RESEARCH AND EDUCATION

Supported byaPostgraduatbAssociate PrcAssociate PrdAssistant PreAssociate PrfAssociate Pr

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Mechanical properties of components of the bonding interfacein different regions of radicular dentin surfaces

Thaís Yumi Umeda Suzuki, DDS, MS,a João Eduardo Gomes-Filho, DDS, MS, PhD,b Juno Gallego, DDS, MS, PhD,c

Sabrina Pavan, DDS, MS, PhD,d Paulo Henrique dos Santos, DDS, MS, PhD,f andAndré Luiz Fraga Briso, DDS, MS, PhDe

ABSTRACTStatement of problem. The mechanical properties of the adhesive materials used in intraradiculartreatments could vary according to the interaction between the restorative material and dentinsubstrate. An evaluation of these properties is essential to determine the success of the lutingprocedures performed on glass-fiber posts.

Purpose. The purpose of this study was to evaluate the mechanical properties of dentin adhesives,resin cements, and the dentin that underlies the bonding interface in different thirds of intra-radicular dentin.

Material and methods. Forty extracted, single-rooted human teeth were used in this study. Afterthe endodontic treatment of the post spaces, the teeth were divided into 5 groups (n=8): AdperSingle Bond 2 + RelyX ARC, Excite DSC + RelyX ARC, Adper SE Plus + RelyX ARC, RelyX Unicem,and Set. The hardness and elastic modulus values were measured at the adhesive interface indifferent thirds of the radicular dentin by using an ultramicrohardness tester. The data weresubjected to 2-way ANOVA and the Fisher protected least significant difference test (a=.05).

Results. In the underlying dentin, the highest Martens hardness values were found in the apicalregion for all groups; the exceptions were the groups with the self-etching adhesive. In the adhesivelayer, the highest Martens hardness values were obtained for the Adper SE Plus + RelyX ARC group;further, no statistical differences were found among the different regions for this group. RelyX ARChad the lowest Martens hardness and elastic modulus values in the apical regions when usedwith Adper Single Bond 2 and Adper SE Plus. No differences were found in the Martenshardness and elastic modulus values for the self-adhesive resin cement in the regions investigated.

Conclusion. The mechanical properties of adhesive materials and the underlying dentin areinfluenced by the interaction between the two as well as by the depth of the analyzed intraradiculararea. (J Prosthet Dent 2015;113:54-61)

Resin cements are commonlyused to lute glass-fiber posts inendodontically treated teeth.1-4

Adhesive cementation tech-niques often involve the useof adhesive systems associatedwith conventional resin ce-ments as well as self-adhesiveresin cements.5-8 Several den-tin adhesives are availablecommercially. These includeetch-and-rinse and self-etchadhesive systems.9-13 Etch-and-rinse adhesive systems requiregreater clinical expertise be-cause the phosphoric acidneeds to be washed off.14-16

During the drying of dentin,the collagen fibers may col-lapse,14 which prevents theresin monomers from diffusinginto the demineralized ma-trix.9,17,18 The excess moisturepresent is undesirable because

it dissolves the solvent and monomer resin, which results in incomplete sealing of the dentin.19,20 In this respect, self-etchadhesive systems, in which the dentin is demineralized and infiltrated by the monomer simultaneously, seem morepromising.1,21-23

Grant 2009/12730-8 from the São Paulo Research Foundation (FAPESP), Brazil.e student, Department of Dental Materials and Prosthodontics, Araçatuba School of Dentistry, Sao Paulo State University (UNESP), Araçatuba, Brazil.ofessor, Department of Restorative Dentistry, Araçatuba School of Dentistry, Sao Paulo State University (UNESP), Araçatuba, Brazil.ofessor, Department of Mechanical Engineering, Ilha Solteira School of Engineering, Sao Paulo State University (UNESP), Ilha Solteira, Brazil.ofessor, Department of Dentistry, Adamantina School of Dentistry (FAI), Adamantina, Brazil.ofessor, Department of Restorative Dentistry, Araçatuba School of Dentistry, Sao Paulo State University (UNESP), Araçatuba, Brazil.ofessor, Department of Dental Materials and Prosthodontics, Araçatuba School of Dentistry, Sao Paulo State University (UNESP), Araçatuba, Brazil.

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Clinical ImplicationsSelecting resin materials with the appropriate me-chanical properties is essential for ensuring thelongevity of cementation procedures performedwith adhesive glass-fiber posts in intraradiculardentin.

