5.2 Generalised destruction, infiltrations and inclusions

Chemically similar to bone, dentine and cementum are also sensitive to mineral dissolution, in extreme cases suffering complete destruction of the microstructure and subsequent cracking (large cracks) and loss of material as seen in Figures 45, 46 and 47. However, the tooth in Figure 45 provides a striking example of how well the enamel protects against non-biological decay, retaining a pristine area directly beneath the protective enamel crown despite severe destruction of the root. Furthermore, the cementum and dentine are, like bone, prone to infiltration of both organic (e.g. humic factors) and inorganic (e.g. iron oxides) material, often observed as staining. In several well-preserved teeth the staining occurred only in the cementum. Various minerals, organic inclusions and other types of material from the surrounding soil may fill cavities, pores and cracks in the tissues. The presence of manganese/iron stains and inclusions within the teeth studied is not surprising, as both elements are commonly found within bone pores (Williams and Potts 1988). The precipitation of manganese in nature is primarily controlled by microbial activity (Toner et al. 2005) and several of the inorganic inclusions observed are probably biominerals, as indicated by close association with fungal remains and empty bacterial MFD (Figures 23, 33, 42). This is interesting as size, morphology and structure of such minerals may be characteristic of different microbial species (Santelli et al. 2011). This may be an as yet unexplored source of taphonomic information in archaeological skeletons.

In Hollund et al. (2012a) we showed that teeth were markedly better preserved in terms of generalised destruction based on higher average values for the General Histological Index than the bone samples. Only a couple of teeth display what could be called micro-fissures, similar to those found in bone. However, these are most likely sample preparation effects. The reason for the lower occurrence of micro-fissuring in teeth compared to bone is unknown but may relate to differences in microstructure and the often better preservation of the organic phase. Turner-Walker (2011) found that tensile strength of bone was dependent on collagen content, lower collagen content giving lower tensile strength, consequently making the material more prone to cracking. In addition one could imagine that the physical protection offered by the enamel and the location in the alveolus limit expansion and absorb some of the impacting forces.