Thermal behavior of modern and archeological enamel and dentin by in situ temperature-dependent Raman spectroscopy

Teeth and bones are important bioarchives, which can be altered because of diagenesis or burning (cooking, funerary cremations, and fires). Though heating and diagenesis are different processes, an experimental heating of modern bioapatite reproduces in a short time effects similar to diagenetic processes occurring over geological time. The thermal behavior of modern and archeological human enamel and dentin using the in situ thermo-Raman spectroscopy at 83-873 K was investigated to assess the structural changes in organic and mineral components of a tooth and their interrelationship. The nu(1)(PO4) vibrational mode in apatite is the most anharmonic and responsible for the reaction of the structure to external influences. The gamma iP isobaric Gruneisen parameters for archeological (0.41) and modern (0.24) enamel are different from those for fluor- (0.17) and chlorapatite (0.17), which indicates a stronger reaction of P-O bonds in bioapatite PO4 tetrahedra to temperature changes as compared with geologic samples. The anomalies of the thermal dependences of the nu(1)(PO4) peak position and Delta corr(PO4)(T) autocorrelation function are caused by the combined effect of different factors such as breaking of hydroxyl and hydrogen bonds, the loss of adsorbed and structural water, collagen denaturation, organic phase combustion, and removal and relocation of B- and A-type carbonate ions. The thermal (273, 313, 341, and 363 K) and cold (similar to 160 K) denaturation of collagen is reflected in the nu(1)(PO4) and Delta corr(PO4)(T) dependences. The Delta corr(PO4)(T) differences between modern and archeological dentin and enamel are contingent on bioapatite composition (proportions of adsorbed and structural water, hydroxyl and carbonate ions, and trace elements as well as different types of organic matter - low-molecular noncollagen compounds and high-molecular collagen). The results obtained contribute to the knowledge about the thermal transformations of the mineral and organic phases of modern and archeological tooth tissues and allow their structural alterations to be evaluated.

Automated summary

Teeth and bones are important bioarchives that can be altered due to diagenesis or burning. The thermal behavior of modern and archeological tooth tissues was investigated using in situ thermo-Raman spectroscopy, revealing structural changes in organic and mineral components of a tooth.