Main

Sadeghrianrizi Å, Forsberg C-M et al. Eur J Orthod 2005; 27: 590–596

In early development, mandibular third molars (L8s) are mesially angulated, and maxillary ones (U8s), distally. In subjects with no orthodontic experience third molar uprighting usually but not always occurs, in early adolescence. This study in a US clinic assessed the effect of 4 premolar extractions on L8 and U8 angulation in 106 subjects (E group) compared with a control group (C) of 51 treated without extractions, with a minimum of 10 yrs follow-up.

Regression models showed that during the treatment phase, U8s uprighted significantly more in E than C, but there was no such effect on L8s. By the time of long-term follow-up, in about ¾ of cases, normal eruption had occurred, while other teeth were impacted in various ways. Further analysis of results suggested that the amount of uprighting during treatment was not a good predictor of impaction. The authors discuss studies with comparable or conflicting findings, and suggest that U8s with distal tipping during treatment, >30° distal angulation, or mesial angulation to the occlusal plane, and L8s with >40° mesial angulation, are at increased risk of impaction.