Comparison of selected microflora of plaque and underlying carious dentine associated with primary root caries lesions.

The composition of the microflora recovered from superficial dental plaque sampled from 81 primary root caries lesions requiring restoration was compared with the microflora of the underlying, infected carious dentine. The numbers of bacteria in the plaque samples were significantly greater than in the dentine samples, and the frequency of recovery of mutans streptococci, streptococci, lactobacilli, gram-positive pleomorphic rods (primarily Actinomyces spp.), and yeasts was not significantly different between the paired samples. However, the proportion of lactobacilli and gram-positive pleomorphic rods was significantly greater in the dentine, while the proportions of streptococci and yeasts did not differ significantly; the proportions of mutants streptococci were similar in both samples. These data indicate that the microflora overlying primary root caries lesions is significantly different from that associated with the infected root dentine. The method of sampling and culturing the microflora of root caries lesions must, therefore, discriminate between the microflora of the superficial supragingival plaque and the microflora associated with destruction of the infected underlying dentine.