Effect of Er: YAG Laser Irradiation on the Flexural Fatigue Strength of a 4YSZ Ceramic

This study aimed to evaluate the effect of Er:YAG laser surface treatment on the flexural fatigue strength of 4YSZ ceramics, with or without resin cement application. Disk-shaped zirconia ceramic specimens (Ø = 15 mm, thickness = 1.2 mm of IPS e.max ZirCAD MT BL) were prepared and randomly assigned to 10 groups based on two factors: "surface treatments" (Ctrl-, no surface treatment, only polished with silicon carbide [SiC] papers; Ctrl+, CAD/CAM simulation in the laboratory; AirAbr, air abrasion with alumina oxide; Laser, Er:YAG laser; and AirAbr + Laser, combination of air abrasion with alumina oxide + Er:YAG laser); and "resin cement" (with or without). Surface topography (n = 2), surface roughness (n = 15), and flexural fatigue strength were evaluated (n = 15). Specimens with resin cement were tested after 24 h of its application. Fractographic and topographic characteristics were qualitatively analyzed. Specific statistical tests (α = 0.05) were applied for each outcome. Surface treatment (F = 125.75, p < 0.001), cement application (F = 6.25, p = 0.014) and their interaction (F = 2.71, p = 0.033) were statistically relevant for flexural fatigue outcomes. Ctrl- presented the highest performance, with or without resin cement. AirAbr showed better performance than Laser. Resin cement was relevant only when associated with AirAbr or Laser. Air abrasion notably improved flexural fatigue strength when combined with resin cement, whereas laser Er:YAG alone did not significantly enhance the results. None of the surface treatments, with or without cement application, replicated the flexural fatigue strength of a polished surface. There were no differences in roughness (Ra and Rz) seen among surface treated conditions, only Ctrl- was smoother (p < 0.05).