Effects of insertion angle and implant thread type on the fracture properties of orthodontic mini-implants during insertion

Abstract

Objective: To determine the effects of insertion angle (IA) and thread type on the fracture properties of orthodontic mini-implants (OMIs) during insertion. Materials and Methods: A total of 100 OMIs (self-drilling cylindrical; 11 mm in length) were allocated into 10 groups according to thread type (dual or single) and IA (0 degrees, 8 degrees, 13 degrees, 18 degrees, and 23 degrees) (n = 10 per group). The OMIs were placed into artificial materials simulating human tissues: two-layer bone blocks (Sawbones), root (polymethylmethacrylate stick), and periodontal ligament (Imprint-II Garant light-body). Maximum insertion torque (MIT), total insertion energy (TIE), and peak time (PT) were measured and analyzed statistically. Results: There were significant differences in MIT, TIE, and PT among the different IAs and threads (all P<.001). When IA increased, MIT increased in both thread groups. However, TIE and PT did not show significant differences among 0 degrees, 8 degrees, and 13 degrees IAs in the dual-thread group or 8 degrees, 13 degrees, and 18 degrees IAs in the single-thread group. The dual-thread groups showed higher MIT at all IAs, higher TIE at 0 degrees and 23 degrees IAs, and longer PT at a 23 degrees IA than the single-thread groups. In the 0 degrees, 8 degrees, and 13 degrees IA groups, none of the OMIs fractured or became deformed. However, in the 18 degrees IA group, all the OMIs were fractured or deformed. Dual-thread OMIs showed more fracturing than deformation compared to single-thread OMIs (P < .01). In the 23 degrees IA group, all OMIs penetrated the artificial root without fracturing and deformation. Conclusions: When OMIs contact artificial root at a critical contact angle, the deformation or fracture of OMIs can occur at lower MIT values than those of penetration.