Dental anthropology - The use of dental evidence in estimating age at death in human archaeological specimens. - Anthropology - http://maxpages.com/mikeparsons/Dental

A review of age estimation in adult archaeological human skeletons using dental wear.

In this review I will look at the use of dental wear in adult human skeletal remains to estimate an age at death for an individual. This review will be limited to adult archaeological specimens and therefore leave out the use of techniques such as tooth eruption which is an accurate method for use with juveniles.

Although there are methods such as Cement layering,secondary dentine deposition and root dentine transparency for determining age these are not directly concerned with wear and and require destruction of archaeological material in the form of sectioning.

Dental wear is the gradual wearing down of the enamel that encases the crown of a tooth
thus exposing the underlying dentine.This degradation of the enamel happens over a period of time that is dependant on factors such as diet, environment, and other variables that are specific to an individual or population.

McKee and Molnar (1988) state that “ Rate and patterns of wear are governed by tooth
developmental sequences, tooth morphology, tooth size, internal crown structure, tooth
angulation, nondietary tooth use, the biomechanics of chewing and diet.” (White,p311)

Hillson (1986) has outlined two types of dental wear, attrition and abrasion.
Abrasion is wear that is not caused by occlusion, but by food particles and is so small it may be microscopic. Attrition is a more direct form of wear caused by contact between the occlusial surfaces of teeth as well as food. This wear is more obvious especially on molars where food is ground along with any other particles present resulting in obvious wear.

Even though there are many factors that can influence dental wear, it is possible to define a population and create a seriation of all material within it.If the wear in that group is at a steady or known rate an individual can be compared to the overall population and an age estimated relative to the wear exhibited by that population.

The first person to propose a seriation based on attrition was Miles (1963) who worked
with the Anglo-Saxon skeletons from Breedon-on-the-Hill, Leicestershire.Miles created a baseline for his population by using skulls from people young enough to be aged using crown and root development . Once this had been established Miles worked out the eruption timing of later permanent molars in relation to the first molar and subsequent wear of later (second) molar.

The attrition from the first molar was taken to last six years, and twelve before the wear began to show on the second molar, this timing of attrition was then extrapolated to account for wear on older skulls in the collection. By comparing skulls from a known age in the same population Miles was able to determine the age of adults in his group.

Hillson (1986) points out the potential problems with this technique regarding the timing
of molar use after eruption and the rate at which they exhibit wear in a specific individual. Hillson states that microscopic examination of some subjects would give another insight to the age of an individual exhibiting wear patterns that further information is being based on. Also pointed out by Hillson is that the rate of attrition may fluctuate within a population due to different wear patterns of different people within the same group at different times in their lives.

It becomes clear that while Miles’ technique is very useful, assumptions regarding the
dental wear of prehistoric populations should be tempered with evidence from other parts of the skeleton in order to use as much information as possible.

Brothwell (1981) used skeletal material from Neolithic and medieval Britain to compile
an ageing method that looked at the rate of attrition in molars.The chart Brothwell provides shows how molars are useful in this manner as the cusp patterns allow for different levels of attrition to be clearly shown as the dentine gets progressively exposed. Brothwell used ten year increments to categorise the amount of dentine exposed due to attrition ranging from 17-25, 25-35, 35-45, >45.
This technique allows for a less rigid age group and would benefit from multifactorial analysis due to the different rates of wear that a population may exhibit.

W. Bass in Human Osteology highlights this fact and calls for as many factors as possible
due to the different rates of wear that specific diets can cause citing the case of American Indians whose dentition shows a rapid rate of attrition. (Bass,1995.p300)

An earlier method is Gustafson’s technique which uses six variables to arrive at an
average “score” to determine age.Gustafson (1950) devised his method to deal with mature
human skeletons that could not be aged using tooth eruption and development.Although this
technique does use six variables it has problems due to the destructiveness of some aspects of it.Gustafson’s technique uses attrition, secondary dentine deposition, periodontosis (recession of gingivae),cement apposition, root resorbtion (at the apex), and root transparency, to arrive at an age.This technique was later tested by Nalbandian and Soggnaes (1960) and found to be accurate although the root dentine aspect was inaccurate and refined by Johansen (1971).
As with other methods Gustafson’s technique is destructive and of limited use in many archaeological contexts.