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The development of self-adhesive resin cements hasmade them an alternative for the cementation process,24

thus eliminating the pretreatment of the dentin.16,25 Thecements contain acidic monomers that demineralize andinfiltrate the tooth substrate, which results in micro-mechanical retention.26,27 A secondary reaction, achemical reaction between the hydroxyapatite and theparticles of aluminum fluorosilicate (glass) present in thecements,28 similar to that which occurs with glass ion-omer cements, can occur.28-30 An understanding of theproperties of the materials and substrates involved indental restorations is essential to ensuring the longevityof the bonded interface.31 The most common parametersused to assess materials are their hardness and elasticmodulus (Eit) values, which can be determined throughindentation tests.7,32 An ideal resin material would have ahigh hardness value, which indicates a greater degree ofpolymerization of the material, while exhibiting an Eitnearly equal to or slightly less than the modulus ofdentin, to facilitate the transmission of the forces at theinterface.

The purpose of this study was to evaluate the me-chanical properties (hardness and Eit) of the componentsof the adhesive interface in different regions of intra-radicular dentin (cervical, middle, and apical). Two nullhypotheses were tested: that the interaction between theadhesive system and the resin cement would not causechanges in the mechanical properties (Martens hardness[MH] and Eit) of the materials and underlying dentin andthat no difference would be found in the mechanicalproperties of the components of the adhesive interface indifferent thirds of intraradicular dentin.

MATERIAL AND METHODS

The materials used in this study are listed in Table 1. Thestudy was approved by the research and ethics commit-tee of the Araçatuba School of Dentistry, Sao Paulo StateUniversity (Protocol 01809/09). Forty single-rooted hu-man premolars from different individuals, extracted fororthodontic or periodontal reasons, were used in thisstudy. All teeth that exhibited clinical signs of caries, rootresorption, cracks, or fractures were excluded. Theanatomic crowns of all teeth were removed 1.0 mmabove the cementum-enamel junction through a trans-versal section, under water cooling, by using a low-speed

Suzuki et al

diamond saw (Isomet 2000; Buehler). The specimensthen were endodontically treated. A no. 10 K-file(Maillefer Instruments) was introduced into the root ca-nal until it was visible at the apical foramen. The workinglength was determined to be 1.0 mm less than thislength. The root canals were instrumented with K-fileswith sizes of up to no. 45 by using the crown-down andstep-back techniques after the preparation process hadbeen completed. This process was performed withHedstroem files of up to no. 60 scaled to be natural andprogressive, and used as an instrument of memory a K-file 2 number lower than the larger caliber used in theapical preparation. Throughout the preparation process,the root canals were irrigated with 2.5% sodium hypo-chlorite. The instrumented root canals were dried withsterile paper points and immediately obdurated by thelateral condensation of gutta percha cones (Dentsply-Maillefer) and calcium hydroxide cement (Seal-apex; KerrCorp). Coronal access was sealed with zinc oxideezincsulfate cement (Coltosol; Vigodent). The endodonticallytreated teeth were stored at 37�C and 100% relativehumidity for 7 days.

The glass-fiber post system used in this study wasReforpost no. 2 (Angelus Industry Dental Products S/A).The post spaces in all the specimens were prepared witha no. 2 low-speed drill (Dentsply-Maillefer). The guttapercha cones were removed to a depth of ±9 mm withreference to the working length of the tooth. After thecompletion of the preparation process, the adaptation ofthe fiber posts was verified to be complete by placingthem in the post space. If the posts penetrated to the 9-mm depth, then they were considered to have adapted.Before the start of the adhesive procedure, the surfaces ofthe glass-fiber posts were treated with 35% phosphoricacid (3M ESPE) for 60 seconds. They were then washedand air-dried. The post surfaces were silanized for 60seconds (Angelus Industry Dental Products S/A) andgently dried with an air jet. Finally, on the basis of thetreatment to be performed in the intraradicular dentin,the adhesive system used on the dentin surface also wasapplied on the post surface if required. Thereafter, toprevent contamination, the post was not furthermanipulated.

The post spaces were irrigated with 2.0 mL distilledwater to remove any gutta percha debris and to maintainthe humidity of the environment. The post space wasdried with air and sterile paper points before the bondingprocedures. The specimens were divided by drawing lotsinto the following 5 groups (n=8) on the basis of theluting procedure.

