Abstract: Objective: To study the influence of femtosecond laser processing on the topographies of yttria-stabilised tetragonal zirconia polycrystal (Y-TZP) and its bonding strength with self-adhesive resin cement. Methods: One hundred and twenty cases of sintered zirconia ceramic specimens were randomly divided into six research groups and treated as follows. Group A: Control group with no treatment; group B: alumina sandblasting; C-F group: surface femtosecond laser linear groove processing, processing repetitions were 2, 4, 6, and 10 times, respectively. Topographic surface analysis and groove depth were performed by laser confocal microscope (CLSM). Surface roughness Ra was measured by atomic force microscope (AFM). Crystal phase was evaluated by X-ray diffraction (XRD). Surface morphology was observed by scanning electron microscopy (SEM). The specimens were then subjected to shear bond strength testing of zirconia ceramic and self-adhesive resin cement before and after aging (5000 cycles with temperature range from (5±1) ℃ to (55±1) ℃ for 30s each). Further, stereomicroscope was used to observe the fracture modes. Results: In this study, regular V-shaped grooves with depths of about 30 μm, 50 μm, 60 μm, and 70 μm were obtained after 2, 4, 6, and 10 times of laser pulses scanning on the surface of zirconia. The surface roughness increased with the increase of laser scanning times. Laser surface treatment does not lead to surface crystal phase transformation. The microstructure showed that after laser ablation by laser, the zirconia ceramic substrate had no craters, holes, ridges, and other defects, but too many scanning times (10 times) could be seen in the casting layer accumulation. The V-shaped grooves on the ceramic surface increased the surface area and formed an interlocking structure with the resin. The shear strength increased from 3.68 MPa and 4.87 MPa in group A (control group) and group B (sandblasting group) to 17.78 MPa (group C), 22.5 MPa (group D), 27.4 MPa (group E), and 27.54 MPa (group F), and the shear strength after aging was still more than 5 times that of the control group. The fracture mode changed from complete bond failure of the control group and the sandblasting group to cohesive failure and mixed failure. The flexural strength of the zirconia ceramic after laser treatment was 457.73 MPa (group E), which met the requirements of clinical application. Conclusion: Femtosecond laser processing is one of the ideal methods for surface modification of dental ceramics. Reasonable microstructure design can significantly improve the bonding strength with self-adhesive resin cement, and has good anti-aging property. It can replace the traditional surface treatment methods such as sandblasting to prolong the service life of dentition defect repair.

Key words: microstructure, femtosecond laser, laser processing, surface textures, adhesive properties