Chemical Bonding to Novel Translucent Zirconias: A Mechanical and Molecular Investigation

Purpose: To investigate direct bonding of a 10-MDP-based cement to two novel translucent yttria-stabilized tetragonal zirconia polycrystal ceramics (4Y-TZP, 5Y-TZP) and observe the influence of thermocycling on this bonding. Materials and Methods: Powders of presintered and isostatically pressed 5Y-TZP, 4Y-TZP and 3Y-TZP were mixed with a 10-MDP-based cement (Panavia F 2.0), then stored in deionized water for 48 h at 37°C or thermocycled 10,000 times. Raman spectroscopy and Fourier-transform infrared spectroscopy were used to assess the presence of a functional group (PO₃^2-) that could indicate bonding before and after thermocycling. X-ray photoelectron spectroscopy was used to identify the presence of the suspected Zr-O-P bond in the same specimens. A shear-bond strength (SBS) test was conducted based on ISO 29022:2013. Results: Marked peaks assigned to the asymmetric vibrations of the PO₃^2- functional group were observed in both zirconias before and after thermocycling. The binding energy corresponding to Zr-O-P interactions (531.5 eV) was masked by the aluminosilicate in the filler of the cement. Shear bond strengths were approximately 20 MPa after water storage and approximately 6 MPa after thermocycling. No differences were found between the control group and the translucent zirconias. Conclusion: Direct bonding of the 10-MDP-based cement to both 4Y-TZP and 5Y-TZP was highly plausible. Both 4Y-TZP and 5Y-TZP may be promising alternatives to glass-ceramic restorations. Keywords: 10-MDP, chemical bond, shear bond strength, thermocycling, translucent, zirconia