Fatigue behavior and internal/marginal adaptation of 4YSZ crowns bonded on dentin analogue substrate: Effect of surface treatments

This study aimed to evaluate the effect of different surface treatments on the fatigue behavior and internal/marginal adaptation of monolithic 4YSZ crowns luted on a dentin-analogue substrate made of FRC material. Fifty crowns were fabricated and randomly assigned to five groups according to the inner surface treatment: control (CTRL), air abrasion with 45 μm aluminum oxide (AlOx), air abrasion with 30 μm silica-coated aluminum oxide (CJT), glaze spray (GLZ), and Zircos-E treatment (ZRC). Internal/marginal adaptation were assessed using the replica technique. The crowns were cemented onto glass fiber-reinforced epoxy resin dies, thermocycled for 25,000 cycles, and stored in distilled water at 37 °C for 20 days. Fatigue testing was performed at 20 Hz using a stepwise loading protocol, starting at 100 N for 10,000 cycles, followed by load increments of 100 N every 10,000 cycles up to 500 N; thereafter, the increment was reduced to 50 N per 10,000 cycles until crack detection. Fatigue data were analyzed using one-way ANOVA and Kaplan-Meier survival analysis with log-rank tests, while adaptation data were analyzed using Kruskal-Wallis and Dunn's post-hoc tests (α = 0.05). ZRC showed the best marginal adaptation in occlusal regions compared to CTRL, whereas no differences were observed in other regions. Surface treatments significantly affected fatigue performance, with CTRL, AlOx, and CJT showing the highest values, ZRC intermediate performance, and GLZ the lowest. SEM analysis revealed distinct surface topographies among treatments. Although internal/marginal adaptation are clinically relevant, they did not predominantly influence the mechanical behavior of monolithic 4YSZ crowns.