Deterioration of restorative materials and the risk for secondary caries.

This article reviews the literature related to marginal deterioration of amalgam restorations and the risk for secondary caries. Background information on this characteristic material failure is provided, including how it is measured clinically, its rate of progress with time, and the responsible microstructural mechanisms. The association between degree of marginal fracture and recurrent or secondary caries is reviewed in clinical and in vitro studies. Earlier clinical investigations and a more recent laboratory study demonstrated a strong correlation between gap size and recurrent caries for a caries-active environment, supporting replacement of defective restorations for preventive reasons. However, more recent clinical data show the complex and equivocal nature of this association. Poor specificity and validity for detection of recurrent caries with an explorer and mirror further complicate interpretation of some trials and decision-making in clinical practice. Improved methods of diagnosing recurrent caries and further studies of the factors influencing its initiation and progression are needed.