Abstract
A phylogenetic comparative study was made between Japanese monkeys and human children to discover the reason for the diversity in human occlusion and for the wide variability in human maxillofacial morphology. The material consisted of longitudinal lateral chephalograms of 20 Japanese monkeys and 20children. Each interval of the cephalograms (0,1,2 years of age and 4,6,8 years of age) corresponded to their dental ages. The linear and angular analysis of both their maxillofacial components were evaluated, and a factor analysis on the amounts of the growth change which the coordinates of landmarks showed was performed.
The results were as follows.
1) From the linear analysis of the monkeys, there were remarkably significant differences in all the measurements both between the first and second year and between the second and third year. However, in human children, the growth of the nasomaxillary complex preceded, and the growth of the mandible, especially in height, was delayed.
2) From the angular analysis of the monkeys, a vivid growth in the anterior parts of the nasomaxillary complex and mandible was observed both between the first and second year and between the second and third year. However, in human children, no significant difference was recognized between these years, so that it seemed the human maxillofacial complex grew while keeping its framework nearly stable in these periods.
3) The main differences in the factor analysis were the timing, numbers and magnitude of factors which were (1) dependency of the growth of the anterior cranial base and its concern with the growth of the nasomaxillary complex, (2) united growth to the anteroinferior direction between the nasomaxillary complex and mandible and (3) independent morphogenesis of the mandible.
4) It is suggested from above results that one of the reasons that human beings have wide variability in their occlusion and craniofacial morphology is the changing growth pattern which, in the period of deciduous dentition, the nasomaxillary complex will grow anteroinferiorly in cooperation with the mandible and, in the period of mixed dentition, the nasomaxillary complex will not be able to grow freely under the control of the growth of the anterior cranial base, and the mandible will grow relatively freely in its morphogenesis.
