Placement and removal torque values of orthodontic miniscrew implants

The purpose of this study was to analyze the maximum insertion torque (MIT) and maximum removal torque (MRT) values of orthodontic miniscrews.

Two hundred eighty titanium miniscrews were placed in several sites in the maxillae and mandibles of orthodontic patients to provide skeletal anchorage. Two types of miniscrews were used: predrilling, cylindrical miniscrews, and self-drilling, conical miniscrews. A force of 50 g was applied with nickel-titanium coil springs 2 weeks after placement. MIT and MRT values were assessed with a digital torque gauge. Torque values were subjected to the paired t test, Student t test, chi-square test, and 1-way analysis of variance (ANOVA) (P <0.05).

MIT values were significantly higher for the self-drilling miniscrews (mean, 14.5 Ncm; 95% CI, 13.6-15.3) than for the predrilling miniscrews (mean, 9.2 Ncm; 95% CI, 8.6-9.9) in all implant sites. For both predrilling and self-drilling miniscrews, the highest MIT values were observed at the midpalatal suture site followed by the dentoalveolar bones of the mandible and maxilla, respectively. In contrast, MRT values were significantly higher for the predrilling miniscrews (mean, 22.6 Ncm; 95% CI, 22.0-23.3) than for the self-drilling miniscrews (mean, 17.6 Ncm; 95% CI, 16.8-18.4). Accordingly, the mean torque ratio of predrilling miniscrews was twice that of the self-drilling miniscrews.

An inverse relationship between MIT and MRT values was observed. The results suggest that relatively lower MIT values were more favorable to osseointegration than higher values.