Polyalkenoate cements

Poly(acrylic acid) and its salts have been known to have useful binding properties for some thirty years they have been used for soil consolidation (Lambe Michaels, 1954 Hopkins, 1955 Wilson Crisp, 1977) and as a flocculant (Woodberry, 1961). The most interesting of these applications is the in situ polymerization of calcium acrylate added to soil (de Mello, Hauser Lambe, 1953). But here we are concerned with cements formed from these polyacids. 

The polyelectrolyte cements may be classified by the type of basic powder used to form the cement. 

Only two of these materials are of practical importance the zinc polycarboxylate cement of Smith (1968) and the glass-ionomer cement of Wilson Kent (1971). Both are used in dental applications and both have been used as bone cements. The glass-ionomer cement is, perhaps, the most versatile of all AB cements. It has many applications in dentistry a 

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. 

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Another development has been the advent of the dual-cure resin cements. These are hybrids of glass polyalkenoate cements and methacrylates that set both by an add-base cementation reaction and by vinyl polymerization (which may be initiated by light-curing). In these materials, the solvent is not water but a mixture of water and hydroxyethylmethacrylate which is capable of taking dimethacrylates and poly(acrylic add)-containing vinyl groups into solution. In the absence of light these materials set slowly and... 

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

Figure 5.4 Hypothetical molecular structures in polyalkenoate cements, where A represents OH- or F-.

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... 

Glass polyalkenoate cement has a unique combination of properties. It adheres to tooth material and base metals. It releases fluoride over a long period and is a cariostat. In addition it is translucent and so can be colour-matched to enamel. New clinical techniques have been devised to exploit the unique characteristics of the material. 

The powders used in glass polyalkenoate cement formulations are prepared from glasses and not opaque sintered masses. In this they resemble the traditional dental silicate cement from which they are descended. The glass plays several roles in the chemistry and physics of the glass polyalkenoate... 

Table 5.6. Composition of oxide glasses used in studies on polyalkenoate cements, parts by mass Wilson et al., 1980 Crisp, Merson Wilson, 1980)...

Table 5.9. Composition %) of oxide /fluoride glasses used in studies on polyalkenoate cements,parts by mass. Generic composition 2SiO.. Alf). 2—x)Ca0.xCaF2 Kent, Lewis Wilson, 1979 ...

Table 5.10. Examples of practical glasses used in glass polyalkenoate cement Crisp, Abel Wilson, 1979 Wilson McLean, 1988 Brook, Craig Lamb, 1991)...

Table 5.11. Effect of +)-tartaric acid on glass polyalkenoate cement properties...

The poly(alkenoic acid)s used in glass polyalkenoate cement are generally similar to those used in zinc polycarboxylate cements. They are homopolymers of acrylic acid and its copolymers with itaconic add, maleic add and other monomers e.g. 3-butene 1,2,3-tricarboxylic add. They have already been described in Section 5.3. The poly(acrylic add) is not always contained in the liquid. Sometimes the dry add is blended with glass powder and the cement is activated by mixing with water or an aqueous solution of tartaric add (McLean, Wilson Prosser, 1984 Prosser et al., 1984). 

Increase in concentration of the polyacid increases solution viscosity, quite sharply above 45% by mass (Crisp, Lewis Wilson, 1977). The strength of glass polyalkenoate cements also increases, almost linearly, with polyacid concentration. This is achieved at the cost of produdng overthick cement pastes and loss of working time. 

The molecular weight of the polyacid affects the properties of glass polyalkenoate cements. Strength, fracture toughness, resistance to erosion and wear are all improved as the molecular weight of the polyadd is... 

The glass polyalkenoate cement system was not viable until Wilson and Crisp discovered the action of (+)-tartaric acid as a reaction-controlling additive (Wilson Crisp, 1975,1976,1980 Wilson, Crisp Ferner, 1976 Crisp Wilson, 1976 Crisp, Lewis Wilson, 1979). It may be regarded as an essential constituent and is invariably included in glass polyalkenoate cements as a reaction-controlling additive. 

Table 5.13. Effect of fluorides on glass polyalkenoate cement compressive strength, MPa (Crisp, Merson < Wilson, 1980)...

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