With the development of materials science and the improvement of people's aesthetic awareness, all-ceramic restorations have been widely used because of their good aesthetic properties. Zirconia ceramic restorations have gradually become the first choice for restoration of posterior tooth defects due to their good mechanical properties, biocompatibility, less impact on the results of radiological medical examinations, and less wear on the natural teeth of the opposite jaw.
Ceramic materials are divided into inert ceramic materials and active ceramic materials. The ceramic materials used in the field of oral restoration are inert ceramic materials. Based on the main components of ceramic materials, oral ceramic materials can be divided into glass-based ceramic materials, alumina-based ceramic materials and zirconia-based ceramic materials.
Good light transmission, beautiful, but poor mechanical properties, suitable for the production of veneers, inlays, and single crowns.
Medium light transmittance, medium mechanical properties, suitable for the production of inlays, single crowns, and three-unit anterior bridges.
Medium light transmittance, but the best mechanical properties, suitable for the production of single crown, multi-unit fixed bridge. Zirconia-based ceramic materials have the advantages of high strength, good tissue compatibility, strong abrasion resistance, and no irritation to the gums. Compared with metal ceramic materials and other ceramic materials, they are being widely used in the field of oral restoration.
Traditional porcelain-fused-to-metal full crown restorations have disadvantages such as the turning of the neck, the soft tissues of the oral cavity are allergic to metal, and the color distortion of the restoration. The physical, chemical and biological properties of the all-ceramic material are stable, and the repair effect is realistic. In 1965, alumina-enhanced dental porcelain materials were used clinically. There are many types of all-ceramic repair systems, which can be divided into alumina ceramics, zirconia ceramics, and silica ceramics according to different materials.
The main component of the zirconia porcelain block is zirconia, and a small amount of yttrium oxide, lead oxide, aluminum oxide and silicon oxide; after the porcelain block is sintered at a high temperature of 1350℃, a stable zirconia tetragonal crystal (Y-TZP) is formed. It has good flexural strength, toughness and wear resistance, heat insulation performance and suitable thermal expansion coefficient. For example, the compressive strength of Cercon's second-generation zirconia all-ceramics is about 900Mpa, which is better than several commonly used metal porcelain materials in the past. Heraeus gold-platinum alloy is about 500Mpa, and the non-precious metal for Songfeng porcelain is about 670Mpa. Its strength can meet the restoration needs of posterior crowns and fixed bridges, and is even better than traditional materials.
In clinical fixed restoration, considering the aesthetics and age-related recession of the gums, the neck edge of the artificial crown often extends below the gum edge. The application of zirconia ceramics to dental materials involves fixed bridge base stents, root canal posts, cores, implant abutments and orthodontic brackets, all of which are in long-term contact with oral mucosa or dental hard tissues. Safety and biocompatibility are particularly important .
Commonly used in clinical porcelain alloy materials, there is the precipitation of metal ions in the oral environment, and the presence of metal ions such as nickel and chromium can be detected in the patient's mouth. In vitro experiments such as nickel-chromium alloys and cobalt-chromium alloys have been proved to have the toxic effects of reducing normal cell growth and metabolism and inhibiting cell proliferation. The densified zirconia ceramic by high temperature sintering is a material with relatively stable chemical properties, but its application in the field of dental restoration is limited due to its high hardness and processing difficulties. The pre-sintered zirconia ceramic can be processed by CAD/CAM technology, and then finally sintered to be completely dense. However, the two-step sintering process may also affect the biological safety of zirconia.