 59% 43.20% 69 86% 100% 100% 100% 100% 100% 0% 83.70% 70

3 46% 57% 66% 47% 60% 60% 48% 54.80% 77 60% 78% 60% 60% 65% 92% 80% 70.70% 78

3 78% 100% 55% 100% 100% 100% 46% 82.70% 85 55% 74% 0% 52% 76% 8% 28% 41.80% 86

3 51% 21% 30% 47% 0% 24% 32% 29.20% 93 100% 100% 100% 100% 55% 67% 29% 78.70% 94

3 24% 34% 7% 37% 100% 11% 48% 37.2 101 100% 100% 41% 24% 4% 22% 57% 49.70% 102

3 48% 14% 24% 7% 11% 3% 17% 18% 109 26.00% 0% 0% 0% 0% 0% 5% 4.40% 110

3 68% 90% 56% 21% 63% 75% 30% 57.50% 117 0% 26% 85% 54% 26% 55% 39% 40.70% 118

4 31% 0% 5% 13% 16% 78% 69% 30.10% 7 80% 69% 42% 66% 58% 80% 75% 67.10% 8

4 5% 23% 32% 60% 27% 54% 70% 38.70% 15 70% 0% 29% 28% 16% 7% 12% 23.10% 16

4 44% 6% 0% 35% 21% 14% 37% 22.40% 23 13% 52% 71% 38% 9% 100% 30% 44.70% 24

4 64% 22% 0% 41% 48% 76% 83% 47.7 31 73% 100% 63% 33% 62% 36% 35% 57.40% 32

4 100% 100% 65% 73% 100% 100% 100% 91.00% 39 69% 56% 76% 100% 100% 100% 89% 84% 40

4 44% 30% 1% 0% 0% 10% 0% 12.00% 47 35% 14% 14% 62% 82% 66% 20% 41.80% 48

4 21% 25% 0% 0% 26% 14% 45% 18.70% 55 22% 0% 0% 0% 0% 0% 0% 3.10% 56

4 25% 0% 13% 0% 5% 6% 7% 15.70% 63 54% 23% 36% 36% 100% 18% 49% 45% 64

4 94% 100% 100% 100% 100% 100% 68% 94.50% 71 70% 100% 100% 100% 81% 81% 100% 90.20% 72

4 100% 47% 53% 85% 100% 100% 93% 82% 79 55% 74% 20% 52% 56% 8% 28% 41.80% 80

4 48% 39% 0% 36% 4% 18% 64% 30.00% 87 70% 30% 20% 11% 19% 23% 55% 32.50% 88

4 88% 79% 14% 76% 100% 0% 21% 54% 95 77% 34% 27% 0% 48% 11% 25% 32.00% 96

4 100% 100% 76% 100% 100% 83% 100% 94.00% 103 44% 65% 77% 69% 66% 32% 25% 54% 104

4 64% 52% 68% 87% 43% 17% 2% 47.50% 111 61% 50% 35% 11% 0% 0% 11% 24% 112

4 34% 14% 55% 88% 65% 58% 61% 53.50% 119 47% 25% 35% 56% 44% 40% 19% 38% 120

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A comparison of gingival marginal adaptation and surface ...

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