Tooth Cementum Annulation

In a comparison with the results accumulated by the morphological age at death analysis, the TCA method, as applied to the Volders archaeological remains, proved to be a useful tool in determining age at death. The results tend to support assertions made by (Kagerer & Grupe 2001a, Wittwer-Backofen et. al. 2004). Incremental line counts provided valuable support, especially in situations where the bone preservation left much to be desired. This method was an important indicator not only for age at death analysis, but also for identifying traumatic events such as bone fractures, events that are visible in the anomalous histological morphology of the cement rings and could be detected in a comparison with known traumata diagnosed on the skeleton acquired during the osteological examination (Kagerer and Grupe 2001b). The morphological method utilized for an age at death estimation still remained necessary for several reasons. Tooth destruction through microbial activity was not uncommon and rendered the affected tooth samples useless for histological analysis. Gross observation during tooth removal yielded no identifiable indicators for the condition of tooth preservation. Only after the tooth had been embedded, sectioned and adhered to a cover slip, was its viability revealed.

Lines were counted manually from the tooth section image on the computer monitor, a print out or directly through the microscope objective. The manual counting of lines proved to be time consuming and required a great deal of precision and patience. Also, it was established

that manual counts were sometimes subject to human error and potentially unreliable, especially during the learning phase, however, experience with the procedure increased reliability dramatically. The computer automated counting procedure was much less time consuming, yet, also showed some weaknesses with respect to counting reliability. This was best illustrated by the experiment involving juvenile individuals of approximate known age which was conducted within the Volders examination to determine the feasibility of the manual counting of incremental lines as compared with the counting ability of the computer program. The superiority of the manual counting procedure quickly became evident, as the automated procedure was shown to overestimate ages in very young individuals. This trend for overestimation was also seen in the elderly. There were also instances where the computer program was unable to provide a count due to inadequate image quality. It was therefore decided that the manual counting procedure results would be used.

Today, highly developed computers in a myriad of areas have the capacity to complete tasks once done by hand and in the process eliminate human subjectivity, error and tedium and there seems to be no end in sight to what the computer is capable of. It is certainly only a matter of time before a simple automated method replaces man as the tool in this procedure. The manual procedure did, however, end up producing the more reliable results, and were often comparable to the morphologically won age at death estimations. As a result of the various situations described throughout the sections devoted to TCA, it becomes clear, that the accuracy of this method for establishing an age at death estimation at this present time, has its foundation not in the perfecting and use of just one procedure (i.e. automated or manual), but in both TCA methods as well as the morphological examination results being utilized in conjunction with one another and so functioning as backups for the foibles each contains.

One of the most valuable assets of this method is the ability to make a relatively reliable assumption about the age at death in the event that bone preservation is poor and insufficient for a morphological estimation. It can contribute valuable information in such situations where previously only a question mark appeared in the anthropological catalogue. The possibility of establishing a chronological age at death quantitatively instead of an age based on biological indicators as seen on the skeleton is an exciting prospect. Although TCA research efforts focused on TCA are striving to develop a sound quantitative method for providing chronological age estimations, yet, the method still remains inextricably bound to biology, relying on a once living tissue for its calculation, and is therefore susceptible to the whims and woes of an organism’s physiology. Awareness of diagenetic effects, mechanical

influences, pathologies, as well as the method’s present weaknesses remains at the moment, paramount when evaluating the age estimations attained. Recently, Renz and Radlanski (2006) indicated that in line counts taken from different sides, i.e. mesial, distal, buccal and lingual, of the same tooth root section, the presence of cementocytes in AEFC, poor line visibility as well as observer error can all result in line count total variability. Although it should be noted, that the images provided by them to support these assertions, which depicted irregularly formed cementum or barely distinguishable lines, would have been excluded from analysis here. Further variables in need of attention are the possible existence of physiologically driven age-related cementum changes that might bias estimates. It is therefore necessary to conduct more known-age studies in an effort to elucidate the effects of aging on cementum histomorphology. In addition, the effects of masticatory loading on cementum production need to be better elucidated (Lippitsch, in prep.). Since one basic function of cementum is to help anchor the tooth in the alveolar socket, it might be inferred that differences in the degree of mechanical stress imposed upon the dental apparatus could result in a variable buildup in incremental layers or in the amount of cementum deposited in each layer. Specifically, it must be clarified whether discernable differences exist between people chewing different kinds of food (e.g. nuts and beef jerky vs. apple sauce and white bread) or between those using their jaws as a clamp for holding objects and as a tool for tearing or stripping fibers with those who do not, which could perhaps be clarified by investigating the cementum layer of individuals displaying temporal-mandibular joint changes.

