13～18岁正常人下颌骨对称性生长发育的纵向研究

Longitudinal study of the growth of mandibular symmetry in 13 18 years adolescents with normal occlusion

目的：分析正常牙合人下颌骨的对称性与变异，探讨其随生长发育的变化趋势。方法：对２６名正常牙合青少年每年同期摄取头颅定位后前位片，连续６年，并进行Ｘ线头影测量分析。结果：在１３～１８岁期间，（１）正常牙合人下颌骨对称性正常变异的范围水平向小于９％、垂直向小于７ｍｍ，且在观察期内保持稳定；（２）相对于颅底，女性左、右侧下颌升支倾斜度、下颌角与髁突的位置关系稳定、对称，男性仅在１５岁时出现对称性的变异，其后随生长又趋于左、右对称；（３）下颌骨各对应区域，男性左、右侧均对称，女性在个别年龄期下颌区、髁突区存在变异，右侧大于左侧，随生长发育变化的趋势为左右对称右侧优势左右再对称。结论：正常牙合人下颌骨存在对称性的正常变异，其范围在１３～１８岁保持稳定，水平向小于９％，垂直向小于７ｍｍ；下颌骨在相对于颅底的位置关系及内部各对应部位之间，具有较好的对称性。

Objective: To study the mandibular symmetry and its variation of adolescents with normal occlusion, and to pursue its growth tendency. Methods: 26 adolescents with normal occlusion were selected. A posteroanterior cephalogram was taken for every subject at the same time each year, lasting for 6 years. Computer aided cephalometrics was carried out. Results:1.In adolescents with normal occlusion, the total variation range of the mandibular symmetry in transverse and vertical directions was less than 9%, and 7 mm, respectively, which was stable in the observed period.2.Relative to the cranial base, in 13 year old to 18 year old adolescants, the mandibular ramus slope, the relative position between the gonion and the condyle, for female was stable and harmonious; there were some symmetric variations in the 15 year old boys. Then it tended to be symmetry with individual growth .3.In corresponding regions of the mandible, they were symmetric for male, and some symmetric variations existed only in the mandible and the condyle regions for female. The growth tendency was symmetry right prodominance symmetry. Conclusion: In mandible of adolecents with normal occlusion, there are some normal symmetric variations. in 13 year old to 18 year old adolescants, its range in transverse and vertical directions is less than 9%, and 7 mm, respectively, and remains stable. Relative to the cranial base, and in its corresponding regions, in 13 year old to 18 year old adolescants, the mandible with normal occlusion keeps good symmetry.