Intercusp differences in enamel prism patterns in early and late stages of human tooth development

Enamel prism-packing patterns reflect the past history of ameloblasts, providing information about growth patterns in tooth development. Here, the area and density of enamel prisms on the cuspal surface of molar teeth were measured to examine if the onset and rate of enamel apposition differ according to stage of development and/or cusp type. Scanning electron-microscopic images were taken from the mesiobuccal and distal cusp tips of 30 mandibular first permanent molars at different stages of development recovered from archaeological sites in Israel dating to the past 10000 years. Selected enamel microstructural characters were measured for each cusp. The mean area of prisms on the mesiobuccal (MB) cusp was significantly larger than that of the distal (D) cusp at all stages of development and the differences in prism area between cusps were significant for each stage of development. Prism density was significantly smaller on the MB cusp than the D cusp at all stages of development but no significant differences were found between early and later stages in each cusp. This was interpreted as indicating that enamel formation in the MB cusp was almost complete, even in the earliest tooth germs studied, whereas in the D cusp it was less advanced. The differences between MB and D cusps are proposed to result from asynchrony of enamel formation between the different cusps of molar teeth in recent populations. The method provides a non-destructive approach to the study of growth patterns in teeth and provides baseline data for comparison with fossil teeth.