Survival rates and reasons for failure of posterior composite restorations in multicentre clinical trial.

n a multicentre clinical trial consisting of 12 centres, 232 amalgam and 932 composite Class I and Class II restorations were placed in 447 adult patients. At the 4-year review 76 per cent of patients with 71 per cent of the restorations were retrieved. In 8 centres after 4 years and 4 centres after 5 years a total of 12 amalgam and 92 Occlusin restorations had been replaced, having been considered to have failed. The reasons for failure were classified into three types: Type 1, related to the restoration (loss of material, recurrent caries and unacceptable marginal adaptation); Type 2, related to the restorative process (pulpal involvement, primary caries, tooth fracture and unacceptable contact) and Type 3, caused by external factors. A greater proportion of the restorations of Occlusin were replaced than the restorations of amalgam. For the restorations of Occlusin the reasons for failure were: Type 1, 59 per cent; Type 2, 32 per cent and Type 3, 9 per cent. Loss of material and recurrent caries accounted for the failure of 35 and 13 restorations of Occlusin respectively. The main Type 2 reasons for failure of the restorations of Occlusin were pulpal involvement (16 restorations) and primary caries (9 restorations). The overall 4-year survival of Occlusin restorations relative to Type 1 and to Type 1 + Type 2 reasons for failure was 96 per cent and 93 per cent respectively. The centre was found to have a significant influence on the survival rate in both analyses.