Effects of insertion angle and body shape on the stability of orthodontic mini screws: iİn vitro study

In this study, we aimed to analyze the maximum insertion torque (MIT), pull-out and shear strength of 3 different mini screws that inserted 30°, 45°, 60°, 90° and compare their stability. The study consist of 216 self-drilling, 1,4×8 mm titanium mini screws (Abso-Anchor conical and cylindrical, Dual-Top cylindrical). Each three group were inserted at four different angles and MIT was recorded. Pull-out and shear force resistance values were measured and recorded until 1.5 mm displacement occured. The data were analyzed with IBM SPSS program. Statistical analyses were conducted with Kolmogorov-Smirnov, 1-way Anova, Tukey HDS and Student t tests. MIT and force resistance values of conical mini screws and the insertion angle of 45° were significantly higher than the other groups. Abso-Anchor conical group was the most resistant to failure. To achieve the best primary stability, conical shape is advisable. The insertion angle of 45 is more favorable than excessive oblique or vertical angles. Key Words: Maximum insertion torque, Pull-out, Shear, Primer Stability