Influence of Varying Airborne-Particle Abrasion Angles on Surface Properties and Flexural Strength of Feldspar...

This study investigated the effects of airborne-particle abrasion angle and nozzle geometry on the surface free energy (SFE), surface roughness (Ra), and flexural strength (FS) of a feldspar ceramic. A total of 70 feldspar ceramic substrates were assigned to seven groups (n = 10). Six groups were air-abraded with 50 µm Al₂O₃ at 0.05 MPa for 10 s using a conventional nozzle at 20°, 45°, 70°, or 90°, or an experimental conical nozzle at 45° or 90°. The control group underwent hydrofluoric acid etching for 60 s. One-way ANOVA with partial eta-squared (η_p²) was performed, followed by Scheffé post hoc tests. Treatment significantly affected SFE and Ra (p < 0.001). The 20° conventional-nozzle group showed the lowest SFE and Ra values (38.3 ± 11.3 mJ/m² and 0.514 ± 0.033 µm, respectively). At 45°, the conventional nozzle produced higher SFE than the experimental nozzle, whereas at 90°, the experimental nozzle produced higher Ra. Mean FS ranged from 121 ± 8.5 to 131 ± 8.0 MPa, without significant differences among the groups (p = 0.074). Under the investigated low-pressure conditions, abrasion angle and nozzle geometry altered surface properties without a statistically detectable reduction in FS. Bond strength, aging durability, and clinical performance were not assessed. Therefore, the present findings alone do not justify a recommendation for replacing hydrofluoric-acid etching with airborne-particle abrasion.