[Study on the dental arch width in Class II malocclusion].

PURPOSE: The aim of this study was to compare the transverse dimensions of the dental arches of Class II division 1 and Class II division 2 malocclusion groups with mild Class I malocclusion subjects. METHODS: Measurements were performed on dental casts of 40 mild Class I malocclusion (mean age: 16.2 years),40 Class II division 1 (mean age: 15.6years), and 40 Class II division 2 (mean age: 15.8 years) malocclusion subjects respectively. The dental arch width in the canine, first premolar, second premolar, and molar regions were measured and the arch differences of each groups were calculated. Independent-samples t test was applied for comparisons of the groups. RESULTS: The results indicated that the maxillary canine, premolar and molar width were narrower in subjects with Class II division 1 malocclusion than in the mild Class I malocclusion sample, but the difference was not significant statistically (P>0.05), and the mandibular widths were not significantly different in subjects with Class II division 1 malocclusion and in the mild Class I malocclusion sample (P>0.05); the maxillary premolar, molar width and mandibular width were significantly narrower in subjects with Class II division 2 malocclusion than in the mild Class I malocclusion sample (P<0.05) statistically; the mandibular width were significantly wider in subjects with Class II division 1 malocclusion than in the Class I division 2 malocclusion sample (P<0.05); the width difference was narrower in subjects with Class II division 1 malocclusion than in the mild Class I malocclusion sample, the canine and second premolar width differences were significantly narrower (P<0.05); the width differences were not significant in subjects with Class II division 2 malocclusion and in the mild ClassI malocclusion sample (P>0.05); the width difference was less in subjects with Class 2 division 1 malocclusion than in Class II division 2 malocclusion sample, the canine width was significantly narrower (P<0.05). CONCLUSIONS: The development of the transverse dimensions of the dental arches are not sufficient in the maxilla of Class II division 1 malocclusion and in the maxilla and mandible of Class II division 2 malocclusion. For that reason, expanding upper arch width of Class II division 1 and both the upper and lower arch width of Class II division 2 are often indicated in clinic.