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Current Products and Practice Section |
Department of Dental health and Development, University Dental Hospital, Heath Park, Cardiff CF14 4XY, U.K.
Introduction
Despite the advent of bonded attachments, preformed stainless steel bands are still routinely utilized in fixed appliance therapy. Banding offers superior reliability due to better resistance to occlusal interferences (Fricker, 1997
). Band cements are necessary for band retention, either by assisting mechanical retention or by true adhesion. They also serve to seal a band to a tooth, filling the irregular gaps to prevent stagnation areas.
Zinc phosphate cement was widely used for band cementation for much of the last century. It has high compressive strength, but suffers from low tensile strength and high solubility, resulting in micro-leakage and demineralisation. Zinc polycarboxylate cements were introduced to orthodontics in the early 1970s and offered the advantage of chemical adherence to enamel. However, physical and handling properties were flawed, due to poor tensile bond strength, solubility, viscosity, and short working time. Both zinc phosphate and polycarboxylate cements have been superceded by new generations of adhesive cements, and are now largely obsolete as banding cements.
Glass Ionomer Cement
Glass ionomer cements (GICs; Table 1) were introduced by Wilson and Kent in 1972 as restorative materials, and subsequently became available as luting cements. The first generation of GICs consist of aluminosilicate glass powder and an alkenoate acid liquid, which undergo an acid base reaction when mixed. the second generation GICs incorporated the acid as a freeze-dried powder blended with the glass and are mixed with distilled water.
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), provides superior clinical performance due to reduced band failure (Fricker and McLachlon, 1985, 1987; Mizrahi, 1988; Stirrups, 1991). Also there is better protection from micro-leakage since bond failure usually occurs at the cement band interface (Millet et al., 1998) and the solubility is low. Furthermore, GICs leach fluoride over prolonged periods, thus reducing the potential for demineralization. There are, however, problems associated with the handling properties. Accurate dispensation of the liquid component is difficult, resulting in inaccurate powder:liquid/ water ratios, and they are susceptible to moisture contamination during the setting reaction. These can both adversely affect the physical properties of the set material. Whilst the development of encapsulated cement has helped, these are more expensive than hand-mixed cements and wastage is likely.
Resin-modified Glass Ionomer Cement
Traditional GICs (Table 2) were modified by the incorporation of resin, and water-soluble initiators and activators, to produce dual cure hybrid cements. These set partly via an acid-base reaction and partly through a polymerisation reaction (Bourke et al., 1992). The advantages they offer are in improved handling characteristics, due to command setting, longer working time, and greater tolerance of moisture (Mennemeyer et al., 1999). The bond strength of modified GICs is reported as superior to traditional GICs (Mennemeyer et al., 1999), although no significant difference in failure rates was found in a clinical study (Fricker, 1997).
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These compomer or composite cements (Table 3) are composed of ion-leachable glass in a polymeric matrix. They set by a light-cured resin reaction, not an acid-base reaction, and rely upon water diffusion into the set polymer to allow fluoride release. The set material can take up and rerelease topical fluoride. These cements are produced both as dual paste systems, which are dual cure, and as single paste systems, which are light cured. Their handling characteristics are generally very good, with minimal mixing and command setting, but the material can be difficult to place in the bands.
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). Comparative laboratory investigations found that an acid-modified composite resin cement had significantly higher tensile strength and significantly lower probability of band failure than a traditional GIC (Mennemeyer et al., 1999; Millet et al., 1998). However, a clinical trial found no significant difference in failure rates between a traditional GIC, a resin-modified GIC and an acid-modified resin cement (Fricker, 1997). In contrast to GICs, these cements tend to fail at the cement/ enamel interface, and there is consequently greater risk of stagnation areas, micro-leakage, and demineralization (Fricker, 1997). Conclusions
There have been significant recent developments in banding cements and new materials are constantly appearing on the market. The properties of the cements currently in use have been compared and the latest product information available from UK suppliers is provided.
References
Bourke, A. M., Walls, A. W. and McCabe, J. F. (1992)Light-activated glass polyalkenoate (ionomer) cements: the setting reaction,Journal of Dentistry, 20, 115–120.
Durning, P., McCabe, J. F. and Gordon, P. H. (1994) A laboratory investigation into cements used to retain orthodontic bands, British Journal of Orthodontics, 21, 27–32.[Abstract]
Fricker, J. P. (1997) A 12-month clinical comparison of resin-modified light activated adhesives for the cementation of orthodontic molar bands, American Journal of Orthodontics and Dentofacial Orthopaedics, 112, 239–243.
Fricker, J. P. and McLachlon, M. D. (1985) Clinical studies of glass ionomer cements—part 1, a 12 month clinical study comparing zinc phosphate cement to glass ionomer, Australian Orthodontic Journal, 9, 179–180.[Medline]
Fricker, J. P. and McLachlon, M. D. (1987) Clinical studies of glass ionomer cements—part 2, a two year clinical study comparing glass ionomer cement with zinc phosphate cement, Australian Orthodontic Journal, 10, 12–14.[Medline]
Mennemey, V. A., Neuman, P. and Powers, J. M. (1999) Bonding of hybrid ionomers and resin cements to modified orthodontic band materials, American Journal of Orthodontics and Dentofacial Orthopaedics, 115, 143–147.
Millet, D. T., Kamahli, K. and McColl, J. (1998) Comparative laboratory investigation of dual-cured vs. conventional glass ionomer cements for band cementation, Angle Orthodontist, 68, 345–350.[Medline]
Mizrahi, E. (1988) Glass ionomer cements in orthodontics—an update, American Journal of Orthodontics and Dentofacial Orthopaedics, 93, 505–507.
Stirrups, D. R. (1991) A comparative clinical trial of a glass ionomer and a zinc phosphate cement for securing orthodontic bands, British Journal of Orthodontics, 18, 15–20.[Abstract]
Wilson, A. D. and Kent, B. E. (1972) A new translucent cement for dentistry: the glass ionomer cement, British Dental Journal, 132, 133–135.[Medline]
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