IM0410

I research _ restoration 08 I implants4_2010 particularlyusefulintheevaluationofdentalprosthe- ses supported by implants.13-16 Two models were sub- jected to FEA study to compare between a wide im- plantrestorationversusthetwoimplantrestorationof lower first molar. _Material and Methods Threedifferentpartsweremodeledtosimulatethe studied cases; the jaw bones, implant/abutment as- sembly, and crown. Two of these parts (jaw bone and implant/abutment) were drawn in three dimensions by commercial general purpose CAD/CAM software “AutoDeskInventor”version8.0.Thesepartsareregu- lar,symmetric,anditsdimensionscanbesimplymeas- ured with their full details. On the other hand, crown is too complicated in its geometry therefore it was not possible to draw it in threedimensionswithsufficientaccuracy.Crownwas modeled by using three-dimensional scanner, Roland MDX-15, to produce cloud of points or triangulations to be trimmed before using in any other application. The second phase of difficulty might appear for solvingtheengineeringproblem,isimportingandma- nipulating three parts one scanned and two modeled or drawn parts on a commercial FE package. Most of CAD/CAM and graphics packages deal with parts as shells(outersurfaceonly).Ontheotherhandthestress analysisrequiredinthisstudyisbasedonvolumeofdif- ferent materials.3 Therefore set of operations like cut- ting volumes by the imported set of surfaces in addi- tiontoaddingandsubtractingvolumescanensureob- taining three volumes representing the jaw bone, im- plant/abutment assembly, and crown.2 Bone was simulatedascylinderthatconsistsoftwoparts.Thein- ner part represents the spongy bone (diameter 14 mm andheight22mm)thatfillingtheinternalspaceofthe otherpart(shellof1mmthickness)thatrepresentscor- tical bone (diameter 16 mm and height 24 mm). Two implants were modeled one of 3.7mm diameter and the other of 6.0 mm. The implants/abutment design and geometry were taken from Zimmer dental cata- logue(Fig.5). Linearstaticanalysiswasperformed.Thesolidmod- eling and finite element analysis were performed on a personalcomputerIntelPentiumIV,processor2.8 GHz, 1.0GBRAM.ThemeshingsoftwarewasANSYSversion 9.0 and the used element in meshing all three dimen- sional model is eight nodes Brick element (SOLID45), whichhasthreedegreesoffreedom(translationsinthe global directions). Listing of the used materials in this analysis is found in Table 1. The two models were sub- jected to 120 N vertical load equally distributed (20 N onsixpointssimulatetheocclusion;oneoneachcusp and one in the central fossa). On the other hand, the baseofthecorticalbonecylinderwasfixedinalldirec- tionsasaboundarycondition.17-21 Fig. 4a_Radiographic view of wide implants used to restore missing lower first molars.1, 24 Fig. 4b_Buccal view of 2 standard 20-degree abutments on 3.5 mm Astra Tech implants for restoration of mandibular right first molar.1, 24 Fig. 4c_Radiographic view of the restoration.1, 24 Fig. 5_Crown, implants and bone assembled in a model (FEA software). Figs. 6a & b_Von Mises stress on crown (a. wide implant; b. two implants). Tab. 1_Material Properties. Material Poisson’s ratio Young’s modulus MPa Coating (porcelain) 0.3 67,200 Restoration (gold) 0.3 96,000 Implants (titanium) 0.35 110,000 Spongy bone 0.3 150 Cortical bone 0.26 1,500 Fig. 6a Fig. 6b Fig. 4b Fig. 4c Fig. 5 Fig. 4a