Glass Ionomer Dental Cement – A Review
S. Subhadharsini, S. Pradeep
Saveetha Dental College and Hospitals, Chennai, Tamilnadu
Aim: To do review regarding Glass ionomer dental cement.
Objective: To understand the important of Glass ionomer dental cement in modern clinical dentistry. Background: Glass ionomer cement is a kind of dental cement made of a silicate glass powder combined with a water-soluble polymer, these cements are also called "giomers." The cement is popular because it adheres to enamel and dentin and has the same natural colour as teeth. In addition, glass ionomer cement releases fluoride ions, which are beneficial to the teeth.
Conclusion: This article reviews the development and history of glass ionomer dental cement and ongoing dentistry.
Glass polyalkenoate cements, more commonly known as glass-ionomers, are made of calcium or strontium alumino-fluoro-silicate glass powder (base) combined with a water soluble polymer (acid). Glass-ionomers were invented in 1969 and reported by Wilson and Kent in the early 1970s . Glass-ionomer cements (GICs) are widely used in various branches of dentistry .One of the advantages of GIC, compared to other restorative materials, is that they can be placed in cavities without any need for bonding agents .This review tracks the development of GIC from the early, relatively unsuccessful product, to the present day.
History of GIC:
One of the characteristic absolutely necessary for an ideal tooth restoration material is its adhesion to tooth structure, particularly to enamel and dentin, and the capacity to withstand pressures resulting from occlusion. From 1950s on, researchers became interested in producing new materials, including the composite resins and GICs. Their aim was to produce a material with thermal, mechanical, and optical properties comparable to those of tooth structure . About this time Smith began an investigation into the standard zinc oxide and eugenol cement, which was already notable for its sedative effect on an inflamed pulp . He decided to use a polyalkenoic acid as the liquid, rather than eugenol, and found that the resultant cement demonstrated a level of adhesion to both tooth structure and gold . However, its physical properties were less than ideal and this class of cement failed to succeed .
The first GIC was produced in late 1960s by Alan Wilson and his group in a chemistry laboratory in London. Since then, commercial companies have made significant improvements to basic GIC formulation involving both glass and poly acid used. Improvements and an increasing endorsement of two particular clinical advantages; long term adhesion and persistent fluoride release, have led to the greater acceptance by clinicians . It has been recognized for many years that micro leakage between the restoration and cavity wall is probably dentistry's greatest hazard, and this prevented by the ion- exchange adhesion of GIC .
During the manufacture of the glass it is necessary to use a fluoride flux to avoid oxidation . Then, fluoride is released after mixing of powder with the poly alkenoic acid and becomes available for absorption by the tooth structure . Presence of fluoride decreases melting point, increases cement strength, improves manipulation properties of cement and finally has a cariostatic effect .
In 1988, Purton and Rodda showed that the cement released not only fluoride ions, but also calcium and phosphate, into the tooth structure .
The early conventional glass-ionomer materials were technique-sensitive, slow setting, opaque when set and sensitive to both desiccation and hydration during setting. This led to premature surface deterioration. Most of these problems have been solved in newer generations of glass-ionomer cement . The problems related to composite materials and adhesive systems have resulted in the indication for the use of glass- ionomer cements (GIC) as restorative materials in low-stress- bearing restorations and as a lining material. GIC exhibit several clinical advantages when compared to other restorative materials . They include physico-chemical bonding to tooth structures . Fluoride release  and low coefficient of thermal expansion . The use of GICs as luting agents has also been reported to having great success. High-caries-risk patients are particularly benefited with the use a luting cement that has leachable fluoride ions and associate preventive dentistry implications .
The setting reaction of GIC is complex and may vary with composition but in general it is an acid base reaction . When the powder and the liquid is mixed, the surface of the powder is dissolved by the hydroxyl ions leaving an ion depleted silica gel layer. The fluoride in the powder is released together with calcium, aluminum and sodium ions . Rapid reaction of the calcium ions with the polyacid chains, followed by later reaction of aluminum ions species, reflecting the more gradual release of the latter ion from its anionic complex. Reaction of metal ions with the carboxylic acid groups displaces water from some of the hydration sites, and leads to some ionic cross-linking of the polyacid chains. Both of these effects lead to insolubilization of the polymer and stiffening of the material.
RESIN MODIFIED GLASS IONOMER CEMENT:
An important advancement in glass ionomer technology that has influenced dentistry for children is development of the resin-modified glass ionomer systems . RMGICs have good retention results, reduced superficial degradation and increased wear resistance when compared to conventional GICs . This material has been on the market for over 13 years and is known for: (1) preventing postoperative sensitivity when placed under direct application resin-based composite restorations, thus protecting against bacterial access to dentinal tubules, (2) its internal fluoride ion release  and (3) its antimicrobial action . Fracture toughness, fracture resistance, and resistance to wear are all improved in the resin-modified glass ionomers .
Some of the evidence suggests that GIC of low viscose/ strength protects pits and fissures of permanent molars against caries at same level as resin-based sealants. However, there is a need for well-designed and standardized RCT’s, particularly including newer high viscose/ strength GIC for fissure protection .
GIC-based materials are clinically popular in several different areas of restorative dentistry – as linings underneath other restorative materials, as luting agents, as well as for core build-up, and for restorations . GICs have very low shrinkage and are thermally compatible with tooth structure. They can even bond to dentin surfaces without the removal of the smear layer and their biologic compatibility is well proved. For these reasons, they can be effectively used as lining materials . They bond to teeth moderately, have optimum flow properties allowing easy seating, are cariostatic and are relatively inexpensive . GIC are used to cement stainless steel crowns for primary teeth, precision cast crowns and fixed prostheses for permanent teeth, space maintainers, and single orthodontic bands . GICs, however, have been the preferred core build-up materials for a long time because of their chemical adhesion to the tooth structure . The use of GICs to restore cervical lesions proved especially successful .
THE FUTURE OF GIC:
Improvements are obviously desirable; this has resulted in. Improved formulations and more controlled techniques. Some light- cured polymer reinforced materials appear to have substantial benefits in most of the established application while retaining the advantages of fluoride release and adhesion . Clinical research is producing scientific evidence that certain resin-modified glass ionomer restorative cement systems can give long-term reliability in dentistry for children . Conventional GIC have been also used in bone contact application. In particular, this has involved their use is augmentation of alveolar ridge in edentulous patients  is used in the maxillofacial and cranio- facial reconstruction surgery .
In contrast to resin bonding, the adhesion of glass-ionomer to tooth structure is not technique sensitive and its quality increases with time. Therefore glass-ionomer might turn out to the more reliable restorative material in minimal invasive dentistry based on adhesive techniques
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