**3. Methods**

This study is only based on dental health and lifestyle and on the potential influence of the socioeconomic status on caries prevalence and enamel composition. However, it has been completed by an analysis on the same influence but on bone growth and composition.

The resulting dental sample consists of 6123 observed teeth. Table 1 gives the details for each sample.

#### **3.1 Recording dental health and defects**

In dental stress and caries assessment it is clearly desirable to record the least subjective stages and observations, in order to minimize the intra- and inter-observer errors (Danforth et al., 1993), both of which are often significant. The intra- and inter-observer error, for the protocol proposed below, has been tested and has been published in a previous paper (Garcin et al. 2010). As the protocol is the same in this study, we do not remind the results but we expose the features quoted and the statistical procedures employed for comparisons.

Both dental caries and enamel hypoplasia have been recorded because they give different information on enamel susceptibility to develop lesions. International dental charts were used to identify the teeth (such as n° 18 to 11 for upper right permanent teeth).


Table 1. Tooth samples for each site
