Results of a prospective randomized controlled trial of posterior ZrSiO(4)-ceramic crowns

The aim of this randomized controlled clinical trial was to evaluate over a 5-year period, the clinical outcome of shrinkage-free ZrSiO(4)-ceramic (KaVo Everest HPC) full coverage crowns on posterior teeth in comparison with conventional gold crowns that served as the control. This study reports results of a 5-year study protocol up to 24 months. Patients totalling 224 were randomly divided into two treatment groups. Of these, 123 patients were restored with 123 Everest HPC crowns, fabricated by the Kavo Everest computer-aided manufacturing (CAM) procedure and 101 patients received 101 gold crowns, but two were excluded from analysis. All crowns were conventionally cemented with glass-ionomer cement. After an observation period of 6, 12 and 24 months, the prospective survival rates (Kaplan-Meier) for the KaVo Everest HPC crowns were 97.9%, 95.1% and 89.8% and for the gold crowns 100%, 94.8% and 92.7%, respectively. There were no significant differences between the two groups (P = 0.2). The 1-year failure rates were 4.9% for the KaVo Everest HPC crowns and 5.2% for the gold crowns. The 1-year cumulative risks for loss of vitality, secondary caries, fractures, loss of crown and extraction of abutment of the analyzed abutments (88) were 8.9%, 0%, 0%, 1.1% and 1.1%, respectively, for the gold crowns and 2.8%, 0%, 4.7%, 0% and 0.9%, respectively, for the ceramic crowns (107 analyzed abutments). No perfect marginal fit was shown by 49.5% of the evaluated ceramic crowns and 26.1% of the gold crowns. Only 1.9% of the KaVo Everest HPC crowns had a marginal crevice. In conclusion, Everest HPC crowns with an adequate occlusal tooth reduction of >1.5 mm are suitable for posterior restorations, but the marginal fit shows a potential for improvement.