Influence of manufacturer, laboratory, clinical, and aging-related factors on the mechanical properties of multilayered zirconia: a systematic review of laboratory studies

To systematically review laboratory studies evaluating how multilayering technologies, laboratory and clinical factors, and aging processes affect the mechanical properties of multilayered zirconia. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, Scopus, and Web of Science were searched for English-language, peer-reviewed laboratory studies published between January 1, 2014, and September 11, 2025. Studies were included if they assessed multilayered zirconia and reported at least one mechanical property. Exclusion criteria included non-laboratory studies, studies focused solely on optical properties or microstructure/composition without mechanical testing, and studies lacking clear descriptions of multilayer technology. The search identified 615 records; 106 full-text articles were evaluated based on eligibility criteria. Ultimately, 58 studies were included. Different mechanical-related properties were assessed, including flexural strength, compressive strength, fracture load, fracture toughness, hardness, elastic modulus, fatigue resistance, wear resistance, and structural reliability metrics. Key influencing factors on the mechanical properties of multilayered zirconia were manufacturer-related (yttria and pigment gradients), laboratory-related (sintering parameters, CAD/CAM strategies/disc positioning, prosthesis design, coloring, surface treatments), clinical (occlusal thickness, finish line design, cementation protocol, core build-up materials, tooth substrate), and aging conditions. The mechanical properties of multilayered zirconia are affected by yttria distribution, multilayering strategy, prosthesis design, sintering parameters, surface treatment, and aging conditions. Higher yttria content enhances translucency but reduces flexural strength and fracture toughness. While composition-gradient systems often demonstrated higher strength under controlled conditions, no multilayering approach showed definitive mechanical superiority. Methodological heterogeneity and moderate risk of bias warrant cautious interpretation. Standardized laboratory protocols and long-term clinical studies are needed to establish more definitive performance profiles.