Evaluation of interdental space of the maxillary posterior area for orthodontic mini-implants with cone-beam computed tomography

Introduction: Our objectives in this study were to measure in a group of patients the interradicular spaces between the maxillary second premolar and first molar, which is often used as placement sites for mini-implants, and to suggest simple guidelines for safe placement. Methods: Cone-beam computed tomography was used in 35 patients to measure interdental spaces and distances between the surface of the cortical bone and the closest interradicular area apically in 1-mm intervals in 9 axial images from the cementoenamel junction (CEJ). The cone-beam computed tomography data were analyzed by using anlaysis of variance (ANOVA) to evaluate the differences in interradicular distances, cortical bone surfaces, and narrowest interradicular spaces. A t test was also performed to evaluate sex and placement side differences. Results: Interradicular space became wider toward the apical area; several axial planes showed statistically nonsignificant differences from the CEJ to the root, and the average distance from the surface of the cortical bone to the area of the closest interradicular space was over 5 mm in the most sections. Conclusions: Guidelines for safe placement are as follows: the initial point for mini-implant placement is near the mucogingival line (2-4 mm from the CEJ) and less than a 45° apical angulation to the long axis of tooth, with a mini-implant diameter of 1.4 to 1.8 mm and length of about 6 mm (bone contact). A larger placement angle would increase the cortical bone contact; however, it is difficult to apply various traction materials and might increase the danger of maxillary sinus perforation.