5.5 How are teeth better?

In sum, teeth seem to have greater potential than bone for containing areas of well-preserved tissue, despite extensive attack. This may explain why the analytical success rate concerning ancient DNA has been reported to be higher in teeth (see review in Hollund et al. 2012a), as diagenetic 'niches' within teeth may contain well-preserved DNA (Geigl 2002; Hiller et al. 2004; Hollund 2013; Salamon et al. 2005). However, as can be seen in Figure 9, bioerosion may cause severe destruction of large areas, including the crown dentine, owing to invasions via the pulp cavity. Although none of the teeth in this assemblage showed the most severe level of decay, very few remained unaffected. Only four out of the 34 samples (12%) displayed the best GHI score of 5 (considering both bioerosion and generalised destruction). Furthermore, teeth may be dislocated from the alveolar socket, affected by attrition or severe carious lesions, directly exposing the cementum and dentine to the environment. Adler et al. (2011) recommends the cementum as source material tissue for ancient DNA analyses owing to higher initial DNA concentrations compared to dentine. This would only hold true for exceptionally well-preserved teeth, as the cementum is frequently affected both by biological and non-biological processes of decay. Alternatively, if the invasion is internal, as seen in Figure 8, the cementum/surface areas would be the better material to sample. As such, a recommendation of which part of the tooth to be sampled for archaeometric analyses can only be carried out after diagenetic analyses have established overall preservation and the main agent(s) of decay involved. In our previous paper (Hollund et al. 2012a), we suggested that this can be carried out on the corresponding bone if teeth are not available for diagenetic screening. However, due to intra-skeletal variation in state of preservation and to minimise destruction of unique remains, the ideal would be a sampling strategy adjusted to allow the destruction of only one tooth for several types of analyses, including histology and ancient DNA assays.