STREPTOCOCCUS-MUTANS AND DENTAL-CARIES IN LONG-EVANS RATS WITH A NATURALLY-ACQUIRED ORAL FLORA

From each of 62 litters, one rat was killed 7, 14 and 21 days after weaning and being fed a cariogenic diet. From each rat, plaque was removed separately from 2 buccal and 2 fissure sites on the right lower first molar tooth. Caries was evaluated at the same sites and its penetration into the tooth was quantitated. Streptococcous mutans occurred in about 25 per cent of 726 plaque samples, and was distributed equally among the 4 tooth sites. Similar numbers of carious lesions occurred in rats with and without Strep. mutans, but the penetration of caries tended to be greater when Strep. mutans was present. In rats with Strep. mutans, there was no correlation between the penetration of caries and the number or proportion of Strep. mutans in plaque. Carries in the lower left teeth was assessed by a different method. In those rats harbouring Strep. mutans on the lower right first molar tooth, the incidence of cavitating fissure lesions and the extent of buccal caries tended to be higher in the lower left first and second molars. This investigation (1) indicates that caries initiation in the Long-Evans rat occurs equally with or without naturally-acquired Strep. mutans, (2) demonstrates that Strep. mutans accelerates the early progression of caries, (3) emphasizes the high caries incidence in rats lacking Strep. mutans, (4) suggests that some rat models may unduly accentuate the role of Strep. mutans in caries and (5) draws attention to differences between species of animal with respect to caries and Strep. mutans. © 1978.