A Cephalometric Study Of Incisal Jaw Mophology In Normal Occlusion Subjects

It is generally believed that the cortical plates of the incisal alveolar bone arc the "anatomic limitations" for tooth movement[1,2,3]. To some malocclusion sufferers, especially the nongrowing individuals or adults,this "anatomic limitations" was often considered an important factor in selecting the therapeutic methods. 169 subjects with normal occlusion in early permanent dentition were studied, including 72 males and 92 females aged from 10-13 years . In order to observe the incisal jaw morphology of the maxilla and the mandible,much index traced from lateral cephalometric radiographs were measured and analyed by simple factorial analysis and multiple factorial analysis.The cephalometric standards obtained from the average-angle subjects with normal occlusion were presented. And the discriminate norms ,which used as a diagnostic index to diagnose the "abnormal" incisal jaw morphology ,wcre also presented. The characteristics of the incisal jaw morphology among three vertical facial skeletal types and four cluster types were discussed detailcdly. The results indicated that:1. The region between point PA and point PC on the maxillary palatal cotical plate may be regarded as the borderline for the palatal movement of maxillaryinsisors. The region between point TB and point TC on the mandibular lingual cotical plate may be regarded as the borderline for the lingual movement of mandibular insisors. These two regions may not be exceeded, when moving the insisal root apex of maxilla or mandible to the palatal side or lingual side.2. Among different vertical facial skeletal types, the smallest distance from the upper or lower central incisive root apex to the labial and the lingual cortical plates,the thickness of the maxillary or mandibular alveolar bones and the thickness of the maxillary or mandibular basal bones have various corresponding compensation changes. The high-angle individuals may have an reduced compensation changes, but the low-angle individuals may have an increased compensation changes .3. Among different vertical facial skeletal types, the smallest distance from the upper central incisive root apex to the palatal plane or from the lower central incisive root apex to the mandibular plane, the height of the upper or lower incisor jaws have various corresponding compensation changes.The high-angle individuals may have an increased compensation changes, but the low-angle individuals may have an reduced compensation changes .4. Relating to the SN plane, incisors and alveolar bones of maxillary incisor jaws in the low-angle individuals inclined more labially than that in the high-angle individuals. Also, relating to the GoGn plane, incisors and alveolar bones of mandibular incisor jaws in the low-angle individuals inclined more labially than in the high-angle individuals.5. Among different vertical facial skeletal types, the compensationally inclined changes of the palatal cortical plates relating to the SN plane and the PP plane bring about the compensation changes of the morphology and structure of the maxillaryincisal jaws on anterioposterior dimension.,and the compensationally inclined changes of the lingual cortical plates relating to the GoGn plane bring about the compensation changes of the morphology of structure of the mandibular incisa! jaws on anterioposterior dimension.6. The inverted compensation changes of the thickness and the height of the incisal jaws lead to the consistent areas of the incisal jaws among different vertical facial skeletal types.7. The compensation abilities for different vertical facial skeletal types on the maxillary incisal jaws may be stronger the that on the mandibular incisal jaws.8. Studied by K-Means Cluster Analysis, the morphology of the maxillary incisal jaws or the mandibular incisal jaws can be divided into four types separately. Owing to the obvious characteristics of morphology in each cluster types , different clinic considerations must be pu...