Evaluation of Mechanical Performance of Orthodontic Mini-Implants With Distinct Designs

Background Orthodontic mini-implants represent one of the most used anchorage systems in daily clinical practice and frequently, these anchorage devices have to be placed between the roots of adjacent teeth reflecting the need to limit its dimensions. Among other factors, it has been suggested that mini-implant’s geometry have a great impact on primary stability. Objectives The aim of this study was to evaluate the primary stability (PS) of commercially available orthodontic mini-implants (MI) of different geometrical designs. Methods Twenty self-drilling MI (1.6 mm × 8 mm) were allocated to two groups (n = 10) according to their geometric design: INP-1 and INP-2. Twenty sections (8 mm ø × 10 mm long) were taken from bovine pelve, immersed in saline solution and stored by freezing (-20°C). Geometric characteristics concerning shape, diameter, length, pitch, thread details (number, angle and depth), thread shape factor (TSF) and conicity were evaluated by using Scanning Electron Microscope (SEM) imaging and all the measurements were carried out with Image-Pro® Insight Software. PS was evaluated by insertion torque (IT) and Periotest (PTV). Intergroup comparisons were made by Student t test. The level of significance was 5%. Results Increased IT values were observed for INP-1 (20.08 ± 3.28 N.cm) (P < 0.05), the group that presented the greatest conicity (33%) and highest thread depth (0.19 mm). Conclusions The wide geometric variability of MI indicates that MI design parameters affect its PS and it could be selected in order to improve its mechanical performance.