J O U R N A L O F T H E M E C H A N I C A L B E H AV I O R O F B I O M E D I C A L M A T E R I A L S 4 ( 2 0 1 1 ) 1 0 7 – 1 1 6

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Research paper

Biomechanical comparison of implant retained fixed partialdentures with fiber reinforced composite versus conventionalmetal frameworks: A 3D FEA study

Erkan Erkmena,∗, Gökçe Meriçb, Ahmet Kurtc, Yahya Tunçc, Atılım Eserd

aDepartment of Oral and Maxillofacial Surgery, Faculty of Dentistry, Gazi University, 8.Cadde 82.Sokak EMEK-Ankara 06500, TurkeybDepartment of Prosthetic Dentistry, Faculty of Dentistry, Near East University, Lefkosa, Mersin 10, TurkeycDepartment of Manufacturing Engineering, Faculty of Engineering, Atılım University, Ankara 06838, Turkeyd Institute for Materials Applications in Medical Engineering, Aachen University, Aachen 52056, Germany

A R T I C L E I N F O

Article history:

Received 22 May 2010

Received in revised form

19 September 2010

Accepted 25 September 2010

Published online 1 October 2010

Keywords:

Biomechanics

Finite element analysis

Implant supported denture

Fixed partial denture

Fiber reinforced composite

A B S T R A C T

Fiber reinforced composite (FRC) materials have been successfully used in a variety of

commercial applications. These materials have also been widely used in dentistry. The use

of fiber composite technology in implant prostheses has been previously presented, since

they may solve many problems associated with metal alloy frameworks such as corrosion,

complexity of fabrication and high cost. The hypothesis of this study was that an FRC

framework with lower flexural modulus provides more even stress distribution throughout

the implant retained fixed partial dentures (FPDs) than a metal framework does. A 3-

dimensional finite element analysis was conducted to evaluate the stress distribution in

bone, implant–abutment complex and prosthetic structures. Hence, two distinctly different

models of implant retained 3-unit fixed partial dentures, composed of Cr–Co and porcelain

(M-FPDmodel) or FRC and particulate composite (FRC-FPDmodel) were utilized. In separate

load cases, 300 N vertical, 150 N oblique and 60 N horizontal forces were simulated. When

the FRC-FPD and M-FPD models were compared, it was found that all investigated stress

values in the M-FPD model were higher than the values in the FRC-FPD model except for

the stress values in the implant–abutment complex.

It can be concluded that the implant supported FRC-FPD could eliminate the excessive

stresses in the bone–implant interface and maintain normal physiological loading of the

surrounding bone, therefore minimizing the risk of peri-implant bone loss due to stress-

shielding.c⃝ 2010 Elsevier Ltd. All rights reserved.

.

d

1. Introduction

In recent years, as a result of advances in oral implantologythe osseointegrated dental implants have been shown tobe predictable options for treatments ranging from the

∗ Corresponding author. Tel.: +90 532 611 0772; fax: +90 312 223 9226E-mail address: drerkmen@gmail.com (E. Erkmen).

1751-6161/$ - see front matter c⃝ 2010 Elsevier Ltd. All rights reservedoi:10.1016/j.jmbbm.2010.09.011

replacement of a single tooth tocomplete arch restorations

(Christensen, 2002; Pietrabissa et al., 2000). In the last decade,

dental implants have been successfully used to support fixed

partial dentures (FPD) (Naert et al., 2001).

.

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Superstructures on dental implants commonly consist ofa metal-framework veneered with ceramic facing. In spiteof the proven clinical success of metal–ceramic restorations,there has been an increase in the use of metal-freeceramic systems because of their superior esthetics, chemicaldurability and biocompatibility (DeHoff et al., 2006). A novelalternative to metal–ceramic and full ceramic restorations inimplant-supported FPDs is fiber reinforced composite (FRC)designs (Ruyter et al., 1986; Behr et al., 2001). FRC materials,which had been successfully used in a variety of commercialapplications, have been more widely used in dentistry.Carbon–graphite fiber-reinforced poly(methyl methacrylate)for complete-arch implant prostheses has been previouslypresented (Björk et al., 1986; Segerström and Ruyter, 2007).Glass FRC for implant supported fixed prostheses has alsobeen suggested (Behr et al., 2001; Freilich et al., 2002). FRCprostheses have been presented with a framework composedof fiber bundles pre-impregnated with a resin matrix and aveneering composite that covers the FRC framework (Freilichet al., 2000).

