Electrical conductance measurements are being used experimentally to diagnose caries. Current equipment, e.g. the electronic caries monitor (ECM), uses a probe to scan occlusal fissures. For full-mouth examination this method is rather time-consuming. A method with which only one measurement is needed for an entire (occlusal) surface would be preferable. However, the enlargement of the area being measured will influence the conductance. It was the purpose of this study to investigate the relationship between the electrical conductance of human teeth and the enamel electrode area, and to compare the range of results of surface measurements with those of the scanning method. Twenty-five sound extracted teeth were selected for the study. The reference electrode of the ECM was connected to the roots. The buccal surface was blotted dry, and a coloured dentifrice was syringed in increments onto the surface. After each increment the surface was photographed together with a metric reference, a conductance measurement was performed by holding the ECM probe tip in the dentifrice, and the ECM reading was recorded. For each tooth between 5 and 10 increments were applied and measured. The photographs were digitised and the electrode areas were calculated. A least squares curve fitting procedure yielded a linear relationship between conductance and electrode area (0.88 ≤ R² ≤ 1.0, mean R² = 0.97). For most teeth the threshold for dentinal caries as used for scanning ECM measurements (ECM reading = 6.00) was reached only when the electrode area exceeded 12 mm2. For 6 teeth this conductance was already reached between 5 and 12 mm². Electrical conductance measurements of the occlusal surfaces of 18 teeth, with electrode areas as projected two-dimensionally of between 5 and 10 mm², showed only 3 measurements above the threshold. None of those 3 came from the group of 6 teeth mentioned before. It was concluded that the relationship between electrical conductance of teeth and electrode area is linear. It was also concluded that when electrical conductance measurements of occlusal surfaces are to be made, the threshold for dentinal caries will probably have to be shifted to a higher conductance level to limit false-positive results.

The use of sealants and sealant restorations has increased considerably over the past 10 years, and with it increased the problem of detecting secondary caries and marginal (micro)leakage. It was the purpose of this study to investigate the validity of electrical conductance measurements (ECMs) in diagnosing marginal leakage into dentine of sealants and sealant restorations. Ninety extracted premolar teeth were divided into three groups. Initial ECMs, denoted ‘baseline ECMs’, were conducted in all three groups by placing the probe tip of an Electronic Caries Monitor in the occlusal fissure which was filled with a dentifrice. The ECMs were divided by the area, yielding ECM/mm2 values. In group A 30 teeth were treated to receive ‘nonleaking sealants’. In the 30 teeth of group B a narrow groove was cut at the occlusal surface reaching the dentine and restored by the application of a sealant without etching of the adjacent enamel to create a high probability of marginal leakage. The samples in group C received the same treatment as those in group B, but in this group the enamel was etched to reduce the probability of marginal leakage. The ECMs subsequently conducted were denoted ‘sealed/restored ECMs’. Teeth in groups B and C were thermocycled 700 times (4–67°C) to provoke leakage, after which ECMs were conducted (denoted ‘ECMs after thermocycling’). The teeth were immersed in fuchsin for 24 h and cut along the fissure system to validate marginal leakage. The electrical conductance decreased significantly from baseline to the sealed/restored stage in all groups (p < 0.05). The electrical conductance per unit area increased in groups B and C after thermocycling. The electrical conductance, irrespective of area, increased significantly after thermocycling (p < 0.05) only in group C. The sensitivities of ECMs per unit area and ECMs were 0.98 and 1.00, respectively, and the specificities were 0.77 and 0.79, respectively. The areas under the receiver operating characteristic curves of ECMs per unit area and ECMs were 0.94 and 0.96, respectively There was no significant difference between the areas under both curves (p > 0.05), denoting that ECMs need not necessarily be expressed relative to the area of the electrode. It was concluded that marginal leakage into dentin of sealants and sealant restorations can be accurately detected by ECM.