Reappraisal of Class II molar relationships diagnosed from the lingual side.

The buccal and lingual molar relationships in 459 clinically diagnosed Class II cases and the impact of upper first permanent molar rotation on this classification were assessed. Of the 459 Class II cases, 99 (10.78%) sides exhibited unilateral neutral molar relationship assessed from both the buccal and the lingual aspect. None of the molars exhibiting Class I relationship were rotated. The 175 (19.06%) sides with mild Class II molar relationship from the buccal aspect were all judged to be Class I lingually and 85% of these molars were rotated mesially. In the case of a moderate buccal Class II tendency, 55% of the molars were in a Class I relationship when evaluated from the lingual side, whereas 45% belonged to mild (1st degrees ) Class II with molar rotations present in 81% of the cases. When a severe (3rd degrees ) Class II was present from the buccal side, its corresponding lingual Class II tendencies were accordingly elevated (83% 2nd degrees, 17% 3rd degrees ). Among these cases, the molar rotations occurred in 74% of the cases. The results suggested the upper mesiopalatal cusp as a pivotal axis around which the upper first molar rotated. This cusp occluded most frequently in the central fossa, less frequently in the mesio-triangular fossa and rarely anterior to the mesio-triangular fossa. Rotations that correspond to these types of lingual occlusion were 85, 81 and 74%, respectively. The correlation between buccal and lingual molar relationships and their correlation with molar rotation were all significant (p<0.001). Moreover, canine relationship was linearly correlated with the conventional (buccal) molar relationship in Class II cases, expressed by Ycanine relation=1.423+0.47 Xmolar relation (p<0.001). The results indicate that a more differentiated diagnosis of the molar relationship will allow for a more causally directed correction of Class II molar relationship.