Effect of primer on the bond strength of resin cement to zirconium oxide ceramic

Abstract

Statement of problem: Zirconium oxide (zirconia) ceramics have low surface energy and smooth intaglios, Which can create insufficient retention and prosthetic restoration loss. Newly introduced primers may enhance the adhesive property of resin cements to zirconia. Independent evaluation of these products is necessary to confirm effectiveness. Objectives: To compare the effect of primers on the bond strength of resin cements to zirconia, in vitro at 24 hours and after 5.5 days under artificial aging conditions. Materials and Methods: For the 24 hours test, 130 specimens measuring 12x12x2mm were sectioned from In-Ceram YZ (Vita) zirconia blocks. All sectioned specimens were fully sintered at 1530[degrees]C per instructions. One newly developed primer Z-Prime (ZP) (Bisco), and another commercially available primer Clearfil Ceramic Primer (CCP) (Kuraray), were applied prior to cementation to 90 specimens, and 40 specimens were left unprimed (controls). Three resin cements were evaluated: Duo-Link (DL) (Bisco), RelyX Unicem (RXU) (3M-ESPE), and SmartCem2 (SC2) (Dentsply). Cements were mixed per manufacturers’ recommendations and applied to the specimens using an Ultradent jig with a 2.38 mm aperture. All bonded specimens set for 20 min under a load of 90g, and were stored in water at room temperature (22[degrees]C) for 24h. Bond strengths of resin cements to zirconia were tested in shear mode in an Instron testing machine using a “flat" blade at 0.5mm/min. Data was analyzed with one-way ANOVA to ascertain effects of primers. For the long-term test, In-Ceram YZ (IC) and Cercon (CE) (Dentsply) zirconia blocks were sectioned into 144 specimens each and sintered. IC and CE specimens were randomly divided into 36 groups of n=8. Half of the groups were bonded with the resin cements and primers, and thermocycled (TC) 5,000 times between 5[degrees]C and 50[degrees]C with dwell times of 30 seconds. The other 18 groups were bonded and stored in 22[degrees]C water (WS) for the equivalent time (5.5 days). All groups were subject to shear bond strength testing. Statistical analysis was performed and random specimens were subject to scanning electron micrography. Results: At 24 hours, DL had significantly higher mean shear bond strengths (MSBS) than did RXU and SC2; RXU and SC2 were not significantly different. There were significant increases in MSBS of between 23% and 257% with ZP specimens, and between 29% and 206% with CCP. In the long term tests, four of the unprimed TC groups (DL/IC, DL/CE, SC2/IC, and SC2/CE) spontaneously debonded. Significant (p[less than]0.05) loss of mean SBS was observed with TC, compared to WS. Three-Way ANOVA showed both primers having significant increases in MSBS in WS and TC. RXU and DL gave significantly higher MSBS than did SC2; RXU and DL were not significantly different. Conclusion: The use of the primers caused a significant increase in MSBS. There was no significant difference in MSBS associated with CE versus IC. The use of DL was associated with significantly higher MSBS than RXU and SC2, and RXU was higher than SC2. Overall, ZP was associated with significantly higher MSBS than CCP. TC caused significant decreases in MSBS versus WS.