Relationship between the color of carious dentin with varying lesion activity, and bacterial detection

Objectives To investigate the relationship between the color of carious dentin with varying lesion activity, and bacterial detection in the lesions. Methods In 26 extracted human molars with coronal dentin caries and four extracted sound human molars, dentin was removed by a round bur every 150 μm from the dentin surface, in the direction of the pulp chamber. Before and after removal, images of nine-color samples and the dentin surface stained with a caries detector dye (1% acid red in propylene glycol) were taken simultaneously by a charge-coupled device (CCD), and dentinal tissue samples were taken with a new round bur. From the images, corrected L*, a* and b* values (CIE 1976 L*a*b* color system) of the dentin surfaces were calculated from the color changes of the nine-color samples. Bacterial DNA in the dentinal tissues was detected by polymerase chain reaction. Results Before removal of dentin, the L* of sound molars (L* > 50) was significantly larger than that of carious molars (L* < 50) (ANOVA, Scheffeʹs F-test, P < 0.05). In addition, the carious molars were divided into type I (a* > 20, characteristics of active caries) and type II (a* < 20, characteristics of arrested caries), and there was a significant difference in the a* value (P < 0.05). For both carious types, the area under the receiver operating characteristic curve of L* was significantly larger than that of a* or b* (univariate Z score test, P < 0.05), and the rate of bacterial detection decreased as the L* of dentinal tissue increased, and bacterial DNA was not detected when L* was >60. Conclusions Sound and types I and II carious dentin were discriminated by the combination of L* and a* values of dentinal tissue stained with the caries detector dye before removal of dentin. In carious lesions, the a* values of carious dentin stained with the dye were related to the carious lesion activity before removal of carious tissue, and the L* values were related to the degree of caries progression.