Over the past several years, dentists have been driven to provide more esthetic and desirable anterior full or partially covered anterior restorations to meet the desires of our patients. This is especially true for the multi-unit anterior bridge. The problem has always been to achieve both strength and esthetics. The porcelain-fused-to-metal crown certainly provides durability with some reasonable esthetics for crowns. And you would not consider anything but a PFM bridge, be it posterior or anterior. However, with the increasing esthetic demands of our patients, even the best PFM crowns and bridges appear too bulky and opaque. And no matter how well they are fabricated, it is only a matter of time before some metal starts to show, and in the anterior this is completely unacceptable.
To alleviate this problem, new materials were provided and laboratory techniques developed to produce an all-ceramic single restoration that was highly esthetic. In fact, the esthetics they were using created restorations that were indistinguishable from natural teeth. One of the major problems, however, was the durability of these restorations. Many of these restorations, crowns, and veneers failed due to fracture within three years of insertion. I know I had my share of failures. Another problem, which has always been a factor, is the wear of the opposing dentition. This is especially problematic with the mandibular anterior teeth. Thus, the challenge now is to fabricate an esthetic but durable all-ceramic that has wear characteristics favorable to the opposing dentition, and is available for anterior multi-unit bridges.
New Technologies, New Materials
The fabrication of all-ceramic, esthetic, and durable anterior crowns and bridges is made possible through the combination of new technology and new materials. The new technology is CAD/CAM, computer aided design/computer aided manufacturing. An example of CAD/CAM technology is CEREC inLab (Sirona), which fabricates and all-ceramic (Zirconia) framework that is not only very thin, light, and durable, but also available in various tooth color shades that improve the life-like esthetics of the final restoration. It must be pointed out that while there are no five-to-ten-year longevity studies for these restorations, three-year data from studies in Germany and Switzerland, where Zirconium-core technology was developed, report no fractures of Zirconia framework (1). One of the newer materials, Zirconia (ZRO2)—an oxidized form of the Zirconium metal—is able to resist high-stress areas internally, such as sharp line angles in the tooth preparation, grinding damage during internal adjustment, and stresses generated by chewing or thermal changes in the mouth (2). In addition, transformation-toughening gives Zirconia excellent mechanical properties: high flexural strength—900 Mpa to 1.2 Gpa—and toughness—7–8 MP.M a –0.5 (3) (fig. 1). Other beneficial properties include good biocompatibility (4).
Another new material for CAD/CAM fabrication of single and multi-unit all-ceramic frameworks is the VITA Y2 Zirconia Block, which when milled and sintered can allow for the framework to be fabricated with a facial thickness of 0.2 mm to 0.3 mm (5)—as opposed to other materials requiring 0.5 to 0.6 mm thickness. It is this thickness that results in a more translucent esthetic and lifelike restoration, when used with VMS porcelain and a material called the effect liner, a technique developed by Edward McLaren and Russell Giordano, II.
The VM9 porcelain by VITA is the final new material to discuss. The key element of VM9 is its fine particle size. A reduction of particle size in a ceramic generally increases the strength and toughness of the material (7). Other clinical benefits include enhanced polishability, and therefore reduced wear of opposing enamel tooth structure. In short, a highly polished VM9 ceramic restoration is not as coarse as older porcelain, and is much kinder to the opposite natural dentition. For their article, “Zirconia-Based Ceramics: Material Properties, Esthetics, and Layering Techniques of a New Veneering Porcelain, VM9,” published in Quintessence of Dental Technology, 2005 Vol. 28—an excellent source for properties of VM9 porcelain—McLaren and Giordano conducted tests on Zirconia, VM9, and other ceramic materials with .23 spec to flexural strengths, roughness, polishability, and wear values as evidenced by their results.
Utilizing these studies and results, Vident™ has introduced a new restoration called InVizion™, which is a CAD/CAM fabricated VITA R Y2 frame veneered with VITA VM9 veneering ceramic material. These restorations can be both single and multiple units, specifically designed for anterior restorations that provide excellent strength and esthetics. The Y2 Zirconia core provides the strength and durability as well as the opportunity to achieve maximum esthetics due to its thickness. VM9 porcelain provides for the lifelike esthetics as well as the similar-wear characteristics of enamel, which is kinder and gentler to the opposing dentition.
Conclusion
In the past, dentists may have sacrificed esthetics for durability with respect to anterior single crowns and multi-unit bridges; however, our patients are now demanding anterior restorations and prosthesis that appear natural and lifelike. New technologies and materials enable dentists to provide the desired restorations with the confidence that they will be esthetic and enjoy longevity. InVizion™ by Vident™ might be just what the doctor ordered.
References
Sailer I, Luthy H, Feher A. et al: 3-year clinical results of zirconia fixed partial dentures made by direct ceramic matching (DCM) (abstract 74) J Dent Res 2003;82:B-21
McLaren EA, Giordano RA: Zirconia-based ceramics: material properties, esthetic and layering techniques of new veneering porcelain, VM9. Quintessence Of Dental Technology 2005; Vol. 28 100
McLaren EA, Giordano RA:. Zirconia-based ceramics: material properties, esthetic and layering techniques of new veneering porcelain, VM9. Quintessence Of Dental Technology 2005; Vol. 28 101
Warashina H, Sakano S, Kitamura S, et al: Biological reaction to alumina, zirconia, titanium, and polyethylene particles implanted onto murine calvaria. Biomaterials 2003; 24: 3655-3661
McLaren EA, Giordano RA: Zirconia-based ceramics: material properties, esthetic and layering techniques of new veneering porcelain, VM9. Quintessence Of Dental Technology 2005; Vol. 28 104
McLaren EA, Giordano RA: Zirconia-based ceramics: material properties, esthetic and layering techniques of new veneering porcelain, VM9. Quintessence Of Dental Technology 2005; Vol. 28 105
Swain MV. Toughening mechanisms for ceramics. Mater Sci Forum1989-; 13:237-253
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