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.