SB2 Group: Adper Single Bond 2 + RelyX ARCPost spaces were etched with 35% phosphoric acid (3MESPE) for 15 seconds, washed, and dried with sterilepaper points without drying the dentin. Adper Single

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Table 1.Materials used

ProductName Product Type Batch No. Compositiona Manufacturer

Single Bond 2 Photo activation adhesivesystem

8TX Bis-GMA, HEMA, dimethacrylates, ethanol, water,methacrylate functional copolymer of polyacrylic andpolyitaconic acids, photoinitiator system, 10% byweight 5.0 nm (diameter) spherical silica particles

3M ESPE

Excite DSC Dual adhesive system N01060 Phosphonic acid acrylate, dimethacrylates, hydroxyethylmethacrylate, highly dispersed silicon dioxide, ethanol,catalysts, stabilizers, fluoride, coated with initiators

Ivoclar Vivadent

Adper SE Plus Self-etching photo activationadhesive system

Liquid A, 8BH; Liquid B, 8BJ Liquid A: water, HEMA, surfactant, pink colorant;Liquid B: UDMA, TEGDMA, TMPTMA (hydrophobic trimethacrylate),

HEMA (phosphates), MHP (methacrylated phosphates),bonded zirconia nanofiller, initiator system based on camphorquinone

3M ESPE

RelyX ARC Conventional resin cement N142162 Base paste: Bis-GMA, TEGDMA, benzoyl peroxide;catalyst paste: Bis-GMA, TEGDMA, photoinitiator system,amine, peroxide, zirconia-silica filler 67.5% by weight

3M ESPE

RelyX Unicem Self-adhesive resin cement 343436 Base paste: methacrylate monomers that contain phosphoricacid groups, methacrylate monomers, silanated fillers, initiatorcomponents, stabilizers; catalyst paste: methacrylate monomers,

alkaline(basic) fillers, silanated fillers, initiator components, stabilizers, pigments

3M ESPE

Set Self-adhesive resin cement S0807171 Methacrylate ester phosphoric acids, UDMA, photoinitiator, glass offluoride aluminum silicate (67 wt%), and pyrogenic silica (45 v%)

SDI Limited

Bis-GMA, bisphenol-A-glycidyl dimethacrylate; HEMA, hydroxyethylmethacrylate; UDMA, urethane dimethacrylate; TEGDMA, tetraethyleneglycol dimethacrylate; TMPTMA, trimethylolpropanetrimethacrylate; MHP, methacrylated phosphate.aAccording to manufacturer documentation.

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Bond 2 bonding system (3M ESPE) was applied in 2consecutive layers by gently shaking a brush saturatedwith the material onto the surface of the dentin for 15seconds. The teeth were gently dried in air to evaporatethe solvent and were light polymerized with a light-emitting diode (Dabi Atlante) for 20 seconds. TheRelyX ARC conventional resin cement (3M ESPE) wasmixed for 10 seconds and placed in the post space withan endodontic file. The resin cement was applied to thepost surface and brought into position within the postspace; any excess cement was removed. Resin cementwas light polymerized for 40 seconds.

EXC Group: Excite DSC + RelyX ARCPost spaces were etched with 35% phosphoric acid (3MESPE) for 15 seconds, washed, and dried with sterilepaper points, without drying the dentin. The Excite DSCdual bonding system (Ivoclar Vivadent) was activatedand applied for 10 seconds with a microbrush in thecanal. Any excess material was removed with paperpoints and by gently blowing air for 3 seconds. Thesystem was light polymerized with an ultra light-emittingdiode for 10 seconds. The RelyX ARC conventional resincement was mixed and inserted into the post space in thesame way as described for the SB2 group. Cement wasapplied to the post surface, the post was placed in po-sition, and any excess material was removed. Resincement was light polymerized for 40 seconds.

SEP Group: Adper SE Plus + RelyX ARCThe post spaces were dried and etched with Adper SEPlus self-etching adhesive (3M ESPE). Primer (Liquid A)was applied throughout the intraradicular dentin with a

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microbrush, without drying the dentin. Adhesive (LiquidB) then was applied by gently shaking a microbrushsaturated with the material for 20 seconds, and the ad-hesive was dried for 10 seconds. A second layer of theadhesive was applied, spread by gently blowing air, andlight polymerized for 10 seconds. The cementation stepfor the glass-fiber posts with treated surfaces was per-formed in the same way as described for the other groupstreated with RelyX ARC resin cement.

