Besides the above factors, glass reactivity also influences the setting characteristics and strength of the cements. As the particle size influences the working and setting time considerably, the selection of ratio of glass to polyacid also needs utmost care so as to achieve optimum luting characteristics. In order to be suitable as glasses for luting purposes, the mean particle size must be smaller than 15 µm. However, there is a clear demarcation between the mean particle size of glasses used for luting and restorative applications. These glasses have been designed mainly from the restorative point of view. The cement-forming ability of aluminosilicate glasses was based on the Al 2O 3/SiO 2 mass ratio. The original composition of the powder phase of cements was based on calcium fluoroaluminosilicate glass (CAS). The resulting cements consist of residual glass particles with a surrounding siliceous layer embedded in a polysalt matrix. The metal cations serve to crosslink the polyacrylate chains resulting in a hard composite material. The released ions form chelates with the carboxylate groups of the polymer. The acid degrades the glass structure releasing metal cations (Ca 2+ and Al 3+). The glass phase acts as a source of metal cations for the preparation of GICs. Glass-ionomer cements can be described as a polymer-based dental composite resulting from a series of acid-base reactions occurring between aqueous solutions of poly (alkenoic acids), e.g., poly (acrylic acid), and calcium-fluoro-aluminosilicate glasses. Although originally developed as an anterior filling material, fine grain versions of GIC were developed later for luting. The production of GICs stemmed from a desire to combine the beneficial aspects of silicate cements (Strength, translucency and fluoride release) with those of polycarboxylate cements (adhesiveness and biocompatibility). The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970s by Wilson and Kent. The microwave melting can be utilized for processing ionomer glasses as it did not alter the structure and properties of G 023 cement. The optimal combination of setting time, strength and radiopacity for the cements examined here was shown by G 022 cements. This has been reflected in their respective setting characteristics and mechanical properties. The substitution of Zn, Sr and Mg for Ca at 1:1 molar ratio increased the reactivity of the respective glasses. The average particle size of the processed glass powders was within specification limits for luting applications (<15 μm). X-ray diffraction and Fourier Transform-Infrared spectroscopy analysis confirmed the structure of the processed glasses. Each glass was then mixed with Fuji Type I GIC liquid in order to evaluate the properties of novel cements at different powder/liquid ratios. G 021 and G 022 glasses were processed by conventional melt quench route, whereas G 023 was processed by microwave melt–quench route. They were coded as the G 021 (Ca: Zn), G 022 (Ca: Sr), G 023 (Ca: Mg). Three glass compositions based on substitution of Zn, Sr and Mg for Ca at 1:1 molar ratio was synthesized. In this study, the influence of substituting Zn, Sr and Mg for Ca of CAS glasses was investigated with respect to the structure and setting characteristics, mechanical properties, and radiopacity of cements designed for luting applications. However, the cements obtained from CAS glasses were found to be radiolucent. Calcium fluoroaluminosilicate glasses (CAS) are used in the formulation of glass ionomer cements for dental applications.
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