Abstract
This study aims to evaluate the overall bone thickness (OBT) and cortical bone thickness (CBT) of mandibular symphysis and to determine the optimal sites for the insertion of orthodontic mini implants. Cone-beam computed tomography (CBCT) images of 32 patients were included in this study. The sample was further categorized into three facial types: low-, average-, and high-angle. OBT and CBT were measured at the mandibular symphysis region. All measurements were performed at six different heights from the cementoenamel junction [CEJ] and at seven different angles to the occlusal plane. Analysis of variance (ANOVA) was used for statistical comparison and a p value less than 0.05 was considered statistically significant. Our results revealed that neither OBT nor CBT was influenced by age or sex, except for the observation that CBT was significantly greater in adults than in adolescents. OBT and CBT were significantly greater in low-angle cases than in average- and high-angle cases. Both OBT and CBT were significantly influenced by insertion locations, heights and angles, and their interactions. CBT and OBT were greatest at the location between two lower central incisors, and became greater with increases in insertion height and angle. Both recommended and optimal insertion sites were mapped. The mandibular symphysis region was suitable for the placement of orthodontic mini implants. The optimal insertion site was 6–10 mm apical to the CEJ between two lower central incisors, with an insertion angle being 0–60 degrees to the occlusal plane.
Highlights
Orthodontic mini implants have been gaining in popularity among orthodontists due to their simplification of orthodontic biomechanics [1]
Due to limited inter-radicular space in the mandibular anterior region, especially among patients with anterior crowding, the clinical application of Anterior orthodontic mini implants have been well-validated for the effective correction of deep bite [5]
Mandibular symphysis grows anteriorly and laterally, resulting in an adequate bony projection anterior to the incisor roots [10]. This renders mandibular symphysis an excellent candidate for extra-alveolar orthodontic mini implants placement that could be used for the intrusion of mandibular anterior teeth
Summary
Orthodontic mini implants have been gaining in popularity among orthodontists due to their simplification of orthodontic biomechanics [1]. Various anatomic sites are available for the insertion of mini implants, e.g., inter-radicular sites, palatal sites and infrazygomatic areas [2,3,4]. Anterior regions are frequently used for the insertion of mini implants to intrude between incisors [5]., Mini implants are less frequently used at the mandibular anterior region compared to the maxillary anterior region due to limited inter-radicular space, especially among mandibular crowding patients [3]. Previous studies that focused on inter-radicular sites for mini implants at the mandibular region suggested that mandibular incisor regions were not feasible for the insertion of mini implants [3,7]. In contrast to inter-radicular regions, the quality and quantity of alveolar bone labial to mandibular incisor roots (mandibular symphysis region)
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