EFFECTS OF INSERTION ANGLE AND BODY SHAPE ON THE PRIMARY STABILITY OF ORTHODONTIC MINISCREWS*

In this study, we aimed to analyze the maximum insertion torque, pull-out and shear strength of the samebrand mini screws with different body structures that were inserted at 30°,45°,60°and, 90° in order to compare their stability. The study consisted of 144 self-drilling, 1.4×8 mm titanium alloy minis crews (Abso-Anchor conical, Abso-Anchor cylindrical). Each group of mini screws were inserted in fresh male bovine hip bone segments at four different angles and the maximum insertion torque was recorded. Pull-out and shear force resistance values were measured and recorded until 1.5 mm displacement occurred. The data was analyzed with the use of the IBM SPSS program. Statistical analyses were conducted with Shapiro-Wilk, One-Way ANOVA, Tukey HSD and Student's t-test. It was determined that the maximum insertion torque and force resistance values of the conical mini screws and an insertion angle of 45° were significantly higher than those of the other groups. The Abso-Anchor conical group was the most resistant to failure. To achieve the best primary stability, the use of aconical shape is advisable. The insertion angle of 45° is more favorable than excessive oblique or vertical angles.