Effect Of Materials And Designs Of Basal Crowns On Passive Fit For Implant-Supported Fixed Protheses

Objective1.To compare the passive fit of implant-supported cement-retained CAD/CAM bridge from zirconia and titanium.2.To evaluate the effect of different designs of basal crown on passive fit.3.To quantify the strain development before and after ceramic veneering.4.To evaluate the distribution of strain around the implants.Material and MethodsEpoxy resin material and catalytic agent were mixed to exhibit an elastic modulus similar to that of mandible and divided the epoxy resin into 32 same cubic clods.Each of them received two one-stage implants which simulated a partially edentulous of the lower left second premolar to the second molar.Four liner strain gauges were bonded on the region around each implant,on the mesial,buccal,distal and lingual aspect.After scanning procedures,32 identical frameworks were fabricated by means of CAD/CAM and were divided into four groups(n=8)according to different materials and designs of basal crowns.Group A:zirconia ceramic implant-supported bridges with regular marginal designs.Group B:zirconia ceramic implant-supported bridges with full circumferential zirconia-collar marginal designs.Group C:titanium ceramic implant-supported bridges with regular marginal designs.Group D:titanium ceramic implant-supported bridges with full circumferential titanium-collar marginal designs.The strain development was recorded during cement setting before and after ceramic veneering.The data were statistically analyzed using SPSS.Results1.All frameworks produced measurable amounts of peri-implant strain.2.Before ceramic veneering,materials and designs affected the strain of basal crown(P<0.01).There was interaction between the two factors(P<0.01).3.After ceramic veneering,materials and designs affected the strains of prostheses(P<0.01).There was interaction between these two factors(P<0.01).4.The strain around implants of group A、B、C and D increased after sintering decorative porcelain than before.There was no difference between groups of different materials(P>0.05),but full circumferential collar marginal designs reduced the discrepancy(P<0.01).5.The strain of each group on the direction of mesiodistal was greater than that on the direction of buccolingual(P<0.05).Conclusion1.The implant-supported fixed bridge that made of CAD/CAM cannot reach the perfect passive fit.2.The zirconia frameworks have better passive fit than titanium based PFM restorations3.Full circumferential collar marginal design can help to reduce the inaccuracy of the fit.4.Ceramic veneering increases strain development and inaccuracy of the fit.Full circumferential collar marginal design can help to reduce the adverse effect of ceramic veneering,but so can’t materials.5.Measures should be taken to reduce the strains on the direction of mesiodistal of the implant-supported bridge around the neck.