Recycling CAD/CAM Lithium Disilicate Ceramic: Effect of Surface Treatment and Aging on the Bond Strength to Resin Cement

Purpose: To investigate the effects of recycling lithium disilicate (LD), surface treatment, and thermocycling on the bond strength to resin cement. Materials and Methods: A total of 72 tablets (10 × 10 × 3 mm) of LD were made according to the recycling cycle with 24 tablets for each strategy: control (conventional sintering), 1R (1 recycling cycle), and 3R (3 recycling cycles). For the recycling groups, tablets were waxed, mounted in a silicone ring, and poured with investment material, and residues of sintered LD tablets were pressed by the lost wax technique. The residual LD was reused as described until it reached 3R. Afterward, the tablets were embedded in acrylic resin, sanded, and divided (n = 15) according to the factors of “surface treatment” (hydrofluoric acid [HF] for 20 seconds [HF20s] and silane, HF for 120 seconds [HF120s] and silane, and Monobond Etch & Prime [MEP]) and thermocycling (TC; with 10,000 cycles and without). After surface treatment, cylinders (diameter: 2 mm) of resin cement were made and submitted to SBS test (100 kgf, 1 mm/minute). Data (MPa) were analyzed by three-way ANOVA, Tukey test (5%), and Weibull analysis. Failure analysis was performed with a stereomicroscope. Results: ANOVA revealed that all factors were significant (P = .000*). The group 3RMEP (105.09 ± 19.49) presented the highest SBS among the experimental groups. The 1RHF20sTc (7.50 ± 1.97) group had the lowest SBS, similar to CHF20sTc (15.69 ± 3.77), 1RHF20s (15.12 ± 3.03), 1RHF120sTc (14.60 ± 3.43), and 3RHF20sTc (15.65 ± 0.97). The Weibull modulus and characteristic strength varied among the experimental groups (P = .0). Failure analysis revealed adhesive and mixed types. Conclusions: The recycling of DL ceramics increases the SBS to resin cement when the ceramic is treated with HF120s and silane or MEP.