Comparison of the mandibular dental and basal arch forms in adults and children with Class I and Class II malocclusions.

INTRODUCTION The mandibular arch form at the levels of both the application point of the orthodontic bracket and the basal bone in adults and children with Class I malocclusion and Class II Division 1 malocclusion was investigated. METHODS One hundred thirteen pretreatment mandibular casts were scanned to generate a 3-dimensional computer model of each cast. The casts were divided into Class I and Class II Division 1 malocclusion groups, and were further divided into adults (age, > or =25 years) and children (age, < or =18 years). Two reference points, FA and WALA, were assigned for each tooth. The FA and WALA arch forms were compared, and the distances between corresponding points and intercanine and intermolar widths were analyzed. RESULTS The mandibular intercanine FA point widths were significantly greater in the Class II Division 1 malocclusion group than in the Class I malocclusion group (P <0.05) and were also significantly greater in the Class I adults than in the Class I children (P <0.05). Both the canine FA and WALA point distances and the molar FA and WALA point distances were moderately to highly correlated (R(2) >0.55) and highly significant (P <0.001) for all groups. The FA and WALA curves for all groups had individual differences, especially in the premolar and molar areas. CONCLUSIONS The Class II Division 1 mandible is essentially the same as the Class I mandible with respect to basal bone and dental arch dimensions. WALA points can be used to predict individual dental arch forms in adults and children. Dental and basal arch forms were not significantly different between adolescents and adults.