Abstract
We conducted the semi-longitudinal study on the maxillofacial morphology in Chinese female twins. The materials consisted of 330 lateral cephalograms taken from 85 twin pairs from 6 year-olds to 11 year-olds. We compared their maxillofacial growth pattern with those of present Japanese girls, and estimated the degree of genetic factors concerning the pattern by the twin method.
The results were as follows:
1. On the average stature curves, the mean value of the Chinese at the age of 6 was 3 cm higher than that of the Japanese. At and over the age of 7, however, the two lines were almost coincident.
2. The angular analysis showed that there were few differences at both SNA and SNB between the Chinese and the Japanese. On the other hand, the postero-inferior shape of the mandible of the Chinese was already similar to that of the Japanese adult female from Stage 3.
3. The linear analysis showed that the difference in the depths between upper and lower faces of the Chinese was smaller than that of the Japanese, and the mandiblular size of the Chinese was relatively larger than that of the Japanese.
4. Superimposition of their profirograms showed that the anterior profile of the Chinese seemed to be less uneven and more upright than that of the Japanese.
5. At the depths of both anterior cranial base and nasal floor, the heritabilities of the Chinese were between 60 and 80%, while which lowered at Stage 4. Concerning the heights and the shape of mandible, the heritabilities of the Chinese were between 70 and 90%, and which were highest at Stage 5.
6. It is suggested that the main morphological differences on maxillofacial cranium between the Chinese and the Japanese at the mixed dentition stage were the postero-inferior shape of the mandible and its size, and the genetic factors strongly influenced them.
