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 MO). 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. Early caries detection remains a fundamental challenge for both the clinician and the epidemiologist entering into the new millennium. In the adolescent and young adult, occlusal caries presents a specific problem in that it is difficult to diagnose accurately from conventional visual and radiographic examination and yet accounts for the majority of carious lesions. In an attempt to overcome the problem associated with occlusal cariesdiagnosis, research into electrical conductance methods have been carried out (1). Electronic readings are based upon the fact that carious enamel and dentine are more porous than the surrounding sound tooth tissue and, when filled with ions from saliva, result in a lower resistance to a small electric current. The majority of research on electrical caries detection has involved taking ‘site-specific’ conductance readings. These readings are taken with a probe tip centred at the exit of an air tube. The airflow around the probe tip breaks down the superficial saliva film and so prevents conductance to the gingival margin and other areas of the fissure system. The conductance readings obtained are therefore both objective and ‘site-specific’. For the clinician planning an individual patient's care, such specific information is important. However, the epidemiologist and clinical investigator may not require such specific detail of a single tooth and a technique has been described for overall or ‘surface-specific’ electrical resistance readings (2). In this technique an electrical contact medium is spread along the entire fissure pattern, the probe tip is placed anywhere in the contact medium and a single electrical resistance reading is taken. The small electrical current generated will take the path of least electrical resistance through the contact medium and the worse carious lesion along the fissure pattern (if present). Thus a single ‘surface-specific’ objective reading reflecting the status of the worse affected area of the occlusal surface is obtained. A number of contact media have been used to take surface-specific readings. Saline was used in conjunction with the Caries Meter L, a Japanese machine no longer available (3). KY Lubricating Jelly impregnated with a dye (2, 4) and toothpaste (5) have also been used in conjunction with the commercially available Electronic Caries Meter ECM (LODE, Groningen, the Netherlands). However, each of these contact media will have different physical properties such as flow and electrochemical properties such as conductance, which may affect the accuracy and reproducibility of the readings. The aim of this in vitro study was therefore to determine the accuracy and reproducibility of surface-specific electronic resistance readings when used in conjunction with four different contact media on molar teeth.