Laboratory studies have shown that FRC materials exhibitflexure strength that is greater than or comparable to metalalloys (Anusavice, 1996). Behr et al. (2001) evaluated that thefracture strength of glass FRC FPD on dental implants wasalmost three times higher than the maximum chewing forcemeasured in young patients with natural dentitions (400 N)(Fontijn-Tekamp et al., 2000).

The use of fiber composite technology for FPDs is a low-cost alternative to metal-alloy, metal–ceramic, or all-ceramicrestorations (Fischer et al., 2004). Moreover, FRC has beensuggested to absorb energy from the masticatory cycle dueto the lower flexural modulus of the material (Meriç et al.,2005). Composite veneer materials have distinct advantagesover porcelain veneers; the former are less brittle, do notwear the opposing dentition, and chemically bond to the FRCframework (Freilich et al., 1998). Recently FRC was found tohave better stress distribution than other materials, such asglass ceramic, gold, alumina and zirconia (Magne et al., 2002).

The transfer of functional loads and accompanying stressdistribution in a bone–implant–prosthesis assembly dependson the physical properties and spatial geometric configura-tion model of each component. The effects of different pros-thetic materials and designs on stress distribution in implantsupported prostheses have so far not been reported.

The aim of the present study was to evaluate and comparethe effects of the framework and veneering materials onstress distribution of implant retained FPDs in the bonearound the implants as well as in the fixture-abutmentcomplex, in the framework and in the veneering part of theprostheses.

2. Materials and methods

To evaluate the stress distribution in and around the bone,the implant–abutment complex and 3 unit FPDs supported bytwo implants, finite element analysis (FEA) was conducted.

2.1. Finite element model

Two three-dimensional finite element models were gener-ated; each representing a 3 unit FPD designed with differ-ent materials. In the first model, FPD was constructed witha metal framework and porcelain (M-FPD) and the secondmodel was designed with an FRC framework and particulatecomposite (FRC-FPD).

The implants were embedded in the first premolar andfirst molar sites (Fig. 1a). Totally edentulous mandibular malebone was used as the basis of a mandibular finite elementmodel. The modeled section of the mandible was composedas a dense cancellous core surrounded by a thick layer ofcortical bone. The average thickness of the cortical bone in thecrestal area was 2.0 mm. Serial axial sections in every 0.5 mmof the edentulous mandible was obtained from a NewTom 3G(Quantitative Radiology, Verona, Italy) Cone-Beam CT (CBCT)imaging System. The CBCT images were stored using DICOM3.0 as a medical image file format and imported into Maxilim(Medicim Company, Mechelen, Belgium) version 2.2.2, 3Dmedical image processing software. The 3D image of themandible was imported with the .stl file format into MSCMENTAT (MSC Software Corporation, Santa Ana, CA, USA)version 2005 for pre-processing and modeling.

In the current study, a model of a 13.0 mm long and4.0 mm in diameter solid-screw Astra Tech implant (Astra-Tech, Astra-Tech AB, Molndal, Sweden) and direct abutmentfor the Astra implants were selected. The geometry ofthe implants and abutments was modeled according toengineering drawings by using MSC MENTAT (MSC. SoftwareCorporation, Santa Ana, CA, USA).

A 3 unit FPD consisting of a first premolar abutment, asecond premolar pontic, and a first molar abutment wasfabricated. In the first model (M-FPD), cobalt–chromium (Bego,Bremen, Germany) was used for the framework (Fig. 1b) andfeldisphatic porcelain was used for the veneering material(Fig. 1f). The thickness of the metal framework and porcelainused in this study were 0.5 mm and 1.5 mm respectively andthe cement thickness was ignored.

