Proper mesiodistal angles for microimplant placement assessed with 3-dimensional computed tomography images

Introduction: To provide information about placement sites and angulations of microimplants between tooth roots, we analyzed 3-dimensional computed tomography images from 25 patients. Methods: The patients in the sample had good interdigitation, no restorations, and no arch length discrepancies in the posterior segments. Three-dimensional images of the maxillary and mandibular second premolars, first molars, and second molars were constructed. The distances and midpoints between the roots at 3 levels were calculated, and the angles between the lines connecting the midpoints and perpendicular lines to the occlusal plane at the contact points were also calculated. Results: The midpoints between the roots were located distally to the contact point and from the cervical to the apical areas. The lines connecting these midpoints from the cervix to the apex of the roots in the mandibular arch had more distal inclination than in the maxillary arch. Conclusions: To minimize root contacts, microimplants need to be inclined distally about 10° to 20° and placed 0.5 to 2.7 mm distally to the contact point to minimize root contact according to sites and levels, except into palatal interradicular bone between the maxillary first and second molars.