The effects of four primers and two cement types on the bonding strength of zirconia.

Background: To evaluate the effects of four ceramic primers and two cement types on the bonding strength and durability between zirconia and resin cement.

Methods: A total of 115 polished and air-abraded zirconia blocks were randomly divided into five groups (with 23 in each group) to test the performance of various primers. Meanwhile, all primer samples were divided into two subgroups randomly to measure the difference between the two cement types. Group No treat - Clearfil SA Cement (NT-C); group No treat - RelyX Unicem Cement (NT-U); group Z-Prime Plus - Clearfil SA Cement (ZPP-C); group Z-Prime Plus - RelyX Unicem Cement (ZPP-U); group Rely X Ceramic Primer - Clearfil SA Cement (RCP-C); group Rely X Ceramic Primer - RelyX Unicem Cement (RCP-U); group Clearfil Ceramic Primer - Clearfil SA Cement (CCP-C); group Clearfil Ceramic Primer - RelyX Unicem Cement (CCP-U); group Monobond-S - Clearfil SA Cement (MS-C); group Monobond-S - RelyX Unicem Cement (MS-U). According to the type of cement, the specimens were randomly selected for electron microscope scanning and energy spectrum analysis, and the tightness of zirconium porcelain resin adhesive interface was observed. The bonding strength of different adhesives and aging experiments were tested by shear test mode, and the shear strength of each experimental group was analyzed by one variable three factor analysis of variance.

Results: All primers in the treated groups maintained a pristine structure without micro-crack, while the non-primer treatment sample exhibited obvious micro-cracks. Furthermore, among the four primers, the sample treated with Clearfil Ceramic Primer (CCP) obtained the highest bonding strength, with a statistically significant difference (P<0.05). However, cohesive failure mainly occurred in the CCP group before thermal cycles, and mixed failure occurred after thermal cycles.

Conclusions: CCP is the superior primer, and can improve the bonding strength between zirconia and resin cement. Because the thermal cycles have a significantly adverse effect on the shear bond strength, CCP can be helpful in improving the durability of the zirconia bonding strength. Furthermore, the two cement types exhibited a similar bonding performance for zirconia.