In the second model (FRC-FPD), an anisotropic continuousunidirectional E-glass FRC (everStick, StickTech, Turku,Finland) was selected to construct the framework of theFPD. The design of the fiber reinforced implant prosthesiswas obtained from the literature (Freilich et al., 2002). Acombination fiber and hybrid composite coping is made tofit over the metal abutment. Veneers were made of isotropicveneering hybrid composite (Estenia, Kuraray; Tokyo, Japan).The composite coping was prepared with horizontal grooveson the facial and lingual surfaces and vertical boxes onthe proximal surfaces that allow for adaptation of theunidirectional FRC material (Fig. 1c). The thickness of thecoping used in this study was 0.5 mm and the thickness ofthe luting composite was ignored. Strips of FRC are placed inthe copings’ proximal boxes, buccal and lingual surfaces, andwrapped around the copings (Fig. 1d). An additional layer wasplaced perpendicular to the previous layers of FRC (Fig. 1e).1.5 mm thick hybrid composite veneer was placed over theframework to obtain the full contour of the prosthesis (Fig. 1f).All the final solid meshes were constituted by tetrahedralelements with four nodes by using MSCMARC (MSC. SoftwareCorporation, Santa Ana, CA, USA).

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M-FPD framework design

FRC-FPD framework design

Fig. 1 – 3D finite element model of mandibular bone, abutment, framework design and fixed partial denture.

Table 1 – Mechanical properties of materials used in thestudy.

Material Young’smodulus(GPa)

Poissonratio

Shearmodulus(GPa)

Cortical bone 14.8 0.30Cancellous bone 1.85 0.30Titanium 110 0.32Cobalt–chromium alloy 220 0.30Feldisphatic porcelain 61.2 0.19Hybrid composite 22 0.27FRC longitudinal (X) 46 0.39 16.5FRC transverse (Y) 7 0.29 2.7FRC transverse (Z) 7 0.29 2.7

2.2. Material properties

The elastic properties of the materials used in the modelswere taken from the literature, as shown in Table 1 (Iplikciogluand Akca, 2002; Shinya et al., 2008).

2.3. Interface condition

The current study simulated osseointegrated screw implants.For simulating such an ideal osseointegrated condition theimplants were rigidly bonded in the bone along their entireinterface. Similarly, the type of bond was provided at theimplant–abutment and abutment–prosthesis interfaces.

2.4. Constraints and loads

Models were constrained in all directions at the nodes on themesial and distal bone surfaces. The literature suggested (Linet al., 2010) the maximum occlusal biting force for naturalteeth is in the range of 297–669 N for adult males, whilethe occlusal loading on the implant supported prosthesis isusually 42–412 N. Thus, in the current study a 300 N staticvertical load was applied along the central fossa of each

superstructure. To simulate the oblique load condition, anoblique static load of 150 N in total was applied to the buccalcusps of the each crown with an inclination of 60◦ buccallyfrom the vertical. 60 N static loads were applied inmesiodistaldirection horizontally to mimic the parafunctional movementof the jaw. The maximum equivalent von Mises stress in theimplant–abutment complex as well as in the framework andveneering material and the maximum principal stress andminimum principal stress in the jaw bone were set as outputvariables to evaluate the effect of differentmaterial propertiesunder 3-unit FPDs.

2.5. Convergence analysis

As there are no appropriate experimental results in theliterature to compare our results to validate the finite elementmodel, six different models for each prosthetic system withchanging numbers of elements were compared and theconvergence of the results was examined using the result ofthe maximum tensile stress in cortical bone under a verticalload condition. The results and the numbers of elements areshown in Table 2. From the table the convergence for the twomodels was reached for the following element numbers andthe results of those models were considered in the rest of thestudy. Therefore, our 3D models consist of 247 342 elementsand 45817 nodes for the M-FPD model and 257486 elementsand 48466 nodes for the FRC-FPD model.

