The electronic diagnosis of caries in pits and fissures: site-specific stable conductance readings or cumulative resistance readings?

A prototype electronic caries meter (ECM II; LODE, Groningen. The Netherlands) was designed to deliver a conductance reading when the reading had remained stable for 3 consecutive seconds. The aim of this study was to determine whether this type of stable conductance reading was optimal for caries diagnosis. The ECM II was connected to a graphic recorder which enabled the continuous resistance to be recorded. The graphic recording was calibrated using a standard, variable resistance box. Stable conductance readings were taken for 76 sites on 32 extracted teeth with no visible sign of cavitation at an airflow of 7.5 l/min. Simultaneous graphic recording of resistance was continued for 10 s and cumulative resistance measurements were calculated by adding the resistance values at 1-second intervals. Histological validation of caries status was carried out on macroradiographs of sections cut to include sample sites. The histological picture was compared with the stable conductance reading and the cumulative resistance value for each site. Sensitivity and specificity values were calculated by randomly choosing stable conductance and cumulative resistance values to differentiate sound and carious sites. The results were presented as a series of receiver operating characteristics (ROC) curves and the optimum sensitivity and specificity values determined. 33% of sites had enamel caries and 32% had enamel and dentine caries. Results showed that both stable conductance readings and cumulative resistance measurements gave high and comparable sensitivity and specificity values for the diagnosis of dentine caries (sens. 92%, spec. 87% and sens. 88%, spec. 81%, respectively). However, when intra-examiner reproducibility was checked, stable conductance readings were more repeatable and achieved in shorter clinical time. In conclusion, stable conductance readings appear to be the most suitable for occlusal caries diagnosis.