Secondary caries related to various marginal gaps around amalgam restorations in vitro

Secondary caries lesions were produced in vitro by immersing human tooth-blocks with amalgam restorations every third day for 4 weeks in glucose- or sucrose-containing broth inoculated with a strain of Streptococcus mutans. The lesions at the cavity walls were related to various standardized micro-spaces (0, 30, 40, 60 and 80 microns) around the restorations. When a thick, sucrose induced layer of plaque covered the margin, dentine caries was found in all cases where a gap was present (30 microns or more). In the presence of a thin, glucose induced layer of plaque, dentine caries was detected only in the specimens with 60 and 80 microns gap-widths. Caries lesions were detected on the outer free enamel surfaces in all specimens. Lesions in the enamel of the cavity walls were observed with polarized light in 46% in the presence of sucrose- and in 21% in the presence of glucose-induced plaque.