This study aims to investigate the mechanical properties, composition and surface preparation for adhesive bonding of the recently introduced zirconia-reinforced lithium silicate (ZLS) glass-ceramic. One single block of ZLS was used to prepare the specimens (n=14). The fracture toughness (Ft) and the Vickers hardness (HV) were measured on specimens partially crystallized (PCs) (n=4) and fully crystallized (FCs) at 840°C for 8 min (n=4). The surface treatment was done using hydrofluoric-acid gel (HF) at different concentrations and times of action on FCs specimens (n=4). SEM-EDX was used to test elemental composition and crystalline phases (n=2). The new ZLS glass-ceramic showed significantly higher values of HV and Ft for FCs, PCs showed a brittle behavior. The surface etching should be made using HF at 4.9% for 20 s.

Within the limitations of this preliminary evaluation, monolithic zirconia full-arch rehabilitations induced a clinically acceptable wear on natural and composite antagonists over a 1-year period; they might be considered a viable solution for implant-supported rehabilitations.

Purpose: To evaluate the reliability of lithium disilicate crowns produced using either CAD/CAM milling or thermopress workflow, for monolithic or veneered framework design for crowns. Materials and Methods: Lithium disilicate crowns (N = 40) were produced using one of four different workflows, namely (a) MTP: monolithic thermopressed crowns, (b) MCM: monolithic CAD/CAM milled, (c) VTP: thermopressed frameworks veneered, or (d) VCM: CAD/CAM milled crowns veneered. The specimens were adhesively luted to resin composite abutments and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA.Weibull distribution values including the Weibull modulus (m), characteristic strength ( 0 ), and probability of failure at 5% (0.05) were calculated. Results: Fabrication method did not significantly influence the mean fracture strength (N) of lithium disilicate crowns (MTP: 3626 ± 283; MCM: 3719 ± 483; VTP: 3754 ± 485; VCM: 3302 ± 604) (p = 0.154). Weibull distribution presented lower shape value (m) of VCM (m = 5.81) followed by VTP (m = 8.83), MCM (m = 8.84) compared to MTP (m = 12.9). Type V failures (severe fracture of the crown and/or tooth) were experienced explicitly in all groups. The monolithic specimens showed a homogeneous structure without porosities. Wake hackles were observed at the fracture surface, with a radial path directed to the cervical area. The veneered crowns presented twist and wake hackles propagated perpendicularly from the cement-ceramic interface. Conclusion: Monolithic or veneered lithium disilicate crowns presented similar fracture strength when frameworks or entire crowns were milled or thermopressed but distribution with Weibull characteristics was more favorable for monolithic pressed crowns and the least reliable for the milled and veneered crowns. Clinical Significance: Lithium disilicate ceramic crowns could be produced either by thermopressing or CAD/CAM milling workflow without sacrificing their reliability.Metal-ceramic crowns still represent the gold standard for single-tooth prosthetic rehabilitation, with a 5-year survival rate of 95.6%.

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