Long-term influences on marginal fracture of amalgam restorations.

A clinical study was conducted in which two operators made 180 class I or II amalgam restorations in a group of fifty-seven adult patients. The restorations were made in a series of six per patient. Each restoration was made of a different alloy (five conventional composition alloys and one high copper alloy). During a period of 5 years the marginal fracture formation of all restorations was yearly quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, patient and operator. The relative importance of significant factors was calculated. The results show that for a period of 5 years the alloy, patient and operator all had a significant influence on the marginal fracture formation. The operator influence was stable in time. This factor was relatively small because the operator sample was highly selected. After 1 year the influence of the patient on marginal fracture was equal to that of the alloy. The patient influence in time was stable. However, the alloy influence increased considerably. The longer the service time of the amalgam restoration the more important becomes the influence of the alloy on the marginal fracture formation.