Comparative Evaluation of Hydrofluoric Acid Etchants on a 3D-Printed Lithium Disilicate-Filled Polymer Resin

Background: This in vitro study compared the effects of four commercial hydrofluoric acid etchants with different nominal concentrations on the surface roughness of a 3D-printed lithium disilicate-filled polymer resin, evaluated after post-polymerization without debinding or sintering. Methods: Seventy-five specimens were randomly assigned to five groups (n = 15): G1, 4.5% hydrofluoric acid (IPS Ceramic Etching Gel, Ivoclar); G2, 4% hydrofluoric acid (Porcelain Etchant, Bisco); G3, 9.5% hydrofluoric acid (Porcelain Etchant, Bisco); G4, 9% hydrofluoric acid (Porcelain Etch, Ultradent); and G5, an unetched control. Etchants were applied for 20 s. Areal surface roughness (Sa) was measured using non-contact optical profilometry. Data were analyzed using Levene’s test, conventional and Welch’s analyses of variance, and Games–Howell pairwise comparisons (α = 0.05). Results: Both analyses of variance identified significant differences among groups (p < 0.001). All pairwise comparisons were statistically significant (p < 0.001). Mean Sa values were 0.1558 ± 0.0159 µm for G5, 0.3159 ± 0.0313 µm for G1, 0.5093 ± 0.0467 µm for G2, 0.7243 ± 0.0409 µm for G3, and 0.9365 ± 0.0408 µm for G4. The 9% Ultradent etchant produced the greatest roughness, approximately six times the control value. Conclusions: All etchants significantly increased surface roughness. However, the ranking did not follow nominal acid concentration, and differences in commercial formulations prevent attribution of the observed effects to concentration alone. These findings characterize surface modification of a 3D-printed lithium disilicate-filled polymer resin and should not be generalized to conventional lithium disilicate ceramics. Further studies are needed to determine whether these topographic changes improve subsequent adhesive bond strength or long-term durability.