Developments in ceramic materials science for dental applications have led to expanded use of zirconia (ZrO2), which provides better fracture resistance and long-term viability when compared to porcelain and other non-metallic alternatives. A clinical problem with ZrO2 implant or prosthetic components is the difficulty in achieving suitable adhesion with intended substrates. Traditional adhesive techniques used with silica-based ceramics do not work effectively with ZrO2. Acid-etching to increase surface area and roughness is ineffective, and air abrasion must be done aggressively to yield suitable morphological changes, but can cause surface flaws that lead to reduced fatigue resistance. Silane chemistry is only viable if ZrO2 surfaces are SiO2-coated, via deposition of a thin SiO2 layer that mechanically adheres to the surface. This allows use of silane and resin cement, but has limitations. Chemically modified resin cements, intended solely for use with ZrO2 are available, but also have limitations. The objective of this project is to explore use of a vapor-phase chloro- silane pretreatment to modify ZrO2 surfaces with chemically attached, nano-scale, silicate films. These films alter surface chemistry to mimic pure silica, and allow the surface to be silane treated effectively with standard silanes. Preliminary data show that the proposed chloro-silane pretreatment results in significant improvements in bond strength of ZrO2 to dental composites using standard resin cements, when compared to untreated surfaces or surface treatment alternatives (i.e. CoJet). This process would enable clinicians to place ZrO2 components effectively using accepted adhesive silane and resin cementation techniques. This technology might also be used to enhance adhesion of veneering porcelain onto ZrO2 substructures. The primary goal of this research is to develop a practical method to chemically modify the surface of ZrO2 bioceramics to facilitate adhesive bonding using commercially available silanes and resin cements. The proposed specific aims are to: 1) Show that a vapor phase chloro-silane pretreatment can be used to deposit specific silicate compounds on ZrO2 to increase viability of silanation treatments; 2) Test the hypothesis that chloro-silane-modified ZrO2 surfaces, silane treated and bonded with resin cement, will display greater bond strengths when compared to unmodified ZrO2 surfaces bonded using phosphate-modified or resin-based luting cements; 3) Test the hypothesis that deposited silicate layers will resist environmentally-assisted degradation, and display fatigue resistance equal to that achieved with silane-modified porcelain; 4) Test the hypothesis that chloro-silane-modified ZrO2 will display greater adhesion to veneering porcelain in a layered ceramic structure when compared to unmodified ZrO2; and 5) Test the hypothesis that the chloro-silane modification will produce a conformal silicate layer on ZrO2 endodontic posts, facilitating enhanced adhesion to composite cores when compared to unmodified ZrO2 posts. It is believed that this proposed technology will have a direct and positive impact on existing dental ceramic applications, enhancing utility and improving long-term clinical efficacy.
High toughness dental ceramics, such as zirconia, offer the best combination of fracture resistance, esthetics, biocompatibility and environmental friendliness available for clinical use. A major problem with these materials is related to difficulties associated with achieving strong, durable bonding to tooth structure or other biological tissues, or synthetic substrates via adhesive cementation techniques. The technology being explored in this study has the potential to significantly improve the ability to adhesively cement zirconia ceramics using currently accepted and well understood silane bonding protocols, which should greatly increase the long term clinical viability of restorations made from these materials.
| Smith, Robert L; Villanueva, Carlos; Rothrock, James K et al. (2011) Long-term microtensile bond strength of surface modified zirconia. Dent Mater 27:779-85 |
| Thompson, Jeffrey Y; Stoner, Brian R; Piascik, Jeffrey R et al. (2011) Adhesion/cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 27:71-82 |
