Grey discoloration for the diagnosis of secondary caries in teeth with class II amalgam restorations: an in vitro study.

Grey discolouration around occlusal amalgam restorations has been found to be useful for the diagnosis of secondary caries. The aim of the present in vitro study was to establish the validity of grey discolouration of buccal and lingual enamel next to the approximal amalgam of class II restorations for the diagnosis of secondary caries. One hundred buccal and lingual areas next to the approximal parts of a class II filling in molars and premolars were included in the study. Fifty-one areas showed grey discolouration. Validation was performed against radiographs of transverse sections. Both radiolucencies and radiopacities were scored as being caries. The results were: sensitivity 92%, specificity 55%, positive predictive value 22% and negative predictive value 98%. It was concluded that grey discolouration of the approximal walls next to class II amalgam fillings is not useful for the detection of secondary caries, but the absence of grey discolouration gives a good prediction for the absence of secondary caries. This is in contrast to grey discolouration around occlusal amalgam restorations, which was considered to be useful for the diagnosis of secondary caries.