In vitro evaluation of long-term bonding of Procera AllCeram alumina restorations with a modified resin luting agent

Statement of problem. Bonded densely sintered aluminum oxide ceramic restorations such as Procera AllCeram laminates rely on a strong and long-term durable resin bond. Air particle abrasion and a phosphate-modified resin luting agent have the potential to provide such bonds to aluminum oxide ceramics, but their efficacy on the Procera AllCeram intaglio surface is unknown. The inherent microroughness of this surface may influence bond strengths, because micromechanical interlocking is a main contributor for adhesion of resins to ceramic materials. Purpose. This study evaluated the bond strength of a phosphate-modified resin luting agent with and without silanization to an air particle-abraded Procera AllCeram intaglio surface compared with a conventional resin-bonding system before and after artificial aging. Material and methods. Sixty square (10 x 10 x 2 mm) specimens of Procera AllCeram alumina ceramic with the Procera intaglio surface were air particle abraded with aluminum oxide. Composite cylinders (2.9 mm in diameter and 3.0 mm in width) were fabricated with Z-250 composite and bonded to the ceramic specimens with either Panavia 21 TC or Rely X ARC (control) and their corresponding bonding/silane coupling agents. In addition, Panavia was used without silanization as suggested in similar studies. Subgroups of 10 specimens were stored in distilled water for either 3 or 180 days before shear bond strength was tested with a universal testing machine (MPa) until fracture. The 180-day specimens were subjected to thermocycling at 2000 cycles every 30 days (12,000 cycles total). Data were analyzed with 1-way analysis of variance and Tukey's multiple comparison (α=.05). Failure modes were examined with a light microscope (original magnification × 25). Results. Differences between short-term and long-term groups were highly significant (P=.000). Bond strength with Rely X ARC and its silane coupling agent (22.75 ± 4 MPa) decreased significantly (P=.000) after artificial aging (3.32 ± 3.62 MPa). Panavia 21 after silanization revealed significantly different (P=.003) early (21.42 ± 4.3 MPa) and late (16.09 ± 2.37 MPa) bond strengths but achieved the highest bond strength after artificial aging. Bond strengths of Panavia without silanization both early (8.06 ± 2.1 MPa) and late (6.91 ± 2.49 MPa) were not significantly different. Failure modes were mainly adhesive at the ceramic surface for all groups. Conclusion. Panavia 21 in combination with its corresponding bonding/silane coupling agent can achieve an acceptable resin bond to the air particle-abraded intaglio surface of Procera AllCeram restorations after artificial aging, which had mixed effects on the other investigated groups. The conventional resin luting agent revealed the most dramatic decrease in bond strength.