Long-term Retention of Cemented Implant-supported Zirconia and Metal-ceramic Single Crowns

Objectives: The objective of this clinical study was to investigate survival rates and the incidence of de-cementation of zirconia and metal-ceramic single crowns (SCs) cemented on implants.
Methods: Five hundred and sixty-seven implant-supported SCs placed in 358 patients (mean age: 57.9 years; 168 male) were evaluated up to 12.8 years. The frameworks were made from high precious Au alloys (n=307) or zirconia (n=260). SCs were cemented with glass ionomer cement (GIC; n=376) or eugenol-free semi-permanent cement (n=191) on standardized abutments (n=446) or customized abutments (n=121). Kaplan-Meier curves were used to calculate the incidence of de-cementation. Significant differences between curves were assessed with log-rank tests. Cox regression analysis was performed to consider multiple risk factors simultaneously.

Results: Twenty-two SCs failed and had to be replaced, predominantly because of technical complications (veneer fracture: 14, loosened abutment: 3, de-cemented and swallowed crown: 1). Only 4 SCs failed because of loss of implants. In contrast to low failure rates a high incidence of 50 de-cementations was observed. Kaplan–Meier analysis revealed a probability of de-cementation of 7% for zirconia SCs and 16% for SCs with Au frameworks after 10 years (log-rank test: p= .011). After 5 years, a higher incidence of de-cementation (p = .014) was found for standardized abutments (12%) compared to customized abutments (2%). A significant effect was evaluated for the type of cement, when semi-permanent cements demonstrated a 20% probability of de-cementation after 10 years compared to 8% for GIC (p = .001). Multivariate regression analysis revealed semi-permanent cement as the only significant risk factor (p = .026) with a hazard rate of 2, whereas the other variables (abutment type, crown material) were not significant.
Conclusions: In contrast to semi-permanent cement, glass ionomer cement provides acceptable long-term retention of cemented implant-supported SCs made from Au-alloys or zirconia. Possible positive effects of individual abutments have to be controlled with larger sample sizes.