Do enamel microstructures have regular time dependency? Conclusions from the literature and a large-scale study.

This paper is structured in two parts. The first briefly reviews a number of lines of published evidence, including direct experimental evidence, supporting the contention that enamel microstructures are time dependent and have a regular periodicity. The second presents the results of a large-scale study designed to test a central assumption underlying most histological ageing approaches in enamel: that the number of cross striations between adjacent striae of Retzius, called the circaseptan interval, are uniform within a tooth and between all teeth in the dentition of an individual. The study uses a sample of 158 anterior teeth from three modern human populations. Teeth were sectioned and circaseptan intervals were determined by dividing measurements of the distance between adjacent striae of Retzius, by cross-striation length. In order to exercise as much procedural rigour as possible, all measurements were made from photomicrographs. Two sections were taken from each tooth, the sampling location within each tooth was recorded, and all populations included multiple teeth from single individuals. Results statistically validate the uniformity hypothesis within the anterior dentition. These, together with the weight of published evidence, suggest that data derived from the use of enamel microstructures in age estimation techniques and growth and development studies, are valid.