Effect of different extraction modes on morphology of chin in adolescents with Class II Division 1 malocclusion

AIM:To investigate the effects of extractions on the morphology of chin in adolescents with Class Ⅱ Division 1 malocclusion.METHODS:A total of 74 subjects were divided into 4 groups:Group 1 of extracting 4 first premolars,Group 2 of extracting upper first premolars and lower second premolars,Group 3 of extracting upper first premolars only,and control group of nonextraction.Pre-and post-treatment changes of chin were compared by cephalometric analysis and statistical analysis was performed with SPSS14 software.RESULTS:No significant difference was found in the height of chin,the tilt angle of chin,and the thickness of chin at Po point in all groups.Proptosis degree of chin increased significantly in all groups.Significant decreases were found in the fossa of chin,the thickness of chin at B point and root tip,the curve of chin,and the depth of mentolabial furrow in groups treated with bimaxillary extraction,but no significant difference was found in maxillary extraction group.CONCLUSION:Changes of morphology of chin are affected by mandibular teeth extraction but the site of mandibular extraction does not seem to have obvious effect on the changes.Orthodontists should choose proper extraction modes to achieve the best results.