3. Results

In the study, von Mises stresses on implants, frameworksand veneering materials and maximum (tensile stress) andminimum (compressive stress) principal stresses (Pmax andPmin) on bony structures were used to assess the stressdistribution.

The von Mises and principal stress values are shownin Figs. 3–5. When the FRC-FPD and M-FPD models were

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Table 2 – Principal maximum stress values for vertical load on cortical bone with changing numbers of elements forconvergence and final numbers of elements and nodes.

# of elements for FRC-FPD model 102 347 137 816 167518 189 216 204628 257 486# of elements for M-FPD model 126 746 134 578 161512 195 216 237441 247 342

Principal maximum stress (Pmax) (maximum tensile stress) MPaFRC-FPD model vertical load case 1.4 3.2 5.3 8.1 9.1 8.9M-FPD model vertical load case 10.7 12.9 24.4 33.9 34.8 35.9

FRC-FPD model M-FPD modelFinal # of elements 257 486 247 342Final # of nodes 48 466 45 817

70

von

Mis

es s

tres

s (M

Pa)

60

50

40

30

20

10

0

V H

implant-abutment

framework veneeringpart

O V H O V H

M-FPD

FRC-FPD

O

Fig. 2 – Highest von Mises stress values recorded at the implant–abutment, framework and veneering part (V: in the case ofvertical load, H: in the case of horizontal load, O: in the case of oblique load).

compared, it was found that all investigated stress values inthe M-FPD model were higher than the values in the FRC-FPD model except for the values of von Mises stresses in theimplant–abutment complex.

A color scale with 12 stress values served to measurequantitatively the stress distribution in the model compo-nents. Since all the values, von Mises, principal minimumand principal maximum stresses were found through differ-ent formulations, they would differ for each individual loadcase. Thus, different scaling values have been selected andused for the corresponding stresses in groups not to representthe yield strength but rather to provide clear visualization ofthe region of stress.

Implant–abutment complexIn the implant–abutment complex increased von Mises

stress values have been determined in the FRC-FPD modelthan in the M-FPD model under all three loading conditions.In the FRC-FPD model the highest resultant von Mises stressvalues were recorded under vertical loads and decreasedunder horizontal to oblique loads respectively. Howevercorrespondingly, in the M-FPD model the von Mises stressvalues have shown a regular increase in vertical andhorizontal to oblique load conditions (Fig. 2). In the FRC-FPD model under all load cases the distribution of stressalong the entire complex has been noted while the stressconcentrated around the implant fixture junction in the M-FPD model (Fig. 5). Mesial and distal implants as well as theabutments were affected equally in vertical and horizontalload cases in both FRC-FPD and M-FPD models.

3.1. Framework

The highest von Mises stress was found in the M-FPD modelwithin vertical horizontal and oblique loads respectively

when compared with the FRC-FPD model (Fig. 2). The stresswas localized distinctly and either stress concentrationsor magnitudes have been noted excessively in the M-FPDmodels. Especially, pontic connectors and themetal couplingswere bearing the increased stresses all the way up in the caseof all three load conditions. The von Mises stress distributionseemed to be concentrated along the collar region and spreadthrough the mesial couplings lingual and distal aspects aswell as the distal couplings mesial and lingual aspects (Fig. 6).Nevertheless, in the FRC-FPD model the longitudinal runningFRC structure has not been loaded intensively (Fig. 6). Onlythe stress was concentrated around the collar region of thecomposite couplings and the underside of the transversallyrunning FRC structure in the case of vertical horizontal andoblique loads (Fig. 6).

3.2. Veneering material

The comparison of the veneering materials revealed that alesser von Mises stress has occurred in the FRC-FPD model(Fig. 2), although the stress patterns recorded in both modelswere similar but the magnitude of the stresses were found tobe distinctly different and higher in the M-FPD model (Fig. 7).

