DIAGNOdent measurements of cultures of selected oral bacteria and demineralized enamel.

OBJECTIVE: Carious tissue fluoresces with a wavelength different from sound tissue when stimulated by light with a wavelength of 655 nm. This difference is thought to have a bacterial origin rather than indicating demineralization. This study aimed to measure fluorescence emitted by normal cultivable caries-associated bacterial flora and typical porphyrin-producing bacteria with DIAGNOdent, and to verify earlier findings that demineralization of the dental hard tissue does not affect DIAGNOdent readings.
MATERIAL AND METHODS: Bacterial samples were collected from five occlusal caries lesions in three subjects. From these, mixed anaerobic flora, Lactobacilli and mutans Streptococci were cultured in up to three different kinds of culture medium. Colonies of Lactobacilli and mutans Streptococci were also measured after transferring them to glass slides. Laboratory teaching strains of Prevotella spp., Porphyromonas gingivalis and Actinomyces odontolyticus were cultured anaerobically and fluorescence measured directly after an appropriate incubation period. Sound enamel surfaces of 15 extracted premolars were demineralized and changes in fluorescence measured.
RESULTS: DIAGNOdent readings > 20 were only obtained from young colonies of Prevotella and from colonies of mutans Streptococci cultured on mitis-salivarius-bacitracin agar. Higher measurements were obtained as the bacterial colonies aged. Lower measurements were obtained after transferring colonies to glass slides. Demineralization of enamel did not affect the DIAGNOdent measurements.
CONCLUSIONS: The change in fluorescence measured with DIAGNOdent has a bacterial origin rather than occurring as a result of demineralization. The measurements are presumably dependent on bacterial metabolites rather than bacteria themselves, and probably record synergistic effects during the carious process rather than the quantity or species of bacteria involved.