Influence of orthodontic treatment on development of third molars.

We aimed to find out whether extraction of lower premolars and subsequent closure of the space by a fixed appliance influenced the chances of mandibular third molars erupting. We compared angular and linear measurements of lower third molars on dental panoramic tomograms in 30 orthodontic patients with similar measurements from 30 patients with impacted third molars in intact arches. We found that the mesial angulation of lower third molars was reduced from 50 degrees to 43 degrees by orthodontic treatment (P< 0.001). Distance to the occlusal plane was reduced from 12 mm to 10 mm (P< 0.001). The space available increased from 4 mm to 11 mm (P< 0.001). We conclude that extraction of lower premolars and orthodontic treatment to achieve complete closure of the space allowed the positions of many impacted lower third molars to improve significantly.