A comparison of the microbial flora in carious dentine of clinically detectable and undetectable occlusal lesions.

It is not known whether the aetiology of occlusal hidden caries lesions (HCL) is identical to that of small visible lesions (SVL). Previous studies of the microflora of HCL suggest that relatively few species can be isolated. The aim of the present study was to compare the bacterial composition of dentine from 10 HCL and 17 SVL in a population of children aged 8-18 years. The following bacteria were identified: Actinomyces spp., mutans streptococci, Streptococcus sanguis, Streptococcus oralis, Streptococcus gordonii. Streptococcus mitis, and Lactobacillus spp. Streptococcus mutans was found more often in the HCL group (p = 0.03), while Streptococcus sobrinus was found more often in the SVL group (p = 0.05). However, proportions of both species were lower in the SVL group as compared with the HCL group (S. mutans p = 0.07; S. sobrinus p = 0.03). Lactobacilli and Actinomyces spp. were found at similar levels in both groups. A more diverse range of streptococcal species and Veillonella was found in the SVL group (p = 0.001). These results show a less complex microflora in HCL as compared with SVL, indicating that the aetiology of hidden caries might be different from that of open caries.