Craniofacial morphology in orthodontically treated patients of class III malocclusion with stable and unstable treatment outcomes

K Tahmina, E Tanaka, K Tanne
American Journal of Orthodontics and Dentofacial Orthopedics 2000, 117 (6): 681-90
The purpose of this study was to investigate morphologic features of the craniofacial skeleton in treated adolescent patients with Class III malocclusion. Fifty-six subjects were divided into 2 groups, with and without acceptable treatment outcomes, which were referred to as the stable and the unstable groups. The mean age at the initial stage was 9 years 3 months in the stable group and 9 years 4 months in the unstable group. All subjects underwent chincup therapy, with a mean duration of 3 years 9 months. On the basis of lateral cephalograms taken at 4 different stages, the means of the z scores for 20 measurements were calculated and compared between the 2 groups by means of the Student t test. Discriminant analysis was also conducted to extract key determinants to discriminate between the 2 groups. The gonial angle was significantly larger in the unstable group than in the stable group at the initial stage, and this increased over time. The mandible of the unstable group exhibited downward-and-backward rotation during early treatment and then rotated in an upward-and-forward direction after the correction of the anterior crossbite. A significant forward growth of the mandible was also found in the unstable group for the same period. Furthermore, the gonial, N-A-Pog, and ramus plane to SN plane angles were selected as the significant variables for discriminating the 2 groups with a high precision. In conclusion, it is shown that upward-and-forward rotation of the mandible, in combination with the forward growth and displacement, is highly associated with unsatisfactory treatment outcomes after pubertal growth in growing Class III patients.

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