关键词: 缺失牙；多生牙；青少年；全颌曲面体层X线片

Abstract: The purpose of this study is to investigate the incidence and mostly happened area of the congenitally missing teeth and supernumerary teeth in Beijing adolescent in order to approach the relation between the anomaly of tooth number and human evolution.
Subjects and methods: 429 panoramic radiographs were observed and analyzed, 163 males and 266 females, aged 12 —23 years. None of permanent teeth have been extracted or hurted.
Result: The incidence of congenitally missing permanent teeth (including third molar) is 42.19 %. The incidence of missing third molar is 35. 43 %. The mostly happenedmissing teeth are maxillary third molar, mandibular third molar, mandibular second premolar, mandibular median incisor, maxillary second premolar etc. the incidence of supernumerary teeth is 3.50 %, supernumerary teeth mostly happened are maxillary incisors.
Conclusion: The incidence of missing teeth is higher than that of supernumerary teeth. Missing teeth mostly were found are the ones which have weaker function. The anomaly of tooth number is mostly due to hereditary factors. Congenitally tooth missing reflexes one of the evolutionary tendencies of the masticatory organ. The occurence of supernumerary teeth is a phenomenon of recapitalation.

Key words: Missing teeth; Supernumerary teeth; Adolescent; Panoramic radiograph