The effect of extraction of four second permanent molars on the incisor overbite

Changes in incisor overbite were compared in 33 subjects who had four second molars extracted and 33 untreated subjects. There was an average increase in overbite of 0.7 mm in the extraction group, significantly different from an average decrease of -0.8 mm in the control group. The tendency to increase in overbite was greater in subjects whose presenting overbite was already reduced. The mechanism responsible for overbite reduction appeared to be a slight distal movement of the dentition, with retroclination of incisors and increase in inter-incisal angle.