Age of failed restorations: A deceptive longevity parameter

There is pressing need to enhance evidence base in respect of longevity of restorations. Currently, there is lack of appreciation of differences between survival data based on the age of failed restorations as compared to gold standard Kaplan-Meier statistics.

This study was undertaken to compare and contrast longevity data for a number of data sets. It investigated if restoration longevity, as calculated by the Kaplan-Meier method, is different from longevity according to the median survival time of failed restorations.

Existing clinical datasets of dental restorations and an artificial dataset were used to calculate longevity according to Kaplan-Meier statistics and by means of calculation of median age of failed restorations.

The findings indicate that median age of failed restorations may be considered as a deceptive measure of restoration longevity. Specially extending the duration of longitudinal studies of restorations apparently leads to higher values for median age of failed restorations. Restorations of materials that tend to exhibit early failures may have lower values for median age of failed restorations, compared to restorations of different materials which tend to exhibit failures later in clinical service, and thereby not giving a true measure of overall restoration longevity.

In absence of all dates of placement and failure for a series of restorations a reliable measure of restoration longevity is not yet available. Kaplan-Meier statistics remains the preferred method of calculating longevity of a group of dental restorations.