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. （J Dent Sci,
1(1):16-22, 2006）
