Implant prognosis is predetermined by stresses in the bone-implant interface. Plateau implants are considered to be highly successful since they reduce bone stress concentrations. For cases with lack of bone height, crestal placement remains a reasonable alternative. Otherwise, subcrestal placement of short implants is advised since it is considered as a crucial factor in preservation of crestal bone. For such scenario, bone biomechanical state is directly dependent on implant insertion depth. The aim of the study was to compare the impact of crestal or subcrestal short plateau implant placement in different bone quality conditions on peri-implant bone stresses and to assess implant prognosis under 120.92 N mean maximal oblique functional loading. 5.0×5.0 mm Bicon Integra-CP™ implant was selected for this comparative study. Its 3D models were placed in four posterior maxilla models with types III and IV bone with 1.0 mm cortical bone thickness. Different insertion depths were simulated: the implant neck was in crestal (C) and -1, -2 and -3 mm subcrestal (S1, S2, S3) positions. All materials were assumed to be linear elastic and isotropic. Elastic moduli of cortical, type III/IV cancellous bone and implants were set to 13.7, 1.37/0.69 and 114 GPa, and Poisson’s ratio was 0.3 for all materials. Finite element (FE) models were analyzed in Solidworks Simulation software. 4-node 3D FEs were generated with a total number of up to 3,570,000. 120.92 N mean maximal oblique load (molar area) was applied to the center of 7.0 mm abutment. Von Mises equivalent stress (MES) distributions in surrounding bone were studied to determine the areas of bone overload with magnitude >100 MPa in cortical and >5 MPa in cancellous bone. Maximal MES magnitudes for all scenarios were found at the implant neck. For C scenario, maximal MES magnitudes were found in crestal cortical bone: 21/28 MPa (type III/IV bone). Maximal MES magnitudes in cancellous bone were approximately 5 MPa for both bone types. For S1, S2 and S3 scenarios, since there was no contact between implant and cortical bone, maximal MES magnitudes were located in cancellous bone at the implant neck. For S1 scenarios they were 18…20 MPa, for S2 and S3 scenarios they were 13…14 MPa, for both bone quality types. Another critical MES area was located at the implant root: for C scenario, maximal MES magnitudes were 2 MPa for both bone quality types, for S1 scenario they were 2.5/3.5 MPa, for S2 – 3.5/4.0 MPa and for S3 – 7/10 MPa (for type III/IV bone). It was found that 5.0×5.0 mm Bicon Integra-CP™ implant in crestal placement generated safe bone MESs and offered favorable clinical prospect. For all subcrestal scenarios, the implant caused exceeding MESs in cancellous bone due to absence of interface between the implant and cortical bone. However, the tested Bicon implant showed low susceptibility to bone quality worsening at studied levels of subcrestal placement. This finding confirms positive clinical experience of Bicon plateau implants.
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