Fracture resistance of ceramic vonlays fabricated from different CAD/CAM materials restoring premolars after cyclic loading (an in vitro study)

INTRODUCTION: The advancement of indirect ceramic restorations helps to establish new boundaries between conservative practices and prosthetics, thus Vonlay restorations were introduced to achieve the desired results in cases that involve the occlusal surface and extends to entire buccal surface due to either esthetic or functional considerations. AIM OF THE STUDY: This in vitro study evaluated the fracture resistance and failure modes of ceramic vonlay restorations fabricated from four CAD/CAM materials: lithium disilicate, zirconia-reinforced lithium silicate, super high-translucent zirconia, and polymer-infiltrated ceramic after cyclic loading. MATERIALS AND METHODS: Fifty-six extracted human maxillary premolars were prepared and restored with vonlays from lithium disilicate glass ceramics (control group), zirconia-reinforced lithium silicate (ZLS), ultra-translucent monolithic zirconia, and polymer-infiltrated ceramic networks (PICNs) (n = 14/group). Restorations were milled, finished, and adhesively luted with dual-cure resin cement. All specimens underwent 500,000 cycles of mechanical loading (100 N, 1 Hz) before static fracture testing. Failure modes were assessed microscopically. Data were analyzed using one-way ANOVA, Tukey's post hoc, and Chi-square/Fisher's exact tests (α = 0.05). RESULTS: Ultra-translucent monolithic zirconia showed the highest fracture resistance, followed by lithium disilicate glass ceramics and zirconia-reinforced lithium silicate (ZLS) while polymer-infiltrated ceramic networks (PICNs) showed the lowest values (p < 0.001). Failure patterns differed significantly among groups (p = 0.005), with polymer-infiltrated ceramic networks (PICNs) having more restorable failures. CONCLUSION: Ceramic material significantly influences the mechanical performance of vonlay restorations. High-strength ceramics, such as lithium disilicate glass ceramics, ultra-translucent monolithic zirconia, offer superior resistance and clinical predictability in premolars under cyclic loading.