BACKGROUNDStreptococcus mutans (S. mutans) is the prime pathogen of dental caries. There are few reports that studied the relationship between S. mutans, bacteria and dental caries in permanent teeth when compared to those in primary teeth. This study aimed to detect S. mutans and bacteria of dental caries and non-caries groups in permanent teeth from a north China population by real-time polymerase chain reaction (PCR) and compare the relationship between the number of these bacteria and the prevalence of dental caries in permanent teeth.

METHODSHuman saliva samples were collected from 142 subjects with permanent teeth. According to their dental tooth (DT), 142 subjects were divided into a dental caries group (DT ≥ 1) and a non-caries group (DT = 0). With specific primers for S. mutans and 16S rRNA, the total number of S. mutans and total bacteria of 142 saliva samples were detected by real-time PCR and statistically analyzed.

RESULTSThere was no significant difference between the detection rates of S. mutans (P = 0.118) and medians of S. mutans (P = 0.115). The ratio of S. mutans to total bacteria in people with dental caries was significantly higher than in those without caries (P < 0.001), but the total number of bacteria in people with dental caries was significantly lower than in those without caries (P < 0.001).

CONCLUSIONSS. mutans had different effects on caries in the permanent teeth of several individuals from a north China population. The ratios of S. mutans to total bacteria in saliva detected by real-time PCR with Sm479F/R and 16S RNA primers were closely associated with the prevalence of dental caries in the same population. These assays may be useful for the assessment of an individual's risk of dental caries.