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Effect of femtosecond laser ablate ultra-fine microgrooves on surface properties of dental zirconia materials.

OBJECTIVES
Zirconia is an important dental implant material, yet it surfaces milling method is still under investigation. To explore the feasibility of laser etching in processing fine micro grooves on the surface of zirconia and to observe fine micro groove structure' influence on mouse embryonic osteoblasts, the survey was conducted.


METHODS
31 zirconia discs were made and polished to mirror surface. Then, they were divided into 3 groups: the mirror group, the femtosecond laser ablated microgroove group and the air blasted + acid etched group. Then, the surface properties of zirconia discs were analyzed by Scanning Electron Microscope/Energy Dispersive Spectrometer (SEM/EDS), X-Ray Diffraction (XRD), Atomic Force Microscope (AFM), water contact angle test and micro-Vickers hardness test. The biocompatibility of each machined zirconia was tested by cell proliferation test and SEM analyze of cell morphology. Then, the effect of these surface treatment to MC-3T3-E1's osteogenic differentiation was evaluated by Q-PCR test.


RESULTS
SEM image showed that the femtosecond laser is a reliable method for forming regular-arranged microgrooves with pitch width of around 5 μm. EDS and XRD indicated that there were stable and purified tetragonal crystal system on the laser-roughened surface. AFM suggested that laser machining generated rougher surface (Ra) (271.7 ± 67.2 nm) than other groups. Furthermore, the contact angle showed laser ablated grooves induced anisotropic wetting. The micro-Vickers hardness test ascertained that laser-ablation strengthened zirconia surface. In vitro experiment showed that MC-3T3-E1 grown along the long axis of microgrooves on the first day. Besides, Real time PCR implied that osteogenesis-related gene expression OPN and ALP was much higher than the rest groups.


SIGNIFICANCE
Femtosecond laser is able to machine zirconia with ultra-fine microgrooves (around 2.5 μm). These structures promoted MC-3T3-E1 cell to line along the microstructure and differentiate into osteogenic cells. Thus, femtosecond laser might be a potential processing options for zirconia micro-texturing.