Fatigue behavior and reliability of pressed lithium disilicate ceramics compared to 5Y-TZP zirconia under different loading protocols.

Objective: To compare the fatigue behavior and reliability of 5 pressed lithium disilicate ceramics and a 5 mol% yttria-stabilized zirconia (5Y-TZP) when 3 dynamic loading protocols were used.

Methods: Bar-shaped specimens (30 × 4 × 3 mm) were fabricated from 5 pressed lithium disilicate ceramics (AMB, CEL, INI, IPS, and LIV) and a 5Y-TZP (ZR) (N = 324). Six specimens from each material were subjected to a static 4-point fracture load test, while the remaining specimens were subjected dynamic loading by increasing the starting load (30 % of the static fracture load) in every 5000 cycles by 50 N (loading protocol 1), in every 5000 cycles by 5 % (loading protocol 2) or in every 1000 cycles by 10 N (loading protocol 3) until fracture (n = 16). The fracture load, flexural strength, and number of cycles until failure were analyzed with 2-way analysis of variance and Scheffé tests. The survival rate was evaluated with Kaplan-Meier analysis and further compared with Mantel-Cox test, while the correlation between the fracture load and flexural strength was analyzed with Pearson's correlation test (α = 0.05). Fractographic analysis was also performed.

Results: The interaction between the materials and the loading protocol affected the number of cycles until failure, while the material type affected fracture load and flexural strength values (P < 0.001). ZR had the highest and LIV mostly had lower fracture load and flexural strength (P ≤ 0.034). A positive correlation was found between the fracture load and flexural strength (r = 0.997, P < 0.001). For lithium disilicate ceramics, loading protocol 2 and for ZR, loading protocols 1 and 3 led to the highest number of cycles and survival rate (P ≤ 0.041). Regardless of the loading protocol, all lithium disilicate ceramics had a similar fragmentation pattern with single compression curls and 2-piece fractures were observed.

Significance: Tested materials are suitable for adhesively luted monolithic single-unit prosthesis as they had mean flexural strength values higher than 100 MPa. Measuring the fracture load with loading protocol 3 can be considered time-efficient to evaluate the fatigue behavior of pressed lithium disilicate ceramics.