Effect of contact media on the diagnostic quality of electrical resistance measurements for occlusal caries

BACKGROUND: Electrical resistance measurements have been used for the diagnosis of occlusal caries. Both site and surface-specific techniques have been described, the latter more suited to clinical trials or epidemiological surveys. For surface-specific measurements the tooth is dried and a contact medium drawn along the fissure pattern to provide an electrical contact between a probe tip and the tooth surface. OBJECTIVES: Different contact media have been used and it was the aim of this study to investigate whether different contact media could influence the diagnostic accuracy and repeatability of surface-specific electrical resistance measurements. METHODS: Electrical resistance readings were taken on 99 molar teeth using saline, KY jelly, toothpaste or dental prophylaxis paste. Readings were repeated on 44 randomly selected teeth. The teeth were serially sectioned and visually examined to establish the deepest lesion if present. RESULTS: The Student t-test showed that there were statistically significant differences between readings taken with different contact media, with the exception of toothpaste and prophylaxis paste, where no difference was found. The strongest relationship between histology and resistance reading was achieved with KY jelly (r = 0.559). The optimum sensitivity and specificity achieved was 0.59 and 0.86, respectively (resistance cut-off 0.1 M(Omega)). ROC analysis showed that the diagnostic performance of saline was significantly inferior to the other contact media (P < 0.05). Limits of agreement were used to assess repeatability which were acceptable for all media except toothpaste. CONCLUSIONS: Differences were found between electronic resistance readings taken with different contact media. KY jelly was found to produce the best overall diagnostic performance and should be the standard material used for surface-specific measurements.