Comparative three dimensional finite element analysis of implant supported fixed complete arch mandibular prostheses in two materials

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1 Originl Article Comprtive three dimensionl finite element nlysis of implnt supported fixed complete rch mndiulr prostheses in two mterils João Pulo Mendes Trist, Dyn Cmpnelli de Moris, Alexndre Ahdl Alonso, Amnd Mri de Oliveir Dl Piv, Alexndre Luis Souto Borges Deprtment of Dentl Mterils nd Prosthodontics, São Pulo University, São Pulo, Brzil Astrct Bckground: The increse of requests for implnt supported prosthesis (ISP) with zirconi s infrstructure hs ttrcted lot of ttention due to its esthetics, iocomptiility, nd survivl rte similr to metllic infrstructure. The im of this study ws to evlute the influence of two different frmework mterils on stress distriution over one tissue simulting mteril. Mterils nd Methods: Two ISP were modeled nd divided into two infrstructure mterils: titnium (Ti) nd zirconi. Then, these rs were ttched to modeled jw with polyurethne properties to simulte one tissue. An xil lod of 200 N ws pplied on stndrdized re for oth systems. Mximum principl stress (MPS) on solids nd microstrin (MS) generted through the jw were nlyzed y finite element nlysis. Results: According to MS, oth models showed strins on peri implnt region of the penultimte (sme side of the lod ppliction) nd centrl implnts. For MPS, more stress concentrtion ws slightly higher in the left posterior region for Ti s r. In prosthetic fixtion screws, the MPS previled strongly in Ti protocol, while for zirconi s r, the cervicl of the penultimte implnt ws the one tht highlighted lrger res of possile dmges. Conclusions: The stress generted in ll constituents of the system ws not significntly influenced y the frmework s mteril. This llows suggesting tht in cses without components, the use of frmework in zirconi hs iomechnicl ehvior similr to tht of Ti r. Keywords: Biomechnics, dentl implnts, finite element nlysis Address for correspondence: Amnd Mri de Oliveir Dl Piv, Av Engenheiro Frncisco José Longo, 777, Jrdim São Dims, São José dos Cmpos, SP, Brzil E-mil: mnd.piv@ict.unesp.r Received: 13 th Jnury, 2017, Accepted: 18 th My, 2017 INTRODUCTION The rehilittion of edentulous jws with protocol prosthesis llowed extensive rehilittions with Quick Response Code: Access this rticle online Wesite: ips.org DOI: /jips.jips_11_17 implnts nd miniml surgicl intervention. [1] However, iomechnicl complictions my impir the performnce of osseointegrted dentl implnts due to the overlod This is n open ccess rticle distriuted under the terms of the Cretive Commons Attriution NonCommercil ShreAlike 3.0 License, which llows others to remix, twek, nd uild upon the work non commercilly, s long s the uthor is credited nd the new cretions re licensed under the identicl terms. For reprints contct: reprints@medknow.com How to cite this rticle: Trist JP, de Moris DC, Alonso AA, Piv AM, Borges AL. Comprtive three-dimensionl finite element nlysis of implnt-supported fixed complete rch mndiulr prostheses in two mterils. J Indin Prosthodont Soc 2017;17: The Journl of Indin Prosthodontic Society Pulished y Wolters Kluwer - Medknow 255

2 cple to induce one remodeling, [2 4] since humn one tissue is cple to dpt to the mount of lod received nd to modify itself y remodeling. [5] For the prosthetic frmework, the increse of undesired stress occurs in the supporting tissues due to the fct tht the lever rm is lrger. [6] To reestlish chewing cpcity in the posterior region, mstictory force my need to exist eyond the lst implnt. [7] Different mterils strength used in frmeworks is nother possile fctor to influence directly the success of implnt rehilittion through the dissiption of chewing lod. [8,9] Assuming tht iomechnicl ehvior of different mterils used in the frmework of Brnemrk implnt protocol ws the gol for severl recent reserches [20,21,25 27] nd due to no study (within the uthors knowledge) used vlidted elstic modulus for lortory studies, the im of this study ws to evlute the influence of different frmework mterils (Ti or zirconi) on stress distriution over one tissue simulting mteril (polyurethne). The purpose of this study ws to use computer simultions to exmine clinicl situtions