Dental Caries

Dental caries in modern humans is among the most common of all infectious diseases. Caries involves the progressive destruction of tooth tissues by microbial activity (i.e. not by attrition, abrasion or erosion). A film (plaque) formed from saliva, food debris and a sample of the normal oral bacterial flora accumulates on the parts of teeth where stagnation is unhindered. Dietary carbohydrates fermented by bacteria (of which, Streptococcus mutans that is known to have co-evolved with modern humans for ~150,000 years is most notable) produce complex gelatinous saccharide-polymers and lactic acid, These adhere to the tooth surface, lower the pH and demineralize enamel and subsequently dentine and or root cementum. Some strains of bacteria are more cariogenic than others and the bacterial composition of plaque in herbivores, carnivores and omnivores differs. For caries to develop the diet must contain fermentable carbohydrates and the right kinds of micro-organisms must be present. Root caries develops only when gingival recession exposes cementum through periodontal disease, a feature of advancing age in many animals. The bacterial flora in root plaque is substantially different to that in crown plaque. Caries in modern humans commonly initiates in occlusal fissures and pits during childhood. Caries in great apes is usually observed later in life when occlusal enamel is lost through wear and approximal enamel that maintains a tight contact between teeth breaks down and allows food and plaque stagnation between teeth. Alternatively, again later in life, root caries becomes common when plaque accumulates on exposed root cementum. In collections of wild-shot apes Gorilla, Pan and Hylobates incisor root caries is common while in Pongo premolars are most affected. Between 2-6% of adult great apes but 13-30% of senile great apes show evidence of carious lesions. The incidence in Pan is greater than in Gorilla or Pongo.