Resin glass polyalkenoate cements

Resin glass polyalkenoate cements Alveolar bone substitute... 

One of the most interesting recent developments has been the advent of the resin glass polyalkenoate cements (Antonucci, McKinney Stansbury, 1988 Mitra, 1989 Wilson, 1989, 1990 Mathis Ferracane, 1989 Minnesota Mining Manufacturing Company, 1989 Albers, 1990). They are dual-cure hybrids that set by a combination of acid-base and polymerization reactions, and there are several types. Polymerization is effected by either chemical or light initiation. 

At its most basic, the resin glass polyalkenoate cement can be seen as a glass polyalkenoate cement in which the water component is replaced by a water-HEMA mixture. HEMA is hydroxymethyl methacrylate, its hydroxy group making it water-soluble ... 

The resin glass polyalkenoate cements are mixed in the same way as conventional materials. In the case of the light-activated systems they... 

The two matrices in these cements are of a different nature an ionomer salt hydrogel and polyHEMA. For thermodynamic reasons, they do not interpenetrate but phase-separate as they are formed. In order to prevent phase separation, another version of resin glass polyalkenoate cement has been formulated by Mitra (1989). This is marketed as VitraBond, which we term a class II material. In these materials poly(acrylic acid), PAA, is replaced by modified PAAs. In these modified PAAs a small fraction of the pendant -COOH groups are converted to unsaturated groups by condensation reaction with a methacrylate containing a reactive terminal group. These methacrylates can be represented by the formula ... 

The freshly set class II (Vitrabond) resin glass polyalkenoate cement appears to have rubbery characteristics and there is some debate as to... 

Table 5.18. Strength of resin glass polyalkenoate cements (Antonucci, McKinney Stansbury, 1988 Wilson McLean, 1988 Mathis Ferracane, 1989 Mitra, 1989 Minnesota Mining Manufacturing Company, 1989 Albers, 1990)...

Both class I and class II resin glass polyalkenoate cements are claimed to bond to dentine. This can be accepted. But that the bond is stronger and develops more rapidly than that of the conventional glass polyalkenoate cement, as is claimed for class II materials (Minnesota Mining Manufacturing Company, 1989) requires confirmation. 

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... 

There is bound to be one problem with resin glass polyalkenoate cement. Because the matrix is a mixture of hydrogel salt and polymer, lightscattering is bound to be greater than in the conventional material. Moreover, the zinc oxide-containing glass of class II materials is bound to be opaque. This makes it difficult to formulate a translucent material and is the reason why their use is restricted to that of a liner or base. However, the class II material cited will be radio-opaque because it uses strontium and zinc, rather than calcium, in the glass. 

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... 

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). 

Figure 5.21 The laminate restoration, showing the glass polyalkenoate cement as a dentine substitute and a composite resin as an enamel substitute.

McKinney, Antonucci Rupp (1987) found that the clinical wear of the glass polyalkenoate cement compared favourably with that of the composite resin, but they noted that it was prone to brittle fracture and chemical erosion. 

Figure 5.23 The two matrix-forming reactions in class I resin-based glass polyalkenoate cements.

These resin-modified glass polyalkenoate cements have both advantages and disadvantages over conventional glass polyalkenoate cements. However, because of their poor translucency they are recommended only as liners or bases. 

Figure 5.24 The matrix of a class II resin-based glass polyalkenoate cement, showing ionic and covalent crosslinks.

A fundamental criticism of the resin-modified glass polyalkenoate cements is that, to some extent, they go against the philosophy of the glass polyalkenoate cement namely, that the freshly mixed material should contain no monomer. Monomers are toxic, and HEMA is no exception. This disadvantage of composite resins is avoided in the glass polyalkenoate cement as the polyacid is pre-polymerized during manufacture, but the same cannot be said of these new materials. For this reason they may lack the biocompatibility of conventional glass polyalkenoate cements. These materials also absorb excessive amounts of water because of the hydrophilic nature of polyHEMA (Nicholson, Anstice McLean, 1992). 

These are mainly polymeric cements formed by bonding of polyions (or macroions)which are anions with small cations called counterions. Good examples are polycarboxylate cements [9], glass-ionomer cement [10], and polyphosphonic cements [11,12]. Zinc polycarboxylate, glass polyalkenoate, and resin glass polyalkenoate are some examples... 

Glass polyalkenoate (glass-ionomer) cement Bonding to composite resins... 

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