Validity of clinical judgements for the presence of secondary caries associated with defective amalgam restorations

Eighty patients were selected, who were each deemed to require the replacement of a defective amalgam restoration. The patients had a mean age of 36.7 years and were dentally fit on average 40 months previously. The main reasons given for the replacement of the defective restorations were perceived radiographic secondary caries (31%), fracture of the restoration (20%), marginal defect (17%), and perceived secondary caries observed clinically (14%). Following the removal of the restorations, a highly significant relationship was found between the consistency and colour of the underlying dentine (P < 0.00001). Soft dentine was found underlying 36 (88%) of the 41 defective amalgam restorations which were diagnosed as having caries associated with them. However, hard dentine was found underlying only 19 (49%) of the 39 teeth where no caries had been diagnosed. The presence of soft dentine where not anticipated was mainly in association with fractured restorations (11 out of 16). Younger patients were more likely to have soft dentine underlying their defective amalgam restorations than older patients (P = 0.005). No relationship was found between the presence of corrosion products on the cavity walls associated with defects and the consistency of the underlying dentine.