Orthodontic Miniscrew Failure Rate and Root Proximity, Insertion Angle, Bone Contact Length, and Bone Density

Objectives: To test the hypothesis that there is no significant correlation between miniscrew failure rate and root proximity, insertion angle, bone contact length, and bone density.

Setting And Sample Population: This study included 107 patients in whom 190 miniscrews had been placed from April 2008 to October 2009 in Tohoku University Hospital (Sendai, Japan).

Materials And Methods: Cone beam computed tomography scans (CBCT) and periapical radiographs were taken before and after miniscrew placement. Differences in root proximity, screw insertion angle, bone contact length, and bone density were statistically compared; comparisons were also made between the CBCT images and periapical radiographs.

Results: A significantly higher success rate was observed in the maxilla than in the mandible. The distance between the miniscrew and the root surface was significantly smaller in the failure group. There were no significant differences in the insertion angle, bone contact length, or bone density between the success group and the failure group. The concordance rate between the periapical dental radiographs and CBCT images was 46.5%.

Conclusion: While bone contact length, miniscrew angle, and bone density did not exert major effects on miniscrew failure, root proximity was the factor that most affected miniscrew failure, especially for miniscrews placed in the mandible. CBCT was superior to periapical dental X-rays for evaluating the proximity of miniscrews to the root. Correction of the X-ray attenuation coefficient value was necessary for measuring bone density using CBCT.