CAD/CAM - international magazine of digital dentistry

I research _ single molar restoration 24 I CAD/CAM 1_2013 _Material and Methods Three different parts were modeled to simulate the studied cases; the jaw bones, implant/abutment assembly, and crown. Two of these parts (jaw bone and implant/abutment) were drawn in three dimen- sions by commercial general purpose CAD/CAM soft- ware “AutoDesk Inventor” version 8.0. These parts are regular, symmetric, and its dimensions can be simply measuredwiththeirfulldetails. 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 tobetrimmedbeforeusinginanyotherapplication. 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 analysis required in this study is based on volume of different materials.3 Therefore set of operations like cuttingvolumesbytheimportedsetofsurfacesinad- dition to adding and subtracting volumes can ensure obtaining three volumes representing the jaw bone, implant/abutment assembly, and crown.2 Bone was simulatedascylinderthatconsistsoftwoparts.Thein- nerpartrepresentsthespongybone(diameter14mm andheight22mm)thatfillingtheinternalspaceofthe other part (shell of 1 mm thickness) that represents cortical 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 catalogue(Fig.5). Linear static analysis was performed. The solid modelingandfiniteelementanalysiswereperformed on a personal computer Intel Pentium IV, processor 2.8 GHz, 1.0GB RAM. The meshing software was ANSYS version 9.0 and the used element in meshing all three dimensional model is eight nodes Brick ele- ment (SOLID45), which has three degrees of freedom (translationsintheglobaldirections).Listingoftheused materials in this analysis is found in Table 1. The two models were subjected to 120 N vertical load equally distributed(20Nonsixpointssimulatetheocclusion; oneoneachcuspandoneinthecentralfossa).Onthe other hand, the base of the cortical bone cylinder was fixedinalldirectionsasaboundarycondition.17-21 _Results and Discussion Results of FEA showed a lot of details about stres- ses and deformations in all parts of the two models 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