Effect of different surface treatments on the surface properties and immediate shear bond strength of 3D-printed zirconia

To investigate the effect of different surface treatment protocols on the surface properties and immediate shear bond strength (SBS) between 3D-printed zirconia and resin cement to provide a reference for clinical practice.

Disc-shaped zirconia specimens (Ø 14 mm× 1.2 mm) with two different surface designs were fabricated using 3D printing technology: a smooth surface (Group S) and microporous surface (Group M), with 40 specimens in each group. Each group was further randomly divided into four subgroups according to surface treatment: untreated (Subgroup U), alumina sandblasting (Subgroup ST), alumina sandblasting + Z-Prime ceramic primer (Subgroup ZP), and alumina sandblasting + Monobond N ceramic primer (Subgroup MN). The surface morphology was examined, roughness was measured, and wettability was evaluated via contact-angle testing. Composite resin cylinders (Ø 3.5 mm× 2.0 mm) were bonded to the zirconia surfaces with resin cement. Immediate SBS was determined by shear testing, and failure modes were analyzed.

Scanning electron microscopy revealed clear micro-grooves (2-5 μm wide) in Subgroup S-U and micropores (approximately 400 μm in diameter) in Subgroup M-U. After sandblasting, the micro-grooves in Subgroup S-ST were partially destroyed with some micro-cracks, while the microporous structure in Subgroup M-ST remained clear. Compared with Subgroups S-U and M-U, sandblasted zirconia specimens (Subgroups S-ST, S-ZP, S-MN, M-ST, M-ZP, M-MN) showed significantly increased roughness and decreased contact angles. Different surface treatments significantly affected SBS between 3D-printed zirconia and resin. Sandblasted groups (Subgroups S-ST and M-ST) had significantly higher SBS than untreated groups (Subgroups S-U and M-U). The application of ceramic primers after sandblasting (Subgroups S-ZP, S-MN, M-ZP, M-MN) further increased SBS; however, there was no statistically significant difference in SBS between the two primers used after sandblasting (Subgroup S-ZP vs. S-MN, Subgroup M-ZP vs. M-MN). Under the same surface treatment, microporous surface groups (Subgroups M-U, M-ST, M-MN, M-ZP) all exhibited significantly higher SBS than smooth surface groups (Subgroups S-U, S-ST, S-MN, S-ZP).

Fabricating a microporous surface using 3D printing technology can improve resin bonding effectiveness. Sandblasting combined with a ceramic primer yields the highest immediate SBS.