Glass carbomers

Glass-ionomers not only release ions, but are capable of taking them up. Studies have shown that cements exposed to natural saliva take up calcium and phosphate ions, and develop a surface of significantly increased hardness [121]. Also, when used as pit and fissure sealants, they interact with saliva to form a substance with increased content of calcium and phosphate that is considerably more resistant to cutting with a dental drill than the original material. Under these circumstances, the cement had become transformed into a material with enamel-like optical and mechanical properties [122]. This observation is the basis of the development of glass-ionomer type materials with even further enhanced bioactivity, the so-called glass carbomers, which are discussed in Chapter 8. 

In recent years, a new type of glass-ionomer material has become available that overcomes this problem of the weakening effect of additional fillers designed to enhance the bioactivity of the cement. Known as the glass carbomer , it overcomes the problem of slow setting by specifying the need to cure with the aid of heat from dental cure lamps. 

Another considerable disadvantage of established members of the glass-ionomer family is their brittleness. Including extra filler in the glass carbomer type in and of itself does not help with this drawback indeed, it makes the situation worse. However, in its final formulation, the glass carbomer also contains a novel component, a silicone oil, which improves the toughness of the set cement and makes the potential durabifity better. 

The components of the enhanced bioactivity conventional glass-ionomer (glass carbomer) are as follows ... 

The glass used in glass carbomer contains a reasonable amount of strontium [21], as well as a small amount of calcium. It is relatively high in silicon compared with the glasses used in the well-established brands of conventional glass-ionomer Fuji IX and Ketac Molar (see Table 8,2), but contains comparable amounts of aluminium, phosphorus and fluoride. 

Results from the Knoop Hardness experiments are shown in Table 8.3. They show that the conventional glass-ionomer was harder than the glass carbomer by an amount that was statistically significant. Unfortunately, no other mechanical data were reported, so that it is not clear from this finding whether the conventional glass-ionomer is mechanically snperior to the glass carbomer, or whether it was simply marginally harder at the time tested. 

Table 8.3 Knoop hardncss values for glass carbomer and conventional glass-ionomer cement [27]...

Overall, though there were only a limited amount of data reported in this study [27], it was useful because they showed that the properties of glass carbomer are at least comparable with those of a well-known conventional glass-ionomer. 

Enhanced bioactivity conventional glass-ionomers (glass carbomers) are intended for use in the same range of applications as conventional glass-ionomers, ie, liners and bases, full restorations of various types, and pit-and-fissure sealants. Because of their similarity to conventional glass-ionomers, it is considered that these materials wiU prove useful in the restoration of primary dentition [15],... 

There have been pubhcations on the effectiveness of glass carbomer as a pit-and-fissure sealant. In one [16], the study compared glass carbomer with a resin-based sealant in 48 teeth in 24 patients. After 6 months, both materials showed 100% retention and after 12 months, they both showed 75% retention. This showed that in terms of one important requirement of fissure sealants, namely retention, the glass carbomer performed quite well. However, further work is necessary to establish whether the enhanced bioactivity confers any further or longer term benefits by way of caries inhibition. 

The materials are described by the manufacturer as bioactive , but there has been no published information about how this bioactivity is achieved, nor whether it is notably better than that of established resin-modified glass-ionomers. For example, there is no indication about whether the materials contain an additive to promote bioactivity, such as hydroxyapatite, like the glass carbomers. It may be that they are bioactive in just the same way that any member of glass-ionomer family is bioactive, namely because of the ionic composition of the glass and the ability to exchange fluoride. 

The glass carbomer has similar properties to conventional glass-ionomers in terms of mechanical strength, adhesion and fluoride release. It is somewhat tougher, though. There do... 

Mix the glass carbomer cement according to the manufacturer s instructions. For hand-mixed cements, ensure that the correct powdenhquid ratio is used. For capsu-lated cements, ensure that mixing is carried out for the correct time. 

N. Zainuddin, N. Karpukhina, R.V. Law, Characterisation of remineralising Glass Carbomer ionomer cement by MAS-NMR spectroscopy. Dent. Mater. 28 (2012) 1051-1058. 

U. Menne-Happ, N. Hie, Effect of gloss and heat on the mechanical behaviour of a glass carbomer cement, J. Dent. 41 (2013) 223-230. 

S.B. Cehreli, R.E. Tirali, Z. Yalcinkava, Z.C. Cehreli, Microleakage of newly developed glass carbomer cement in primary teeth, Eur. J. Dent. 7 (2013) 15-21. 

K. Gorseta, D. Glavina, A. Borzabadi-Farahani, R.N. Van Duinen, I. Skrinjaric, R.G. HUl, E. Lynch, One-year clinical evaluation of a glass carbomer fissure sealant, a preliminary study, Eur. J. Prosthodont. Restor. Dent. 22 (2014) 67-71. 

W. Van Duinen, R.N. Van Duinen, Self hardening glass carbomer composition, US Patent application 20060217455 Al, 2004. 

P. Subramaniam, S. Jayasurya, K.L. GirishBabu, Evaluation of glass carbomer sealant and a moisture tolerant resin sealant - a comparative study, InL J. Dent. Sci. Res. 2 (2015) 42-48. 

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