Objectives: To investigate the number and potential activity of cariogenic bacteria (Lactobacilli) remaining in affected dentin after caries removal with a polymer bur system. Methods: One-hundred and seventeen dentinal caries lesions were selected. After removal of unsupported enamel, carious dentin removal was standardized using a polymer instrument in 81 cavities, while 36 lesions served as control group with no dentin removal. Dentin sampling was standardized using a moistened #4 round bur at 350 rpm. The samples were processed for qPCR and RT-qPCR analyses to determine bacterial cell numbers and potential activity, respectively. The Lactobacilli were identified using specific primers, (5'-CTC AAA ACT AAA CAA AGT TTC-3' and 5'-CTT GTA CAC ACC GCC CGT CA-3'), designed based on a conserved region of 16S rDNA. The obtained data was calculated using a standard curve with known bacterial DNA numbers. The comparison of Lactobacilli cell numbers within the two groups was assessed by the Mann-Whitney test (p<0.05). The bacterial activity was analyzed descriptively. Results: All control group samples presented detectable numbers of Lactobacilli, while 56.7% of the test group was below detection level (p<0.001). The average number of detectable bacteria was 1.88E+4 and 6.80E+3 in the control and test groups, respectively. The RT-qPCR revealed that all samples in the control group presented detectable level of activity, expressed in mRNA number (3.67E+5), while no activity was detected in the test group. Conclusion: The self-limiting polymer system for caries removal effectively reduced the number of Lactobacilli in the residual affected dentin. In part supported by NIH-DE013298 , CAPES–BEX 340404-8 and SS White USA.

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