Mandibular buccal shelf characteristics for orthodontic miniscrew placement on Class I and Class III skeletal patterns

Mandibular buccal shelf miniscrews are commonly used in patients with skeletal Class I and Class III. The sagittal skeletal discrepancy between these groups may influence the anatomical characteristics of the buccal shelf, which are crucial for determining appropriate miniscrew placement. Therefore, this study compared buccal shelf characteristics between patients with skeletal Class I and Class III for orthodontic miniscrew placement. Sixty cone-beam computed tomography (CBCT) images from patients with skeletal Class I ( n = 30) and Class III ( n = 30) were collected. Four variables were measured: slope, total bone thickness, cortical bone thickness of the buccal shelf, and the proportion of simulated miniscrew–root contact. The slope was measured at the contact area between the first and second molars, mesiobuccal (MB) and distobuccal (DB) cusps of the second molar on both the left and right sides. The other three variables were measured at these same positions, with each position assessed at two vertical levels: 5 and 7 mm apical to the cementoenamel junction (CEJ), on both sides. Comparisons between skeletal Class I and Class III groups and among different positions were performed using two-way analysis of variance (ANOVA) and chi-square tests. No statistically significant differences were observed in buccal shelf slope, total bone thickness, cortical bone thickness, and the proportion of simulated miniscrew–root contact between the skeletal Class I and Class III groups. When analyzed by position, the slope decreased significantly from anterior to posterior. Total bone thickness and cortical bone thickness tended to increase posteriorly and inferiorly. Furthermore, no root contact was observed with miniscrew insertion on the buccal shelf adjacent to the distobuccal cusp of the second molar at 5 and 7 mm apical to the CEJ, and at the mesiobuccal cusp of the second molar at 7 mm apical to the CEJ. Considerations for miniscrew placement on the mandibular buccal shelf did not differ between normodivergent skeletal Class I and Class III subjects in terms of slope, total bone thickness, cortical bone thickness, and the proportion of simulated miniscrew–root contact.