Bicon short implants have successfully proven themselves in the maxillary molar region with insufficient bone height and poor bone quality. To improve crestal bone healing, autogenous bone is placed in the gap between implant neck and implant bed. But even for such approach, the quality of the augmented bone is not fully predictable, though cortical bone strength is the key criterion of implant success. Finite element (FE) method allows precise analysis of this complex biomechanical system. The aim of this study was to evaluate the prospect of different-sized short plateau implants placed in atrophic posterior maxilla depending on the degree of augmented bone quality under oblique functional loading. 5.0 mm length and 4.0 (N), 5.0 (M), 6.0 (W) mm diameter Bicon SHORT ® implants were selected for this comparative study. Their 3D models were placed crestally in twelve posterior maxilla segment models with type III bone. They were designed using CT images in Solidworks 2016 software with 1.0 mm crestal/sinus cortical and 4.0 mm cancellous bone layers. Each model geometry was 10×30×19 mm. Implant and bone were assumed as linearly elastic and isotropic. Elasticity moduli of cortical/cancellous bone were 13.7/1.37 GPa. Four degrees of augmented bone quality were simulated: 100% (E1=13.7 GPa), 75% (E2=10.3 GPa), 50% (E3=6.85 GPa) and 25% (E4=3.43 GPa). Bone-implant assemblies were analyzed in FE software Solidworks Simulation. 4-node 3D FEs were generated with a total number of up to 4,040,000. 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 were studied to determine the areas of bone overload. Analysis of MESs distributions in cortical bone has showed that their maximal magnitudes were found in crestal area. The spectrum of maximal MESs in augmented bone was between 9.5 MPa (W,E4) and 37 MPa (N,E1). They were influenced by implant diameter and augmented bone quality. MES reduction due to diameter increase from 4.0 to 6.0 mm was 52.7, 54.5, 55.4 and 54.8% for E1, E2, E3 and E4 bone quality. MES reduction due to two-fold augmented bone quality decrease (E1 versus E3) was 24.3, 30.2 and 28.6% for N, M and W implants. However, reduction of augmented bone quality caused significant overload of cancellous bone (5-17 MPa). Only for E1 bone, maximal MES in cancellous bone was approximately 5-7 MPa. In all other scenarios, maximal MES substantially exceeded 5 MPa strength of cancellous bone. N implants were found to be the most susceptible to the quality of augmented bone: E1 to E4 bone quality reduction has led to 126 and 82% MES rise for N and W implants. Under mean maximal functional loading, sufficient influence of augmented bone quality on crestal bone-implant interface was established. However, crestal bone overload is highly unlikely because MESs were found to be lesser than 100 MPa ultimate bone strength. Contrarily, E2-E4 bone quality scenarios are critical from the viewpoint of cancellous bone overload and implant failure. Placement of wider implant allows to decrease this risk.
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