Fracture Resistance of Lithium Disilicate and Hybrid Ceramic Crowns with Two Finish Line Thicknesses: An In Vitro Study

Aim: This study assessed the fracture resistance of posterior crowns made from fully crystallized lithium disilicate (LDS) and hybrid polymerinfiltrated ceramic network (PICN) ceramics in comparison with partially crystallized LDS with two finish line thicknesses: 0.5 and 1 mm.Materials and methods: Thirty sound molars extracted for orthodontic or periodontal reasons were prepared for full coverage crowns and divided into three groups (N = 10): (1) partially crystallized LDS (Em), (2) fully crystallized LDS (Li), and (3) hybrid PICN (Ve).Each group was subdivided by finish line thickness (n = 5): 0.5 and 1 mm.Samples were subjected to thermocycling for 5,000 cycles, followed by fracture resistance testing utilizing a universal testing machine.Failure patterns were assessed using scanning electron microscopy (SEM).All data were subsequently recorded and statistically analyzed.Results: Mean fracture resistance values were 2,532.6 ± 612.3 N for partially crystallized LDS, 1,916.5 ± 549 N for fully crystallized LDS, and 1,325.3± 336 N for hybrid ceramic.Finish line thickness (0.5 mm: 1,923.8± 687.8 N; 1 mm: 1,925.8± 744.9 N) had no significant effect (p = 0.992).Fracture resistance was significantly affected by the type of ceramic (p < 0.001), with partially crystallized LDS showing the highest values and hybrid ceramic the lowest.Scanning electron microscopy analysis revealed favorable type II failure in all samples, with fractures confined to the restoration.Conclusion: Partially crystallized LDS exhibited the highest fracture resistance, followed by fully crystallized LDS, while hybrid ceramic had the lowest value.However, fracture resistance values of all tested materials exceeded normal masticatory forces.Clinical significance: Fully crystallized LDS demonstrated high fracture resistance, supporting its safe use even at minimal thicknesses while reducing chairside time.Findings of this study guide clinicians in selecting the appropriate restorative material and preparation design for posterior teeth, supporting minimally invasive approaches without compromising mechanical performance.