Development of novel micaceous glass ceramics for dental applications using CAD/CAM Systems

The original aim of this project was to develop and characterise machinable glass-ceramic materials for dental applications with the final outcome of producing a range of materials matching tooth enamel for aesthetics and mechanical properties.
The candidate glass is a micaceous glass-ceramic which is compositionally based on a ternary phase system of 90 molar % Ba-phlogopite (Ba0.5Mg3(Si3AlO10)F2), 6 molar % calcium phosphate (Ca3(PO4)2) and 4 molar % cordierite (Mg2Al4Si5O18). Initial assumptions about the structure and phase composition of this material have been proven wrong. Since effective material development can only occur where one is knowledgeable of its prior state; a significant amount of work was focused on phase characterisation using a number of novel techniques such as single crystal diffraction, acid dissolution and spray drying in conjunction with neutron diffraction at ILL and conventional powder XRD. Results have been analysed with an array of software including GSAS and Shelx ’97 for refinement of powder and single crystal data, respectively. Successful data refinement has significantly advanced understanding of phase formation and development in this material.
A thorough analysis of mechanical properties is also presented and includes BFS (biaxial flexure) and Vickers microhardness tests with comparisons between samples after different heat treatments. DTA analysis including activation energy and nucleation temperature determination has been performed on two variants of the same composition in order to determine the sensitivity of this composition to the effects of differing grades of feedstocks on the resulting material; and is the basis of an assessment of commercial viability. Optical/SEM micrographs and EDS/EMPA data sets are also presented. Progress in the colouring of these glass-ceramics with the aim of matching natural dental shades is encouraging and work includes colour-space data for the first time. Ultimately, the final goal is the production of a machinable glass-ceramic, suitable for dental restoration, which possesses a high degree of machinability and is also reproducible under industrial high-volume conditions.