Plateau short implants have become popular in critical cases of edentulous posterior maxilla. For insufficient bone height, the standard protocol of subcrestal placement is inapplicable, so crestal insertion becomes the only option. Unfortunately, it often leads to stresses increase in bone-implant interface, which causes implant failure. Finite element (FE) method provides biomechanical evaluation of bone-implant structures and influence of bone quality and implant parameters on bone stresses. The aim of the study was to evaluate the impact of crestal placement of particular short plateau implants on stress magnitudes in atrophic posterior maxilla under oblique functional loading to predict bone overload and implant failure. Nine Bicon Integra-CP™ implants with 5.0 (S), 6.0 (I), 8.0 (L) mm length and 4.5 (N), 5.0 (M), 6.0 (W) mm diameter were selected for this study. Their 3D models were placed in 36 posterior maxilla segment models with types III and IV bone, 1.0 (A) and 0.5 (B) mm crestal cortical bone thickness. These models were designed using CT images in Solidworks 2016 software. Implant and bone were assumed as linearly elastic and isotropic. Elasticity modulus of cortical bone was 13.7 GPa, cancellous bone – 1.37 GPa (type III) and 0.69 GPa (type IV). Bone-implant assemblies were analyzed in FE software Solidworks Simulation. 4-node 3D FEs were generated with a total number of up to 2,518,000. 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 magnitudes of MESs were found in crestal cortical bone in the plane of critical bone-implant interface. The spectrum of maximal MESs was between 15.2 and 40.5 MPa. The highest MESs were found for all N,IV,B scenarios (34.4-40.5 MPa), while the smallest magnitudes were determined for all W,III,A scenarios (15.2-16.5 MPa). For all tested implants, maximal MES magnitudes were significantly influenced by cortical bone thickness and implant dimensions, yet they were not susceptible to bone quality: for type IV bone scenarios compared to type III, MES increase was within the range of 12-19%. Besides, for 0.5 mm cortical bone thickness scenarios, 18-19% increase was determined and it was not dependent on implant diameter. MESs around N implants were found to be prone to their length decrease, especially for 0.5 mm cortical bone. The outcomes of this study enhance understanding of the stress characteristics in the maxilla surrounding different-sized short plateau implants. Studied Bicon implants have not caused 100 MPa ultimate stresses in crestal bone under mean, and even 275 N maximum experimental load. This study supports clinical success of plateau implants in posterior maxilla due to their low susceptibility to poor bone quality. It provides a rationale for appropriate implant selection for posterior maxilla.
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