Influence of fabrication techniques and artificial aging on the fracture resistance of different cantilever zirconia fixed dental prostheses

Purpose: To evaluate the influence of dynamic fatigue on fracture load and failure mode of different types of adhesive zirconia restorations. Materials and Methods: Eighty adhesive cantilever fixed dental prostheses (CFDP) were fabricated and assigned to four equal groups (n = 20) using the following materials and techniques. Group 1: machine copy-milling zirconia (Cercon), group 2: manual copy-milling technique (ZirkonZahn), group 3: slip casting technique (Vita In-ceram Zirconia), group 4: metal-ceramic CFDP. Specimens in groups 1and 2 received selective infiltration-etching surface treatment, specimens in group 3 were acid etched with hydrofluoric acid and silanated, while those of group 4 were airborne particle abraded. All specimens were bonded with resin cement (Panavia F2.0) and thermocycled (5000 cycles/ 5 to 55°C). Then, half the number of the specimens of each group (n = 10) underwent dynamic loading (one million cycles at alternating loads between 10 and 40 N in a water bath at 37°C). All specimens were subjected to one-cycle loading to failure to evaluate fracture resistance. One-way and two-way ANOVA and Bonferroni post-hoc tests were used to analyze the data (α = 0.05). The intaglio surfaces of fractured specimens were examined using stereomicroscopy and scanning electron microscope (SEM). Results: Statistical analysis revealed that the failure load of metal (413 ± 26 N) and machine copy-milled zirconia (368 ± 24 N) restorations was significantly higher (F = 129, p < 0.001) than manually copy-milled (316 ± 18) and In-ceram zirconia (210 ± 17) restorations. Dynamic fatigue significantly (p < 0.03) reduced failure load of the manually copy-milled and In-ceram zirconia restorations, while metal and machine copy-milling zirconia restorations were not influenced by fatigue. Conclusions: The fatigue strength of adhesive zirconia restorations is influenced by cyclic loading and the technique used to manufacture these restorations.