Cephalometric predictor variables for treatment of Class II Division 2 malocclusions

To many orthodontists, it is clinically relevant to avoid extractions in the treatment of Angle's Class Ⅱ Division 2 (Class Ⅱ/2) malocclusions. The most commonly cited side effects from extraction treatment are a tendency toward flattening of the facial profile and deepening of the bite. The aim of this study was to select a model of cephalometric predictor variables for treatment decision-making for Class Ⅱ/2 malocclusions with premolar extraction versus non-extraction. The pretreatment lateral cephalograms and study models of 92 patients (46 boys and 46 girls) with a Class Ⅱ/2 malocclusion were analyzed. Discriminant analysis was applied to select pretreatment predictive variables for the treatment options. Stepwise variable selection of the cephalometric and model measurements at the first observation identified 5 predictive variables (p＜0.001). In order of significance, they are ANB, overjet (OJ), S to Go (S-Go), lower (L) arch-length discrepancy, and lower lip to the E-plane (L lip-E plane). The discriminant function generated was Dz = -0.5652(ANB) + 0.6271(OJ) + 0.4126(S-Go) + 0.6183 (L arch-length discrepancy) -0.3496(L lip-E plane). Using this discriminant function, a standardized score (Dz) ＞ 0 can roughly be translated into non-extraction treatment. For a score ＜ 0, extraction treatment can be assigned. The cutoff score for this function was Dz = 0. The group membership correctly classified was 83.7%. The majority of the misclassified patients were grouped around zero. This study showed that the discriminant function was dependent upon ANB, OJ, S to Go, lower arch-length discrepancy, and the lower lip to the E-plane in order to make an extraction decision for Class Ⅱ/2 malocclusions.