UNI Group: RelyX UnicemThe post spaces were dried and RelyX Unicem self-adhesive resin cement (3M ESPE) was manipulated andinserted in the post space with an endodontic file. Thecement was applied to the post surface, the post wasplaced in position, and any excess cement was removed.Finally, the resin cement was light polymerized for 40seconds.

SET Group: SetThe post spaces were dried, and Set self-adhesive resincement (SDI) was manipulated and inserted into the postspace with an endodontic file. Next, the cement wasapplied to the post surface, the post was placed in position,and any excess cement was removed. Finally, the resincement was light polymerized for 40 seconds.

All the teeth were stored for 7 days.33,34 The teethwere sectioned perpendicular to the long axis with a low-speed diamond saw under water cooling with an Isomet2000 (Buehler) to obtain slices approximately 1.3 mm inthickness. These were analyzed from each third (cervical,middle, and apical). The slices were embedded in acrylicresin (Classico); manually finished with no. 320-, 600-,

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D E

1.3 mm

1.3 mm

1.3 mm

Post-lutingprocedure

Finishing andpolishing

Ultra-microhardness tester

Martens hardness andelastic modulus

A

1 mm

B

Endodontictreatment

C

Post spacepreparation

Post(Ø ± 1.0 mm)

Figure 1. Specimen preparation. A, Removal of anatomic crown of tooth 1.0 mm above cementum-enamel junction. B, Endodontictreatment performed with gutta percha cones and calcium hydroxide cement. C, Intraradicular post space preparation. D, Post-lutingprocedure. After 7 days, slices approximately 1.3 mm in thickness were obtained for each third to be analyzed (cervical, middle, andapical). E, Martens hardness (HM) and elastic modulus (Eit) measurements with load of 3 mN.

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800-, and 1200-grit silicon carbide paper (Extec Corp);and polished with diamond pastes (6, 3, and 1 mm) for aperiod of 4 minutes each. The specimens were cleaned inan ultrasonic unit (model 2210; Branson Ultrasonic Corp)with deionized water for 2 minutes between the stepsand at the end of the process.

The MH and Eit values were measured with anultramicrohardness tester (DUH-211; Shimadzu) under aload of 3 mN at a speed of 0.2926 mN/s; the holding timewas 5 seconds. The regions analyzed were those thatcorresponded to the components of the adhesive inter-face: resin cement, adhesive system, and dentin thatunderlies the bonded interface. A Vickers tip was used,and 3 indentations were made in each region (Fig. 1). TheMH and Eit values were calculated automatically by thesoftware program installed with the tester. Statisticalanalyses were performed with 2-way ANOVA, whenconsidering the experimental groups (the luting pro-cedures) and the different regions of intraradicular dentin(cervical, middle and apical dentin) as the factors. Sub-sequently, the Fisher protected least significant differencetest (a=.05) also was performed.

RESULTS

The results of ANOVA of the HM values indicated sta-tistically significant differences among the groups(P<.001) and the different thirds of intraradicular dentin

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(P<.001). There was no interaction among these factors(P=.356). Similarly, for the Eit values, no significant dif-ferences were found among the groups (P<.001) orintraradicular thirds of dentin (P=.048). There was nointeraction between these factors (P=.271).

The HM and Eit values for the different thirds of theintraradicular dentin are given in Table 2. The apical thirdexhibited the highest HM values for all groups. No sta-tistically significant differences were found among thevalues of the middle third for the SB2 group, the cervicalfor the EXC group, and the cervical and the middle forthe SEP group. The groups with self-adhesive resincement (UNI and SET) had the highest HM values fordentin for all the regions studied (P<.05). The SEP grouphad a mean that was statistically similar to those of theUNI and SET groups; the exception was the apical third,for which the dentin in the SET group had higher valuesthan the dentin in the SEP group (P=.005).

