Incidence of fractures and lifetime predictions of all-ceramic crown systems using censored data

Purpose: To determine Kaplan-Meier survival estimates and Weibull lifetime predictions for four all-ceramic crown systems from long-term data (>5 yrs) . Materials and Methods: Single unit crowns of Cerestore (n=30), Dicor (n=3 0), Hi-Ceram (n=22) and In-Ceram (n=68) were placed in 95 patients treated in a university clinic. They were cemented using glass-ionomer (GI) for Cer estore, zinc phosphate (ZP) for Dicor, and 75% ZP (n=51), 20% GI (n=13) and 5% resin-based cement (n=4) for In-Ceram crowns. The follow-up times were 8 yrs for Cerestore, 7 yrs for Dicer, 6 yrs for Hi-Ceram and 5 yrs for In-C eram. The statistical analyses were based on censored data sets. A progress ively censored Weibull distribution allowing for lifetime predictions beyon d the actual observation time was used as well as the Kaplan-Meier Survival Product Limit Estimate (PLE), which provides survival estimates up to the maximum time of follow-up. Results: Cerestore, Dicer and Hi-Ceram demonstra ted molar fractures in the first 2 yrs, whereas for In-Ceram these occurred during the third and fourth year of the study. The Kaplan-Meier Survival P LE was 69% for Cerestore at 8 yrs, 86% for Dicer at 7 yrs, 81% for Hi-Ceram at 6 yrs, 92% for In-Ceram at 5 yrs. The predicted Weibull characteristic time To (time at which 63% of the restorations would have failed) was 23 yr s for Cerestore, 34 yrs for Dicer, 31 yrs for Hi-Ceram, and 16 yrs for In-C eram. However, when using data sets arbitrarily limited to the three first years of follow-up, To decreased significantly for Cerestore, Dicer and Hi- Ceram due to the number of early fractures. Such Weibull lifetime data illu strate the risk of predicting long-term (>5 yrs) survival using short-term (less than or equal to3 yrs) data on ceramic restorations, which exhibit fr acturing in the initial years.