Evaluation of bone turnover around short finned implants in posterior maxilla with thin cortices

Abstract

Background : Bone turnover is regulated by bone strains, their excessive magnitudes result in implant failure. Higher bone strains are common for molar regions due to larger functional loads. In the maxilla, this area is often characterized by poor bone quality and quantity, so implant function may be initially challenging. Numerical simulation is usually applied to correlate bone and implant parameters with bone strain spectrum to evaluate bone turnover and to establish implant prognosis. Aim/Hypothesis : The aim of the study was to evaluate the impact of short finned implants and crestal cortical bone height on strain level in adjacent bone to describe the bone turnover in posterior maxilla. Materials and Methods : Six Bicon short implants (4.5x5.0, 4.5x6.0, 4.5x8.0, 6.0x5.0, 6.0x6.0, 6.0x8.0 mm) were investigated. Their 3D models were placed in posterior maxilla segment models with type III bone and 0.2…1.0 mm crestal cortical bone thickness. These models were designed in Solidworks 2016 software. Bone and implant materials were assumed as linearly elastic, isotropic, implants were fully osseointegrated. Young modulus of cortical/cancellous bone was 13.7/1.37 GPa. Numerical analysis of bone-implant models was carried out in FE software Solidworks Simulation with 4-node finite elements (FEs). 120.9 N mean experimental oblique load (molar area) was applied to the center of 7 Series Low 0° abutment. First principal strains (FPSs) were analyzed in bone-implant interface. Results : Safe 520…1320 microstrain maximal FPSs were found in the crestal cortical bone, besides 6.0 mm diameter implants caused 520-660 microstrain, while 4.5 mm-780-1320 microstrain. FPSs were dependent on both cortical bone thickness and implant length. The smallest FPSs were found for scenarios with 1 mm cortical bone thickness. 4.5 mm diameter implants were more prone to cortical bone thickness than 6.0 mm: its increase from 0.2 to 1.0 mm was 32% for 4.5x5.0 mm implant and 11% for 6.0x8.0 mm implant. Critical FPSs (up to 3250 microstrain) were located in the vicinity of the first fin of 4.5 mm diameter implants. This area around 6.0 mm diameter implants was characterized by FPSs of similar magnitude as in crestal cortical bone (400-730 microstrain). Conclusions and Clinical Implications : Bone strains were influenced by implant dimensions and cortical bone thickness. 6.0 mm diameter implants caused positive bone turnover for all investigated scenarios. 120.92 N functional loading of 4.5 mm diameter implants resulted in higher strains, especially in cancellous bone, where they slightly exceeded 3000 microstrain MESp threshold by Frost. These findings should be used when planning short finned implants in posterior maxilla.