Compensation trends of the angulation of first molars: retrospective study of 1 403 malocclusion cases

We investigated the compensatory trends of mesiodistal angulation of first molars in malocclusion cases. We compared differences in the angulation of first molars in different developmental stages, malocclusion classifications and skeletal patterns. The medical records and lateral cephalogrammes of 1 403 malocclusion cases taken before treatment were measured to evaluate compensation of molar angulation in relation to the skeletal jaw. The cases were stratified by age, Angle classification and skeletal patterns. Differences in the mesiodistal angulation of the first molars were compared among the stratifications. We observed three main phenomena. First, angulation of the upper first molar varied significantly with age and tipped most distally in cases aged <12 years and least distally in cases aged >16 years. The lower first molar did not show such differences. Second, in Angle Class II or skeletal Class II cases, the upper first molar was the most distally tipped, the lower first molar was the most mesially tipped, and opposite angulation compensation was observed in Class III cases. Third, in high-angle cases, the upper and lower first molars were the most distally tipped, and opposite angulation compensation was observed in low-angle cases. These data suggest that the angulation of the molars compensated for various growth patterns and malocclusion types. Hence, awareness of molar angulation compensation would help to adjust occlusal relationships, control anchorage and increase the chances of long-term stability. Examining the angulation of molars could inform orthodontists about the best way to treat malocclusions, according to a large Chinese study. Malocclusion, or misalignment of teeth, has often been classified based on the position of incisors but molars are arguably more important for maintaining strong tooth anchorage. Tian-Min Xu at Peking University in Beijing and co-workers examined medical records and X-rays from 1, 403 malocclusion patients to extract data on molar angles. The data showed that the upper first molar tended to angle towards the back of the mouth in adolescents but angled forwards in adults. The team also found significant relationships between molar angulation and the relative positions of the maxilla and mandible. This unprecedented dataset should help dental practitioners to understand the long-term effects of orthodontic appliances on tooth anchorage and alignment.