Selection of dentofacial measurements for an orthodontic treatment priority index.

A battery of thirty dentofacial measurements was studied in an attempt to identify those measurements most closely related to a clinical assessment of the need for orthodontic treatment in the Dutch population. This was done by inspecting the mean values of these measurements computed within several treatment priority groups, a stepwise regression analysis relating treatment priority scores to these dentofacial measurements, and a quadratic discriminant function analysis between the group of children requiring orthodontic treatment and the group for which treatment was deemed unnecessary. The variables identified by inspection were 1) overjet, 2) overbite, 3) upper molar arch width, 4) the angle defined by articulare-gonion-menton, 5) lower arch length and 6) the ANB angle; the first four of these proved to be the most important when the contributions of all thirty of the variables to the TPI were assessed by means of the stepwise regression analysis. Overjet was also found to be an important predictor variable by Freer in relating Grainger's orthodontic TPI to dentofacial measurements in a group of patients with distoclusion; the ANB angle was found to be the most effective discriminator between normal and Class II American children. The results of the present study then, to this extent at least, agree with those found in other populations. It would appear that any "universal" TPI would have to involve those aspects of dentofacial morphology measured by overjet and the ANB angle. Within the context of the Dutch population the variables identified proved to be effective discriminators in the decision of "to treat or not to treat," correctly classifying 100% of the children in the sample who were judged by two experienced orthodontists as requiring treatment. While this decision rule did suggest treatment for 17% of the children judged to not require treatment, these cases were in the "doubtful" category (Table I) and might therefore warrant continued monitoring before any final decision is reached.