Testing Stable Isotopes of Human Dental Calculus as a Nondestructive Proxy for Paleodiet
For over thirty years, bioarchaeologists have used stable carbon and nitrogen isotopes to evaluate the dietary habits of earlier human populations. Given that bone preserves better than skin, fingernails, and hair in most taphonomic contexts, the primary biomaterial used in isotope analysis is collagen. This protein, the organic fraction of calcified bone, is not directly available for analysis so methods used to isolate collagen are destructive. In contrast to collagen, dental plaque is a biofilm that forms on the teeth of humans and other animals. When plaque accumulates and is not removed, it calcifies to form dental calculus. In 2008, calculus was collected from medieval and post-medieval Basque skeletons from Vitoria, Spain with the aim of isolating plant phytoliths. The goal of this project was to determine if researchers could observe directly the introduction of edible plants from the New World to Spain, with special emphasis on maize. Unfortunately, processing calculus samples to find phytoliths was minimally successful. With 58 samples and diminished hopes of finding phytoliths, five calculus samples were sent to the geochemistry lab at the University of Nevada, Reno for stable isotope analysis. The researchers could find no evidence in the literature that anyone had ever attempted to obtain stable isotope signatures from calculus, so they were not optimistic there would be enough carbon and nitrogen to get a good signal from a biomaterial primarily made up of calcium and phosphate minerals. The initial analysis of five samples yielded surprising results. There was more carbon than anticipated, it yielded ratios that could be replicated on repeated trials, and these ratios were close to the values obtained from bone collagen for earlier European populations. When the samples were tested for nitrogen, a similar result was found. There is sufficient nitrogen in calculus to get a good isotope estimate and the results were consistent with values for earlier European populations based on bone collagen. This project does not center on the utility of stable carbon and nitrogen isotopes in paleodietary analysis as that has been demonstrated in hundreds of studies over the past 35 years. The project goal is to determine whether a new biomaterial " dental calculus" can be used to estimate C and N ratios, especially in instances where destructive analysis is prohibited. The key is that calculus is not part of the skeletal or dental system but is an add-on that goes through a cycle of addition and removal (by a dental hygienist) in modern human populations. Prior to dental hygiene, emphasis was more on addition and less on removal so calculus is common on the teeth of earlier humans. While results to date are encouraging, this project will conduct the necessary additional tests to determine if dental calculus can be a consistent and effective proxy for isotope analysis. Calculus samples will be obtained from human groups with divergent subsistence patterns, including Greenlandic Inuit, Greenlandic Norse, classic and colonial Maya, and prehistoric Peruvians, to determine if isotopes from calculus exhibit differences in protein consumption and the varied use of C3 and C4 plants. If consistent results can be obtained, dental calculus might provide a much more accessible source of data and may also avoid resistance by Native American groups to this sort of analysis using destructive analyses techniques on human skeletal remains. The project will validate a method of isotopic analysis that is faster, non-destructive and less expensive than the current standard testing bone collagen, which would be a major contribution to the sub-field of paleo-diet studies.