Abstract:

Objective：To investigate the compensation of the anterior alveolar bone thickness in skeletal class Ⅲ patients treated with orthodontic-surgical treatment. Methods: The samples consisted of 54 ske-letal class Ⅲ patients treated with orthodontic-surgical treatment. Lateral cephalograms were taken before treatment. Descriptive statistics were calculated for corresponding variables, and the differences between the samples and the norms from Peking University normal occlusion sample library were assessed by independentsample t test. Correlation analyses were performed to find associations between skeletal characteristics and anterior alveolar bone thickness. According to skeletal anteroposterior discrepancy/vertical type (ANB, criteria=-4°; SN-MP, criteria=37.7°), the samples were allocated into group A (severe anteroposterior discrepancy/hypodivergent vertical type, n=11), group B (moderate anteroposterior discrepancy/hypodivergent vertical type, n=16), group C (severe anteroposterior discrepancy/hyperdivergent vertical type, n=14), and group D (moderate anteroposterior discrepancy/hyperdivergent vertical type, n=13),and one-way ANOVA with SNK multiple comparison test were performed. Results: The anterior alveolar bone thickness of the skeletal class Ⅲ patients were thinner compared with norm values (P<0.05). Correlational analyses showed that，both the upper and lower anterior alveolar bone thickness was correlated with the skeletal vertical discrepancy (P<0.05), but the anteroposterior type was only correlated with the lower anterior alveolar bone thickness (P<0.05). For the 4 groups according to skeletal anteroposterior discrepancy/vertical type, hypodivergent vertical type had thinner lower ligual and total bone thickness (LP, LW, P<0.05). while for upper alveolar bone thickness (UW), group C and group B exhibited the thinnest and thickest (the values of UW were 7.86 mm and 9.05 mm). Conclusion:The upper and lower anterior alveolar bone thickness of skeletal class Ⅲ patients are thinner compared with normal occlusion. Different skeletal anteroposterior discrepancy/vertical type results in differences in the anterior alveolar bone thickness, so decompensation should be treated differently and carefully.

Key words: Malocclusion, Angle class Ⅲ, Cephalometry, Alveolar bone loss