Clinical Evaluation of Glass-ionomer Cement Restorations Avaliação Clínica De Restaurações De Cimento De Ionômero De Vidro

General structure and properties Glass-ionomer cements were developed by Wilson and McLean at the Laboratory of the Government Chemist in England in 196527. They were a logical addition to the family of water-based dental cements, comprising silicate cement, zinc phosphate cement and zinc polycarboxylate cement. Since their commercial introduction, they are now available in essentially two types. ‘Conventional’ glass-ionomers consist of a fluoroaluminosilicate glass, usually a strontium or calcium salt, and polyalkenoic acid liquid, for example polyacrylic, maleic, itaconic and tricarbalyllic acids. The conventional materials sent by an acid-base reaction between the acidic liquid and the basic powder26. More recently, in order to improve the physical properties and decrease the water sensitivity of the conventional materials, the so called resin-modified glass-ionomer cements have become available. These contain a polymerisable resin, commonly hydroxyethylmethacrylate (HEMA), and therefore have the additional setting reaction of resin polymerisation, which may be self-cure and/or light-cure23. The significant properties of the glass-ionomers are adhesion to calcified tooth structure, release of fluoride, minimal effect on the pulp, and that they are tooth-coloured. However, they are sensitive to dehydration early in the setting process, particularly the conventional cements, and they are brittle materials and therefore unsuitable for use in load-bearing areas26. In view of these properties, they have a wide range of uses, including fissure sealants, anterior approximal restorations, cervical restorations (both carious and non-carious), in deciduous teeth, as lining and luting cements, and as orthodontic band and bracket materials. A convenient classification of glass-ionomer cements is based on their clinical application. Type 1 cements are luting materials, Type 2 cements are restorative materials, and Type 3 cements are lining cements and fissure sealants26. As mentioned above, one of the most significant properties of glass-ionomer cement is their adhesion to calcified tooth structure. The bonding mechanism of the conventional glass-ionomer is very complex, but consists initially of the wetting of the tooth surface by free polyacrylic acid, followed by ionic bonding between the carboxyl group in the cement liquid and calcium ions in the tooth structure. Recent work has established that a so-called ‘ion exchange’ layer is formed between the cement and the calcified structures, consisting of a complex of carboxyl, calcium and phosphate ions, derived from both the cement and from the enamel and dentine. This ion exchange layer is a few micrometres thick, and is an extremely strong, such that