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A novel etching technique for surface treatment of zirconia ceramics for improved adhesion between resin based materials and zirconia ceramics

 

Objectives:

Bonding of zirconia crowns and bridges to abutments is important, not only bonding of the thin resin layer to the abutment, but also bonding to the zirconia ceramic is crucial. Both mechanical as well as chemical adhesion is desired. Mechanical retention of dental porcelain achieved by etching with moderately concentrated hydrofluoric acid is not possible with zirconia ceramics. The purpose of this study was to show that etching is possible with relative low melting fluoride compounds (such as ammonium hydrogen difluoride and potassium hydrogen difluoride).

 

Methods:

Before melting the fluorides can be introduced as powders or as an aqueous slurry to the contact surfaces of the zirconia. SEM of the etched yttria-stabilized zirconia surface revealed a surface similar to an HF-etched dental feldspathic porcelain surface. Shear bond testing (n=10) was done with zirconia attached to zirconia with the Duo-Link composite luting cement (Bisco) after treatment of the etched zirconia surfaces with Bis-Silane (Bisco) and the Porcelain Bonding Resin (Bisco).

 

Results:

Values ranging from 20 to 68 MPa for adhesive strengths with surfaces etched with: powders; K[FHF] (31.2±7.5) MPa; NH₄[FHF] (31.0±11.8) MPa, and slurries: K[FHF] (42.7±12.7) MPa; NH₄[FHF] (40.3±10.0) MPa (mean and standard deviation). A composite, Charisma A3 (Heraeus Kulzer), attached to zirconia with the same bonding system and surface treatments gave results ranging from 7.5 to 15.2 MPa with the zirconia surfaces etched with: powders; K[FHF] (11.1±2.2) MPa; NH₄[FHF] (12.9±2.0) MPa, and slurries: K[FHF] (10.0±1.8) MPa; NH₄[FHF] (11.9±1.7) MPa. The lower adhesion strength values of the composite/zirconia system than with zirconia/zirconia system were probably due to strains induced during polymerization shrinkage accompanied by ~ 78/268 ~ internal stresses.

 

Conclusions:

Good adhesion to zirconia can be achieved by the procedure including etching with selected melted fluoride compounds.

 

Authors:
Eystein Ruyter, Ketil Kvam, Nalini Vajeeston, Torbjørn Knarvang. NIOM – Nordic Institute of Dental Materials, Oslo, Norway.