A review of the literature on the prevalence of Class III malocclusion and the mandibular prognathic growth hypotheses

From this review of the literature it appears that we may draw the following conclusions. The incidence of Class III malocclusions is at most 4.2% (Goose et al. 1957, Ast et al. 1965; Knowles 1966, Thylander and Myrberg 1973). The development of various condyle growth hypotheses have lead us to believe that the condyle behaves in a rather unique manner. The condyle does not appear to be an epiphysis, neither does it behave the same as the cranium. It is a unique cartilaginous structure that cannot grow against intermittent or continuous forces (Copray 1985). The cybernetic model as proposed by Petrovic and co workers (1977) that eloquently describes the condyle to be stimulated by a cybernetic switch that connects to the periodontal ligament also does not seem to have much validity. It appears that the lateral pterygoid muscle and the temporo-mandibular condylar frenum have been ascribed capabilities that do not comply to the results of condylotomy studies. Gorette-Nicaise, Awn, and Dhem (1983) as well as the study by Whetten, and Johnston (1985) have shown that neither the absence of the lateral pterygoid muscle nor the physical volumetric expansion of the airway increases condylar growth. It appears that increase in the pressure applied to the condyle could decrease condyle cell proliferation (Armstrong 1961; Thilander 1963; 1965: Janzen and Bluher 1965; Graber 1969; Petrovic 1972; Graber and Muller 1974; Graber 1975;) with resulting growth attenuation. Accordingly, condylar growth is controlled by physical restraint, the absence which leads to incremental growth. The presence of mechanical pressure of adequate duration and magnitude, thus, should limit growth of the young actively growing condyle.