Relationship of Three-Dimensional Bone-to-Implant Contact to Primary Implant Stability and Peri-implant Bone Strain in Immediate Loading: Microcomputed Tomographic and In Vitro Analyses

Purpose: The relationships between three-dimensional (3D) bone-to-implant contact (BIC), cortical bone height, and trabecular bone density were measured by microcomputed tomography (micro-CT) to determine correlations with primary implant stability and peri-implant bone strain in an immediate loading scenario. Materials and Methods: The 3D BIC ratios of artificial sawbones models with cellular foam of four densities representing trabecular bone (0.12, 0.16, 0.20, and 0.32 g/cm3) and with cortical shells of four thicknesses (0, 1, 2, and 3 mm) were evaluated by micro-CT. Statistical methods and a linear correlation model were employed to investigate the significance of the relationships between 3D BIC ratios and peak insertion torque, implant stability quotient, and Periotest value, as well as with peri-implant bone strain as measured with strain gauges. Results: The 3D BIC ratio increased from 20.5 to 39.4 and from 27.4 to 45.2 as the height of cortical bone and the density of trabecular bone increased from 0 to 3 mm and from 0.12 to 0.32 g/cm3, respectively. A decrease in the 3D BIC ratio was associated with decreases in peri-implant bone strain and primary implant stability. In addition, there was a strong linear correlation between cortical BIC and primary implant stability (R2 > 0.8). Conclusions: The use of an immediately loaded implant in cases with a low 3D BIC ratio (resulting from a thin cortical shell and/or low trabecular bone density) can diminish primary stability of an implant and lead to high strains in the peri-implant bone.