The periodicity of enamel laminations in human deciduous molars

Enamel laminations are closely spaced incremental lines that run parallel to Retzius lines or the developing enamel surface. Here, the timing of enamel laminations is calculated for naturally exfoliated deciduous molars (n = 111) from three modern-day populations (Aotearoa New Zealand, Britain and Canada).

Teeth were sectioned using standard histological methods and examined using a high-powered microscope. Mean daily secretion rates (DSR) were calculated for the outer enamel of each molar in cuspal, lateral and cervical enamel regions. These DSRs were used to determine the periodicity of enamel growth across laminations in each region. Lamination periodicity was compared between populations and sexes, and within molars to assess the relationship between lamination periodicity and the angle between laminations and the outer surface.

Laminations were present in 57 % of all molars (n = 63 out of n = 111). Their presence did not vary between populations or by sex. A mean two-day periodicity was observed in cuspal and lateral outer enamel sampling regions. A mean one-day periodicity was observed in the cervical outer enamel. The angle of laminations relative to the outermost surface of the enamel was significantly related to the presence of laminations.

A two-day periodicity for laminations indicates that this incremental marking is not a reliable proxy for a circadian 24-hour rhythm in human deciduous molars. The orientation of laminations was similar to Retzius lines but differed to the orientation of cross-striations.