Finite Element Analysis of Implant-Abutment Micro-Gaps Under Oblique Loading

Objectives: To investigate the formation of micro-gaps at the implant-abutment interface of conical connection with different screw torques under oblique loading.
Methods: Three-dimensional finite element analyses of implant-abutment assemblies with conical connection were conducted using a simulated screw torque of 20 Ncm (Group A) and 30 Ncm (Group B), and an oblique load ranging from 10 to 220 N. The material properties used are listed in the table below. The micro-gap formation process, critical load for bridging of the internal implant space, and the size of the micro-gaps were investigated.
Results: The area in contact decreased with increasing load for both groups. Bridging of the internal implant space occurred when over 70% of the interface was opened (see figure below). The load predicted for bridging was 105 and 150 N for Group A and B, respectively. Although the maximum gap reached 450 μm, less than 60% of the interface had a gap larger than 1 μm when the load was lower than 100 N. After unloading, residual gaps were predicted, covering close to 35% of the interface. Most of the residual micro-gaps (>95%) were under 0.8 μm. Group B had much higher mean and residual screw stress during and after loading, respectively.
Conclusions: Increasing the screw torque from 20 to 30 Ncm increased the load required for bridging the internal implant space by over 40%. However, this would also increase the screw stress, potentially shortening the fatigue life of the prosthesis.