Effects of insertion speed and pre-drilling on the mechanical properties of orthodontic mini-implants: in vitro mechanical study

Objective: To investigate the effects of insertion speed and pre-drilling on the mechanical properties of orthodontic mini-implants (OMIs, also known as temporary anchorage devices). ❧ Materials and methods: A total of 60 OMIs (self-drilling type, 1.45 mm in external diameter and 7 mm in length; Biomaterials Korea Inc.) were allocated into 6 groups according to insertion speeds (30, 60, and 90 rpm) and pre-drilling (0 and 3.0 mm; pre-drilled with a drill-bit of 1 mm in diameter) as follows: Control-30, Control-60, Control-90, Predrill-30, Predrill-60, and Predrill-90 (N=10 per group). The OMIs were installed in artificial bone blocks with two layers that simulated the cortical bone (3.0 mm thickness) and cancellous bone (15 mm thickness) (Sawbones®, Pacific Research Laboratories Inc.). After maximum insertion torque (MIT), total insertion energy (TIE), peak time (PT), and TIE/PT were measured, Kruskal-Wallis test and Bonferroni correction were performed for statistical analysis. ❧ Results: The Control-90 and Predrill-90 groups exhibited higher MIT than other groups [(Predrill-30, Predrill-60, Control-60)