4.5. Data Record

Digital image procedures were used on histological thin sections of the teeth to examine dental cementum layers in order to estimate age at death. Out of a total of 150 teeth examined, we were able to count the annulations in all but two of them. It was not possible to analyse these two teeth due to the poor preservation of the dental tissue. For a further 25 teeth in the sample, the estimates can only be considered approximate. Using phase contrast microscopy, an assessment of the age at death was not possible in 52 cases, and for 24 teeth the estimates are only approximate.

There was some variation observed in the number of cementum layers recorded in different histological sections of the same tooth, but there was no directional increase/decrease of cementum layers in adjacent sections along the root. This can be largely attributed to the differential state of preservation of the dental tissue, due to such factors as diagenesis, local micro-fractures, residues, etc. (see Chapter 5.1). In addition, the cutting procedures used to create the histological thin sections may also contribute to the variation (cutting marks, etc.).

To-date, the standard method for the assessment of age at death using cementum annulations is based on the calculated mean of the values derived from different areas of one histological section, or the values obtained from more than one section of the same specimen. If it is accepted that a single annulation is formed homogeneously in the root each year, then any observed variability between different areas of the same section, or between different sections, can only be explained by the localised loss of external layers of the tooth (i.e., due to localised damage of the specimen or due to problems encountered during the cutting procedure), or by the inaccuracy of the method in counting all the annulations. In any event, these factors would only reduce the number of annulations recorded in a normal tooth, but never increase them. An increase in the number of annulations observed could only occur in a tooth with hypercementosis, a condition easily identifiable due to a characteristic swelling of the dental tissue, accompanied by many thin and twisting annulations that can be easily seen in histological sections. Stein and Corcoran (1994) found that the number of annulations counted in human teeth with hypercementosis were double the expected values for 'normal' teeth (for a similar study on Macaca mulatta, see Kay et al., 1984).

Consequently, our age at death estimates were determined by using the highest number of 'normal' annulations counted in different areas of the same section and different histological sections of the same tooth.