During the analysis of the Eit values, the highestvalues were exhibited by the SEP group (Adper SE Plus),the UNI group (RelyX Unicem resin cement), and theSET group (Set resin cement). No statistically significantdifferences were found among the thirds analyzed; theexception was the SET group, which had statisticallylower values in the cervical and middle thirds comparedwith the apical third. Further, the SB2 group, unlike theother groups, exhibited higher Eit values for the cervicalthird, there being statistically significant differences for

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Table 2.Mean (standard deviation) (GPa) values of Martens hardness (HM) and elastic modulus (Eit) of dentin categorized according to cementingprocedure and root third

Mechanical Property and Region SB2 Group EXC Group SEP Group UNI Group SET GroupHM

Cervical 0.24 ±0.08Bb 0.30 ±0.17ABb 0.46 ±0.10Aa 0.47 ±0.06Ba 0.47 ±0.13Ba

Middle 0.33 ±0.16ABbc 0.26 ±0.08Bc 0.43 ±0.10Aab 0.48 ±0.10Ba 0.50 ±0.10Ba

Apical 0.42 ±0.15Ac 0.43 ±0.14Ac 0.48 ±0.17Abc 0.59 ±0.09Aab 0.70 ±0.16Aa

Eit

Cervical 28.58 ±16.65Aa 15.00 ±5.82Ab 36.75 ±14.06Aa 35.63 ±12.09Aa 27.23 ±7.63Bab

Middle 15.44 ±8.02Bb 15.82 ±8.83Ab 36.96 ±17.06Aa 31.52 ±6.62Aa 28.44 ±7.53Ba

Apical 17.19 ±6.76ABb 23.21 ±12.87Ab 38.17 ±17.13Aa 38.23 ±11.99Aa 36.10 ±6.53Aa

SB2, Adper Single Bond 2 + RelyX ARC; EXC, Excite DSC + RelyX ARC; SEP, Adper SE Plus + RelyX ARC; UNI, RelyX Unicem; SET, Set.Different superscript uppercase letters in columns and lowercase letters in rows indicate statistically significant differences (P<.05).

Table 3.Mean (standard deviation) (GPa) values of Martens hardness(HM) and elastic modulus (Eit) of adhesive systems in different rootthirds

Mechanical Property and Region SB2 Group EXC Group SEP Group

HM

Cervical 0.13 ±0.06Ab 0.12 ±0.06Bb 0.24 ±0.04Aa

Middle 0.06 ±0.04Bb 0.16 ±0.06ABa 0.23 ±0.10Aa

Apical 0.07 ±0.05Bb 0.24 ±0.12Aa 0.19 ±0.10Aa

Eit

Cervical 10.54 ±5.90Aa 9.62 ±5.80Aa 8.93 ±2.33Aa

Middle 3.03 ±2.27Bb 8.74 ±0.83Aa 9.04 ±4.21Aa

Apical 3.96 ±4.46Bb 9.24 ±3.61Aa 9.23 ±5.42Aa

SB2, Adper Single Bond 2 + RelyX ARC; EXC, Excite DSC + RelyX ARC; SEP, Adper SE Plus +RelyX ARC.Different superscript uppercase letters in columns and lowercase letters in rows indicatestatistically significant differences (P<.05).

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the middle and apical thirds (P<.001). The 2-wayANOVA for HM found a statistically significant differ-ence among the groups (P<.001); however, no statisti-cally significant difference was found among the differentthirds of the intraradicular dentin (P=.134). In addition,there was no interaction between these factors (P=.165).In contrast, the Eit values of the groups had a significantdifference (P=.002), and there were significant in-teractions among the factors (P=.007). Finally, no differ-ence was found in the different thirds analyzed (P=.097).

The HM and Eit values of the different adhesivesystems used in the SB2 group (light polymerized), theEXC group (dual polymerized), and the SEP group (self-etched) are given in Table 3. The SEP group exhibited thehighest HM values. In this group, there was no statisticaldifference among the thirds analyzed (P>.05). In contrast,the SB2 group had the lowest HM values. HM valuesdecreased significantly in the cervico-apical direction(P<.05). With regard to the Eit values, the EXC and SEPgroups exhibited statistically similar values, which wereindependent of the regions. In these groups, there wasno difference among the thirds. The lowest values wereexhibited by the SEP group in the middle and apical

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thirds (P<.05). The results of ANOVA of the HM valuesindicated a statistically significant difference among thegroups (P<.001) and among the different thirds of theintraradicular dentin (P<.047); however, the interactionsbetween these factors were not statistically significant(P=.070). For Eit values, the ANOVA results indicated asignificant difference among the groups (P<.001) and theregions analyzed (P=.002). Significant interactions alsowere found among these factors (P=.022).

