抄録
Measurements and morphological studies were conducted on the teeth of Yayoi ancients that had been excavated at the Hirota site, Tanegashima island, Kagoshima Prefecture. The study was mainly directed to detect morphological features of the teeth of these ancients, to compare the findings with those of modern Japanese counterpart and to get some information of the possible age change of the teeth by the aid of anthropological or phylogentical concepts. Principal points of interest were summarized as follows. 1. The size of teeth from the ancients was larger in their length, especially in length of root part. In contrast to this, breadth of tooth crown was smaller than that of modern Japanese tooth crown. Such elongation of the tooth root should be interpreted in terms of an adaptation of tooth to coarser and harder diets taken at the time which would require the tooth to develop greater stability in the socket of jaw, and hence the longer root. 2. The presence of blind foramen, incisura obliqua and caninization, all of which are regarded as sings of retrogression in the upper lateral incisor could be observed less frequently than in modern Japanese counterpart. Also less frequent was the occurrence of the shovel-shaped incisors, especially in upper central incisors, in the ancients men as compared with the dentition of modern Japanese. 3. In view of the groove type of occlusal surface in the upper premolars and the manner in which the root was branched, it was suggested that these teeth, especially the 1st premolar tended to show relatively primitive shape as compared to modern Japanese. 4. With lower premolars, the way in which the cusps and the occlusal grooves occurred in the teeth of ancients suggested an age change of these teeth which was more marked in the 2nd rather than in the 1st premolar. 5. With upper molars, the 1st molar in the ancients showed with no exception 4 completely formed cusps and the 2nd molar was also quadruply cusped in the majority of cases, suggesting that they kept more primitive form as compared to modern Japanese dentition. 6. With regard to occurrence of cusp number and the type of occlusal groove in lower molar of the ancients, the most frequent was so-called Dryopithecus Pattern (Y_5) in the 1st molar where 5 cusps and Y-shape groove were common, and in the 2nd and 3rd molars the groove shapes +_4 and X_4 were respectively most predominant, showing little, if ever, deviation from patterns of modern Japanese dentition. No significant variation was noticed in number and shape of the tooth root, and the 1st and 2nd molars had almost all 2 roots. Occurrence of supernumerary tubercle such as Protostylid, 6th cusp and 7th cusp was very rare. Conclusions were drawn form the above findings that the lower jaw teeth in Hirota ancients showed no significant deviation from comparable teeth of modern Japanese in every morphological traits examined, while teeth from upper jaw of Hirota ancients deviated in some way or other from those of modern Japanese.
