Objectives : We have recently reported the processing and physico-chemical characterization of a yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic produced via coprecipitation with mechanical properties comparable to commercially reinforced ceramic materials. The purpose of the present investigation was to study the bond durability between the experimental zirconia and a phosphate monomer resin cement after two surface conditioning methods. The hypothesis tested was that bond strength is influenced by both the surface conditioning methods and storage conditions.
Materials and methods : Y-TZP ceramic powders stabilized with 3 mol% of yttria were pressed and sintered at 1500 °C. Polished ceramic blocks (6 mm × 5 mm × 5 mm) were randomly assigned into 3 groups according to surface conditioning: SC-1: (Al 2 O 3 ) airborne-particle abrasion + silanization, SC-2: (SiO x ) tribochemical silica coating + silanization and SC-3 (control): no surface treatment. Resin cement containing phosphate monomer 1 was used as adhesive cement. After 24 h storage in distilled water (37 °C), the specimens were reduced to bonding areas of approximately 0.6 mm 2 . The 3 groups of specimens were subdivided and microtensile testing (1 mm min −1 ) was performed in the as-processed condition (dry) and after storage for 150 days and thermocycling (12000×, 5–55 °C). Tensile stress to failure was analyzed at 95% level of significance. Failure mode was assessed using scanning electron microscopy (SEM).
Results : Both the surface treatment ( p < 0.01) and the storage conditions ( p < 0.01) affected the results significantly (Two-way ANOVA, Tukey’s). Interaction terms were not significant ( p = 0.232). The highest percentage of pretest failures were experienced in the non-conditioned group (dry: 9%, aged: 87%). Bond strength values obtained for the tribochemical silica coating conditioning method (17.6 ± 4.4 MPa) were only slightly higher yet statistically significant than those obtained with airborne-particle abrasion (Al 2 O 3 ) (15.1 ± 6.9 MPa) and control (12.4 ± 5.0 MPa). Long-term water storage and thermocycling however reduced the bond strength values significantly ( p < 0.001). Overall the mean bond strength values obtained from long-term water stored and thermocycled conditions (1.5–4.0 MPa) were significantly lower than those of the dry (immediately tested) groups (12.4 ± 5.0–17.6 ± 4.4 MPa). SEM evaluation showed that all the fractures were mixed in all experimental groups.
Conclusions : Panavia F did not deliver acceptable bond strengths when the tested zirconia surfaces were not conditioned. Hence, even though in dry conditions favorable results were obtained with both particle abrasion methods, after aging, the results were poor.
1 Panavia F, Kuraray Co, Japan.