Bonding Between Zirconia and Resin Cement - Effect of Surface Treatment

Abu Ruja, Mahmood 1, 2 ;   De Souza, Grace M. 1 ;  Tam, Laura E.  1 ;  Simmons, Craig A.  1, 2 ;  Finer, Yoav  1, 2

1. Faculty of Dentistry, University of Toronto; 2. Institute of Biomaterials and Biomedical Engineering, University of Toronto

Background: Yttria-tetragonal zirconia polycrystalline (Y-TZP) is a non-silicate ceramic of great interest due to its excellent mechanical properties. However, Y-TZP has poor bond strength to the cement and the underlying tooth accordingly due to the absence of SiO2. It can be hypothesized that surface treatment of Y-TZP could change surface properties and improve its bond strength.

Objective: To assess the effect of Y-TZP surface treatments by sandblasting (SNB) or tribochemical silica coating (SIL) on its surface properties and bond strength to resin cement.

Methods: Fully sintered Y-TZP (4×8.8×8.8mm) received either no treatment (CTL) or one surface treatment (SNB or SIL). Surface roughness (profilometer), quantification of crystalline phases (X-ray diffraction-XRD), contact angle (goniometer), and chemical composition (Energy-dispersive x-ray spectroscopy-EDS) were evaluated for each group (n=3/group). Y-TZP slices (n=5/group) were cemented to resin composite using resin-based cement combined with a silane and 10-methacryloyloxyidecyl-dihydrogen phosphate (MDP)-containing adhesive. Specimens were transversely cut to produce 1x1mm2 beams using a water-cooled sectioning saw (3 beams/specimen). The beams were incubated in distilled water, and microtensile tested after 48 hours storage at a crosshead speed of 0.5mm/min. Statistical analyses included one-way analysis of variance and Tukey’s test (P<0.05).

Results: SIL significantly increased microtensile bond strength (SIL:9.90±1.45>SNB:6.40±0.70>CTL:5.30±0.74, all in MPa), and significantly reduced contact angle (SIL:6.57°±2.37°<SNB:20.64°±4.45°<CTL:50.97°±6.30°). Surface roughness values (Sa) for SIL and SNB were higher than CTL (SNB:0.56±0.19=SIL:0.39±0.06>CTL:0.22±0.05). Surface treatments increased the relative monoclinic phase (SNB:29.33%±2.52%= SIL:26%±2%>CTL:0%).

Conclusion: SIL is an effective treatment to improve the short-term bond strength between Y-TZP and resin cement, but further research is necessary to ensure the long-term effect and assess whether degradation of the bond is increased by this treatment.

Significance: The results of this study provide the basis for a further exploration aiming at optimizing the application of surface treatments for enhancement of the bond between zirconia and the tooth.