The relation between long-period incremental markings in dentine and daily cross-striations in enamel in human teeth

Ground sections of human permanent teeth were chosen where fluorescent labels in the dentine, resulting from repeated doses of tetracycline antibiotic, were unambiguously associated with accentuated markings in the enamel developing at the same time. Counts of daily cross-striations in enamel were continued from one tooth to another in a developmental sequence over a period of some 1200 days such that the time interval between doses of tetracycline could be calibrated. Long-period incremental markings in the dentine, spaced on average between 15 and 30 μm apart (and first described by Andresen in 1898) were easily visible in the coronal dentine when the ground sections were viewed with polarized light. The total number of long-period incremental markings in the dentine between the consecutive fluorescent labels was also counted. A regression plot of daily incremental lines in enamel against long-period lines in dentine demonstrated a regular and consistent relation between the two (r = 0.997) over a 1200–1300-day period. These data support the hypothesis that long-period markings in dentine are in fact regular incremental markings with a constant periodicity in an individual. They also suggest that regular long-period markings in dentine can be used to reconstruct the timing of tooth growth or to retrieve developmental information about dentine formation rates in forensic, archaeological and palaeontological studies with some confidence.