Prognosis of Metal-ceramic and All-ceramic Implant-supported Single Crowns

Objectives: The objective was to evaluate the survival rate and the incidence of complications of all-ceramic and metal-ceramic implant-supported single crowns.
Methods: From a prospectively documented clinical study, 658 implant-supported crowns placed in 408 patients (mean age: 58ys; 197 men) with a minimal observation period of 6 months (maximum: 12.8ys) were evaluated. Selection criterion was a conventional loading protocol. The material included 67 anterior and 591 posterior crowns, when 306 crowns were placed in the maxilla and 352 in the mandible. The frameworks of the crowns were predominantly made of Au-alloys (n=320), CoCr (n=39) and Zirconia (n=289). Full-coverage ceramic veneers were placed on 320 Au-crowns, 36 CoCr-crowns and 93 Zirconia-crowns, whereas 153 monolithic Zirconia-crowns were not veneered. In further 43 Zirconia-crowns a partial veneer was placed on the buccal surface only. Eight crowns were screw-retained, 216 were cemented with temporary cements and 434 crowns with permanent cements.
Results: A total of 26 failures were caused by loss of implants (n=6), ceramic fractures and chipping (n=15), loosening of the abutment (n=4) or swallowing of a de-cemented crown (n=1). Kaplan-Meier analysis revealed a probability of survival of 95% after 5 years and 92% after 10 years. Lithiumdisilicate crowns and Zirconia-crowns with full coverage veneers demonstrated higher failure rates compared to the other combinations of framework materials and veneering techniques. Separate analysis of the most frequent complication chipping (n=61) revealed that posterior location and full coverage veneers were significant risk factors for chipping (p<0.02). Monolithic Zirconia-crowns and Zirconia-crowns with partial veneers demonstrated significantly lower complication rates. De-cementation accounted for 52 additional complications. Using permanent cements (Glasionomer or Zinc-oxide-phosphate) reduced the risk of de-cementation significantly, when individual abutments also resulted in lower de-cementation rates.
Conclusions: The success rate of implant-supported crowns can be significantly improved if full-coverage veneers are avoided.