The study of arch width in class II malocclusion during the early permanent dentitions

Objective To explore the relationship between arch width and morphological characteristic of mandible in class Ⅱ malocclusion patients.Methods Forty-six patients with class Ⅱ malocclusion and twenty-two patients with class Ⅰ malocclusion were selected from the Affiliated Stomatological Hospital of China Medical University from 2005 to 2007.Patients with class Ⅱ malocclusion were recruited as study cases and patients with class Ⅰ as controls.Study cases were divided into two groups by classified method of Angle:class Ⅱ division 1 group and class Ⅱ division 2 group.Eleven indexes of dental casts and cephalogram of the patients were measured before treatment.The significance of these parameters was analyzed.Results A statistically significant difference in SNA,ANB,Go-Pg,Co-Pg,maxillary first premolars,maxillary second premolars and maxillary intermolar width was found between the three groups(P 0.05).Conclusions The maxillary middle transverse arch width and posterior transverse arch width are narrower in patients with class Ⅱmalocclusion than in patients with class Ⅰ malocclusion.Patients with class Ⅱ division 1 malocclusion show that mandibular retrusion is associated with the narrowing of the maxillary transverse arch;the mandibular retrusion of the class Ⅱ division 2 malocclusion group is concerned with the hypodevelopment of mandible.