Drift characteristics of miniscrews and molars for anchorage under orthodontic force: 3-dimensional computed tomography registration evaluation

Introduction Although miniscrews have been used as absolute anchorage for a long time, their behavior under orthodontic loading is still unclear clinically. Therefore, this study was designed to evaluate the behavior of miniscrews under loading by retrospective 3-dimensional registration. Methods Sixty adult patients who had miniscrews as anchorage for en-masse retraction of anterior teeth were studied. Computerized tomography scans were made before force application and after closure of the extraction spaces, respectively. The 3-dimensional reconstruction and registration of before and after computerized tomography data were performed to assess the displacement of the miniscrews, first molars, and maxillary central incisors. Results The miniscrews and the maxillary first molars drifted mesially 0.23 and 0.91 mm apically, and 0.23 and 0.92 mm coronally; the amounts of maxillary incisor retraction at the edge and the apex were 5.94 and 1.40 mm, respectively, with 1.84 mm of maxillary central incisor intrusion. Conclusions Our results indicated that the miniscrews and the maxillary first molars were mesially displaced under orthodontic loading. A mesial site for miniscrews might be a better choice for long-term stability.