Statement of problem: Fracture of veneering ceramics in zirconia-based restorations has frequently been reported. There is a need to investigate the fracture mode of implant-supported all-ceramic restorations by using clinically relevant laboratory protocols.

Purpose: This study compared the mode of fracture and number of cyclic loadings until veneering fracture when all-ceramic and metal-ceramic restorations were supported by implants.

Material and methods: Thirty-two implant-supported single-tooth restorations, 16 all-ceramic and 16 metal-ceramic restorations, were used. The palatal surfaces of the crowns were exposed to cyclic loading of 800 N with a frequency of 2 Hz, which continued to 4.2 million cycles or until fracture of copings, abutments or implants. The number of cyclic loadings and the fracture modes were recorded.
The fracture modes were analysed by descriptive analysis and Mann-Whitney test, and the differences in loading cycles until veneering fracture were estimate by Cox proportional hazards analysis.

Results: Veneering fracture was the most frequently observed fracture mode. The severity of fractures was significantly higher in all-ceramic restorations compared to metal-ceramic restorations.
Significantly more loading cycles until veneering fracture were estimated with metal-ceramic restorations compared to all-ceramic restorations.

Conclusion: The metal-ceramic restorations demonstrated less and minor fractures compared to all-ceramic restorations. Furthermore, the metal-ceramic restorations resisted more cyclic loadings than the all-ceramic restorations.


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