Relationship between S. mutans and the autofluorescence of carious dentin.

PURPOSE: To investigate the relationship between the presence of S. mutans and the autofluorescent signal detected in carious dentin, using confocal laser-scanning microscopy. METHODS: Experiment 1:15 visually caries-free freshly extracted premolars were coated with varnish except for two 2 mm x 2 mm windows; five were subjected to a 15-day bacterial artificial caries system using Streptococcus mutans while 10 underwent a 7-day controlled, lactic acid (0.5 M, pH 2.7) demineralization protocol. At the end of both periods, all teeth were longitudinally sectioned and the 20 bacterial and 40 acid-induced artificial lesions were examined by confocal laser-scanning microscopy. The media containing the S. mutans was also examined for autofluorescence. Experiment 2: 20 750 microm-thick caries-free coronal dentin disks were prepared from 10 healthy premolars. Ten underwent a demineralization protocol using 0.1 M EDTA (pH 4.8) for 21 days. All 20 were finally subjected to the same artificial bacterial caries system as above for 15 days and then examined for autofluorescence using confocal laser-scanning microscopy. RESULTS: Experiment 1 results showed that acid-demineralized lesions did not generate any autofluorescence. Lesions created by the bacterial system did exhibit autofluorescence. The media with or without S. mutans did not exhibit autofluorescence. Experiment 2: bacteria-induced lesions on dentin that had previously been acid-demineralized generated a visibly stronger autofluorescence signal than those lesions grown on sound dentin. It is hypothesized that dentin demineralization during the carious process exposes more matrix to a bacteria-matrix interaction, thus generating or refining the matrix chromophore responsible for the autofluorescence signal detected in carious dentin.