| Sumario: | Objective: This study investigated the influence of restoration type (partial‐coverage versus crown) and ceramic‐layer thickness on the fatigue behavior and failure load of monolithic composition‐gradient multilayer zirconia (4Y‐PSZ/5Y‐PSZ) molar restorations. Material and Methods: Seventy‐two CAD/CAM‐fabricated monolithic zirconia restorations (IPS e.max ZirCAD‐Prime‐Esthetic, Ivoclar‐Vivadent) were assigned to six groups (n = 12), based on restoration type—partial‐coverage restoration (PCR) or crown (C)—and ceramic thickness (occlusal/buccal: 0.5/0.4, 1.0/0.6, or 1.5/0.8 mm). All restorations were adhesively bonded to standardized dentin‐analogue dies. Specimens underwent thermomechanical fatigue (1.2 million cycles, 49 N, 1.6 Hz, 5°C–55°C), followed by single load to failure testing. Data were analyzed using ANOVA, Tukey's post hoc test, and independent t‐tests (α = 0.05). Results: All specimens survived fatigue. Evident cracks were observed post‐fatigue; one each in PCR‐0.5 and C‐0.5 groups, resulting in an overall success rate of 97.22%. Mean failure loads (N) were: PCR‐0.5: 2047, PCR‐1.0: 2018, PCR‐1.5: 2777, C‐0.5: 695, C‐1.0: 1957, C‐1.5: 3503. Ultrathin (0.5 mm) PCRs demonstrated significantly higher failure loads than ultrathin crowns (p < 0.001), whereas crowns at 1.5 mm thickness outperformed PCRs (p = 0.005). No significant difference was observed at 1.0 mm thickness (p = 0.634). Conclusion: At ultrathin thicknesses (0.5 mm), partial‐coverage designs showed superior failure loads over crowns. Both restoration types are mechanically viable at 1.0 mm and 1.5 mm thicknesses. Clinical Significance: Composition‐gradient multilayer‐zirconia demonstrates high fatigue resistance and is well‐suited for minimally invasive, non‐retentive PCR molar restorations. However, a minimum thickness of 1.0 mm should be maintained for single crowns.
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