Some surface treatments for improving the durability of zirconia-based restorations

Abstract

Zirconia has now been increasingly used in modern dental prosthetic practice due to its high mechanical strength, good esthetics, and excellent biocompatibility. However, the application of zirconia-based dental restorations is still constrained by its chemical inertness and the resultant relatively weak bonding properties, including porcelain to zirconia bonding, and resin to zirconia bonding. Therefore, many investigations have been carried out on the development of an effective method of surface modification on zirconia for improving its bonding ability. The aim of this laboratory study was to evaluate the effects of some new modified surface treatments on the adhesion durability of dental zirconia prosthetic system.

In Part I and Part II, the application of laser surface treatment was examined. Laser energy was utilized and applied on zirconia surface before porcelain veneering procedure. Its influence on porcelain zirconia integration interface was mechanically tested and compared with sandblasting treatment. The changes in porcelain zirconia shear bond strength and mechanical strength values of zirconia with the modulation of output energy were recorded. In Part III and Part IV, several types of coating treatment, such as tribochemical approach, silica powder coating, and zirconium silicate coating, were compared with their effects on resin zirconia bonding. The changes in resin zirconia shear bond strength under different aging conditions were observed. The elemental analysis was also performed for clarifying the chemical composition of zirconia surface.

The application of laser produced a flake-like micro-retentive structure on zirconia surface. Laser irradiation with the output energy higher than 11.3 W/cm2 was effective in increasing porcelain to zirconia bond strength values. The biaxial flexural strength of zirconia was not significantly affected by laser irradiation with the settings in this study. However, most of the laser treatments still demonstrated slightly lower flexural strength values compared with the control group. No changes in crystalline structure were detected after laser treatment with X-ray Diffraction (XRD) technique. Resin to zirconia shear bond strength was significantly increased after surface coatings. Without surface treatment the bonding between resin and zirconia was susceptible to artificial aging effects. Zirconia and silica-coating groups demonstrated the highest resistance to hydrolytic influence. On the other hand, the chemical changes of zirconia surface were still in need of clarification.

It was concluded that porcelain zirconia bonding could be effectively enhanced by applying both sandblasting and a new laser irradiation approach. Laser irradiation might be a potential approach as a surface treatment for improving the quality of porcelain zirconia bonding interface. The strong and reliable resin zirconia integration could not be achieved without appropriate surface pre-treatment. This coating treatment is a promising approach for strengthening resin to zirconia adhesion.