3.3. Cortical bone

In the cortical bone, the highest Pmax stress in the M-FPDmodel in the case of the horizontal load condition has beentraced lingually and distolingually as slightly greater aroundthe mesial implant neck than the distal one (Fig. 8). Inthe vertical load case the Pmax stresses were concentratedhomogenously around the implant necks in the M-FPD and

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Pm

ax (

MP

a)P

min

(M

Pa)

M-FPD

FRC-FPD

40

30

20

10

0

-10

-20

-30

-40

-50

V H O

V H O

Fig. 3 – Highest principal maximum and principal minimum (tensile maximum and compression maximum) valuesrecorded at the cortical bone (V: in the case of vertical load, H: in the case of horizontal load, O: in the case of oblique load).

Pm

ax (

MP

a)P

min

(M

Pa)

M-FPD

FRC-FPDV H O

V H O

30

20

10

0

-10

-20

-30

Fig. 4 – Highest principal maximum and principal minimum (tensile maximum and compression maximum) valuesrecorded at the cancellous bone (V: in the case of vertical load, H: in the case of horizontal load, O: in the case of obliqueload).

Fig. 5 – von Mises stress values and stress distribution patterns recorded in implant–abutment complex; (a) FRC-FPD modelin the case of vertical load, (b) M-FPD model in the case of horizontal load.

FRC-FPD models together with a remarkable increase in theM-FPDmodel. In the case of oblique load, stress concentrationpatterns have been found similar to each other in the M-FPD and FRC-FPD models and distal and distolingual cortical

surroundings have been affected equally in distal and mesialimplants (Fig. 8). However, the magnitude of the stress hasbeen recorded as greater in the M-FPD model (Fig. 3). Thecomparison of M-FPD and FRC-FPD models in respect of Pmin

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Fig. 6 – von Mises stress values and stress distribution patterns recorded in framework; (a) M-FPD model in the case ofvertical load, (b) FRC-FPD model in the case of vertical load, (c) FRC-FPD model in the case of oblique load.

Fig. 7 – von Mises stress values and stress distribution patterns recorded in the veneering part; (a) M-FPD in the case ofvertical load, (b) FRC-FPD in the case of vertical load.

stress values revealed that in all three loading conditions thehighest values have been recorded on the opposite side wherePmax stress occurred.

3.4. Cancellous bone

In cancellous bone, the highest Pmax stress was found in theM-FPDmodel lingually within the horizontal load case (Fig. 9).The stress patterns in both models have been evaluated asdistinctly different to each other. In the FRC-FPD model whencompared with theM-FPD there was no significantly traceablestress pattern in all three loading conditions. Additionally thePmax stress values which occurred in the cancellous bonewere dramatically lower in the FRC-FPD model (Figs. 4 and9). In the vertical loading condition the Pmax stress has been

concentrated at the collar area extended all around themesialand distal housings in the direction of distally in the M-FPDmodel (Fig. 9). The Pmin values in the case of horizontal andoblique loads have been determined on the buccal aspectof both the mesial and distal housings whereas the verticalloads generated the stress at the lingual side (Fig. 10) in theM-FPD model. The Pmin values for the FRC-FPD model wereunremarkable for the standard load cases (Fig. 10).

4. Discussion

The present study focused on the problem of the biome-chanical effects of implant supported dental bridges which

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Fig. 8 – Pmax stress values and stress distribution patterns recorded in the cortical bone; (a) M-FPD in the case of horizontalload, (b) M-FPD in the case of oblique load, (c) FRC-FPD in the case of oblique load.

