Production and characterization of feldspathic-muscovite glass composite for dental prosthesis.

The principal objective of this studywas to produce and characterize a machinable glass ceramic containing muscovite-mica as the main crystalline phase to be used as a dental restorative material. The secondary objective was to evaluate the use of muscovite-mica to improve machinability and generate a toughening mechanism in the experimental glass ceramic. After fine milling of a feldspathic glass frit was milled and then mixed with muscovite-mica, die-pressed, and sintered under vacuum at 850 to 1,150 degrees C. The resulting sintered composite was characterized by X-ray diffraction, scanning electron microscopy, and had its fracture toughness evaluated by micro-indentation. The results were as follows: (a) improved thermal stability of muscovite-mica crystals in the composite; (b) improved leucite crystallization in the feldspathic glass matrix by increasing sintering temperature in the studied range ; (c) the composites consisting of glass + 10% muscovite and glass + 20% muscovite sintered at 1,050 degrees C presented fracture toughness values of 9.0 +/- 1.2 and 8.4 +/- 0.6 MPa.m1/2, respectively, which are higher than those found in the literature for glass ceramics. Feldspar frit blocks with addition of muscovite-mica (up to 20%) can be densified at temperatures between 1,050 and 1,150 degrees C. This material was stable at a temperature substantially higher than the stability limit of pure muscovite and also showed indentation fracture toughness values greater than those reported in the literature for other glass ceramics.