Alveolar bone modeling and bone modeling/ tooth movement ratio during mandibular incisor retraction: a retrospective study
Abstract Background: The objective of this study was to explore the limit of orthodontic tooth movement by evaluating changes of alveolar bone during mandibular incisor retraction and comparing the bone modeling/tooth movement (B/T) ratio among patients with different vertical facial types. Methods: There were 103 patients with bimaxillary dentoalveolar protrusion evaluated with cephalograms in this study. The alveolar bone thickness (ABT) and cortical plate remodeling at cervical level (S1), middle level (S2) and apical level (S3) in Tip and Torque groups were measured, and B/T ratio in patients with different vertical facial types was calculated. Results: After excluding growth effect, buccolingual ABT at S1 and S2, as well as labial ABT at S1 in both Tip and Torque group decreased significantly. Cortical plate at three levels in Torque group remodeled to the lingual side. But in Tip group, cortical plate at S1 remodeled to the lingual side and cortical plate at S2 and S3 remodeled to the labial side. Regarding the B/T ratio, high-angle patients was smaller than average-angle and low-angle patients. Conclusions: In conclusion, resorption of alveolar bone was more than apposition during mandibular incisor retraction. The direction of alveolar cortical modeling was as same as tooth movement and the modeling amount was proportional to the distance of tooth movement. In addition, the B/T ratio was different among patients with different vertical craniofacial patterns. Close attention should be paid to high-angle patients with narrower ABT and smaller B/T ratio. Keywords: alveolar bone modeling, orthodontic tooth movement limit, incisor retraction, vertical facial patterns