Performance and reproducibility of a laser fluorescence system for detection of occlusal caries in vitro

The diagnosis of occlusal caries at non-cavitated sites remains problematic, especially since clinical visual detection has limited sensitivity. Electrical methods of detection show considerable promise, but specificity is reduced. The aims of this in vitro study were: (1) to assess the validity of a new laser fluorescence device - the DIAGNOdent - (and compare the values with those of a fixed-frequency electrical device); (2) to determine the optimum cut-off points of the new device for different stages of the caries process, and (3) to assess the reproducibility of the new laser device. For validity and determination of optimum cut-off points, 105 extracted teeth with macroscopically intact occlusal surfaces were measured by a single examiner, using both the laser fluorescence device (on both moist and dried teeth) and an Electronic Caries Monitor. The teeth were subsequently examined histologically to determine the specificity, sensitivity and likelihood ratio at the D-2 (caries extending through more than half of the enamel thickness) and D-3 (caries involving dentin) levels. The values obtained for the laser device ranged from 0.72 to 0.87 (specificity), 0.76 to 0.87 (sensitivity) and 3.0 to 5.6 (likelihood ratio). Those for the ECM ranged from 0.64 to 0.78 (specificity), 0.87 to 0.92 (sensitivity) and 2.4 to 4.1 (likelihood ratio). To determine intra- and interexaminer reproducibility of the DIAGNOdent, 11 dentists recorded two different measurements at the same site on a separate set of 83 extracted molar teeth, and these were compared using Cohen's kappa (at D-2 and D-3 levels) and Spearman's correlation coefficient. The average intra-examiner kappa scores were 0.88 (D-2) and 0.90 (D-3), with a Spearman correlation of 0.97. For interexaminer reproducibility, the average kappa values were 0.65 (D-2) and 0.73 (D-3), with a Spearman correlation of 0.84. It is concluded that for occlusal caries (1) the new laser device has a higher diagnostic validity than the ECM, and (2) in vitro, measurements using the device are highly reproducible. Thus, the laser device could be a valuable tool for the longitudinal monitoring of caries and for assessing the outcome of preventive interventions.