Combination of laser-assisted surface modification and chemical etching on zirconia-based biomaterials: effect on the psichochemical and mechanical properties
Document typeMaster thesis
Rights accessOpen Access
Tetragonal zirconia polycrystal stabilized with 3% mol of yttria (3Y-TZP) is a ceramic material frequently used to replace traditional titanium dental implants given to its high flexural strength, biocompatibility, and aesthetic advantage. Additionally, it is demonstrated that surface topographical modification of zirconia at micro- and nano-scale levels encourages osseointegration and cell response, two crucial factors for successful dental implantation. Among the available treatments, hydrofluoric acid (HF) etching and laser patterning are two effective methods for roughening zirconia surfaces without severely damaging the surface implant. In fact, the main benefit of laser treatment over alternative methods is the ability to engrave precise structures on the material's surface in addition to producing microtopography. Subsequently, chemical etching produces homogeneous nanoscale roughness. The aim of this master’s thesis was to investigate the influence of the combination of laser patterning and acid etching on the psychochemical properties, microstructure and mechanical reliability of yttriastabilized zirconia for dental application. Zirconia discs were prepared by cold isostatic pressing and sintered at 1450ºC. Then, the samples underwent a surface modification using a nanosecond laser. The topographical pattern consisted on parallel grooves with a periodicity of 50 µm. Afterwards, half of the laser-structured samples were subjected to chemical etching using a hydrofluoric acid solution (40% HF for one hour). Mirror-like polished, only etched and only lasered surface specimens were used for the comparison with laser and etched samples. The topography of the specimens was characterized by means of confocal laser scanning microscopy (LSCM), contact profilometer, and scanning electron microscopy (SEM). Microstructural changes and the wettability of the samples were evaluated by Xray diffraction (XRD) and contact angle measurement, respectively. Furthermore, ball-on-three-balls (B3B) test was performed in order to characterize the mechanical properties of the samples. Results showed that the laser treatment was able to engrave well-defined and repeatable groove structures on the surface of 3Y-TZP, but side effects were generated such as pileup and microcracks. Furthermore, the pileup structures were eliminated and a nano-topography was generated by applying a chemical etching after the laser patterning. In terms of the microstructure analysis, the volume of monoclinic phase was found to be insignificant under every circumstance. Therefore, the treatments do not affect the stability of zirconia. Besides, the mechanical test revealed that the mean flexural strength was preserved on the chemically etched samples, but it decreased when laser treatment and laser treatment combined with etching were performed. Lastly, etched surfaces exhibited a lower contact angle.