Linings and caries in retrieved permanent teeth with amalgam restorations

Possible correlations between the presence or position of cavity linings and the incidence of caries were studied in a sample of 57 extracted permanent teeth with amalgam fillings. Linings could be detected if their thickness was greater than approximately 20 microns, and if they were observed on 74% of the teeth. On 53% of the teeth caries were found adjacent to the restorations, and on 11% not adjacent to the restorations. The incidence of adjacent caries on the teeth with lined cavities was not lower than on the unlined ones. In 36% of the teeth with linings, evidence was found for washout of linings which had been present at the cavosurface margin. These teeth showed a significantly higher incidence of adjacent caries than the unlined ones. Carious sites associated with washout of linings were found in 31% of the lined specimens.