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Dentists Be Damned

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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).

Sample_Deciduous teeth_Permanent teeth_Total

MkB 894 651 1545

MkK 1103 1790 2893

Pk_823_862_1685

Total 2820 3303 6123

Table 1. Tooth samples for each site

3.1.1 Dental caries

The presence of caries was scored in all tooth types that is to say on deciduous and permanent teeth when detected macroscopically. When there was a doubt on caries development because of the tooth preservation, the development of the lesion was tested by a dental probe.

Four features were observed and scored for the lesions:

• The number of caries per tooth;

• The area & side where the lesion occurred: occlusal, buccal, lingual or interproximal lesions.

• The location of the lesion on the anatomical tooth: the root, the cement-enamel junction (also referred as cervical region or neck), and the crown;

• And finally, the severity of the lesion was quoted on a three-stages scale (fig. 3):

• Stage 1: small lesion which affects only the enamel and less than 10% of the tooth surface;

• Stage 2: medium lesion which affects both enamel and dentin and spread from 10% to 50% of the tooth surface;

• Stage 3: large lesions penetrating all the dental tissues, enamel, dentin and pulp. They take more than 50% of the tooth surface.

These simple stages are easy to define, thus the results of scoring would be less prone to errors, because in archaeological record there are some cases of complex observations (Hillson, 2001), even if we cannot totally avoid subjectivity in such study. This subjectivity is all the more right when we attempt to analyze dental enamel hypoplasia.

3.1.2 Dental enamel hypoplasia

Hypoplastic defects occur in three forms: linear, pitting and plane. However, their expression is different on deciduous and permanent dentition (Lukacs et al., 2001a; Lukacs et al., 2001b; Ogden et al., 2007). We chose to take into consideration the enamel hypoplasia only on the permanent teeth for the quoted features. Nevertheless, a paragraph in the results will be devoted to the different expressions of enamel hypoplasia on deciduous teeth. The presence of macroscopically observed enamel hypoplasia was noted in all types of permanent teeth.

Four characteristics have been recorded:

• The number of hypoplasia per tooth;

• The type of hypoplasia: linear, pitting or plane;

• The severity of the defect on a three-stages scale (only for linear defects) (fig. 4):

• Stage 1: the defect is macroscopically detectable, but is less than 0.1mm width;

• Stage 2: the defect is obvious, but the enamel is not distorted around the line;

• Stage 3: is the most severe with formation of shoving on the enamel surface;

The location of the defect is the third of the affected crown: cemento-enamel junction third, middle third or occlusal third.

Fig. 3. Illustration of the three-stage severity scale for scoring dental caries (photos: V. Gonzalez-Garcin)

Stage 1 Stage 2 Stage 3

Fig. 4. Illustration of the three-stage severity scale for scoring dental enamel hypoplasia (photos: V. Gonzalez-Garcin)

Stage 1 Stage 2 Stage 3

Fig. 4. Illustration of the three-stage severity scale for scoring dental enamel hypoplasia (photos: V. Gonzalez-Garcin)

The distance between the cement-enamel junction and the defect for the calculation of the time of appearance of the defect (Reid & Dean, 2000), was not taken because we only made macroscopical analysis. Charts relative to age differ according to different authors and thus mineralization is not really taken into account. In such large studies, with this method the stages cannot provide accurate chronological sequences (Fitzgerald & Saunders, 2005; Hillson & Bond, 1997; Ritzman et al., 2008). However, a global chart has been made in order to evaluate which developmental stage is the most concerned by enamel hypoplasia.

3.2 Estimating age-at-death

In archaeological samples, the first step for anthropological studies is the age-at-death estimation. This estimation will be useful to compare the different sites, because, dentition is also related to age. Currently, the most reliable methods to estimate an age are those based on dental mineralization and developmental stages (Boldsen et al., 2002; Ritz-Timme et al., 2000; Scheuer & Black, 2000b; Schmitt, 2005). We chose to estimate age-at-death in our sample with the method of Moorrees et al. (1963a,b), because we are working on teeth and we wanted a uniform method and no combination of several methods. Moreover, we just needed some different stages to compare our sites, that is why we classified the individuals in 5 age classes (usually used in historical demography): 0, 5-9, 10-14, and 15-19 years.

A last comparison has been made using the dental mineralization sequences. This approach use the mineralization stages of Moorrees et al. (1963a,b), as a base for determining a dental sequence. These basic sequences (one for each individual) are in a second time grouped following the big tooth developmental phases in order to simplify the data (many combinations are possible). Six final groups are defined and used for comparison:

• Group 1: from the beginning of deciduous crown formation to the end of the emergence of all deciduous teeth;

• Group 2: latency period of deciduous teeth. The permanent incisors and the first permanent molars complete their crown formation.

• Group 3: this group corresponds to the mixed dentition. The first deciduous teeth are replaced by permanent incisors (most standard sequence). The first molar emerges anatomically*. This is the first step of permanent teeth emergence.

• Group 4: stability period where the roots of permanent teeth (incisors and first molars) complete their formation. The roots of the other teeth just initialize their mineralization.

• Group 5: secondary phase of tooth emergence for permanent canine, premolars and second molars.

• Group 6: completion of the permanent dentition (except third molars which were not taken into account.

The illustration of the six resulting groups is presented in fig. 5.

3.3 Statistical procedures

The analyses were performed in three steps. First, in order in order to calculate the frequencies of dental enamel hypoplasia, the total number of available teeth, fully erupted and/or isolated, has been used for observation. Tooth germs in both the mandible and maxilla were not taken into account. With the same objective, frequencies of dental caries were calculated using only the teeth in occlusion. The usual calibrations (Erdal & Duyar, 1999; Hillson, 2001; Lukacs, 1995) adjusting the proportions of tooth type and ante mortem tooth loss were applied.

In a second time, inter-population comparisons were conducted using the non-parametric x2 statistical. Finally, we studied the interrelationship between caries and hypoplastic defects

* The emergence is a localized phenomenon, which corresponds to the appearance of the tooth in the mouth. We distinguish the clinical emergence where the tooth pierces the gingival tissue from the anatomical emergence where the tooth passes over the alveolar bone.

in order to evaluate the role of enamel structure on caries development. All statistical procedures and calculations were carried out by using Statsoft® Statistica version 7.1 and Microsoft® Office Excel 2007.

Fig. 5. Representation of the established groups from the dental mineralization sequences (adapted from Ubelaker, 1978)

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