Durability of Resin Bonding to Zirconia Ceramic Using Different Primers

Purpose: The purpose of this in vitro study was the evaluation of the bond strength and its durability to zirconia ceramic after using two phosphate monomer-containing primers. Materials and Methods: Plexiglas tubes filled with composite resin were bonded to zirconia ceramic disks (Cercon) which were air abraded (50 µm Al2O3 at 2.5 bar pressure) and ultrasonically cleaned in isopropanol for 3 min. Groups of 16 specimens each were bonded with Multilink Automix using either no primer (NO) or using a metal primer (AP: Alloy Primer, Kuraray) or a metal and zirconia primer (MZ: Metal/Zirconia Primer, Ivoclar Vivadent). Another group bonded with a phosphate monomer (MDP) containing resin (PF: Panavia F, Kuraray) served as control for an established bonding method to zirconia ceramic. Prior to tensile bond strength testing, subgroups of 8 bonded specimens were stored in distilled water (37°C) for either 3 or 150 days. Additionally, the 150-day specimens were thermocycled (TC) between 5° and 55° 37,500 times. Statistical analyses were conducted with the Wilcoxon rank sum test. Results: Without primer, the median initial bond strength of Multilink Automix to zirconia ceramic was relatively low (12.4 MPa). The primers improved the bond strength significantly (p = 0.05), increasing them to 38.5 MPa (Metal/Zirconia Primer) and 53.6 MPa (Alloy Primer). The Alloy Primer group did not differ significantly from the control group Panavia F with 51.8 MPa. After 150 days storage and TC, specimens without primer (NO) debonded spontaneously, while the other groups showed significantly reduced bond strengths ranging from 19.7 to 37.2 MPa. Conclusion: Using phosphate monomer-containing primers on air-abraded zirconia ceramic improves bonding to zirconia ceramic significantly. Keywords: artificial aging, zirconia ceramic, composite resin, tensile bond strength, ceramic primer, metal primer