with IPS in edentulous mndiles nd identify the iomechnicl ehvior of two different mterils. A lrge numer of mterils re ville to produce prosthesis infrstructure. It is recommended tht metllic lloys exhiit high tensile strength (>300 MP) nd elstic modulus (>80,000 MP) sufficient to prevent deformtions nd the cntilevers frctures. [10] The titnium lloy (Ti) hs corrosion resistnce, iocomptiility, low cost, nd mechnicl properties similr to uric lloy (good mechnicl properties, ut high cost) tht mkes Ti vile mteril for the friction of prosthesis infrstructure on implnts. [11,12] The increse of requests for metl free prostheses led to the development of cermics with esthetics nd iocomptiility. [13] The use of implnt supported prosthesis (ISP) with zirconi infrstructure hs ttrcted lot of ttention. As well s esthetics, it presents survivl rte similr to metllic infrstructure. [14 16] Using finite element nlysis (FEA) method, it is possile to study the stress generted in periimplnt one tissue on preventive wy. [17,18] FEA consists of promising noninvsive methodology tht provides consistent results through mesurement of stress, compression, nd displcement in implnts nd structures involved in rehilittion. [19] This technique is considered complex due to the involvement of iomterils properties nd microstructurl detils. [11,13] However, it is widely used in dentl implnt nlyzes. [9,11,13,17,18,20 24] Severl studies tht evlute the iomechnicl ehvior of ISP s serch to simulte clinicl sitution nd end up lso studying the one dptive property. [20,21,25 29] However, the corticl one properties my vry in cdvers [22] ecuse this tissue hs nisotropic ehvior mking its elstic property vry ccording to the orienttion of the cells nd fiers present. [28] Thus, to stndrdize in vitro studies nd isolte iologicl vriles, resinous mterils whose elstic modulus pproches the one tissue re used, [29] such s, polyurethne. [30] MATERIALS AND METHODS Using computer ided design Rhinoceros softwre (Version 5.0 SR8, McNeel North Americ, Settle, WA, USA), model of n edentulous jw ws mde following the min ntomicl chrcteristics: size, shpe, nd sence of pthology. Initilly, ntomicl lines were constructed so tht ech fce of the outer surfce could e otined y the union of three or four lines. After surfces cretion, they were fixed forming volumetric solid ody of hemi jw. For complete construction of the virtul jw s model, the one structure ws mirrored from the midline, llowing symmetry etween the ntimere sides. Then, Boolen union ensured tht solid rcde ws creted. Then, externl hexgon implnts (10 mm 4.1 mm) were modeled. The externl threds dimeter ws estlished ccording to the dimensions provided y the mnufcturer (s technology Titnium Fix São José dos Cmpos, Brzil), nd the pltform showed 4.1 mm in dimeter such s conventionl regulr implnt. The externl hexgon ws extruded 0.7 mm high nd ttched to the previously creted cylindricl ody. The first implnt ws centrlly ttched to the mentl formen so tht the other four implnts could e positioned equidistnt from the center [Figure 1]. After modeling ll implnts in their idel positions, Universl Cstle Long Autment (UCLA) components were creted ccording to the individul height of ech implnt nd ttched to stndrd frmework model. The retining screw ws lso shped nd llocted in its idel position. The r presented height of 6 mm from the one surfce nd 10 mm lever rm on ech side. The orifices of ll screws were creted to simulte clinicl sitution of structurl strength of this mteril. Finlly, t the end of the r, two circles with 2 mm dimeter were creted on the upper outer surfce to stndrdize the lod ppliction. 256 The Journl of Indin Prosthodontic Society Volume 17 Issue 3 July-Septemer 2017

