ABSTRACT

To investigate the correlation between initial torque and removal torque of orthodontic mini-screws.

Sixty-four orthodontic mini-screws (measuring 1.5 × 4.4 mm, 1.6 × 4.7 mm, 1.7 × 5.5 mm, and 1.8 × 5.6 mm) were used. All mini-screws were inserted into the fibulas of 8 male rabbits. The initial torque values were immediately recorded using a digital torque gauge. For 2 months, 115 g force was applied to mini-screws inserted into the right fibula of the rabbits. The same procedure was followed for inserting the mini-screws into the left fibula of the rabbits but without applying any force. After 2 months, the removal torque values were recorded for all mini-screws. All statistical analyses were performed using SPSS version 14.0 for Windows. Spearman's correlation coefficient was used to analyze the relationships between initial and removal torque values.

Intragroup comparison of all brands of mini-screws showed similar features. There were no statistically significant differences between the initial torque values of all mini-screws (p > 0.05). The Spearman correlation coefficient showed that correlations between the initial and removal torque values were insignificant (p>0.05).

The results of this study suggest that the initial torque value is not a reliable method for predicting the success of a mini-screw.