Dental materials, glass-ionomers

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... 

These low values for flexural strength and fracture toughness compared with the values for composite resins and dental amalgams make the glass-ionomer cement less suitable than these materials in high-stress situations. 

The glass-ionomer cement is the most versatile of all the dental cements and has been developed for a variety of applications (McLean Wilson, 1974, 1977a,b,c Swift, 1988b van de Voorde, 1988 Wilson McLean, 1988 Mount, 1990). Many of its applications depend on its adhesive quality which means that, unlike the non-adhesive traditional filling materials, it does not require the preparation of mechanical undercuts for retention and the consequent loss of sound tooth material. 

Goldman, M. (1985). Fracture properties of composite and glass ionomer dental restorative materials. Journal of Biomedical Materials Research, 19, 771-83. 

Mathis, R. S. Ferracane, J. L. (1989). Properties of a glass-ionomer cement resin-composite hybrid material. Dental Materials, 5, 355-8. 

Nakamura, M., Kawahara, H., Imia, K., Tomoda, S., Kawata, Y. Hikari, S. (1983). Long-term biocompatibility test of composite resins and glass-ionomer cement (in vitro). Dental Materials Journal, 1, 100-12. 

Osborne, J. W. Berry, T. G. (1986). Clinical assessment of glass ionomer cements as Class III restorations a one-year report. Dental Materials, 2, 147-50. 

Prati, C., Nucci, C. Montanari, G. (1989). Effects of acid and cleansing agents on shear bond strength and marginal microleakage of glass-ionomer cements. Dental Materials, 5, 260-5. 

Prosser, H. J., Richards, C. P. Wilson, A. D. (1982). NMR spectroscopy of dental cements. II. The role of tartaric acid in glass-ionomer cements. Journal of Biomedical Materials Research, 16, 431-45. 

Smith, D. C., Ruse, D. N. Zuccolin, D. (1988). Some characteristics of glass ionomer cement lining materials. Canadian Dental Journal, 54, 903-8. 

Sneed, W. D. Looper, S. W. (1985). Shear bond strength of a composite resin to an etched glass-ionomer. Dental Materials, 1, 127-8. 

Wilson, M. A. Combe, E. C. (1991). Effects of glass composition and pretreatment on the reactivity of a novel glass polyalkenoate (glass ionomer) dental cement. Clinical Materials, 7, 15-21. 

Dental silicate cement was once the most favoured of all anterior (front) tooth filling materials. Indeed, it was the only material available for the important task of aesthetic restoration from the early 1900s to the mid 1950s, when the not very successful simple acrylic resins made their appearance (Phillips, 1975). In the mid sixties there were some 40 brands available (Wilson, 1969) and Wilson et al. (1972) examined some 17 of these. Since that time the use of the cement has declined sharply. It is rarely used and today only two or three major brands are on the market. The reason for this dramatic decline after some 50 years of dominance is closely linked with the coming of modern aesthetic materials the composite resin from the mid 1960s onwards (Bowen, 1962), and the glass-ionomer cement (Wilson Kent, 1971) from the mid 1970s. 

Systematic attempts to formulate improved materials have met with no success (Manly et al., 1951 Rockett, 1968). The last and, in some ways, most promising attempt at improving the dental silicate cement was made by Pendry (Pendry Cook, 1972 Pendry, 1973) who improved its resistance to acid by adding indium to both powder (5-8 %) and liquid (5-65 %). The cement, however, lacked suflScient translucency, and by this time the glass-ionomer cement had arrived with its advantages of translucency and resistance to staining and acid attack. 

McComb, D. (1982). Tissue reactions to silicate, silicophosphate, glass ionomer cements and restorative materials. In Smith, D. C. Williams, D. F. (eds.) Biocompatibility of Dental Materials. Volume III. Biocompatibility of Dental Restorative Materials, Chapter 4. Boca Raton CRC Press Inc. 

Compomers are properly called polyacid-modified composite resins and are a group of aesthetic materials chemically similar to the well-established composite resins [266], They were introduced to the dental profession in the early 1990s [267], and were intended to combine the benefits of traditional composite resins and glass-ionomer cements, and their trivial name reflects this, being derived from the names of these two parent materials, the comp coming from composite, and omer from ionomer [268], These materials are now considered a distinct class of dental restorative, with well established uses in clinical restoration, particularly in children s dentistry [269],... 

A.D. Wilson, B.E. Kent, The glass ionomer cement, a new transluscent dental filling material, J. Appi Chem. Biotechnol. 21 (1971) 313. 

J.W. McLean, J.W. Nicholson, A.D. Wilson, Proposed nomenclature for glass-ionomer dental cements and related materials. Quintessence Int. 25 (1994) 587-589. 

Polyelectrolyte-based dental cements or restorative materials include zinc polycarboxylates, glass ionomers, a variety of organic polyelectrolyte adhesives as well as alginate-based impression materials. Dental cements are primarily used as luting (cementing) agents for restorations or orthodontic bands, as thermal insulators under metallic restorations, and as sealents for root canals, pits and fissures. They are also sometimes used as temporary or permanent (anterior) restorations. For further introduction to dental materials the reader is referred to standard texts [122,123]. 

Zinc polycarboxylate, the first polyelectrolyte dental material, was developed and used as early as 1968 [124]. These materials are formed by the reaction of a zinc oxide powder with an aqueous solution of poly(acrylic acid). The zinc ions cross-link the polyacid chains and form a cement. A few years after the development of zinc polycarboxylate cements, Wilson and Kent introduced the first glass-ionomer cement (GIC) [125]. Glass-ionomer cements are formed... 

Lack of adhesion of a dental restoration to tooth structure results in microleakage at tooth-restoration interface. This occurrence can result in discoloration at the margin of the restoration, or in the formation of caries. Occlusal forces on the restoration and differences between the coeffidents of thermal expansion of the cement and tooth material can lead to leakage. In addition, oral fluids and moisture may affect the adhesion. Microleakage of composite resin restorations has been reviewed by Ben-Amar [233]. Microleakage is not as serious a problem with glass-ionomer cements as it is with resin-based restorative materials, due to reduced polymerization shrinkage [234]. 

The results of Figure 8.18 show that most commercially available dental restorative materials have wear rates that are lower (better) than human enamel. All of the materials listed in Table 8.15 have nominal colors equivalent to that of human teeth and are of acceptable biocompatibility. In particular, glass ionomer ceramics have become increasingly popular due to their favorable adhesion to dental tissues, fluoride release, and biocompatibility. 

Basic types of dental restorative material composite resins and glass-ionomer cements... 

As we have seen, in the classification of tooth-coloured dental restorative materials, the composite resins represent one of the major types [1,6], The other major type is the glass-ionomer cement. 

Polyacid-modified composites were introduced into clinical use in about 1992, and aimed to combine the benefits of traditional dental composite resins with those of glass-ionomer cements [2]. Details of the latter materials are found in Chapter 6. The trivial name compomer was applied to these modified composite materials, the term being derived from the words composite ( comp- ) and glass-ionomer ( -omer ). 

One of the key features of polyacid-modified composite resins is their lack of adhesion to tooth tissnes [5]. This is a feature that they share with conventional dental composite resins, and the contrasts with the behaviour of the glass-ionomer cement. It is further evidence that these materials are essentially composite resins, and have very little of the anticipated hybrid character of composites and glass-ionomers. Bonding therefore reqnires the type of bespoke bonding agents used for conventional composite resins, together with the appropriate preparation of the freshly cut tooth surface [6]. 

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