Validity of electrical conductance measurements in evaluating marginal leakage around resin composite restorations.

This in vitro study evaluated the influence of the cavity size of restoratives on a new electrical method for detecting marginal leakage. Cavities were prepared on the buccal coronal and root surfaces of 32 extracted non-carious human molars and were divided into four groups having different cavity depths (0.5 approximately 4.0mm) or margin sizes (long axis or diameter: 2.0 approximately 4.0mm). All cavities were filled with resin composites without a bonding system. After physiological saline was applied, then wiped off, the change in conductance was measured continuously across the margin from the composite surface to the tooth surface. Conductance was measured at the same location after filling and before cavity preparation. In coronal and root surface cavities, the change in conductance after filling increased as the depth of cavity increased. There were significant differences in the change of conductance among the three groups with different cavity depths (p < 0.05). The differences between large and small cavity margin groups were not significant for either surface cavities. This method was shown to discriminate between deep and shallow marginal leakage, with the detection of marginal leakage being independent of margin size.