The European Ceramic Society
YCN Newsletter 14 : Article by Evita Willems
Today ~60% of dental restorations are made of ZrO2 ceramics as they exhibit excellent mechanical properties, are chemically stable, are biocompatible, and have natural aesthetics.
3 mol% yttria stabilized zirconia (3Y-TZP) is the most commonly used type of ZrO2 for dental restorations. 3Y-TZP is a submicrometer-grained, transformation toughened ceramic with high performance mechanical properties allowing it to be used for both anterior and posterior restorations and fixed dental prostheses (dental bridges). Currently, ZrO2 dental restorations are mostly produced by subtractive manufacturing (SM) using computer aided design (CAD) and/or computer aided manufacturing (CAM).
CAD/CAM milling uses a small, precise milling tool to create the restoration from a pre-sintered or sintered ZrO2 block. After sintering to full density, these restorations are coated with a colored porcelain layer and thermally treated, creating a natural look. Additive manufacturing (AM) is emerging as a new production technique, in which the component is built up layer by layer using an extensive variety of technologies. Over the past 40 years, AM has advanced enormously and has enabled the production of a wide range of materials (polymers, metals, ceramics). Although 3D printing of ceramics is still in its infancy, it has been predicted that the use of AM for dentistry will be one of the fastest growing industries. AM allows to move from mass production to quick production of customized products. The use of AM for dental restorations will help to tackle the typical issues of SM, like milling tool wear and high loss of material (up to 90% waste) to name a few. In addition, AM makes it possible to manufacture specific complex shapes with details that cannot be made by conventional milling as well as gradient colored materials.
My PhD research focused on producing monolithic fully-dense 3Y-TZP dental restorations using indirect slurry based AM techniques, like digital light processing (DLP). DLP uses a digital light processor to cure a full layer of UV-curable ceramic slurry to create the ceramic material in a layerwise addition. The right combination of monomers, diluents, ceramic powder and dispersants were determined to create an in-house slurry that could be used to create crack-free, highly dense (99.8% T.D.) 3Y-TZP ceramics. Amongst the investigated printing parameters, a decreasing layer thickness was found to largely improve the mechanical performance of the printed and sintered material. A high dependency of the mechanical performance to the building direction was also observed. A 3-point bending strength of 730 ± 64 MPa was achieved. The limited bending strength was due to the pores and surface defects still present in the material. Finally, highly accurate maxillary four-unit fixed dental prostheses (FDPs) and partial implants with a complex surface design were manufactured using the developed ZrO2 slurry. The mechanical performance of the 3D printed dental materials is currently under investigation and being compared to standard discs and bars.
YCN Newsletter 18 - New YCN Representative call
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