Load-bearing capacity and Weibull characteristics of inlay-retained fixed dental prosthesis: Effect of zirconia type, bonded substrate and aging

OBJECTIVES: This study evaluated the load-bearing capacity and reliability of different zirconia materials used for inlay-retained fixed dental prostheses (IRFDPs), considering the influence of substrate type (tooth substrate or resin composite) and thermo-mechanical aging. MATERIALS AND METHODS: IRFDPs (N = 160) were fabricated using four zirconia materials: IPS e.max ZirCAD LT (3Y-TZP), Katana YML (3Y-5Y graded zirconia), Katana HTML Plus, and Katana STML (n = 40 each). Restorations were adhesively cemented onto tooth or resin composite substrates and tested either under dry conditions or after thermo-mechanical aging (1,200,000 cycles, 50 N, 5-55 °C). Fracture load was determined using monotonic load-to-fracture testing. Data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Reliability of durability was assessed using Weibull analysis. RESULTS: Under dry conditions, material (p = 0.0047), substrate (p = 0.0237), and their interaction (p = 0.0004) significantly influenced fracture load. YML-composite (1406 ± 386 N) and HTML-composite (1142 ± 249 N) showed higher values than STML-composite (553 ± 246 N). No significant differences were observed on tooth. substrate After aging, material and interaction effects remained significant (p < 0.05). HTML-tooth showed the highest fracture load (1727 ± 351 N), while STML-composite showed the lowest (718 ± 292 N). Weibull analysis indicated comparable reliability after aging. CONCLUSIONS: Zirconia type and substrate significantly influenced mechanical performance of IRFDPs. High-translucent and graded zirconia showed substrate-dependent behavior, whereas 3Y zirconia was more stable. CLINICAL RELEVANCE: Zirconia selection and bonding substrate influence fracture resistance of IRFDPs. High-translucent zirconia requires careful substrate selection, while 3Y zirconia provides more consistent performance in posterior applications.