The effect ofHydrofluoric acid concentration and etching time on the surface topography and chemistry of yttria-stabilized zirconia was assessed. Besides, to understand the etching mechanism, the reaction products present in solution and on the surface were characterized. The results indicate suitable parameters for a fast and uniform roughening of zirconia. The formation of adhered fluoride precipitates on the surface is reported for the first time and highlights the importance of cleaning after etching. Finally, it is shown that monitoring the time allows controlling the surface roughness, smooth–rough transition and fractal dimension, which should make possible the fabrication of implants with an optimal topography. Rough surfaces have been shown to promote osseointegration, which is one of the keys for a successful dental implantation. Among the diverse treatments proposed to roughen zirconia, hydrofluoric acid (HF) etching appears to be a good candidate, however little is known about this process.

Among the different surface chemical treatments already exper-imented in the literature to achieve this purpose, hydrofluoric acid(HF) etching appears to be a good candidate. Although other chem-icals, such as hypophosphorous acid or an equimolar mixture ofpotassium hydroxide and sodium hydroxide, have been reportedto successfully etch Y-TZP, HF presents the advantage tobe a fast etchant at room temperature. More importantly, Gahlertet al. evidenced that HF etching of zirconia implants enhances bone apposition resulting in high removal torque values. Besides, HF etching can be successfully associated to sandblasting.Ito et al. showed that the combination of both treatments leads toan increase in the proliferation rate and expression of ALP activity ofosteoblast-like cells (MC3T3-E1) and Bergemann et al. foundrecently that it enhanced the human primary osteoblast maturation.

Despite of numerous studies in which Hydrofluoric acid  has been used forthe etching of Y-TZP, to the best of the knowledge of the authors,very little is known about the chemical reaction involved. Besides,the influence of parameters such as time and concentration is notdocumented. The objectives of the present work are therefore todetermine suitable conditions for a fast and uniform rougheningof dental zirconia, to provide a complete surface characterizationwith a special emphasis on topography and to contribute to theunderstanding of the etching mechanism. Questions related to theinfluence of etching on the mechanical properties and long-termreliability are treated in a second article.