[Importance of posterior discrepancy in the development of skeletal Class III malocclusion]

The purpose of this communication is to explain regarding with relationship between the development of skeletal Class III malocclusion and the tooth-to-denture base discrepancy especially those in the posterior part of dentition (posterior discrepancy). Four cases which had skeletal Class III malocclusion and had experienced unsuccessful orthodontic correction were presented to evaluate the causative factors of skeletal Class III malocclusion. The observation of serial cephalograms led us to the conclusion that the continuous forward displacement of the mandible was associated with superversion of maxillary and/or mandibular molars caused by the "squeezing out" effect of poterior discrepancy. Moreover, superversion of molar provides a less steep maxillary occlusal plane in the denture frame. Accordingly, a vertical expression of the posterior discrepancy may provide one of the best explanation for development of skeletal Class III malocclusion.