Craniofacial morphology of skeletal Class Ш malocclusion in mixed dentition

Objective To investigate the difference of mesiodistal and vertical intermaxillary relationship between skeletal Class Ⅲ malocclusion and normal occlusion in mixed dentition and to speculate the etiologic factors of malocclusion.Methods Thirty-eight children with skeletal Class Ⅲ malocclusion in mixed dentition were selected as a sample group,other 40 children at similar mean age with normal occlusion were selected as a control group.Each child took the lateral cephalometric radiograph at central occlusion.Results In linear analysis of hard tissues,10 variables of male and female respectively were significantly different between the sample group and the control group.Five variables in the ratio of linear measurement and 17 variables in angular measurement of hard tissues were also found significantly different between the two groups.Conclusion Mandibular hyperplasia may be mainly responsible for Class Ⅲ malocclusion in mixed dentition.Morphologic changes of mandible and the anterior repositioning of condyle make the intermaxillary discrepancy more serious.The craniofacial type with normal maxilla and high angle protrusive mandible is the most common morphology type.A trend of backward displacement and hypoplasia are found in maxilla.