Biology Reference
In-Depth Information
FIGURE 10.5
Cross-section of a molar with histologically visible structures of the enamel identified. Drawing
by Lon Hunt.
relevance to understanding environmental pressures on individuals and populations at the
time that teeth were forming.
Cross striae and striae of Retzius have a circadian periodicity (they occur at regular inter-
vals) and the extension of this is that surface perikymata could be used to calculate the age of
individuals.
Bromage (1991)
examined histological sections of maxillary first molars taken
from known-age neonatal pigtailed macaques (Macaca nemestrina), to test this periodicity.
Prenatally, the macaques had been administered three different fluorescent bone labeling
substances at two-week intervals both through their mother's bloodstream and directly into
their hard tissues. These bone-labeling substances were taken up into the hard tissues and
provided researchers with a clear way to measure bone and tooth growth within the specific
time frame. Following sacrifice,
6
the teeth were removed, processed, and sectioned. As the
absolute time between administrations of the dyes was known, disruption of the enamel
formation could be compared with the appearance of the dyes (
Bromage, 1991
).
The assumption of circadian periodicity was confirmed by matching up the number of
prisms between the labeled sections with the time of dye administration. In a series of papers
including a greater number of observations, Smith and colleagues extended the implications
of Bromage's paper by revealing additional features that seem to share a circadian periodicity
with the striae (
Smith, 2006, 2008; Smith et al., 2006
).
Due to the record of growth and life history in the developing tooth, histological analysis
of teeth can provide a remarkable longitudinal record of an individual's growth over the
6
See DiGangi and Moore (Chapter 2), this volume, for a discussion of ethical concerns when doing research
on humans or animals.
