Abstract: Objective: To analyze the changes of labial-palatal alveolar bone in the maxillary incisor region in patients with bimaxillary protrusion, and to provide potential reference for a safe orthodontic tooth movement. Methods: Twenty-three adult patients who were diagnosed with bimaxillary protrusion were enrolled in the study. All patients were treated with straight wire appliances after extraction of four first premolars. Sliding mechanics with en masse retraction were utilized in the all subjects. CBCT images were taken before and after treatment. Following variables were measured to analyze the alveolar bone remodeling in the maxillary incisor region: (1) alveolar bone thickness (ABT); (2) labial and palatal cementoenamel junction-alveolar bone crest height (ABH); (3) labial and palatal alveolar bone area (ABA). Results: The labial ABT at mid-root and apical levels increased significantly in both central and lateral incisors (P<0.05), while the palatal ABT at all three levels consistently decreased after treatment (P<0.05). Regarding the changes of total ABT, significant reduction was observed in central incisors at the crestal and mid-root levels, and in lateral incisors at all three levels (P<0.05). ABA consistently reduced on the palatal side and increased on the labial side after treatment (P<0.05). Significant increase in the palatal ABH was observed at both central and lateral incisors after treatment, while an increase in the labial ABH was found at lateral incisors (P<0.01). Conclusion: Retraction of maxillary incisors in bimaxillary protrusion patients reduced periodontal bone support on the palatal side, leading to less alveolar bone in the maxillary incisor region. Potential risks of reduced alveolar bone on the periodontal sequalae should be further evaluated in the long term.

Key words: bimaxillary protrusion, orthodontic tooth movement, alveolar bone remodeling, periodontal