Buccal bone thickness of posterior mandible for microscrews implantation in molar distalization

This study explored the inter-radicular space and buccal bone thickness of the posterior mandibular region to provide an appropriate miniscrew insertion site for lower dentition distalization.The cone-beam computed tomographic (CBCT) records of 63 subjects were collected. Buccal bone thickness (BBT) was measured at four sections: (I) the root of the second premolar(P1); (II) the mesial root of the first molar(P2); (III) the distal root of the first molar(P3); (IV) the mesial root of the second molar(P4). The narrowest inter-radicular space of the four sections was also detected. Both BBT and inter-radicular space were measured at 4 height levels, 2, 4, 6 and 8 mm from the alveolar ridge.The largest BBT was observed at the mesial root of the second molar at 6 and 8 mm, demonstrating a thickness of 6.77 ± 2.50 mm and 7.46 ± 1.94 mm, respectively. It provided sufficient coverage for mini-implants inserted 10°- 30° oblique to the root. Therefore, during distalization of the mandibular dentition, roots have sufficient space to bypass the inclined mini-implants on the lingual side, avoiding miniscrew-root contact. The width between the mesiodistal roots of the first molar was the smallest, showing 1.53 ± 0.69 mm and 2.13 ± 0.65 mm at 4 and 6 mm. Miniscrews implanted in this region had an increased risk of root proximity.The most appropriate insertion site at the mandibular buccal shelf was the mesial point of the second molar at 6-8 mm from the alveolar ridge, and an insertion angle of 10°- 30° was recommended to avoid miniscrew-root contact. CBCT analysis is recommended before implantation due to individual differences.