Causes of failure among cuspal-coverage amalgam restorations: A clinical survey

Background. Investigations of cuspal-coverage amalgam restorations suggest that tooth fracture is the leading cause of failure, while for Class I and II restorations, the leading cause is caries. In this study, the authors ev aluated the causes of failure for a large number of cuspal-coverage restora tions. Methods. The causes of failure for 706 cuspal-coverage amalgam restorations were determined through the use of a questionnaire. Dentists from a variet y of dental schools; Army, Navy, Ar Force, Public Health and Veterans Affai rs dental clinics; and private practice were asked to record pertinent info rmation regarding patients and restoration failures from choices provided o n a survey form. Results. The survey documented 706 failed restorations. Mandibular first mo lars accounted for 36.25 percent of all failures. The majority of failures were caused by fractured teeth (24.3 percent), caries (20 percent) and frac tured restorations (17.1 percent). Among all of the failed restorations, 82 .15 percent were restorable, 9.35 percent were repairable and 8.50 percent were nonrestorable. Among the fractured teeth, 80 percent were restorable, 14.5 percent were nonrestorable and 5.5 percent were repairable. Among the carious teeth, 84 percent were restorable, 8 percent were nonrestorable and 8 percent were repairable. A chi(2) analysis revealed that tooth fracture was more likely to be associated with nonrestorability than either caries ( chi(2) = 5.013, P <.05) or restoration fracture (chi(2) = 6.202, P <.05). Conclusions. The leading cause of failure among the 706 restorations was to oth fracture, which resulted in significantly greater numbers of nonrestora ble teeth than either caries or fractured restorations. Clinical Implications. Tooth fracture creates a greater risk of nonrestorab ility than any other cause of failure. Replacement or coverage of fracture- prone cusps is likely to improve the life expectancy of complex amalgam res torations.