IADR Abstract Archives
Barium Fluorphlogopite Machinable Glass-Ceramics of Varing Boric Oxide Content
Objectives: Barium mica, barium fluorphlogopite glass-ceramics can be machined to shape without resorting to using diamond tipped tooling.They are therefore attractive for CAD-CAM dental crowns inlays onlays and veneers. Objectives to investigate the incorporation of boric oxide on the crystallisation, microstructure and hardness of barium fluorphlogopite BFM glass-ceramics.
Methods: Three BFM glasses with varying mole fractions of boric oxide (0. 0.37 and 0.7?) were synthesised by a high temperature melt quench route at Cera Dynamics Ltd Stoke using a proprietary shoe box Kiln. The resulting glasses were characterised by Xray Fluorescence XRF, high temperature differential scanning calorimetry, DSC, X-ray powder diffraction, XRD Scanning Electron Microscopy, SEM. Just above the original Tg and microhardness. Optimum nucleation curves were determined using the Marrotta method.
Results: The XRF analysis of the glasses was identical to the prefired compositions with no significant loss of fluorine. The glass transition temperature Tg reduced with increasing boric oxide content. The two lowest B2O3 content glasses exhibited a pronounced optimum nucleation temperatures, which corresponded to the presence of two Tgs, indicating nucleation occurring as a result of prior amorphous phase separation into two glass phases.
Heat treatment in the range 950-1100oC resulted in the development of an interlocked microstructure consisting of BFM plates termed a “house of cards microstructure” associated with machinability. Crystal aspect ratio and crystal size increased with increasing heat treatment temperature and time. The original glasses had a hardness of about 6GPa that reduced on crystallisation of BFM and reduced further on formation of the house of cards microstructure to values less than that of enamel (3.6GPa).
Conclusions: BFM glass-ceramics are attractive for CAD-CAM restorations in Dentistry. Having a restoration with a hardness less that of enamel is attractive in preventing wear of opposing teeth.
Methods: Three BFM glasses with varying mole fractions of boric oxide (0. 0.37 and 0.7?) were synthesised by a high temperature melt quench route at Cera Dynamics Ltd Stoke using a proprietary shoe box Kiln. The resulting glasses were characterised by Xray Fluorescence XRF, high temperature differential scanning calorimetry, DSC, X-ray powder diffraction, XRD Scanning Electron Microscopy, SEM. Just above the original Tg and microhardness. Optimum nucleation curves were determined using the Marrotta method.
Results: The XRF analysis of the glasses was identical to the prefired compositions with no significant loss of fluorine. The glass transition temperature Tg reduced with increasing boric oxide content. The two lowest B2O3 content glasses exhibited a pronounced optimum nucleation temperatures, which corresponded to the presence of two Tgs, indicating nucleation occurring as a result of prior amorphous phase separation into two glass phases.
Heat treatment in the range 950-1100oC resulted in the development of an interlocked microstructure consisting of BFM plates termed a “house of cards microstructure” associated with machinability. Crystal aspect ratio and crystal size increased with increasing heat treatment temperature and time. The original glasses had a hardness of about 6GPa that reduced on crystallisation of BFM and reduced further on formation of the house of cards microstructure to values less than that of enamel (3.6GPa).
Conclusions: BFM glass-ceramics are attractive for CAD-CAM restorations in Dentistry. Having a restoration with a hardness less that of enamel is attractive in preventing wear of opposing teeth.