Fatigue Performance of Adhesively Cemented Glass-, Hybrid- and Resin-ceramic Materials for CAD/CAM Monolithic Restorations

Objective: To evaluate the fatigue failure load, number of cycles until failure, and survival probability of adhesively cemented materials with different microstructures (glass-, hybrid- and resin-ceramic) used to manufacture CAD/CAM monolithic restorations.

Methods: Disc-shaped specimens (n=15; Ø=10mm; thickness=1.0mm) were produced from CAD/CAM blocks as follows: feldspathic (FEL); leucite (LEU); lithium disilicate (LD); zirconia-reinforced lithium silicate (ZRLS); polymer-infiltrated ceramic network (PICN); and resin nanoceramic (RNC). Adhesive cementation was performed onto epoxy discs (dentin analogue- Ø=10mm; thickness=2.5mm). The cemented assemblies were subjected to fatigue testing using a step-stress approach (400N-2200N; step-size of 200N; 10,000 cycles per step; 1.4Hz). Fatigue data were analyzed using Kaplan-Meier and Mantel-Cox (log-rank) tests (p<0.05) and Weibull statistical analysis. Fractographic analysis was also performed.

Results: All RNC specimens survived the fatigue test (100% probability of survival at 2200N; 100,000 cycles) and presented occlusal deformation in response to loading, while all other tested materials failed in distinct loading steps with radial cracks starting from the bonding surface. LD (1146.7N; 47,333) and ZRLS (1013.3N; 40,666) materials obtained the highest fatigue failure loads and cycles until failure, meanwhile all PICN specimens failed during the first step (0% probability of survival at 400N; 10,000). FEL had similar Weibull modulus to LD and ZRLS and higher than LEU for both load and number of cycles outcomes.

Significance: The microstructure of adhesively cemented glass-, hybrid- and resin-ceramic CAD/CAM restorative materials influence their response during fatigue testing, which aids in suggesting the best clinical indications.