Glass-ionomers

Glassines Glass-ionomer Glass-ionomer cement Glass lonomers Glass, laminated Glassmaking... 

Glass—Ionomer Cement. The glass—ionomer polyelectrolyte system was developed primarily as a restorative for anterior teeth and erosion cavities a general cement a cavity liner and a base, pit, and fissure sealant (27,43—48). 

One approach for ameliorating the highly brittle nature of these cements has involved the use of tougher, more ductile fillers (62,63). Another approach for improving the overall properties of traditional glass—ionomer cements involves the development of hybrid cement-composites and resin-modified cements (64—68). 

Resin-Modified Glass—Ionomer Cements. Resin-modified glass—ionomer cements are based on poly(alkeonic acid) systems that have... 

Resin-modified glass—ionomer lining and restorative materials add a multifunctional acidic monomer to the poly(acryhc acid) [9003-01 Hquid component of the system. Once the glass powder and Hquid are mixed, setting can proceed by the acid—glass—ionomer reaction or the added monomer can be polymerized by a free-radical mechanism to rapidly fix the material in place (74,75). The cured material stiH retains the fluoride releasing capabiHties of a glass—ionomer. 

Gl ss-Ionomers. Glass-ionomers show fluoride release at levels that are usually higher than those found in composite materials. The fluoride is found within the aluminosihcate glass, which is melted with fluoride fluxes and ground to form powder filler. The fluoride is added as calcium fluoride [7789-75-5] aluminum fluoride [15098-87-0] and sodium fluoride [7681-49-4] in a combined proportion of approximately 20% by weight in the final powder (284,285). 

A. D. Wilson andj. W. McLean, Glass-Ionomer Cement, Quintessence Publishing Co., Chicago, 1988. 

Jonck, L. M., Grobbelaar, C. J. Strafing, H. (1989). The biocompatibility of glass-ionomer cement in joint replacement bulk testing. Clinical Materials, 4, 85-107. 

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

Water is also a component of set AB cements. In glass-ionomer cements, for example, it may serve to coordinate to certain sites around the metal ions. It also hydrates the siliceous hydrogel that is formed from the glass after add attack has liberated the various metal ions (Wilson McLean, 1988). Such reactions continue long after the initial hardening of the cement is complete, and for this reason water must be retained as far as possible during the first hours and days after formation of the cement. If water is lost from the cement and desiccation occurs, these post-hardening... 

Water occurs in glass-ionomer and related cements in at least two different states (Wilson McLean, 1988 Prosser Wilson, 1979). These states have been classified as evaporable and non-evaporable, depending on whether the water can be removed by vacuum desiccation over silica gel or whether it remains firmly bound in the cement when subjected to such treatment (Wilson Crisp, 1975). The alternative descriptions loosely bound and tightly bound have also been applied to these different states of water combination. In the glass-poly(acrylic acid) system the evaporable water is up to 5 % by weight of the total cement, while the bound water is 18-28 % (Prosser Wilson, 1979). This amount of tightly bound water is equivalent to five or six molecules of water for each acid group and associated metal cation. Hence at least ten molecules of water are involved in the hydration of each coordinated metal ion at a carboxylate site. 

Glass-ionomer cements become less susceptible to desiccation as they age, because a greater proportion of the water in older cements has become tightly bound . Early contact with moisture is also damaging, and this problem is overcome clinically to some extent by using some sort of protection such as clear nail varnish to seal the cement during its early life (Wilson McLean, 1988). However, this does not give perfect results, and as yet there is no ideal barrier material for this purpose (Earl, Hume Mount, 1985). 

Earl, M. S. A., Hume, W. R. Mount, G. J. (1985). Effect of varnishes and other surface treatments on water movement across the glass-ionomer cement surface. Australian Dental Journal, 30, 298-301. 

Hornsby, P. R. (1980). Dimensional stability of glass-ionomer cements. Journal of Chemical Technology and Biotechnology, 30, 595-601. 

Wilson, A. D., Crisp, S. Paddon, J. M. (1981). The hydration of a glass-ionomer (ASPA) cement. British Polymer Journal, 13, 66-70. 

Wilson, A. D. McLean, J. W. (1988). Glass-Ionomer Cement. Chicago, London, etc. Quintessence Publishers. 

Polyelectrolytes are polymers having a multiplicity of ionizable groups. In solution, they dissociate into polyions (or macroions) and small ions of the opposite charge, known as counterions. The polyelectrolytes of interest in this book are those where the polyion is an anion and the counterions are cations. Some typical anionic polyelectrolytes are depicted in Figure 4.1. Of principal interest are the homopolymers of acrylic acid and its copolymers with e.g. itaconic and maleic adds. These are used in the zinc polycarboxylate cement of Smith (1968) and the glass-ionomer cement of Wilson Kent (1971). More recently, Wilson Ellis (1989) and Ellis Wilson (1990) have described cements based on polyphosphonic adds. 

Nicholson, J. W., Brookman, P. J., Lacy, O. M. Wilson, A. D. (1988b). Fourier transform infrared spectroscopic study of the role of tartaric acid in glass-ionomer cements. Journal of Dental Research, 67, 145CM. 

Wilson, A. D. Ellis, J. (1989). Poly-vinylphosphonic acid and metal oxide or cermet or glass-ionomer cements. British Patent Application 2, 219, 289A. 

Wilson, A. D. Kent, B. E. (1971). The glass-ionomer cement a new translucent cement for dentistry. Journal of Applied Chemistry and Biotechnology, 21, 313. 

The glass-ionomer or glass polyalkenoate cement (Section 5.9)... 

The invention and development of the zinc polycarboxylate and glass-ionomer cements was brought about by a change in basic attitudes in materials science in dentistry. This largely revolved around the necessity of inventing materials which would adhere to tooth enamel and dentine. 

Unlike other aqueous dental cements, the zinc polycarboxylate retains plastic characteristics even when aged and shows significant stress relaxation after four weeks (Paddon Wilson, 1976). It creeps under static load. Wilson Lewis (1980) found that the 24-hour creep value for one cement, under a load of 4-6 MPa, was 0-7 % in 24 hours, which was more than that of a zinc phosphate cement (0-13 %) and a glass-ionomer cement (0-32%), but far less than that of the zinc oxide eugenol cement (2-2%). 

Glass polyalkenoate (glass-ionomer) cement 5.9.1 Introduction... 

The glass polyalkenoate cement, formerly known as the glass-ionomer cement, was invented by Wilson and Kent in 1969 (Wilson Kent, 1973) and is now well established as a material that has an important role in clinical dentistry. It has proved to have considerable development potential and has been subjected to continuous development, improvement and... 

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