THE EFFECT OF AIR-FLOW ON SITE-SPECIFIC ELECTRICAL CONDUCTANCE MEASUREMENTS USED IN THE DIAGNOSIS OF PIT AND FISSURE CARIES IN-VITRO

There has been renewed interest in the electronic diagnosis of occlusa l caries using measurement of conductance or impedance. One of two pre viously manufactured electronic caries detectors (the Vanguard electro nic caries detector, Massachusetts Manufacturing Corporation, Cambridg e, Mass., USA) had a probe tip with an integral air supply. Airflow is essential for removing superficial moisture and preventing surface co nduction to the gingival margin. The aim of this study was to determin e the effect of airflow on electronic diagnosis of occlusal caries usi ng a prototype electronic caries meter (ECM II. LODE, Groningen, The N etherlands) fitted with a flow meter. Stable conductance readings were taken at 76 discrete sites on 32 extracted teeth with no visible sign s of cavitation, at 3 airflows: 5, 7.5 and 10 litres/min. The stable c onductance scale was a continuous scale from -0.45 to 13.25 and set by the manufacturer. Histological validation was carried out on macrorad iographs of sections cut to include each sample site. The histological picture was compared with the stable conductance readings taken at va rious airflows. Sensitivity and specificity were calculated using diff erent conductance readings to differentiate sound and carious sites, a nd receiver operating characteristic (ROC) curves constructed. Of the sites, 32% had enamel and dentine caries and 33% had enamel caries. Th e ROC curves showed airflow to be highly relevant. An airflow of 5 lit res/min was shown to be inadequate and led to large numbers of false-p ositive diagnoses. A minimum airflow of 7.5 litres/min was required to achieve optimum sensitivity (92%) and specificity (87%) for dentine c aries diagnosis.