Long-term Bond Strength to Zirconia Ceramic after Different Surface Conditioning

Objectives: The purpose of this in-vitro study was to evaluate the influence of the surface conditioning parameters on the long-term bond strength to zirconia ceramic.

Materials and Methods: Zirconia ceramic disks were made from of Cercon ceramic (Degudent, FRG) and polished down to 600 grit with abrasive paper. Plexiglas tubes (inner diameter 3.2 mm) filled with resin Clearfil F2 (Kuraray, J) were bonded with composite luting resin (Multilink Automix, Ivoclar-Vivadent, FL) to the zirconia disks. Three surface conditions (unconditioned, air-born particle abrasion at 0.05 MPa, air-born particle abrasion at 0.25 MPa) and four priming conditions (no priming, priming with Metal/Zirconia Primer (Ivoclar-Vivadent), priming with Alloy or Clearfil Ceramic Primer (both Kuraray)) were tested. Subgroups of 8 specimens of each combination were bonded and stored in distilled water (37°C) either for 3 days without thermal cycles (TC) or for 120 days with 37,500 TC from 5°C to 55°C. Tensile bond strengths (TBS) were determined with a universal testing machine (Z010/024, Zwick, FRG) at a crosshead speed of 2 mm/min. Statistical analysis was performed with the Wilcoxon rank sum test adjusted according to Bonferroni-Holm for multiple testing at a=5%.

Results: Medians of TBS in MPa to zirconia ceramic after different surface treatments and storage times were:

Priming conditions	No Primer	Metal/Zirconia Primer	Alloy Primer	Clearfil Ceramic Primer
Surface conditions	3 d          150 d	3 d          150 d	3 d         150 d	3 d         150 d
Unconditioned	0Db               0**	8.1Cb              0*b	17.7Bb          0*b	24.1Ac         0*b
Air-abrasion 0.05 MPa	15.5Ca            0C*	28.2Ba        17.1Ba	42.7Aa        32.2Aa	40.0Ab       28.7Aa
Air-abrasion 0.25 MPa	12.1Ca            0C*	36.2Ba       19.2Ba	44.8A,Ba     23.2Aa	48.5Aa       30.7Aa

Statistically different medians (p<0.05) are indicated by different superscript upper case letters (within a row for the same storage time) or by different subscript lower case letters (within a column). *All specimens debonded spontaneously, no statistical test conducted.

Air-born particle abrasion and priming improved long-term TBS to zirconia ceramic, while reduction of air-pressure had no significant effect.

Conclusions: Blasting pressure of air-abrasion might be reduced to minimize surface damage of zirconia ceramic during conditioning.