The effect of variations in the mandibular plane angle on the Pont's Index.

The purpose of this study was to investigate whether a relationship existed between Pont's Index and mandibular plane angle, in a group of 48 Chinese adult subjects with orthodontically untreated excellent Class I dental occlusion and good facial balance. Results of the study showed a weak correlation between the combined mesiodistal maxillary incisor widths and the interpremolar (r = 0.27) and intermolar archwidths (r = 0.21). The correlation between mandibular plane angle and interpremolar archwidths (r = 0.58) and intermolar (r = 0.46) archwidths was fair. By taking into account the variations in the mandibular plane angle, the Pont's Index could be predicted with greater accuracy. The correlation between the combined mesiodistal maxillary incisor widths and the corrected interpremolar and intermolar archwidths were very strong (r = 0.85 and 0.82, respectively). For a given mesiodistal maxillary incisor widths, the interpremolar and intermolar archwidths in our Chinese sample were smaller than those published by Ponts. This variation could be attributed to differences in the genetic inheritance in different racial types.