Abstract: Objective: To study the symmetry of the upper and middle face, 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 upper and middle face symmetry in transverse and vertical directions was less than 8% , 9 mm respectively, and it was stable in the observed period. 2. Relative to the cranial base, from 13— 18 years, the nasal cavity, the maxilla were stable and harmonious. 3. In corresponding regions of the middle face: the whole maxillary regions were symmetric for male, and for female they were symmetric except the lateral maxillary region at some age; the nasal region was symmetric for female but some variations existed only at some age for male; the lateral facial region was asymmetric at some ages for male and female respectively. The growth tendencies of the symmetry-variation-regions were symmetry- right predominance- symmetry except male lateral facial region, which was asymmetry ( right predominance )-symmetry-asymmetry ( the same predominance ). 4. There was a potential tendency of predominance during facial bone growth. Conclusions: In the upper and middle face with normal occlusion, there are some normal symmetric variations. From 13— 18 y ears, its range in transverse and vertical directions is less than 8% , 9 mm respectively, and remains stable. Relative to the cranial base, and in their cor- responding regions, from 13— 18 yea rs, the middle face of adolescents with normal occlusion keeps good symmetry.

Key words: Normal occlusion, Facial symmetry, Growth, Cephalometrics