Dental restoration longevity: survival functions and statistical indices in low and high failure rate groups

A group of 71 patients was examined to determine the longevity of restorations placed at the University of North Carolina School of Dentistry. Patients with an overall restorations failure rate of equal to or greater than 40 per 1000 restoration-yr were categorized as having a "high failure rate" and those below that were considered "low failure rate". An investigation was made to determine statistical differences between these two groups of patients using survival analysis and various statistical indices. Time of exposure and age of patients for both groups were similar. High rate patients had a greater number of anterior restorations and anterior teeth restored. In addition, the number of restorations per tooth was significantly greater in anterior and posterior teeth of the high failure rate group. No single variable was found to account for the differences in the failure rates in the two groups of patients. A prospective study is needed in order to examine possible causes for restoration failures.