Reliability Analysis of Lithium Disilicate Crowns: Effectof Veneering and Milling Production Workflow.

Abstract

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.