An Effective and Convenient Way to Improve the Adhesion Property of the Dental Zirconia Prosthesis by Ar Plasma Jet With the Control of Environmental Humidity

Argon plasma jet is applied to the dental zirconia prosthesis to improve its hydrophilicity, so as to enhance its adhesion property. The relationship among the environmental humidity, hydrophilicity, and adhesion property of zirconia is investigated. The results show that the ·OH density, which mainly results from the electron excitation temperature and metastable Ar atom, is affected by the environmental humidity, and there are remarkable decrease in carbon content and increase in oxygen-containing functional groups on zirconia surface, which is induced by the ·OH. In addition, it is observed that the surface morphology is changed by the plasma. The double effects of functional groups and surface morphology contribute to the hydrophilicity of zirconia. Meanwhile, the hydrophilicity has an impact on the adhesion property of zirconia. The plasma treatment with the environmental humidity of 59.4% achieves the best results in this paper. It reduces the water contact angle to the minimum value of 3.4° ± 0.6° and brings an improvement of 50% in the bonding strength of zirconia. In order to apply the research achievements perfectly to practice, the environmental humidity has to be fixed at 59.4%. In fact, it is very difficult to precisely control. Hence, the shear bond strength test at the environmental humidity of 54%-66% is carried out. The results show that the shear bond strength of zirconia maintains at approximately 137.5%. This means that the variation of humidity in small scale has a little influence on the shear bond strength.