Influence of 3D printed surface micro-structures on molding performance and dental bonding properties of zirconia

Objectives: To investigate the influence of the 3D printed micro-structured surfaces on the bond strength of zirconia to resin cement. Methods: Zirconia specimens were divided into five groups based on manufacturing technique and surface preparation: (1) milled zirconia (M group); (2) milled zirconia airborne abraded (MA group); (3) printed zirconia (M group); (4) printed zirconia airborne abraded (PA group); and (5) printed zirconia with micro-structured surface (PM group). The surface morphology, cross-sectional morphology, and elemental composition were observed using a scanning electron microscope (SEM). Surface roughness was measured using a laser scanning confocal microscope (SLCM). Shear bond strength (SBS) was measured using a universal testing machine after bonding resin cement (n = 10). The failure modes of the bonded fracture interfaces were observed and counted using a stereomicroscope and a SEM. In addition, boundary dimensional accuracy (n = 10) and micro-structural dimensional accuracy (n = 20) of printed zirconia specimens with micro-structured surfaces were measured using digital calipers and Fiji software. The crystalline phase changes before and after surface treatment were investigated using X-ray diffractometry. Data was analysed using one-way ANOVA and Tukey HSD post-hoc tests (alpha = 0.05). Result: The surface micro-structures of the PM group had regular morphology and no obvious defects. The surface roughness results showed that the PM group had higher Sa (42.21 +/- 1.38 um) and Ra (21.25 +/- 1.80 um) values than the other four groups (p < 0.001). The SBS test showed that the bond strength of the PM group reached 11.23 +/- 0.66 MPa, which was 55.97% (p < 0.001) higher than that of the P group (7.20 +/- 1.14 MPa). The boundary dimensional accuracy of the PM group was proficient (diameter: 99.63 +/- 0.31%, thickness: 98.05 +/- 1.12%), and the actual fabrication dimensions of the hexagonal micro-structures reached 77.45%-80.01% of the original design. The micro-structured surface did not affect the crystalline phase of zirconia. Conclusions: The current study illustrates that 3D-printed microstructured surfaces effectively improve the bond strength of zirconia to resin cements. Clinical significance: With the advantage of 3D printing, this study provides a new idea for improving the bonding properties of zirconia.