Cephalometric variables to predict future success of early orthopedic Class III treatment.

BACKGROUND: The objective of this study was to select a model of cephalometric variables to predict future Class III growth patterns based on the results of early orthopedic treatment with a protraction facemask.

MATERIAL: Sixty-four patients with Class III malocclusion were treated with a protraction facemask. Cephalometric radiographs were taken before treatment and a minimum of 3 years after treatment. The sample was divided into 2 groups: successful and unsuccessful according to overjet and molar relationships. Eleven linear and 5 angular measurements were made on the pretreatment radiograph. A logistic regression model was used to identify the dentoskeletal variables most responsible for the prediction of successful and unsuccessful outcomes in subjects receiving treatment.

RESULTS: Stepwise variable selection generated 4 variables significant in predicting successful treatment outcomes: position of the condyle with reference to the cranial base (Co-GD, P = .02), ramal length (Co-Goi, P = .03), mandibular length (Co-Pg, P = .01), and gonial angle (Ar-Goi-Me, P < .0001). The gonial angle was found to be significantly larger in the unsuccessful group. Controlling for other variables, the probability of successful treatment is an increasing function of Co-GD and Co-Goi, and a decreasing function of Co-Pg and Ar-Goi-Me. A logistic equation was established that is accurate in predicting successfully treated Class III patients 95.5% of the time and unsuccessful ones 70% of the time.

CONCLUSIONS: These results suggest that Class III growing patients with forward position of the mandible, small ramal length, large mandibular length, and obtuse gonial angle are highly associated with unsatisfactory treatment outcomes after pubertal growth.