Improving fatigue behavior of CAD/CAM-ground 4YSZ via finishing, polishing, and surface treatments

It evaluated the effect of an internal finishing and polishing protocol, combined with surface treatments, on the fatigue flexural strength and topography of 4YSZ ceramic after CAD/CAM grinding. Ceramic bars (18×5.2×2.4 mm; IPS e.max ZirCAD MT, Ivoclar) were assigned in six groups (n=15) based on two factors: 'Surface condition' - with (POL) or without (non-POL) internal finishing and polishing using F, FF diamond burs and polishing tips (Optragloss, Ivoclar); and 'Surface treatments' - CTRL (no treatment), AB (air-abrasion with 45 µm aluminum oxide), or GLZ (glaze spray). Surface roughness was measured, and a cyclic flexural three-point bending fatigue test (20 Hz, 10,000 cycles/step, step size 25 MPa starting at 75 MPa) was conducted. Fractographic and topographic analyses were also performed. Fatigue data were analyzed by Two-Way ANOVA, Kaplan-Meier, Mantel-Cox (Log-Rank), and Weibull analyses, while roughness data underwent Two-Way ANOVA and Tukey's tests. 'Surface condition' significantly influenced fatigue strength (F=18.38, p<0.05), while 'Surface treatment' and the interaction between factors were not significant (p>0.05). POL groups exhibited higher fatigue behavior than non-POL groups: CTRL (POL vs. non-POL, p = 0.000), AB (POL vs. non-POL, p = 0.049), GLZ (POL vs. non-POL, p = 0.004). Roughness showed POL consistently smoother than non-POL in every comparison: non-POL-CTRL > POL-CTRL, non-POL-AB > POL-AB, and non-POL-GLZ > POL-GLZ. Topographic analysis indicated that air abrasion produced uniform surfaces, while glaze partially filled in defects. Fractures originated from surface defects in tensile regions. Internal finishing and polishing after CAD/CAM grinding enhance the flexural strength of 4YSZ, with air-abrasion and glaze yielding comparable fatigue performance.