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J. Stampfl, J.-A. Schönherr:
"Analysing the precision of lithography-based additively manufactured glass ceramic parts";
Talk: Euromat 2019, Stockholm; 09-01-2019 - 09-05-2019.

Introduction
Lithography based additive manufacturing (AM) is one of the oldest 3d-printing processes and was developed in the early 1990´s. This technology still provides the best feature resolution and surface quality and generates outstanding material properties at the same time. This was demonstrated for different material classes from thermoplastic-like polymers to ceramics. Focussing on ceramics the process is called Lithography-based Ceramic Manufacturing (LCM). It is possible to structure different ceramics with high resulting biaxial bending strengths like alumina (521MPa) zirconia (1098MPa) or 45S5Bioglass® (124MPa). AM technologies are very valuable for customized parts in small quantities as it is often needed in biomedical applications. Dental restorations for example require high precision, optical and material properties at the same time which can be reached by using the LCM-process.
Methods
This study concentrated on the verification of the precision of manufactured glass ceramic dental crowns. Therefore, it is necessary to digitize the final sintered part. However, there are different methods which have been tested with regard to their suitability such as optical methods like light microscopy with focus variation, dental laboratory scanner or micro CT as well as a contact method the tactile scanner.
Results and Conclusion
The different scanning methods have been compared on one sintered part and the feature resolution as well as the surface quality have been analysed. However, the micro CT showed the best results especially compared to optical methods. The acquired digital file has been compared to the original one by specialized software. This comparison allowed an analyse of the restrictions of the precision and in further consequence an optimization of the process. For example sinter structures have been developed to reduce and control sinter distortion. A resolution of 25 µm in all spatial directions was achieved.