The most often used method of evaluating dental wear in adult human archaeological
specimens is the Miles(1963) method.This method of age determination is based on the rate of attrition that has been observed in a baseline within a specific population.This rate of attrition is observed in a juvenile subsample and extrapolated forward using the timing of the molars and their functional age.It is the use of the juvenile base line within a population that gives this method its accuracy as it is the closest reference that can be obtained for comparison.

Only molars are used due to their relatively constant rate of wear, a functional age is
obtained by comparison with the baseline and a chronological age determined. Factors such as diet and cultural practices influence the interpretation of these two ages and it is therefore important to have a population specific baseline.

Howell(1978) tested Miles’ method using skeletal material from the Tepe Hissar
collection that dates to around 2400-1300 B.C. Nowell separately aged the maxillae and
mandibles of 120 adults and 19 juviniles from the collection. The dental ages of the seperated components were compared to each other to test the accuracy of the method.

Howell found that upon comparison the ages for each set of teeth had no significant
differences in their mean ages (r=0.87, p < 0.001). When the differences between the ages of the maxillae and mandibles were tabulated it was found that 66% of the individuals were aged to within two years of each other and 93% to within five years.(Howell,1978.p273) The method was further tested by Howell when he selected a subsample of twenty specimens and aged them using the the Mckern and Stewart (1957) method for the pubic symphasis.It was found that the differences in the mean age comparisons between the first and second ageing of the subsamples were insignificant and showed the validity of the use of the Miles method for this particular site.(Howell,1978.p273) When the population was divided into five subsamples according to age, manner of ageing,and presence or absence of occlusial partners there was again a small but insignificant difference between the mean ages.(Ibid.) A high correlation between the results from the Miles method and the Mckern and Stewart methods is shown in the study with a difference of +1.84 years . Given the high correlation with the post cranial information Howell disusses the validity of using this method in relation to three major assumptions these are; 1,That dental wear is continuous during the functional life of the tooth, 2,That wear on all three molars is at comparable rates through similar states and patterns, 3,Wear and diet are effectively uniform within the population. After stating that the first consideration is a moot point Howell states that these questions are of little consequence due to the “ general,clear progression of degrees and patterns of wear in all three molars” (Howell,1978.p274) It is at this stage important to remember that the strenght of the Miles method is in its population specific nature. Due to the fact that ages are derived from observations of juveniles from that population, wear patterns are assumed to be reasonably consistent. Although there are cultural and genetic factors that can affect an individuals attrition rates Howell noted that the wear of all skeletal material from one site had similar general rates of attrition. The importance of this is stated by Howell and he uses the Australian aboriginees (Murphy1959)and Miles’(1963) anglo-saxons as examples of the differnece in wear rates. In New Zealand, Taylor(1963) looked at rates of dental wear in prehistoric Maori and found them to have specific rates of attrition due to the inclusion of fern root diet in thier diet.(Taylor,1963,p105). Howell beleives in the validity of using the Miles method as long as the limitations of it are realised. One problem is the need to have adequate juveniles from the population to create a baseline, this is important as any error in calculating the emergance of molars and subsequent rates of wear is magnified when older teeth are examined. Also, the sampling strategy needs to be refined to encompass a wide range of people within a population,(rich and poor,old,young) to ensure that the rates of attrition are indeed indicative of the population. This last problem is the reason a demography was not proposed for the Tepe Hissar site as well as accounting for some inaccuracies in using the pubic symphasis It is when the information is tested on postcranial remains that it becomes apparent that this method is accurate once the problems with it are realised.If the information is not used to try and say more than it can , then the Miles method can be a reliable indicator of dental age.Due to the fact that this is an age based on the functional life of the molars it is important to assimilate as much information from any other means such as pubic symphasis etc. I believe that of all the methods for determining age at death from the dentition of archaeological skeletons, attrition provides the best answer.This needs to be used in conjunction with as many other methods on different parts of the skeleton as possible especially the pubic symphysis. So much relies on having an appropriate reference collection on which to base conclusions that a multifactorial analysis is the only way to test the accuracy of these methods. >

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