3 This study hd the chrcteristic to not llowing results in the mndiulr rnches. Thus, they were removed from the model to void spent elements while exporting idle geometries. Finite element nlysis preprocessing The Young s modulus nd Poisson s rtio of the mterils [Tle 1] were ssigned to ech solid component with isotropic, homogeneous, nd linerly elstic ehvior. All contcts were considered onded since torque filure is not the purpose of the study. The sme three dimensionl model ws used to receive mterils properties nd generte different results. Mesh genertion The solid geometries were exported to ANSYS softwre (ANSYS 16.0, ANSYS Inc., Houston, TX, USA) in STEP formt. Then, tetrhedrl elements formed the mesh. A convergence test of 10% determined the totl numer of control elements of the mesh for [Figure 2]. Lodings nd fixtions The ppliction of n xil lod (200 N) followed the delimited re in CAD: unilterl posterior superior region (left side) in the direction of one. For the fixtion condition of the system, the jw se ws selected, ensuring only movement restriction on the Z xis. In this wy, the deformtion generted in ll directions inside the mndile could e computed. Tle 1: Properties of the mterils used in finite element nlysis methodology Young s modulus (GP) Poisson s rtio References Titnium [23] Zirconi [24] Polyurethne 3.6 GP 0.3 [31] RESULTS The generted results show the mximum principl stress (MPS) in the ductile solids nd in the simultor model of the humn one tissue, the microstrins (MSs) generted were evluted. In oth models, greter tendency of totl one displcement occurred in the mrginl re to the lst implnt (sme side of the verticl lod ppliction). The energy concentrtion ws slightly higher in the left posterior region for Ti s r compred to zirconi s r [Figure 3]. Initilly, the MS ws presented sed on the theory of one remodeling s function of the lod. According to the imges of Figure 4, the regions with mstictory overlod my initite n unwnted one remodeling. In the generted results, the regions of concentrtion of strins re oth very similr, in which it is not possile to evidence significnt difference in the colorimetric grph etween oth jw models. The lst two implnts on the lod side received most of the mstictory forces, which shows the consistency of the system. The proximl regions of the periimplnt tissue of these two implnts were more ffected, which suggests the initition of ny one ltertion in this region during this loding. The MPS showed res of tensile, which cn e understood s res of possile filure of the structure in the function. In ductile components of the system, the MPS ws lso displyed in color scles. For prosthetic fixtion screws, the stress previled strongly in Ti protocol [Figure 5]. While for zirconi s r, the pltform of the penultimte implnt ws the one tht highlighted lrger res of possile dmges [Figure 6]. Figure 1: Three dimensionl model of jw mde in computer ided design with fixtion of the five implnts equidistnt positioned Figure 2: Mesh formed y tetrhedrl elements The Journl of Indin Prosthodontic Society Volume 17 Issue 3 July-Septemer

4 Figure 3: Displcement pttern in the models with energy concentrtion in the mrginl re t the lst implnt for the r in () titnium (presenting greter tension represented y the red color) nd () zirconi Figure 4: Microstrin distriution pttern in jw s models under r in () titnium nd () zirconi Figure 5: Mximum principl stress in prosthetic fstening screws. () The sitution with titnium r. () Sitution with r in zirconi DISCUSSION In this study, FEA ws used to investigte the influence of the two prosthodontic frmeworks sumitted to n xil lod on the iomechnicl ehvior of isotropic jws. The nlysis of totl displcement, consistency, nd connectivity of the mesh [Figures 2 nd 3], MPS nd MS demonstrted tht this is vile model for the nlysis using the FEA method. To ensure tht the qulity of the results would not e compromised due to the complexity of the model s geometry, it ws necessry to divide the structure into finite numer of elements with 10% convergence. The results show not only the stress distriution on the surfce of the one crest ut lso, the iomechnicl ehvior of different constituents of this type of rehilittion tretment with implnts. This demonstrted tht the frmework mteril minimlly influences the distriution of stress in the simulted jw nd implnts. In vivo studies reveled the vlues of occlusl mstictory force round 220 N in the posterior region. [1,21,32] Thus, lod of 200 N ws used in n ttempt to simulte result closer to tht oserved in vivo. Ruo nd Souz (2008) [9] ffirmed tht the lower elstic modulus, the greter exerted force on the utments closest Figure 6: Mximum principl stress on implnts. () Sitution with titnium r. () Sitution with zirconi r to the lod. Therefore, if ruer structure ws used, the entire lod would