The HM and Eit values of the resin cements in thedifferent thirds of the intraradicular dentin are presentedin Table 4. After analyzing each group separately, nostatistically significant difference was found among thethirds for the EXC, UNI, and SET groups for both pa-rameters studied (P<.05). In groups SB2 and SEP, thehighest HM values were found in the cervical third.Regardless of the third analyzed, the groups representedby the self-adhesive resin cements (UNI and SET) hadhigher HM values than did RelyX ARC resin cementassociated with the different adhesive systems. Withrespect to the Eit values, groups EXC, UNI, and SETexhibited no variations in the values when the differentthirds were compared. In the case of Adper SingleBond 2 (the SB2 group), RelyX ARC had higher valuesfor the cervical third, there being a statisticallysignificant decrease in the remaining thirds (P=.001).

DISCUSSION

The hardness and Eit of a material are mechanical prop-erties that can be used to indirectly evaluate the degree ofconversion of the material and, consequently, its extent ofpolymerization.1 In the present study, theHMvalues weredetermined based on both elastic and plastic deformationsand the local Eit values (cervical, middle, and apical) of thefollowing materials: resin cements, adhesive systems, andthe dentin that underlies the bonding interface. In general,the results found that the mechanical properties of theadhesive-interface components depend on the interactionbetween the restoration material and the substrate, and,therefore, the first null hypothesis of the study was

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Table 4.Mean (standard deviation) (GPa) values of Martens hardness (HM) and elastic modulus (Eit) of resin cements in different root thirds

Mechanical Property and Region SB2 Group EXC Group SEP Group UNI Group SET Group

HM

Cervical 0.25 ±0.10Ab 0.25 ±0.11Ab 0.36 ±0.05Aab 0.43 ±0.18Aa 0.40 ±0.14Aa

Middle 0.07 ±0.07Bc 0.33 ±0.16Ab 0.26 ±0.10Bbc 0.56 ±0.39Aa 0.37 ±0.18Aab

Apical 0.08 ±0.05Bb 0.31 ±0.04Aa 0.14 ±0.09Cb 0.36 ±0.10Aa 0.38 ±0.23Aa

Eit

Cervical 15.03 ±7.17Aab 12.99 ±7.52Ab 11.87 ±2.32Ab 19.56 ±7.73Aa 13.37 ±3.08Ab

Middle 4.20 ±5.79Bc 17.70 ±8.79Aa 9.40 ±4.36Abc 16.65 ±10.91Aab 10.04 ±3.71Ab

Apical 4.27 ±2.94Bb 15.55 ±6.86Aa 5.25 ±3.04Bb 12.51 ±3.54Aa 11.54 ±4.88Aa

SB2, Adper Single Bond 2 + RelyX ARC; EXC, Excite DSC + RelyX ARC; SEP, Adper SE Plus + RelyX ARC; UNI, RelyX Unicem; SET, Set.Different superscript uppercase letters in columns and lowercase letters in rows indicate statistically significant differences (P<.05).

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rejected. Furthermore, the mechanical properties variedduring canal preparation. The differences among the rootthirdswere analyzed, which led to a rejection of the secondnull hypothesis.

In the dentin that underlies the bonded interface, thehighest HM values were obtained for the groups in whichthe self-adhesive resin cements RelyX Unicem and Setwere applied (Table 2). These materials do not requirethat the dentin substrate be treated or an adhesive sys-tem be applied before use. The bonding process occursthrough the chelation of calcium ions by the acidicgroups, which results in chemical adhesion with thehydroxyapatite of tooth structure28: the hardness ofintraradicular dentin is not affected during the process.The dentin exhibited intermediate HM values when theself-etching adhesive Adper SE Plus was used (Table 2).This type of adhesive system also eliminates the need forprior etching with phosphoric acid, thereby simplifyingthe bonding technique.10 These products contain phos-phate methacrylates, which partially condition the dentinand creates patterns of micromechanical retention for thepenetration of the adhesive polymerized into the tooth.11

Moreover, these phosphoric acid methacrylates reactwith the residual hydroxyapatite of the hard tooth tis-sue.24 As for the Eit values, especially those measured inthe middle and apical thirds, the dentin that underliesthe bonded interfaces of RelyX Unicem and Set resincements as well as that beneath Adper SE Plus self-etching adhesive, had higher values than did dentintreated with phosphoric acid (Table 2). Accordingto Goracci et al,1 the methacrylate phosphate present inself-etching or self-adhesive materials has a lowerdemineralization capacity than that of phosphoric acid.

