Distribution of Various Maxilla-Mandibular Positions and Cephalometric Comparison in Chinese Skeletal Class II Malocclusions

Aim:To obtain the distribution of different maxilla-mandibular characteristics in Chinese skeletal class II mixed dentition patients and to compare the differences of cephalometric variables among different maxilla-mandibular types. Materials and methods:A cross-sectional study was conducted among 310 skeletal class II patients in mixed dentition.The patients were divided into 6 groups according to SNA and SNB angle of the cephalogram.A total of 38 cephalometric measurements were measured on their cephalograms.Differences among groups were tested by one-way analysis of variance.Results: There were 34 (10.97%)patients in group I, 10 (3.23%) in group II, 4(1.29%) in group III, 69 (22.26%) in group IV, 133 (42.90%) in group V, and 60 (19.35%) in group VI.In all, 14.19% of the patients exhibited maxillary protrusion (MxP), and 62.26% exhibited mandibular retrusion (MnR) with either normal or retruded maxilla.Groups II and III were excluded for statistical comparison due to a limited sample size.Statistical differences were found in 25 cephalometric measurements among the other 4 groups.Patients with MnR (groups V and VI) exhibited bigger sella angle, gonial angle, Frankfort mandibular plane angle, and smaller mandibular body length and ramus height than patients without MnR (p value < 0.05). Conclusion:The most common etiology forming skeletal class II malocclusion in Chinese children was MnR, which was mainly caused by the small size and hyperdivergent growth direction of mandible.Clinical significance: The study presents various cephalometric characteristics of Chinese skeletal class II malocclusions.The results indicated that for the early orthodontic treatment of Chinese class II children with mixed dentition, orthodontists might emphasize more importance to mandibular length augmentation and growth direction change in mandible.