In vitro assessment for primary stability of self-drilling orthodontic mini-implants: Pull-out testing at different insertion angles.

Achieving optimal primary stability of orthodontic mini-implants remains a clinical challenge because the ideal insertion angle for self-drilling mini-implants has not been clearly established. Therefore, it is of interest to evaluate and compare the primary stability of self-drilling orthodontic mini-implants inserted into artificial bone blocks at four different angles (30°C, 45°C, 60°C and 90°C) using pull-out resistance testing. Eighty titanium alloy mini-implants (1.6 mm diameter, 8 mm length) were randomly allocated into four groups (n=20 each) and inserted into standardized synthetic bone blocks simulating D2 bone density with a custom angular guide, followed by pull-out testing in a universal testing machine at a crosshead speed of 1 mm/min. Mini-implants placed at 60°C showed the highest mean pull-out force (324.67 ±28.43 N), followed by 45°C (298.52 ±31.76 N), 90°C (267.38 ±25.91 N) and 30°C (231.14 ± 33.82 N), with statistically significant differences between the groups. Thus, insertion at 60°C to the bone surface provided the high primary stability. It may be considered the biomechanically most favorable angulation for self-drilling orthodontic mini-implants.