Factors Affecting the DIAGNOdent's Ability to Detect Small Occlusal Caries

Objectives: The DIAGNOdent (KaVo, Germany) is designed to identify occlusal caries by detecting the fluorescence of bacterial pigments excited by laser light. Areas of occlusal caries can be deep in the fissure system. This in-vitro study investigated the effect of distance between this pigment and the DIAGNOdent probe-tip on the instrument's reading. Methods: A bacterial pigment (protoporhyrin) in mineral oil dispersion was made that induced a maximum DIAGNOdent reading of 99, when the probe-tip was separated from the dispersion by a cover slip. The effect of changing the distance between the probe-tip and the pigment was investigated. Also the effect of placing moist slices of dentin between the pigment and probe-tip was assessed. In order to determine how distance affects DIAGNOdent caries readings, nonprobeable occlusal caries in extracted human teeth were measured with the DIAGNOdent before and after removing the occlusal enamel. Results: A decrease in DIAGNOdent reading was first detected with a probe-tip to pigment separation of 0.7mm. Increasing the separations to 1.1mm and 1.9mm caused 50% and 75% reductions in DIAGNOdent readings respectively. A 0.67mm thick dentin slice reduced the DIAGNOdent reading 44.4% more than an equivalent separation without dentin. Reducing the thickness of the dentin slice resulted in an increase in DIAGNOdent reading. 12 areas of nonprobeable caries in 5 teeth had a mean DIAGNOdent reading of 30.6±18.6 (mean±SD), when recorded from the surface. Following removal of the occlusal surface, the readings increased to 62.7±31.1. This difference was statistically significant (2-tailed t test p<0.01). Conclusion: DIAGNOdent readings from small occlusal lesions can be reduced by a combined effect of distance and tooth structure separating the pigmented lesion from the instrument's probe-tip. Thus the DIAGNOdent readings are not a measure of lesion severity per se and need to be interpreted with caution.