Comparison of the Flexural Strength of Monolithic Zirconia After Three Different Surface Treatments: An In Vitro Study

Background Monolithic zirconia is increasingly used in dental restorations for its high strength and biocompatibility. However, the impact of surface treatments—glazing, polishing, and air abrasion—on its flexural strength remains unclear due to inconsistent findings in existing studies. Methods Thirty zirconia specimens (25 × 6 × 3 mm) were milled from SuperfectZir disks using CAD-CAM technology and sintered at 1,350°C–1,500°C. Specimens were randomly assigned to three groups ( n = 10). Group A was glazed at 790°C, Group B was subjected to grinding and polishing using diamond burs and ceramic kits, and Group C underwent airborne-particle abrasion with 110 µm alumina at 400 kPa. Flexural strength was tested using a universal testing machine via the three-point bending method. Results Group B (Grinding and Polishing) showed the highest mean flexural strength (748.70 ± 79.95 MPa), followed by Group C (Air Abrasion) (689.90 ± 76.95 MPa), and Group A (glazing) (553.30 ± 131.75 MPa). Mann–Whitney U tests showed significant differences between Group A and Groups B ( p = .002) and C ( p = .041), but not between Groups B and C ( p > .05). Conclusion Surface treatments significantly influence the flexural strength of monolithic zirconia. Polishing most effectively enhances strength by reducing flaws. Glazing reduced strength, likely due to thermal stress, while air abrasion showed moderate improvement. Clinical choice should balance strength and aesthetics.