Secondary caries has been often related to the restorative material used. In clinical studies,
failure for secondary caries has been less frequently found for amalgam than composite
restorations. Some factors could contribute to this finding, such as the surface
deterioration of resin composites leading to an increase in surface roughness11 and decrease
in surface hardness, the elution of unpolymerized monomers from composites and dentinbonding
agents stimulating the growth of cariogenic microorganisms, and the
polymerization shrinkage, leading to microgap formation and microleakage.