Elsevier

Dental Materials

Volume 14, Issue 1, January 1998, Pages 64-71
Dental Materials

Bonding to zirconia ceramic: adhesion methods and their durability

https://doi.org/10.1016/S0109-5641(98)00011-6Get rights and content

Abstract

Objectives. Resin bonding to yttrium-oxide–partially-stabilized zirconia ceramic (YPSZ) cannot be established by standard methods that are utilized for conventional silica-based dental ceramics. It was our hypothesis that adhesive bonding methods suitable for glass-infiltrated alumina ceramic can also be used to bond successfully to YPSZ. To prove this hypothesis, bonding methods suitable for alumina ceramic were used on YPSZ and the tensile bond strength and their durability evaluated in vitro.

Methods. Plexiglass tubes filled with resin composite were bonded to YPSZ discs following various adhesion protocols. Groups of 16 samples were bonded using seven different bonding methods. Subgroups of eight bonded samples were tested for tensile strength following storage in distilled water (37°C) for either 3 or 150 days. In addition, the 150 day samples were thermal cycled 37 500 times as a method to stress the bond interface. The statistical analysis was made with the Kruskal–Wallis test followed by multiple pair-wise comparisons of the groups using the Wilcoxon rank sum test.

Results. Sandblasting alone, the additional use of a silane or acrylizing resulted in an initial bond of a conventional BisGMA resin composite to YPSZ which failed spontaneously over storage time. The use of the BisGMA resin composite after tribochemical silica coating of YPSZ and the use of a polyacid-modified resin composite after sandblasting of YPSZ resulted in an initial bond which decreased significantly over storage time (p=0.05). A durable resin bond to YPSZ was achieved only after sandblasting the ceramic and using one of two resin composites containing a special phosphate monomer.

Significance. A durable bond to YPSZ was achieved only by using resin composites with a special adhesive monomer. Therefore, the hypothesis of the study was partially proved as a durable bond to alumina ceramic is achieved with the same resin composites. However, it was partially disproved as tribochemical silica coating of YPSZ did not result in a durable resin bond as it does on glass-infiltrated alumina ceramic.

Introduction

Pure zirconia exhibits a polymorphic phase transformation from a cubic to a tetragonal to a monoclinic phase accompanied by a high volume change when cooling down from high temperatures after sintering which makes the sintered body unstable (Yanagida et al., 1996). However, the addition of 3–6 wt% Y2O3 stabilizes the zirconia in the tetragonal phase which is otherwise not stable at room temperature (Green et al., 1989, Yanagida et al., 1996). Zirconia with Y2O3 added in concentrations less than those required to stabilize zirconia completely is called yttrium-oxide–partially-stabilized zirconia (YPSZ) when the sintered ceramic contains a mixture of cubic and tetragonal phases (Green et al., 1989, Yanagida et al., 1996). YPSZ has optimized physical properties and exhibits much more fracture toughness and fracture strength than alumina ceramic (Takagi et al., 1985, Rieger, 1989).

Since the late eighties, YPSZ has been used in orthopaedics for total hip replacement (Christel, 1989, Cales et al., 1994). In dentistry, YPSZ has been successfully tested in animals as a material for oral implants (Akagawa et al., 1993). Recently, YPSZ posts for restoring endodontically treated teeth have been introduced (Sandhaus and Pasche, 1994, Meyenberg et al., 1995, Simon and Paffrath, 1995, Dietschi et al., 1997, Kern et al., 1997), and YPSZ abutments for dental implants are currently being developed (Studer et al., 1996).

For the more recent dental applications of YPSZ, methods are not known for achieving a long-term durable resin bond to YPSZ. In the literature, only limited data regarding bonding methods to zirconia ceramic is published. Hydrofluoric etching and silanization, which enhances the resin bond to conventional silica-based ceramics, does not improve the resin bond strength to alumina or zirconia ceramics (Salmang and Scholze, 1982, Pape et al., 1991). However, it has been shown that silica coating followed by silanization can be successfully used for bonding glass-infiltrated alumina ceramic (Kern and Thompson, 1995a). In the same study, phosphate monomer-containing resin composites were successfully bonded to sandblasted alumina ceramic, while using a conventional BisGMA resin composite a durable resin bond to alumina ceramic was not achieved.

It was our hypothesis that bonding methods suitable for alumina ceramic can also be used to bond successfully to YPSZ. It was assumed that bonding conventional BisGMA resins to YPSZ requires silica coating prior to silanization, while bonding with phosphate monomer containing resins does not need a silica layer to achieve a stable resin bond sandblasted YPSZ.

The purpose of this study was to prove this hypothesis. Therefore, alternative adhesive methods for bonding to zirconia ceramic were evaluated by investigation of the long-term bond durability and bond failure modes as determined by SEM characterization. Bond stability was evaluated by a combination of long-term water storage and frequent thermal cycling, as it has been shown that both parameters influence different bonding systems differently, but an acceptable bonding system should not be affected by either of these clinically relevant ageing parameters (Chang et al., 1993).

Section snippets

Materials and methods

Experimental industrial manufactured yttrium-oxide–partially-stabilized zirconia ceramic discs (94.9% ZrO2 stabilized by 5.1% Y2O3, BCE Special Ceramics, Mannheim, Germany) were used for this study. The discs had a diameter of 7.0 mm and a thickness of 3.4 mm. The ceramic surface was industrially machined with diamond discs by the manufacturer (Ra=0.44 μm). All samples were then sandblasted with 110 μm Al2O3 at 2.5 bars (0.25 MPa) pressure (13 s) at a distance of 10 mm and then ultrasonically cleaned

Results

The tensile bond strength values are summarized in Table 2 for all seven bonding groups and the two storage conditions. Statistically significant differences between the bonding groups and between the storage times are indicated in the same table.

The bond strength of the BisGMA resin composite to sandblasted or sandblasted and silanated YPSZ (groups SAND and SIL) was initially relatively low with medians of 14.0 MPa and 15.1 MPa, respectively. During the 150 day storage time with 37 500 thermal

Discussion

Long-term water storage at a constant temperature or thermal cycling are the most often used conditions to simulate aging of resin bonds. However, it has been shown that different bonding systems are influenced differently by these two parameters (Chang et al., 1993). As both are considered to be clinically relevant aging parameters (Bailey and Bennett, 1988, Atta et al., 1990, Chang et al., 1993), in this study long-term water storage was combined with thermal cycling at regular intervals to

Acknowledgements

The authors thank DeTrey/Dentsply in Konstanz, Espe in Seefeld, Heraeus Kulzer in Wehrheim, all Germany, and Kuraray, Osaka, Japan, for providing materials and equipment.

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