Li2O-MgO-B2O3-Al2O3-SiO2 GLASS-CERAMIC FOR DENTAL VENEERING APPLICATION
Keywords:
Spodumene-cordierite glass ceramic, borosilicate glass, silicon nitride ceramic, dental coreAbstract
Spodumene-cordierite (Li2O-MgO-Al2O3-SiO2) glass ceramic and borosilicate glass (Pyrex) are usedas veneering materials due to theirbio-inertness, high thermal shock resistance, and low thermal expansion coefficient which is compatible with silicon nitride ceramic dental cores. This study has focused on the study of the phase analysis, hardness, and improved appearance of glass ceramics prepared by melting 1.9 wt% Li2O, 3.2 wt% MgO, 7.4 wt% B2O3, 16.5 wt% Al2O3, 65.8 wt% SiO2, 2.5 wt% ZrO2, 1.25 wt% P2O5, and an addition of 2.5 wt% Na3AlF6 (cryolite) at 1450oC for 1 h. The glass melts were then quenched in water to make glass frits. After dry grinding with aplanetary mill at 300 rpm for 30 min, the prepared veneer powders were mixed with polyvinyl alcohol solution as a binder and were then coated on the sintered silicon nitride ceramic dental cores using a paint brush. The specimens were fired in an electrical tube furnace in the temperature range of 900-1100oC for5 min and then soaked at 790oC for 1 h. The veneered specimen at 950oC shows a good appearance, rather white and semi-opaque, and a smooth and glossy surface without any defects or crazing. The veneering materials have a low thermal expansion coefficient of about 2.7-5.0 × 10-6oC-1 which is suitable for the silicon nitride ceramic dental cores. The Vickers hardness of the prepared samples is about 4.0-4.5 GPa which is close to that of human teeth.
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