Cements for glass

Aero Research Ltd., Duxford, Cambridge, for information on cements for glass... 

Other. Silver chloride, AgCl, has interesting optical properties as it can be made transparent it also is a cement for glass. Silver nitrate, AgNOj, also called lunar caustic, the most important silver compound, is used extensively in photography. 

Other. Vinyl acetate resins are useful as antishrinking agents for glass fiber-reinforced polyester mol ding resins (165). Poly(vinyl acetate)s are also used as binders for numerous materials, eg, fibers, leather (qv), asbestos, sawdust, sand, clay, etc, to form compositions that can be shaped with heat and pressure. Joint cements, taping compounds, caulks, and fillers are other uses. 

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). 

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... 

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. 

Fracture toughness values for glass polyalkenoate cement vary from 0-25 to 0-55 MN (Lloyd Mitchell, 1984 Goldman, 1985 Lloyd Adamson, 1987). The values are generally higher than those found for the traditional dental silicate cement but lower than those found for anterior composite resins (Lloyd Mitchell, 1984 Goldman, 1985) and much lower than those for posterior composite resins and dental amalgams (Lloyd Adamson, 1987). 

The glass polyalkenoate cement was originally intended as a substitute for dental silicate cements for the aesthetic restoration of front (anterior) teeth (Wilson Kent, 1972 Knibbs, Plant Pearson, 1986a Osborne Berry, 1986 Wilson McLean, 1988). It is suitable for restoring anterior cavities in low-stress situations, that is when the restoration is completely supported by surrounding tooth material. These cavities occur on the adjacent surfaces of neighbouring teeth (class III cavities) and at the gum line (class V cavities). 

It may be, because of the slowness of the acid-base reaction in resin glass polyalkenoate cements, that free poly(acrylic acid) is available for a longer period than in conventional glass polyalkenoate cements, for the... 

Brook, I. M., Craig, G. T. Lamb, D. J. (1991b). Initial in-vitro evaluation of glass-ionomer cements for use as alveolar bone substitutes. Clinical Materials, 7, 295-300. 

Komatsu, H. (1981). Glass ionomer cement for caries prevention. Journal of... 

Schmidt, W., Purrmann, R., Jochum, P. Glasser, O. (1981b). Mixing compounds for glass-ionomer cements and use of a copolymer for preparing the mixing components. European Patent Application 24,056. 

Little information is available on other tests of strength. Isolated measurements give a flexural strength of 24-5 MPa (0ilo, 1988) and a tensile strength of 13-6 MPa (Kent Wilson, 1971). These values lie within the range of those recorded for glass polyalkenoate cement. Translucency is easily achieved as values for the inverse property of opacity show (Table 6.10). 

The composition of the leachates does not correspond to the composition of the cement at all (Wilson Batchelor, 1967a,b). The predominant species eluted are the soluble sodium salts of phosphate and fluorides, although sodium is only a minor constituent of the cement. For one example of cement examined, the leachate contained 0-28 % sodium and 0-20% phosphate (expressed as a percentage of the amount of the species contained in the cement). For the major constituents of the glass the figures were 0 07% fluoride, 0 02% Al Oj, 0 01 % SiOj and 0 003% CaO. 

The silicophosphate cement originated with the dental silicate cement, for there is no doubt that early investigators experimented with mixtures of aluminosilicate glass and zinc oxide (Fletcher, 1878,1879 Eberly, 1928). It appears to have no particular advantages. As is often the case with hybrids, it can combine the worst features as well as the best of the parents, and often properties have intermediate values. Nevertheless, it continues to have a small but persistent usage arising from its one advantage over the... 

Its resistance to early contamination by water is very good and much superior to that of the glass polyalkenoate cement. The solubility of a seven-minute-old cement is 0-5 % which compares favourably with values of 10-21 % reported for glass polyalkenoate cement (Wilson McLean, 1988a). The solubility of one-hour-old cements is infinitesimal (< 0 05%) and very much lower than that of the glass polyalkenoate cement (0-17-0-33%). 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

Colour and opacity have been foimd to be connected for glass-ionomer cements (Crisp et al., 1979 Asmussen, 1983), with darker shades giving increased opacity. However, this is merely a consequence of the underlying physical relationships, and is not thought to be a clinical problem (Wilson McLean, 1988), mainly because the stained tooth material for which the darker shades are necessary for colour match is itself of reduced translucency. 

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