Objectives: A glassceramic, which is based on the lithiumsilicate system, has been optimized for dental CAD-CAM by a two-step crystallization process. Industrial produced bulk glassblocks are converted to a lithiummetasilicate (LS) glassceramic. This glassceramic is particularly suited for the machining process. During a short heat treatment the milled restoration is converted to lithiumdisilicate (LS2) glassceramic, a material with high strength and fracture toughness. The aim was to control the microstructure after each crystallization step separately for optimum performance. A simplified model, which is based on the classical nucleation theory, describes the complex crystallization. Methods: Nucleation and crystallization parameter were varied. The crystallization process was investigated by differential scanning calorimetrie, high temperature x-ray diffraction and scanning electron microscopy. Results: The sequence of crystallization is determined by the nucleation. The precrystallized material consists of about 40% isolated LS-crystals in residual glassy phase. This microstructure prevents chipping during the machining process. The finally crystallized sample consists of 65% interlocking LS2-crystals, which are responsible for high strength and high fracture toughness. Conclusion: A model is presented, which can describe the crystallization of LS-crystals, the exsolution of LS-crystals and the crystallization of LS2.
2:00 PM-4:00 PM, Friday, 11 March 2005 Baltimore Convention Center Exhibit Hall E-F
Back to the Dental Materials: III - Ceramics and Cements Program
Back to the IADR/AADR/CADR 83rd General Session (March 9-12, 2005)