Three main topics will be discussed in this last part. The first one deals with the assets and the drawbacks of archaeological collections in a study of dental health. The second develops the influence of socioeconomic status on dental mineralization. And finally, we will discuss the differential enamel susceptibility to be affected from defects and lesions.
5.1 Archaeological collections: assets and drawbacks in the study of socioeconomic influence on dental health
There are many studies on the influence of lifestyle and/or socioeconomic status on dental health (Bodorikova et al., 2005; Duray, 1990; Kim & Durden, 2007; Vodanovic et al., 2005). However, they concern both living and past populations. Moreover, the protocol of observation and statistical analyses differ from one to another. Thus, it is very difficult to compare the results and to be confident in our interpretations. That is why we chose to work only on huge archaeological samples, even if they also have some downsides. The tooth sample size in archaeological collections are mostly important (several hundreds of teeth), especially for medieval cemeteries. Large burials places are excavated, giving many individuals, including juveniles. The sample size is sufficient to provide reliable statistical results. Nevertheless, regarding the bone and teeth preservation, data are as often as not missing, and we do not have all dentition for each individual (Duyar & Erdal, 2003; Hillson, 2001). That is why different calibrations are calculated to adjust the frequencies and to take into account the missing data.
The second advantage of archaeological collection is that we can have homogeneous collections, that is to say that population of a same cemetery comes from a global same lifestyle and the admixture (thus the influence of genetic part) is less pronounced than in living population. However, in such collection, we have the problem of age-at-death estimation. When studies based on living populations have accurate age of the subjects under study, in our case estimations (even with reliable methods) give at best age classes (Albert and Greene, 1999; Cole, 2003; Heuze & Cardoso, 2008; Lewis & Gowland, 2007). This study uses a little the age-at-death estimation that is why we try to free from this bias using dental mineralization stages. The obtained results and differences highlighted show that this is a way to work to enhance the quality and reliability of our study.
The third point to discuss also deals with reliability, but on the recording methods. It has been mentioned in the second part of this chapter that we have evaluated the intra- and inter-observer error of our protocol for both caries lesions and enamel hypoplasia. To go back on the terms of Ulijaszek & Lourie (1997), we must compare something comparable. Yet, recording dental caries and enamel hypoplasia is always a little bit subjective. The data must be as quantitative as possible and thus at least qualitative (Landis & Koch, 1977). The results of intra- and inter-observer errors in our last study (Garcin et al., 2010), show that even if the results are satisfactory, we cannot completely be completely free from this bias (Berti & Mahaney, 1995; Danforth et al., 1993; Hillson, 1992).
Being aware from these main biases, we can discuss the influence of socioeconomic status on dental health and development.
5.2 Have you spoken of a possible socioeconomic influence on dental health and development?
Our results show that except an inferior global prevalence of LEH and less invading caries in the higher socioeconomic status collection, there is no difference between the individuals of Mikulcice. On the other hand, Prusanky individuals differ from the other more often, especially on dental caries. Do these results intend that the lifestyle have more influence on dental health than the socioeconomic status? We explained in the materials paragraph that it is quite difficult to define a clear socioeconomic status in archaeological populations even if they are relative homogeneous. To answer clearly this question in the big site of Mikulcice, it should be interesting to compare all parts of the area. However, comparing the prevalence of LEH in other mediaeval/modern groups in Europe (Coulon et al., 2008; Herold, 2008; Slaus et al., 2002) it is apparent that our values are relatively low, but overall features are similar to the other studies. It is the same for the caries lesions even if the results are hardly comparable (Espeland et al., 1988; Rudney et al., 1983; Watt et al., 1997; Williams & Curzon, 1985). Nevertheless, our results counteract several other studies (on past and present populations), which claim that the socioeconomic status influence the health (Goodman et al., 1988; Hauser, 1994; Henneberg et al., 2001; Kim & Durden, 2007). Although a direct parallel is difficult, this is a striking result. We must keep in mind the limits of such studies and thus accept that we give only trends, especially on the relationship between the dental development and the socioeconomic status. To our point of view, in past population, we should take into account the global lifestyle rather than searching to define a clear socioeconomic status. Besides we found in our last studies clear differences between rural and urban lifestyle, what was confirmed by many studies (Betsinger, 2007; Budnik & Liczbinska, 2006; Riva et al., 2009; Van de Poel et al., 2007; Williams & Galley, 1995). We also must take in mind that in past population, we must deal with the "osteological paradox" (Byers, 1994; Wood et al., 1992; Wright & Yoder, 2003). The juvenile individuals we study are those who have not survived and who have never reached the adulthood (Saunders & Hoppa, 1993). On the contrary, the individuals showing dental defects and lesions survived sufficiently a long time to develop the trait we wanted to record. Thus, healthy past populations are not necessarily those who the most suffer from biological stress and who had the best dental care. That is why it is interesting to focus on biological traits only, avoiding abusive interpretations. The relationship between dental development and health seem to be a good track to go into in depth.
5.3 Dental mineralization, enamel susceptibility, and health
Until now, relatively few studies have considered the possible relationship between enamel hypoplasia and dental caries (Khan et al., 1999; Schneider, 1986; Sweeney et al., 1969; Walker & Hewlett, 1990). Even if tooth susceptibility is different for the two indicators, we could imagine that enamel with defects is more sensible to bacterial attacks. This hypothesis was examined by establishing a chart given the frequency by age class having one of the traits or both traits under study (Table 5).
This table clearly shows that there is slight correlation between caries and hypoplasia. Indeed, the individuals of Mikulcice Kostelisko and Prusanky can develop both traits in the same time but it is not a sweeping statement. Only older age classes (after 5 years old) show the possible relationship, but most of the defects and lesions appear separately. What is striking is that the individuals having the localized hypoplasia on deciduous teeth also have LEH on permanent teeth, and also caries lesions. This caries susceptibility seem to be related to hypocalcified teeth (Duray, 1990), and repeated stress periods. This observation was also made in several studies, but not only on human but also in Great Apes (Lukacs, 1999a; Lukacs, 1999b; Lukacs, 2001; Skinner & Goodman, 1992). Moreover, most of the authors link this observation to a low nutritional status (Noren, 1983; Skinner & Hung, 1989; Sweeney et al., 1971; Taji et al., 2000). Even if genetics mainly lead dental development, the environmental conditions and stress periods also influence the dental mineralization and thus the enamel susceptibility to be affected by caries. Even if it is difficult to demonstrate, it seems that after passing a certain threshold, the underlying aetiological factors resulting in caries and enamel hypoplasia interact, creating a vicious cycle - physiological balance is disturbed through pathogens and inadequate nutrition, compromising metabolism and the immune system. This makes the afflicted individual susceptible to further infections and ultimately even more unable to cope with additional stresses (Obertova, 2005; Obertova &
Thurzo, 2008). This last remark corroborates our comparisons with the biological groups, which show that juveniles are more likely to develop both traits on permanent teeth.
Even if this study raises only some trends and being aware of its limits, we do not want misinterpret, the relation to age and indirect influence of the socioeconomic status on defects and lesions are obvious. We must find now the methodological and theoretical framework to prove them.
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