Bacterial composition and red fluorescence of plaque in relation to primary and secondary caries next to composite: An in situ study

Background/hypothesis: Secondary caries has been suggested as the main reason for restoration replacement. We hypothesized that more caries-associated bacteria are found on composite resin restoration material, compared to sound tooth tissue.
Methods: Both restored and unrestored dentin and enamel samples were placed in a full denture of eight subjects for 20 weeks. The microbiological composition of approximal plaque and the association between caries-associated bacteria and red autofluorescence of dental plaque was studied. Every 4 weeks the specimens were microradiographed using transversal wavelength independent microradiography (T-WIM). After 1 and 20 weeks red fluorescence pictures and plaque samples were taken. Samples were cultured for total anaerobic counts, mutans streptococci, lactobacilli, candida and Actinomyces odontolyticus.
Results: Lesion depth in the dentin and enamel was positively associated with lactobacilli, and lesion depth in dentin was positively associated with A. odontolyticus, whereas no association was found between mutans streptococci and lesion depth. The red-fluorescent bacteria A. odontolyticus and lactobacilli did not correlate with red-fluorescent plaque, indicating that red fluorescence is probably not caused by a single species of these bacteria. After 20 weeks, a higher proportion of combined mutans streptococci and lactobacilli was found on restored tissue compared to non-restored tissue (P = 0.04).
Conclusion: The higher proportion of caries-associated bacteria on restored tissue indicates that the ecology on the surface of primary lesions differs from that on lesions next to composite, and that secondary caries next to composite may differ from the primary caries process.