Fatigue behaviour of direct and CAD/CAM indirect restorative materials bonded to a dentine analogue substrate

Objectives This study aimed to investigate the fatigue behaviour of direct and CAD/CAM indirect restorative materials cemented to a dentine analogue substrate. Materials & methods Two resin-based direct restorative materials (G-ænial Universal Injectable, GU; Filtek Supreme Flowable Restorative, FS), and two CAD/CAM indirect restorative materials (IPS e.max CAD, EM; Tetric CAD, TE), were tested. Flexural properties (flexural strength and flexural modulus) and energy dissipation parameters (modulus of toughness, elastic recovery, and their difference) were determined via the three-point bending (3PB) test (n = 10). After the monotonic pilot trial, the wet cyclic fatigue test was performed following the staircase approach (initial load: approx. 40% of the monotonic load; step size: approx. 5% of the monotonic load; 500,000 cycles per specimen; 20 Hz; n = 15). Mean fatigue failure load (FFL), standard deviation (SD), and 95% confidence interval (CI) were calculated using the Dixon and Mood method. FFLs were also evaluated with Weibull statistics. Specimen survival or failure was examined visually and under a stereomicroscope, then fractographic analysis were conducted on sectioned specimens under the SEM. Finite Element Analysis (FEA) was performed using the mean FFLs and 300 N axial load on tri-layer models, respectively. SPSS 26.0 was used for statistical analysis and the significant level was pre-set as α = 0.05. Results EM showed significantly higher flexural strength and elastic modulus than the three resin-based composites (RBCs) (p < 0.001). Nevertheless, three energy dissipation parameters of RBCs were significantly higher than those of lithium disilicate, ranking TE > FS > GU > EM. The mean FFL showed a similar trend, ranking TE (353.93 ± 43.01 N) > GU (276.79 ± 34.24 N) > FS (255.33 ± 47.30 N) > EM (184.00 ± 76.92 N). EM presented the lowest Weibull parameters and the highest RSD values, while TE presented superior fatigue resistance and structural reliability. Distinct failure characteristics and stress distribution patterns between EM and three resin-matrix materials were found. Significance Distinct fatigue behaviours were discovered between lithium disilicate and resin-based materials, including the fatigue failure load, failure mode, and stress distribution pattern. Resin-based composites outperformed lithium disilicate in the cyclic fatigue test, among which the CAD/CAM indirect RBC material performed the best fatigue resistance. Energy dissipation parameters may serve as preliminary predictors to the fatigue properties.