Comparison of the effects of different implant apical designs on the magnitude and distribution of stress and strain in bone: a finite element analysis study.

Abstract

The aim of this study was to investigate the effects of implant design on the apex area and on stress and stress patterns within surrounding bone. Three commercially available implants with the same diameter (3.5 mm), same length (10-11 mm), and same complement abutment were selected for modeling as follows: (1) flat apical design with light tapering degree, (2) dome-shaped apical design with light tapering, and (3) flat apical design with intense tapering in one-third of the apical area. According to human conebeam computed tomography (CBCT), the bone was modeled using a cortical thickness of 2 mm and cancellous bone. Forces of 100 N and 300 N in the vertical and 15° angle directions were applied to the entire abutment surface, and the equivalent stress and strain were calculated using finite element analysis (FEA) methods. In all models, stress was concentrated on the cortical bone around the implant neck; in non-axial loads, stress was concentrated on the buccal side. The maximum strain recorded was a microstrain of 7200 μm μm-1 around the apex of sample C, which also showed the highest level of stress detected in cancellous bone (4.4 MPa). We observed the pathologic overload in the apical area of sample B (with a dome-shaped apex); however, the strain value was less than that of sample C. FEA revealed that great sudden changes in diameter along the fixture increases stress and strain in peri-implant bone. Therefore, uniform tapering should be considered as a standard feature for most clinical situations, and a flat apical design, which creates a better stress and strain distribution in surrounding bone than dome-shaped bone, should also be used.