Despite having a correct anterior occlusal relationship between upper and lower teeth with canines in perfect Class I, some patients have imperfect posterior occlusal relationships with first molars in positions that are slightly Class II or Class III owing to an arch length discre pancy in the upper and lower buccal segments.

From this study of 62 subjects treated with full banded appliances and no bicuspid extrac tions we were able to determine the ideal relationship of the widths of the lower bicuspid and molar teeth with their upper antagonists, one that make it possible for the attainment of Class I relationships of both canines and first molars. This ideal value is 1.062.

We discuss the therapeutic implications of this finding, notably its influence on extraction decisions and propose solutions for cases of frank disharmony.