Being able to determine how old people were when they died from their skeletons is vital for looking at mortality in the past. It is also essential for understanding rates of disease, as these tend to increase with age. For non-adult human remains (that is, those under about 18 years old) determining age-at-death is a relatively straightforward procedure, as teeth develop at known ages. For adults, however, the process is more difficult. Bony changes in immovable joints, such as those of the pelvis or ribs, are sometimes used to determine age-at-death, but these are not very reliable. In the past, people consumed coarse diets that caused their teeth to wear down steadily with age, and this is probably a better way of estimating the age of adults in archaeological populations.
Previous studies in Britain have generally relied on a chart relating dental-wear to age published by Don Brothwell back in 1963. He claimed this chart could be used to estimate age in skeletons from the Neolithic to the medieval period – in the post-medieval period, diets, at least in towns, became much softer so dental-wear was much less, meaning the method was no longer applicable. Unfortunately, neither the details of the method used to create the chart, nor the skeletal remains on which it was based, were ever published. In this month’s ‘Science Notes’, we explore a recent paper that tests some of the assumptions behind Brothwell’s chart and develops a more up-to-date one. This research was conducted by Simon Mays from Historic England, and Sonia Zakrzewski and Sammy Field from the University of Southampton, and was recently published in open-access form in the Journal of Archaeological Science: Reports (https://doi.org/10.1016/j.jasrep.2022.103707).
Developing a tooth-wear chart for a specific skeletal assemblage is relatively straightforward. If you have a large juvenile population (6-18 years old, as permanent molar dentition is required), you first estimate their age based on dental development. You can then assess the degree of wear seen on the first, second, and third molars, which erupt at approximately 6, 12, and 18 years of age. The rate of wear can then be estimated by measuring the difference in wear between each tooth and comparing it with how long each tooth has been in use. For example, by the time the second molar erupts, the first molar has been masticating for roughly six years, while by the time the third molar erupts, the first molar has been in use for 12 years and the second one for six. Once this baseline has been constructed, age can be estimated in successively older adults. For example, an individual with 12 years’ worth of wear on a second molar and six on a third will have an estimated age of about 24 years.
Doing this for every archaeological site is not always achievable, however, because many cemetery excavations do not yield enough burials, especially juveniles. To create a chart that can be used in these circumstances, the team compiled a large database, incorporating 870 adult and juvenile skeletons from 106 archaeological sites across Britain and ranging in date from the Neolithic to the post-medieval period (they included some rural post-medieval skeletons, as it is thought that highly processed foods reached these populations later than urban ones).
Overall, they found that, like Brothwell thought, wear-rates were similar from the Neolithic to the medieval period. They were also similar in the rural post-medieval group. They found that upper molars generally wore at a slightly faster rate than lower ones, but the difference was not sufficient to make it worth drawing up separate age-estimate charts for upper and lower teeth. An imporant finding was that the molar wear-rate was found to be somewhat slower than that reported in the Brothwell chart. The difference was enough to warrant an updated chart, which they supply in their paper, based on their assessments.
The preference continues to be for osteologists to develop their own molar-wear chart for each specific population under study. For British assemblages where this is not possible, however, the team advise osteologists to use the new chart to estimate age- at-death in adults using dental-wear.