For the purpose of studying secular changes of tooth and jaw reduction as well as the occurrence and progress of tooth to denture base discrepancy, the authors have already investigated dental diseases of Japanese skeletal remains from several periods. However, no dental caries of deciduous teeth has been found so far, possibly because very few samples of deciduous or mixed dentition have been obtained.
Recently, the authors had an opportunity to examine 183 skeletal remains ranging from the early stages of the Jomon to the Kofun periods stored at the Department of Anatomy, Faculty of Medicine, Nagasaki University. Among these materials, there were 21 crania with deciduous or mixed dentition, three from the later Jomon period,17 from the Yayoi period and one from the Kofun period. The present paper deals with the results of dental examination based mainly on samples from the Yayoi period, for it seems quite uncommon to meet such a large number of samples of this kind.
There were eight cases of normal occlusion, three of anterior cross-bite and two cases of crowding out of 13 cases with good conditions for orthodontic diagnosis of their occlusions. With respect to the pathogenic factors of malocclusion, there were three cases involving the skeletal factor(23.1%), one case involving the functional factor (7.7%) and two cases involving the discrepancy factor (15.4%). There was no evidence of dental caries of deciduous teeth in the Jomon nor Kofun periods. However, several cavities were found on deciduous teeth in the Yayoi period, namely two carious teeth in 15 maxillary deciduous central incisors, two in 27 maxillary first deciduous molars, and four in 53 maxillary and mandibular second deciduous molars, which included four C₁ and four C₂.
Suspicious traits of marginal resorption of the alveolar bone were observed at the deciduous molar region in only one case, but it was not confirmed whether periodontal disease was already in existence among the Yayoi children.
Based on roentgenographic cephalometrics, it was evident that the madnible of this period showed a well developed pattern even in early stage of mixed dentition corresponding to the findings in adult samples, which seemed to explain the higher rate of anterior cross-bite with the skeletal factor. The size of the total discrepancy according to Tweed (1944,1945) could be estimated in only two cases giving a mean value of plus 2.4 mm.
It was conclussively shown that 1. the Yayoi people had a quite defferent facial pattern from the former habitants of Japan,2. it was a time in which the environmental pollution in the mouth was the severest among the various historic periods, and 3. the discrepancy between teeth and jaw bones, and consequently its influence on dental diseases were not so dominant in that period.