Diagnosis and staging of caries using spectral factors derived from the blue laser-induced autofluorescence spectrum

Objective: The aim of this study was to identify the factors derived from the 405 nm laser-induced autofluorescence (AF) spectra that could be used to diagnose and stage caries. Materials and methods: Teeth (20 teeth per stage) were classified as sound, stage II, III, and IV based on a visual and tactile inspection. The specimens were re-examined and reclassified based on micro-CT analysis. From the teeth, the AF was obtained using a 405 nm laser. Three spectral factors (spectral slope at 550-600 nm, area under the curve at 500-590 nm, and two-peak ratio between 625 and 667 nm) were derived from the AF spectra. Using these factors, the diagnosis and staging of caries were tested, and the results were compared with those of DIAGNOdent. Results: After micro-CT analysis, only 13, 11, and 13 teeth were reclassified as stages II, III, and IV, respectively. The reclassified groups showed less data overlap between the stages, and the spectral slope was 40.1-74.6, 27.5-39.6, 11.1-27.4, and 1.0-9.7 for sound, stage II, III, and IV, respectively. The differentiation of stages III and IV using DIAGNOdent appeared to be difficult due to the considerable data overlap. Conclusion: Among the factors tested, the spectral slope at 550-600 nm showed the best match with the caries specimens, in which their stage had been identified precisely. Clinical significance: The 405 nm laser-induced AF spectra can be applied to the diagnosis and staging of caries alone or in conjunction with conventional methods, such as visual, tactile, and X-ray inspection.