The gender difference in the mechanism of skeletal Angle's Class III malocclusion

Objective To investigate the mechanism of skeletal Angle's class Ⅲ malocclusion, especially the gender difference.Methods The study selected 58 patients with skeletal Angle's class Ⅲ malocclusion who have ANB less than 0° in cephalometric tracing and an unretrudable mandible in clinical examination,and 48 subjects with normal occlusionwho have ANB from 0° and 5°. Both groups had same number of boys and girls aged from 12 to 15 years. All of the patients requested for whole set of permanent dentition and had no history of orthodontic treatment. Thirteen measurements were obtained from cephalograms, which described the essential components of craniofacial skeleton; the other 14 described the basic faceal patterns and saggital and vertical relationships between jaws. After standardizing liner measurements to get rid of individual differences, independent sample t-test was performed compared the differences between the class Ⅲ group and the normal group; and then between the males and the females.Results In the male group, shortening of maxillar length, anticlockwise rotating of mandibular ramus, and opening of gonial angle were the main causes for skeletal class Ⅲ malocclusion. In the female group, in addition to all of the above factors, anticlockwise rotating of posterior cranial base and lengthening of mandibular ramus and mandibular body were also important contributors. It was more obvous in females that the face tended to be elongated in skeletal class Ⅲ malocclusion. Gender differences were demonstrated in the combined patterns of craniofacial skeletal components in skeletal class Ⅲ malocclusion.Conclusion Out study observed gender differences in the mechanism of skeletal class Ⅲ malocclusion in patients aged from 12 to 15. More studies are needed to investigate the variation is due to a gender difference or just a temporary phenomenon during growth spurt.