[A study of skeletal types of class III malocclusion]

300 class III cases of mixed dentition, early permanent dentition were discriminated quantitatively according to their SNA, SNB and SN-MP angles. Six quite different types were grouped: 1. Mandibular prognathism with normal maxilla. Most common type, in which about 40% are "high angle" or "low angle" cases, which show more severe class III skeletal face than normal SN-MP angle ones; 2. Maxillary retrognathism with normal mandible. More than 50% cases are with high SN-MP angle, which show less severe class III skeletal face than those with normal one; 3. Normal maxilla and mandible type, the "high" and "low" angle cases are fewer. The severity of class III skeletal face is slight; 4. Maxillary retrognathism and mandibular prognathism type, the class III skeletal face, especially for those with high SN-MP angle cases is most severe; 5. Bimaxillary prognathism type, it is the expression of racial feature of Chinese face and 6. Bimaxillary retrognathism.