Abstract
Objectives
The current recommended protocol for bonding zirconia restorations to teeth involves the use of an adhesive system containing phosphate monomers. But there is limited evidence that phosphate monomer produces a bond comparable to an etched silanised glaze layer on zirconia. This study evaluated the effect of using an etched and silanised glazed porcelain layer on the interfacial fracture toughness between a zirconia ceramic and resin cements. The effect of a phosphate monomer primer on resin bond to glazed zirconia was also used in this study.
Methods
Forty rectangular-shaped yttrium stabilised zirconia ceramic plates (VITA In-Ceram YZ, VITA, Bad Sackingen, Germany) (length: 20mm; width: 7mm; thickness 2mm) were sintered prior to air abrasion with 100 µm Al2O3 at two bar pressure. Twenty specimens were glazed with Akzent Glaze Spray (VITA Zahnfabrik; Bad Sackingen, Germany) and then etched with 9% hydrofluoric acid for 180 seconds prior to being silanised with Monobond-S (Ivoclar Vivadent; Schaan, Liechtenstein). Glazed and non-glazed specimens (controls) were further divided into two groups (n = 10) and randomly allocated to one of two resin bonding systems, Variolink II and Multilink-Automix (Ivoclar Vivadent). The Multilink-Automix groups were then treated with Metal/Zirconia Primer (Ivoclar Vivadent). Specimens were aged for 24 hours in a 37 °C water bath. Utilising the method described by Cheng et al. (1999), 12mm glass rods were bonded to zirconia plates using the two resin bonding systems and brought to failure using a universal testing machine. Critical plane strain energy values were calculated. The de-bonded specimens were examined under bi-focal optical microscope and scanning electron microscope to determine the mode of failures. Data were analysed using analysis of variance and Dunnett-T3 post-hoc tests with SPSS with a statistical significance set at 5%.
Results
The use of a glazed zirconia surface significantly improved the mean critical plane strain energy value (19.04 J/m2 to 202.35 J/m2) in the Variolink II group (p < 0.05), however there was no significant change (p > 0.05) with the Multilink-Automix Metal/Zirconia Primer group (59.40 J/m2 to 68.51 J/m2). In comparison to Variolink II, the mean value of Multilink-Automix group was significantly higher in the non-glazed group (19.04 J/m2 to 59.40 J/m2) (p < 0.05). Fractographic analysis showed predominantly cohesive (resin-resin) failure for the glazed groups and adhesive (resin-zirconia) failure in the non-glazed groups.
Conclusion
The interfacial fracture toughness for glazed zirconia bonded to Variolink II resin cement was superior to air-abraded zirconia that had been surface treated with a phosphate monomer primer bonded to Multilink-Automix resin cement. The additional application of Metal/Zirconia Primer on a pre-silanised glaze layer reduces the resin bond efficacy.