Interaction of zirconia primers with yttria-stabilized zirconia surfaces

Objectives Recently several zirconia primers have been introduced to mediate bonding of dimethacrylate resins to yttria-stabilized zirconia frameworks (Y-TZP). The aim of the study was to evaluate the changes in surface chemistry of Y-TZP frameworks induced by zirconia primer treatments. Methods Polished Y-TZP discs (Lava, 3M ESPE), ultrasonicated for 10 min in ethanol, water-rinsed and air-dried were treated as follows: A: Reference (no treatment), B: Treatment with Z Prime Plus (Bisco), and C: Treatment with Z-Bond (Danville Materials). The primer films formed on Y-TZP surfaces were air-dried, left intact for 5 days (dark storage, 37 °C, 40% RH), rinsed with 10 ml acetone to remove the loosely bound fractions, air-dried and studied by: (a) reflection optical microscopy, (b) reflection Fourier transform infrared microscopy (RFTIRM) and (c) scanning electron microscopy/energy dispersive X-ray microanalysis (SEM/EDX). Results An amorphous thick film was observed on primed and acetone rinsed Y-TZP surfaces after B treatment, whereas C treatment formed a thinner film with phase-separated aggregates. The RFTIRM study showed that both primers induced carboxylate salt formation on Y-TZP. Phosphate groups in a dissociative form have been identified on Y-TZP, as well, indicating formation of phosphate salts. EDX analysis showed increased C, O and P content on the films, which masked the substrate contributions. Significance The primers tested formed carboxylate and phosphate salts on Y-TZP, promoting thus chemical adhesion. However, the differences in the film forming properties and water solubility between the carboxylate and phosphate salts may affect the strength and the durability of adhesive resin interfaces with Y-TZP, as mediated by these primers.