The durability of primary molar restorations: I. Observations and predictions of success of amalgams.

The durability of amalgams in primary molars was examined retrospectively using an audit of the records of 226 pediatric dental patients attending a dental school clinic. Individual amalgam histories were followed for up to 9 years, computerized, and durability assessed in terms of amalgam replacements and length of service, using compu ter-appropriate definitions for failure and success. The replacement frequency of amalgams was unaffected by the child’s history of exposure to systemic fluoride. Of l 898 first-placement amalgams, 73 % (68 % Class I; 76 % Class II) were successful either to tooth exfoliation or to the end of the study; and 27% were failures requiring replacement due to restoration failure (18% "true" failures) or further extension (9% "false" failures). The highest failure rate was seen among Class II amalgams placed in children younger than 4 years. Regardless of age of child at first placement, true amalgam failures occurred within 18-24 months. In children younger than 4 years at placement, false failures combined with successful amalgams were successful for at least 48 months (mean). Use of these data allowed the statistical prediction that 75% of Class I amalgams in children younger than 4 years at placement would be successful for at least 6 years of service.