Morphological Study of the Dentino-enamel Junction of the Upper First Deciduous Molar

抄録

The dental morphology of the outer enamel surface (OES) is basically determined by the form of the dentino-enamel junction (DEJ) and the thickness of the enamel substance covering the DEJ. In our series of studies of morphological traits observed on the DEJ of deciduous molars (Sasaki, 1997; Sasaki and Kanazawa, 1999, 2000), we demonstrated that the traits are observed clearly on the DEJ as a distinct ridge or a process, even when they are not distinct on the OES. In this paper, we report characters originating from the buccal cingulum, the occurrence of occlusal ridges, and cusp number on the OES and DEJ of the upper first deciduous molar. The combined frequencies of (+) and (++) morphology of several traits were as follows: buccal cingulum: 62.2% (DEJ) and 15.4% (OES), mesiobuccal marginal ridge: 79.1% (DEJ) and 52.3% (OES), distobuccal marginal ridge: 33.9% (DEJ) and 7.7% (OES), mesiobuccal tubercle: 86.7% (DEJ) and 61.7% (OES), crista obliqua: 80.0% (DEJ) and 72.5% (OES), trigonal hypocone crest: 36.4% (DEJ) and 4.6% (OES). The frequencies of trait occurrence on the DEJ were higher than on the OES, because the original characters were not obscured by the enamel. Although previous observers had different opinions concerning the number of cusps of the upper first deciduous molar, three or four cusps were found on the DEJ suggesting that this tooth is more morphologically differentiated than the successional first premolar tooth. The results of this study suggested that phylogenetically conservative crown characters were retained more frequently in the anterior molar of the primary dental series from dm¹ to M².