Microscopic examination of ground and decalcified sections of enamel and dentin shows an incremental stratification of pairs of alternating light and dark layers. These layers follow a concentric pattern in transverse sections and resemble the annual rings in trees. The incremental stratifications have been more generally known as the striae of Retzius (enamel) and Owen's lines of contour (dentin). They are of physiologic significance because they reflect the nutritional and metabolic variations that occur during the growth and calcification of the dental tissues. Since no calcium withdrawal occurs in the teeth such records are permanent. The purpose of this study was to make a quantitative analysis of the incremental layers and to investigate their constancy and rhythmic nature in the teeth of various species.
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Schour et al. (1939) studied this question.