Fatigue behavior of CAD-CAM composites versus lithium disilicate glass-ceramic.

Objective: To assess the fatigue properties of four CAD-CAM composites and compare them with lithium disilicate glass-ceramic.

Methods: The materials studied were: Brilliant Crios (BRI); Cerasmart 270 (CER); Grandio (GRN); and Tetric CAD (TET), and a lithium disilicate glass-ceramic (IPS e.max CAD, EMX) as a reference. Blocks were cut into bars and used for: 1) 3-point flexural test (n = 30/material); and 2) constructing S-N curves (n = 35/material). Fatigue tests were conducted in 36 °C water bath at a frequency of 1 Hz lasting up to 3 × 10⁶ cycles. The S-N curves were plotted using the Basquin model, assuming a distribution of fatigue life following the Weibull statistics. Digital microscopy was used to study the creep of a runout composite sample (CER), and fractured surfaces of selected samples were analyzed using laser confocal microscopy and scanning electron microscopy.

Results: Compared to EMX, CAD-CAM composites have a shorter lifespan but comparable fatigue degradation (fatigue to flexural strength ratios) at 5 × 10⁴ cycles (0.57-0.65 versus 0.58). Their slow crack growth parameter (n) were close, ranging from 10.4 to 13.3 for CAD-CAM composites and 14.2 for EMX. Fatigue data of CAD-CAM composites showed less variability than EMX. Creep was detected in CAD-CAM composites at 3 × 10⁶ cycles.

Significance: Despite CAD-CAM composites having shorter lifetimes than EMX, they show similar resistance to fatigue degradation. Time-dependent factors seem to significantly influence composites fatigue at lower stress levels. Thus, extended fatigue testing in water, despite being time-consuming and costly, is essential for understanding material behavior under clinical conditions.