The initial acidity of self-adhesive resin cements re-sults in fast action and a rapid increase in the pH.24,27,30

Therefore, the interaction that occurs with superficialdentin is not sufficient to allow for the formation ofresinous tags.24,27-30 According to Pavan et al,28 theacidity of such cements is not sufficient to cause dentinaldemineralization and the exposure of dentinal tubules,which could explain the higher HM and Eit values

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observed in this study. The lowest HM and Eit values fordentin were noticed for the groups that used the total-etch adhesive systems, Adper Single Bond 2 and ExciteDSC. This can be explained by the fact that the treatmentof intraradicular dentin with 37% phosphoric acid resultsin the removal of the smear layer. It also opens thedentinal tubules and exposes the collagen fibers, whichthus enables the penetration of the hydrophilic mono-mers of the adhesive system into the collagen network.This establishes a mechanism of micromechanicalretention.17 However, these highly concentrated acidsolutions often demineralize the dentin to levels at whichthe adhesive cannot completely fill the dentin tubulesand results in the formation of a fragile zone,15 whichexposes the collagen peptide chains to degradation.22

From a clinical aspect, the probability is high that thegel remains on the intraradicular dentin for longer pe-riods, thus increasing the potential for excessive demin-eralization of the dentin and resulting in only partialinfiltration of the adhesive.20

When comparing the different thirds of intraradiculardentin, we found a tendency for the apical third to exhibitthe highest HM values; the exception was the dentinhybridized with the self-etching adhesive Adper SE Plus(Table 2). The higher values for the apical third could beattributed to several factors, including apical sclerosis,35

cavity configuration,36 difficulty in visualization, level ofaccess to the apical portion, or restricted cement pene-tration into the deeper portions of the post space.3 In thisrespect, the application of phosphoric acid withthe adhesive and resin cements would be more difficult.3

A few areas of the apical intraradicular dentin wereprobably not conditioned and/or hybridized correctly.Cervical and middle thirds would be more susceptible toconditioning by phosphoric acid or self-etching mate-rials4 and would most likely undergo demineralization togreater degrees. The HM and Eit values were calculatedin the adhesive layer for the first 3 groups, for which theconventional resin cement RelyX ARC was used. AdperSingle Bond 2 and Excite DSC are conventional adhesivesthat require that the dentin be etched with acid, with the

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first system being photoactivated and the second beingdual activated. The third group used Adper SE Plus, aphotoactivated, self-etching adhesive system that doesnot require prior etching.

The specimens that corresponded to Adper SingleBond 2 had the highest values of HM and Eit in thecervical thirds. These were statistically different than thevalues of the other thirds (Table 3). This adhesive re-quires a light source for the conversion process. Becausethe polymerization of the adhesive system was occlusal,in other words, on the more coronal portion of the postspace, more of the irradiating light could reach the ad-hesive system in the cervical third.4 Therefore, a decreasein the amount of light energy delivered could decreasethe degree of conversion of the adhesive homoge-neously37 and degrade its mechanical properties.Although Adper SE Plus also is activated by light, thevalues that correspond to this material found no statis-tically significant differences with respect to the analyzedthirds. This self-etching adhesive only promotesa modification in the smear layer during the hybridiza-tion process, which results in a less sensitive technique inrelation to a moist environment.12 This should lead tomore homogeneous results.

In the group for which the dual-polymerizing adhe-sive Excite DSC was used, no statistically significantdifference was found in the Eit values. In addition toinitially requiring light for polymerization, this adhesivealso undergoes chemical polymerization,6 which cancompensate for the absence of light in places it cannotreach, for example, the apical third. Furthermore, benzoylperoxide and tertiary amines generate free radicalsthrough a redox reaction. Hence, the polymerization re-action occurs even in the absence of light.7

During the analysis of the mechanical properties ofresin cements for the groups SB2 and SEP, in which thecement RelyX ARC was used with photoactivated ad-hesives, the materials exhibited higher MH and Eit valuesin the cervical third, with statistically significant differ-ence for the values of the middle and apical thirds(Table 4). As described previously, a photoactivated ad-hesive is not completely polymerized in the deepest re-gions of the preparation. Thus, polymerization does notoccur homogeneously, especially in the most apical re-gions.37 If the adhesive is not polymerized properly, thenthe residual acidic monomers present in the adhesivelayer react with the tertiary amines of the resin cement,which has an alkaline pH.13 Thus, the amines areneutralized and cannot reduce the benzoyl peroxidepresent in the cement during the redox reactionresponsible for the polymerization of the compositeresin.8 However, this factor is not as critical in the case ofthe cervical third because most of the monomers presentin the cement are converted to polymers during thephotoactivation process. In the cervical third, where light

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reaches the adhesive and resin cement effectively, theissue of incomplete polymerization is not relevant.