Fig. 9 – Pmax stress values and stress distribution patterns recorded in the cancellous bone; (a) M-FPD in the case ofhorizontal load, (b) FRC-FPD in the case of oblique load, (c) M-FPD in the case of vertical load.

were differently designed and fabricated with distinct mate-rials. The use of fiber composite technology in the creationof metal-free implant prostheses may solve many problemsassociated with a metal alloy framework such as corrosion,toxicity, complexity of fabrication, high cost and esthetic lim-itations. However, limited information is available on the im-plant retained FRC-FPD’s longevity and clinical behaviour. Inthis FEA study stress transfer properties of implant retainedFRC-FPD were evaluated and compared with the stress trans-fer properties of M-FPD (Pietrabissa et al., 2000). In a clinicalpoint of view, it was also aimed in the current study to seeka feasible alternative to prosthetic material in implant den-tistry, which may lead to either mechanical or biological ad-vantages over the conventional materials for superstructures.

The use of FEA in implant-retained prosthesis has beenwidely demonstrated and published (Kong et al., 2008;Limbert et al., 2010). Because the geometries involved withmodelling implants, prosthesis and alveolar processes arevery complex, FEA is considered the most suitable tool foranalyzing them. FEA is a mathematical model of a real objectand it is usually impossible to reproduce the entire detailsof natural behaviour. Thus, an experimental or clinical studycannot be completely replaced by a numerical test. On theother hand, a mathematical model has greater superiorityover in vivo tests in aspects of repeatability and controllability(Simsek et al., 2006). Moreover by means of FEA optimallayouts of resin matrix and fibres in FRC restorations can beachieved (Shi and Fok, 2009).

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Fig. 10 – Pmin stress values and stress distribution patterns recorded in the cancellous bone; (a) M-FPD model in the case ofhorizontal load, (b) M-FPD model in the case of oblique load, (c) FRC-FPD model in the case of horizontal load.

In the current study, several assumptions and simplifica-tions have been made with regard to the material proper-ties and model generation. In FEA models bone is frequentlymodelled as isotropic, in fact it is anisotropic (O’Mahonyet al., 2001; Meyer et al., 2001). The properties of the ma-terials modelled in the study, particularly the living tissues,however, are different. For example, it is well known in re-ality that the actual cortical bone of the mandible is trans-versely isotropic and inhomogeneous (Meyer et al., 2001; Ash-man and Van Buskirk, 1987). The structures in themodel wereall assumed to be homogenous, isotropic and linear elasticdespite the anisotropic nature of the fiber reinforced compos-ite. The implants were assumed to be 100% osseointegrated.Furthermore, histomorphometric studies indicated that thereis never a 100% bone–implant interface. In addition, in thisstudy, the modelled section of the mandible was composedas a cancellous core surrounded by a 2 mm homogenous cor-tical layer. An actual mandible has more compact bone at theinferior border and less compact bone on the superior border.Therefore, inherent limitations of FEAmust be acknowledged.

Recently the design and fabrication of fiber reinforcedimplant prostheses have been described, and the reportedclinical behavior of the prostheses in a small group ofpreliminary subjects was encouraging (Freilich et al., 2002).In the current study the mechanical behavior of theexisting design of prostheses in terms of stress distributionwas evaluated. This should be considered to improve theprostheses design for the long-term clinical success of FRC-FPDs. Nevertheless, the load transmission from the implantinto the bone is a condition of the success or failure ofa dental implant (Limbert et al., 2010). Hence, the stresstransfer patterns under different prosthetic designs mayelucidate further implant related problems to be solved suchas marginal bone loss and long term implant longevity.

When applying FEA to dental implants not only axial andhorizontal loads (moment-causing loads) but also a combinedload (oblique occlusal load) must be considered because the

latter representsmore realistic occlusal directions (Zhang andChen, 1998). A wide range of magnitudes for chewing forceshas been reported in the literature (Simsek et al., 2006). A ratioof 5:2.5:1 was found for vertical, oblique, and horizontal loadsduring chewing by Mericske-Stern et al. (1992).Thus, vertical,horizontal, and oblique static loads were applied accordinglyto each crown of the whole system in the present study.

