Isotope analysis of human dental calculus δ¹³CO₃²⁻: Investigating a potential new proxy for sugar consumption

Rationale Dental calculus (mineralised dental plaque) is composed primarily of hydroxyapatite. We hypothesise that the carbonate component of dental calculus will reflect the isotopic composition of ingested simple carbohydrates. Therefore, dental calculus carbonates may be an indicator for sugar consumption, and an alternative to bone carbonate in isotopic palaeodiet studies. Methods We utilised Fourier transform infrared attenuated total reflectance analysis to characterise the composition and crystallisation of bone and dental calculus before isotope analysis of carbonate. Using a Sercon 20-22 mass spectrometer coupled with a Sercon GSL sample preparation system and an IsoPrime 100 dual inlet mass spectrometer plus Multiprep device to measure carbon, we tested the potential of dental calculus carbonate to identify C4 resources in diet through analysis of δ13C values in paired bone, calculus and teeth mineral samples. Results The modern population shows higher δ13C values in all three tissue carbonates compared to both archaeological populations. Clear differences in dental calculus δ13C values are observed between the modern and archaeological individuals suggesting potential for utilising dental calculus in isotope palaeodiet studies. The offset between dental calculus and either bone or enamel carbonate δ13C values is large and consistent in direction, with no consistent offset between the δ13C values for the three tissues per individual. Conclusions Our results support dental calculus carbonate as a new biomaterial to identify C4 sugar through isotope analysis. Greater carbon fractionation in the mouth is likely due to the complex formation of dental calculus as a mineralized biofilm, which results in consistently high δ13C values compared to bone and enamel.1 Introduction 1.1 Dental calculus and potential for isotopic analysis 2 Materials and methods 2.1 Materials 2.2 Methods 2.2.1 FTIR with attenuated total reflectance (ATR) 2.2.2 Bone collagen extraction 2.2.3 Bone preparation for carbonate analysis 2.2.4 Enamel preparation for carbonate analysis 2.2.5 Dental calculus preparation for carbonate analysis 2.3 Analytical measurements 2.3.1 Bone collagen 2.3.2 Bone, enamel and dental calculus carbonates 2.4 Suess effect correction 2.5 Statistical analysis 3 Results and discussion 3.1 FTIR-ATR analysis of bone and dental calculus 3.1.1 Infrared splitting factor 3.1.2 Carbonate-to-phosphate ratio (C/P) 3.1.3 IRSF and C/P relationship 3.2 Isotopes 3.2.1 Correlations between tissues 3.2.2 Carbonate δ13C tissue offsets 3.2.3 Dietary interpretation from the three types of tissues 4 Conclusion