One definitive and unavoidable drawback to the TCA method is that bioarchaeological material, albeit a relatively small amount, must be sacrificed in order to perform the examination. The decision to physically tap valuable ancient finds or fossil remains should be carefully considered, and some researchers have voiced their concern over the irrevocable loss of material. The question arises if this method should be employed at all in certain instances and if we can’t live with the morphologically based estimates in these special situations until the method is perfected or another better one replaces it. Other procedures such as radiocarbon dating, isotope and trace element analysis, and histomorphological examinations also require the removal of material, and here too efforts are in progress to decrease sample size and reduce the damage incurred.

Aspects of life history seen in incremental lines

Another significant prospect, in addition to providing a true quantitative method for calculating age at death, is the potential of identifying traumatic experiences such as bone fractures based upon the incremental line form itself. Researchers have indicated that

fractures, pregnancies or other physiologically taxing experiences will have a direct influence upon cementum formation. In a study conducted using dental patients whose life histories were well documented, Kagerer and Grupe (2001b) found that in cases where an individual had suffered a traumatic injury or gone through other physiologically taxing circumstances such as a pregnancy, that the cementum layer formation during this period was affected and resulted in a visible alteration of the line as seen histologically. The lighter colored complement to the dark line appears broader, owing perhaps to an extended formation interval due to a reduction in available calcium, phosphate or other minerals required for normal cementogenesis, because they were being used as building blocks to repair damaged or develop new tissues elsewhere in the body (see Fig.10.1).

Figure 10.1. Burial 56, adult female. Several broad, light incremental lines (arrow) can be observed at various points in the section.

A mere three bone fractures were diagnosed amongst the Volders group, a relatively low rate of bone injury for a rural, working medieval population. Burials 61, an adult male who suffered a severe tibial fracture with subsequent anatomical dislocation, and 101, an adult female with a healed fracture of the ulna, both showed abnormally broad light lines at the fifth and sixth, and for burial 101, seventh line from the eruption line, perhaps indicating that the fractures occurred around the ages of 17 and 19 respectively. Images taken from other individuals, males and females alike, also showed similarly broad white lines, however, no causal agent could be identified during the skeletal analysis. Burial 24 contained an adult

male who had suffered a fractured clavicle, yet in contrast to the previous two individuals, exhibited no markedly altered incremental lines. It can be conjectured, however, that should broadened, light colored lines in fact exist, that they perhaps can be interpreted as indicators for the occurrence of traumatic or physiologically trying experiences.

The automated counting procedure software program is a good start towards developing a more reliable and efficacious counting procedure while at the same time alleviating the strain and tedium involved during manual counts. The guarantee of accuracy, however, with respect to the computers ability in deciphering true lines from image anomalies, remains somewhat unclear and certainly represents the aspect of this procedure where refinement is necessary. It is also apparent that the state of tooth root preservation and the image clarity are of no trivial importance with respect to the accuracy of age computations. The use of the maximum line count established by the automated procedure does not appear to be a feasible variable for calculating age at death estimates. The assertion made by Czermak et al. (2006), that the “mode” or line count calculated most often should be used in the estimation of ages, is certainly correct.

The desire to categorize age is quite ancient. The Greek philosopher Aristotle wrote in De Anima II that age can be categorized in three main phases, nutrition, growth and demise. It is a wonderful aphorism, and in retrospect, principally correct and descriptive of the basic physiological and anatomical metamorphosis each person goes through from birth to death, however, for the purposes of today’s bioarchaeological analyses, it is lacking in the requisite conciseness. Age estimations based upon morphological examinations are susceptible to inaccuracies resulting from observer subjectivity, differences in the amount of wear and tear features that create biologically older or younger “looking” skeletons, lack of necessary bone characteristics used in ageing (e.g. cranial sutures, pubic symphysis) and a significant amount of variability in those features. Current attempts focused on improving the accuracy of age determinations in skeletal remains are in full swing, and the quest to develop new methods or refine existing ones like TCA moves on.