e concentrted in the implnt closest to the point of lod ppliction. The uthors concluded tht the more rigid structure the more uniform stress dissiption nd the less dmge cused to the fstening screws due to the ending of the reduced metl structure. In the present study, two rigid structures were used (Ti nd zirconi) with different elstic modulus. The results otined re consistent since the stress dissiption did not concentrte t specific points s would occur if flexile structure were used. [9] It is recommended tht if metllic lloy is going to e used, it must hve high strength (>300 MP) nd high elstic modulus (>80 GP) to prevent deformtion nd structures filure. [33] These re chrcteristics of less rigid mterils thn those used in this study. For oth jw protocol models, the stress fields showed no significnt discrepncies. However, trend of displcement in wider re of the Ti r ws oserved in the region of the lever rm [Figure 3]. The presence of lever rm hs remrkle effect on stress concentrtion, [5] nd increses of 5 mm elevte the mximum von Mises stress y round 30% to 37% round the implnts. [9] According to Glntz, [34] the mount of strin of the lever rm is directly proportionl to the length nd inversely proportionl to the width nd height of it. In ddition, there is direct reltionship etween the mount of strin nd the pplied 258 The Journl of Indin Prosthodontic Society Volume 17 Issue 3 July-Septemer 2017

5 lod nd elstic modulus of the used mteril. Since zirconi s elstic modulus is 55% lrger thn Ti modulus, it seems tht the influence of the r s geometry (similr for oth models) is much more influentil in the results since they were within 10% of convergence [Figure 4]. The results corroorte with the findings of Bnkoglu nd Yilmz, [13] where the uthors oserved tht in fixed prtil nterior prosthesis with horizontl lod, the mximum stress ws similr in the models with zirconi nd Ti infrstructure. Although minute results nd similr ehvior for the rs, inferences cn e mde: in the simulted jw, the generted strins were slightly higher with zirconi r ecuse stress res were oserved in the penultimte nd centrl implnts while compression res encircled the lst implnt chrcterizing it s fulcrum in distl rottion tendency of the system [Figure 5]. This tendency of rottion ws reflected on the fixtion on n inverse wy for the two mterils. While Ti with similr elstic modulus of the screw llowed stresses pssge etween them s single ody with less dmge to the implnt, the zirconi with ll the rigidity chrcteristic of its crystlline structure tended to further dmge the prosthetic connection nd less the screw [Figure 6]. Currently, zirconium oxide is incresingly used s n infrstructurl mteril for fixed prtil implnt supported prostheses [10] since zirconi hs high flexurl strength ( MP) nd hrdness (1200 Hv), s well s chemicl properties such s low corrosion potentil nd low therml conductivity. [35,36] A selection fctor for the use of zirconi s n infrstructure mteril is optimized esthetics due to the nturl shdow of the sustrte, eliminting the gryish effect in the cervicl res of prostheses with metllic lloy infrstructures. [37] As for longevity, severl studies hve shown tht zirconi is not significntly ffected y the ging test suggesting long lifetime. [38] In the cse of the dissiption of mstictory force, other studies otined high stress levels locted under the pplied lod, tht is, in the working side implnts. [20,39] The results otined in this work suggest tht the prosthesis does not trnsmit the lod identiclly through ll implnts, ut these differences were not significnt. CONCLUSIONS Within the limittions of this study, it is possile to conclude tht the stress generted in ll constituents of the system ws not significntly influenced y the r s mteril. This llows suggesting tht in cses without utments, the use of frmework in zirconi hs iomechnicl ehvior similr to tht of Ti r. Finncil support nd sponsorship Nil. Conflicts of interest There re no conflicts of interest. REFERENCES 1. Mló P, Rngert B, Nore M. All on Four immedite function concept with Brånemrk System implnts for completely edentulous mndiles: A retrospective clinicl study. Clin Implnt Dent Relt Res 2003;5 Suppl 1: Jemt T, Crlsson L, Boss A, Jörneús L. 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