Factorial analysis of variables affecting bone stress adjacent to the orthodontic anchorage mini-implant with finite element analysis

Abstract

Mini-implants are now widely accepted as anchorage for orthodontic tooth movement because of the convenience of the placement procedure, their comparative low cost, and the fact that they can be immediately loaded after surgery. In this study, we incorporated a finite element approach and factorial analysis to determine the biomechanical effects of exposure length of the mini-implant, the insertion angle, and the direction of orthodontic force. Twenty-seven finite element models were constructed to simulate the biomechanical response of the alveolar bone adjacent to the mini-implant. Factorial analysis was performed to investigate the comparative influence of each factor. The simulation results showed that the exposure length of the mini-implant had a statistically significant influence on bone stress, with a contribution of 82.35%. Increased exposure length resulted in higher bone stress adjacent to the mini-implant. Whereas all factors investigated had a statistically significant influence on cancellous bone stress, the stress values associated with cancellous bone were much less than those of cortical bone. Increased exposure lengths resulted in higher bone stresses adjacent to the mini-implant. The percentage of contribution of the insertion angle of the mini-implant (6.03%) was also statistically significant but much less than that of the exposure length (82.35%). The direction of orthodontic force had no significant effect on cortical bone stress.