In the literature principal stress and von Mises stress areequally used in the calculation. The current study focused onthe stress formed in both cortical and cancellous bone as wellas the metal framework and veneering material. Von Misesstress values are defined as the beginning of deformationfor ductile materials such as implants, frameworks and alsofor veneering material. Thus, these values may be importantfor interpreting the stress occurring within these structures.However, the bone can be classified as brittle from anengineering point of view. Therefore, principal stress valuesare appropriate while analyzing such materials.

According to the results of the current study, using lessrigid material for the superstructure of the implant retainedprostheses decreased the stresses within the framework andveneering parts of the superstructure due to the flexiblenature of the material that absorbs stresses.

Skalak (1983) reported that the prostheses prepared witha rigid material such as metal might result in high impulseloading of the implant and supporting bone; on the otherhand resin prosthesis absorb shock, and thus reduce stresseson the implants and their supporting osseous structure.However, in the current study it was shown that prosthesesprepared with FRC and particulate composite induced higherstresses at the implant–abutment complex while leading todecreased stresses at the bone. The lower elastic modulusof FRC and particulate composite compared to metal andporcelain produced a larger bending of the prosthesis underthe functioning loads and consequently greater bending ofthe implants towards the pontic (Stegaroiu et al., 1998). In theFRC model, this led to higher stress in the implant–abutment

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complex, and to a lesser extent, in the cortical bone. Thegeometry of themodel (an implant–abutment complex rigidlyfixed in a bone) allowed bending rather than tilting of theimplant–abutment complex. Therefore, the stress differenceswere much more significant in the implant–abutmentcomplex than in the cortical bone, and they were absent inthe cancellous bone.

As confirmed by several clinical studies, osseointegratedimplants can fail mainly as a consequence of bone weakeningor loss at the peri-implant region (Holmes and Loftus,1997). The bone resorption process affects mainly in theimplant neck region and can be activated by overloading thebone–implant interface (Carter et al., 1996). In the currentstudy, it was shown that stresses both in the cortical andcancellous bone created by FRC-FPD were much lower thanfor M-FPD.

5. Conclusions

A 3-dimensional FEA was constructed to investigate theeffect of two different framework materials (metal andFRC) and two different veneering materials (porcelain andparticulate composite) under the functional loading. Withinthe limitations of the study, the following conclusions may bemade:

1. When FRC and particulate composite superstructureswere used instead of metal and porcelain, less stressvalues were obtained in the framework and veneeringparts of the prostheses; however higher stress values wereobtained in the implant–abutment complex.

2. The implant supported FRC-FPD does not only eliminatethe excessive stresses in the bone–implant interfacebut also maintains normal physiological loading of thesurrounding bone. Therefore it minimizes the risk of peri-implant bone loss due to stress shielding.

3. FRC-FPDs may be a good alternative as opposed toconventional metal FPDs for implant-supported prosthesisin the future. Further clinical studies are needed to moreintensively evaluate the potential of these materials inimplant prosthodontics.

The results of the study have led to the clinical use of theimplant retained fixed partial dentures with FRC due to thestress shielding properties of the material. Good physical andhandling characteristics of the FRC material are also otherreasons to prefer them as a prosthodontic material in clinicaluse.

R E F E R E N C E S

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Ashman, R.B., Van Buskirk, W.C., 1987. The elastic properties of ahuman mandible. Adv. Dent. Res. 1, 64–67.

Behr, M., Rosentritt, M., Lang, R., Chazot, C., Handel, G., 2001.Glass-fibre-reinforced-composite fixed partial dentures ondental implants. J. Oral Rehabil. 28, 895–902.

Björk, N., Ekstrand, K., Ruyter, I.E., 1986. Implant-fixed, dentalbridges from carbon/graphite fibre reinforced poly(methylmethacrylate). Biomaterials 7, 73–75.

Carter, D.R., Van Der Meulen, M.C., Beaupre, G.S., 1996. Mechanicalfactors in bone growth and development. Bone 18, S5–S10.

Christensen, G.J., 2002. Implant prosthodontics: from single toothto complex cases. J. Oral Implantol. 28, 244–248.

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