Distribution of dental caries in Yayoi people

The distribution and site characteristics of dental caries previously identified in a Yayoi population using the aforementioned procedure. We examined 5010 teeth, 941 teeth were classified as antemortem teeth, and 998 teeth were classified as postmortal loss (Otani et al., 2009) (Table 1). The number of teeth in each individual ranged from a minimum of 2 to a maximum of 32, with an average of 19.5. The total number of carious teeth was 883, for a cares ratio of 17.6%. The percent of individuals with caries was 79.1%, and the percent of individuals with root caries was 65.8%

Our analyses indicated that among the Yayoi people, most caries occurred in the root area, particularly on the approximal surface of the tooth root (Haraga, 2006). Moreover, Figure 3 shows the distribution of caries by tooth surface. When categorized into 3 groups, namely occlusal, , the occlusal surface percentage was 10.4%, the crown and root were compared, the crown ratio was 37.4% and the root ratio was 52.2%. When Caries location was classified into 9 tooth surfaces as follows: occlusal surface, crown buccal surface, crown lingual surface, crown approximal surface, root buccal surface, root lingual surface, and root approximal surface. The caries frequency was highest in the root approximal surface area, followed in order by the crown approximal surface and root buccal surface, while it was lowest in the buccal and lingual surfaces of both the crown and root.

Number of teeth present

Mean number of teeth present per person(SD)

Number Numbe Number of r of of teeth antemort postmo lost at em teeth rtem teeth unknown timing

Number of carious teeth

Root prevale nce (%)c

5010

65.8

a Rate of caries: Number of carious teeth / Number of teeth present x 100

b Caries prevalence (%): Number of individuals with caries/ Number of individualsx 100

c Root caries prevalence (%)c: Number of individuals with root caries/ Number of individualsx 100

Table 1. Number of teeth present, deciduous teeth, and teeth with caries, and rate and prevalence of caries.

Fig. 3. Distribution of caries by tooth surface

In contrast, we analyzed caries in the Yayoi people and determined the first caries attack site (Haraga, 2006). For determining where caries began in Yayoi people, only caries observed independently on the occlusal surface, crown and root were counted by tooth surface (Figure 4). Large cavities (e.g., spreading in both the tooth crown and root) were excluded from this analysis, and the carious surfaces that were located in only a limited area, such as pits and fissures, crowns, and root surfaces, were determined with certainty as cases. As for the third molar, caries beginning in the occlusal surface accounted for 33.3% in the maxilla and 44.4% in the mandible. Caries beginning in the occlusal surface area were not observed in the upper first premolars and the first molars, the lower first and second premolars, or the first molars. Caries that began in the molars most often originated in the root (70.5% to 86.3%). The percentage of caries beginning in the occlusal surface, crown, and root was

6.9%, 26.9%, and 66.3%, respectively. Thus, most of the molar surfaces affected during the first caries attack were located in the root area. Therefore, these carious lesions may have been initiated in the root area in the Yayoi people. These observations indicate a different pathology from that seen in modern people. Thus, the mechanisms underlying the development of root and coronal caries in the people of the Yayoi period may be different from those in modern people.

Fig. 4. Distribution of "primary caries" by tooth surfaces in Yayoi people

We have presented here the frequencies of carious lesions in younger and elderly people according to tooth type in Yayoi people (Fig. 5). It is clear that the frequncy of carious lesions was higher in the elderly (Haraga, 2006). In the modern Japanese, the caries ratios in the first molars of younger and elderly people are very similar (Fig 6). These findings also support the suggestion that most of the caries was found in the root area in Yayoi people, likely following the establishment of periodontal disease.

The location of dental caries in the people of the Yayoi period differs from that seen in modern Japanese people. In the skeletal remains of the Yayoi, most carious lesions were located in the root area, while in modern populations, most of these lesions are in the crown. This difference is considered to be associated with dietary variation, particularly the consumption of cariogenic foodstuffs. During the digestion of staple foods, such as rice, acid production causes tooth decalcification (Tayles et al., 2000). Moreover, cooked starch is more easily degraded and fermented by bacteria (Lingstrom et al., 1989). The Yayoi people engaged mainly in agriculture, in contrast to their forebears, the Jomon. Indeed, the Yayoi utilized an advanced system of wet-rice agriculture, which supported an increase in population density in western Japan during the Yayoi period. The increase in whole dental caries was associated to a great extent with the increase in root caries.

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