Effects of Predrilling Depth and Implant Shape on the Mechanical Properties of Orthodontic Mini-implants during the Insertion Procedure

Abstract

Objective: To investigate the effects of orthodontic mini-implant (OMI) shape and predrilling depth on the mechanical properties of OMIs during insertion procedure.

Materials and Methods: A total of 30 OMIs (self-drilling type, 7mm in length; Biomaterials Korea Inc.) were allocated into six groups according to OMI shape (cylindrical and tapered type) and pre-drilling depth [(control, 1.5mm- and 3.0mm-predrilling; predrilled with a drill-bit(1mm in diameter)]: C-con, C-1.5, C-3.0, T-con, T-1.5, and T-3.0 groups (N=5 per group). The OMIs were installed in artificial bone blocks with two layers that simulated the cortical and cancellous bone (Sawbone®, Pacific Research Laboratories Inc.). Total insertion time (TIT), maximum insertion torque (MIT), total insertion energy (TIE), and inclination of the time-torque graph (INC) were measured. Mann-Whitney U-test, Kruskal-Wallis test, and Mann-Whitney U-test with a Bonferroni correction were performed statistical analysis.

Results: Within the same shape group, although predrilling groups exhibited shorter TIT than control groups (control > 1.5, 3.0; P < 0.05), there was significant no difference in TIT between 1.5mm- and 3.0mm-predrilling. MIT and TIE decreased in the order of control, 1.5mm- and 3.0mm-predrilling (control < 1.5 <.3.0; P < 0.05), but INC revealed a pattern of increase from control to 1.5mm-predrilling and decrease from 1.5mm- to 3.0mm-predrilling within the same shape group (control, 3.0 < 1.5; P < 0.05). MIT and INC of C-con were smaller and less steep than those of T-con (MIT; P < 0.01, INC; P < 0.05). In the same predrilling depth, no differences were observed in MIT, INC, and TIE between cylindrical and tapered groups.

Conclusions: In cases of thick cortical bone, predrilling might be an effective tool for reducing possible microdamage without compromising OMI stability.