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.