Semiporous Reinforcing Fillers for CompositeI Resins: II. Heat Treatments and Etching Characteristics

Candidate experimental semiporous rein-forcing filler particles were prepared by heat treatment of certain glass compositions, fol-lowed by crushing and etching. Optical microscopic techniques were aided by the use of certain dyes and staining procedures to manifest submicroscopic interconnected porosity in the surface of the particles. The goal of this endeavor was to develop semi-porous glass reinforcing fillers for the im-provement of dental composite materials. In a previous study, ' a number of glass com-positions were prepared and their responses to quenching and heating in a gradient fur-nace were described. In compositions that could be quenched to form clear glasses, sub-liquidus temperatures at which opalescence developed were determined. The absence of perceptible birefringence in most of these suggested that both phases were vitreous and that the compositions were within a liquid-liquid immiscibility region. If sufficiently near the center of a miscibility gap, the viscous, separating phases can form three-dimensional, randomly interconnecting net-works, both of which are vitreous at lower (room) temperatures. In the present study, the more promising compositions were further examined to de-termine which ones, if any, are capable of forming two continuous interconnected phases with dimensions small enough so as not to perceptibly scatter light