AN AESTHETIC GLASS-CERAMIC FOR USE IN COMPOSITE RESTORATION INSERTS

The objective of the preliminary work reported here was to prepare an improved formulation of intrinsically colored microcrystalline glass-c eramic. Applications could include ''megafillers'' for direct composit e restorations, precision castings, and CAD-CAM prostheses. The experi mental glassceramic reported here contained SiO2 56.9, Al2O3 19, LiO2 7, ZnO 6, MgO 5, TiO2 2, ZrO2 2, P2O5 2, and CeO2 0.1 mole %. The batc h materials were melted and stirred at 1,610 degrees C for 2 h, quench ed in water and also formed into a block of a clear, slightly yellow g lass. To identify the crystalline phases that developed during transfo rmation of the glass to the ceramic, x-ray diffraction was used on ten aliquots taken during 15 h of stepwise heating from 750 to 1050 degre es C. With heating, the yellow color deepened to a very translucent '' dark yellow'' dental shade, then lightened with gradually increasing o pacity during formation of secondary crystalline phases. X-ray opacity was approximately equivalent to that of dental enamel. The refractive index of the glass, n(D)(25) 1.554, increased during nucleation and g rowth of the crystalline phases to a maximum of 1.586. Intrinsic color ation of these glass-ceramic materials can be controlled by varying th e heat treatment and/or composition to match typical dental shades.