Some limiting factors should be taken into consid-eration, such as the difficulty of standardizing thepreparation in areas of difficult access; difficulties indrying the canal to ensure a properly conditioned dentin,especially for materials that require acid etching; and thenonhomogeneity of the substrate, because each regionhas its own peculiarities. Thus, future studies shouldinvestigate the intracanal cementation process by eval-uating the bonding interface over time and the interac-tion of the MH and Eit with other properties such as thedegree of conversion and nanoleakage. The search forimprovements in the adhesive process, if linked to amore conservative intraradicular preparation, could leadto more predictable and clinically stable rehabilitativetreatments.

CONCLUSION

On the basis of the results of this study, it can beconcluded that the MH and Eit of adhesive materials, andthe underlying dentin substrate are influenced by theinteractions of the resins materials used with the dentinas well as by the intraradicular depth. In the case of resinmaterials, the apical third tended to exhibit lower valuesfor the parameters analyzed. This should lead to moreconservative post spaces.

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Noteworthy Abstracts of

Making sense of complication reporting asso

Walton TInt J Prosthodont 2014;27:114-8

The current reporting of complications associated with FDPs isignificant monetary costs, will particularly impact the percefrom their prostheses. Effective documentation of complicatioand severity. The fiscal burden of treatment should be quantechniques, and procedures should be meaningful. Data collashould allow for comparisons within and between different pfiscal consequences of complications, achieves these objectivconjunction with actual or projected survival data and persorealistic information of the expected clinical service of dental

Reprinted with permission of Quintessence Publishing.

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30. Aguiar TR, Di Francescantonio M, Ambrosano GMB, Giannini M. Effect ofcuring mode on bond strength of self-adhesive resin luting cements todentin. J Biomed Mater Res B Appl Biomater 2010;93:122-7.

31. Mecholsky JJ Jr. Fracture mechanics principles. Dent Mater 1995;11:111-2.32. Shahdad SA, McCabe JF, Bull S, Rusby S, Wassell RW. Hardness measured

with traditional Vickers and Martens hardness method. Dent Mater 2007;23:1079-85.

33. Mumcu E, Erdemir U, Topcu FT. Comparison of micro push-out bondstrengths of two fiber posts luted using simplified adhesive approaches. DentMater J 2010;29:286-96.

34. Onay EO, Korkmaz Y, Kiremitci A. Effect of adhesive system type and rootregion on the push-out bond strength of glass-fibre posts to radiculardentine. Int Endod J 2010;43:259-68.

35. Paqué F, Luder HU, Sener B, Zehnder M. Tubular sclerosis rather than thesmear layer impedes dye penetration into the dentine of endodonticallyinstrumented root canal. Int Endod J 2006;39:18-25.

36. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometricfactors affecting dentin bonding in root canals: a theoretical modelingapproach. J Endod 2005;31:584-9.

37. Roberts HW, Leonard DL, Wanderwalle KS, Cohen ME, Charlton DG. Theeffect of a translucent post on resin composite depth of cure. Dent Mater2004;20:617-22.

Corresponding author:Dr Paulo Henrique dos SantosAraçatuba School of Dentistry (UNESP)Rua José Bonifácio, 119316015-050 Araçatuba, SPBRAZILE-mail: paulosantos@foa.unesp.br

Copyright © 2015 by the Editorial Council for The Journal of Prosthetic Dentistry.

the Current Literature

ciated with fixed dental prostheses

s inadequate and misleading. Complications, which incurived value (worth or importance) that patients derivens should include type (biologic and technical), incidence,tified. Comparisons of different restorative materials,ted prospectively or retrospectively and pooled over timeractice settings. The proposed classification, based on thees. Effective documentation of complications innal clinical experience will enable clinicians to provideprostheses.

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