Dental Lab Products Tech Guide 2008 - (Page 14) techtomorrow LIQUID ZIRCONIA (LEFT) Exhibiting life-like esthetics, this porcelain crown was fabricated over a new-generation zirconia framework. (RIGHT) Scharf using leading edge imaging and software technology. his engineering/materials scientist mind leapt into full gear. “I went on a quest to develop the next-generation solution for zirconia. Our ultimate goal is to eliminate cutting tools altogether, thus eliminating material waste. As anyone who owns a CAD/CAM system knows, approximately 75% of a milled zirconia block is waste.” Because Espritdent isostatically presses its own zirconia milling blocks, Scharf originally attempted to ball mill leftover zirconia blocks to recycle them into something usable. However, he found that the proprietary binder used to hold the zirconia powder together prevented a controlled mixture of binder to zirconia, resulting in blocks that when fired did not possess the desired density level. Enlisting help from chemical engineers, his next attempt at creating a next-generation zirconia material looked more promising. By adding a slurry polymer binder with chemical reactants to the zirconia powder, Scharf was able to create a zirconia liquid material that could be poured into milling block molds and hardened via a chemical heat reaction. What resulted was a plastic-like milling block that was 50% more dense than conventional pre-sintered zirconia milling blocks yet more wear kind to bur technology, increasing tool life. Controlling bur wear is critical to controlling the consistency, accuracy, and fit of each substructure milled. Once sintered, substructures made from this new zirconia block tested stronger than those milled and sintered from presintered zirconia. In the near future he plans on commercializing these blocks for the industry. Now on the right track, Scharf realized he still had the material wastage issue because he was CAM milling these new softer blocks. He wanted to eliminate wastage by fabricating zirconia substructures without the use of milling burs. Immediately, he began work on the last phase of material development, which was to create a liquefied zirconia that could be injection molded into customized tooth forms manufactured by advanced technology and hardened by chemical heat reaction. Colorants could be added to the liquefied material to produce tooth shades that correspond to the Vita shade guide or even customized colors that mimic gingiva or adjacent dentition. The tooth forms are manufactured complete with sprue vents for the injection molding process. During the heat-generated hardening process, the mold material burns off, and the zirconia substructure handled conventionally, either using conventional pressing or layering techniques, once sintered. The future Scharf is still not finished with his quest to find newgeneration materials. He is now experimenting with a laser technology that has been used in the automotive industry to strengthen the ceramics in automotive fuel injectors. Subjecting zirconia or any ceramic framework to this laser light for less than 5 seconds more than doubles its megapascal strength. In a market that is impressed with framework strength, this technology may hold great promise in the future for all ceramic materials. lab 14 techguide2008 dentallabproducts
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