24.10.2014
Aim: To evaluate the bonding ability of composite to unset glass-ionomer cement (GIC) using different self-etching bonding systems. GC Fuji II is a self-cured, glass ionomer restorative featuring high resistance to water which can be finished in just 15 minutes (under water spray). Excellent mechanical properties – high compressive strength, minimal abrasion, and excellent surface hardness. Primarily a permanent cementing agent for conventional dental prosthesis, it is also an orthodontic band cement, coronal buildup material and cavity liner.
Materials and Methods: One hundred samples of composite bonded to unset GIC were prepared and were divided into four groups. Shear bond strength evaluation of resin composite bonded to glass-ionomer cement using self-etching bonding agents with different pH: In vitro study. A rationale use of dental materials in posterior direct resin restorations in order to control polymerisation shrinkage stress.
Shear bond strength of chemical and light-cured glass ionomer cements bonded to resin composites.
A clinical trial of the glass ionomer cement-composite resin "sandwich technique" in class II cavities in permanent premolar and molar teeth. Flexural strength of resin-modified glass ionomer cements and their bond strength to dental composites.
Bond strengths between composite resin and auto cure glass ionomer cement using the co-cure technique. Shear bond strength evaluation of resin composite bonded to GIC using three different adhesives.
Aggressiveness of contemporary self-etching adhesives, part II: Etching effects on unground enamel. The effect of depth of dentin demineralization on bond strengths and morphology of the hybrid layer.
Comparative shear bond strength analysis of strong, intermediary strong and mild 'self­ etch' systems, and a hypothesis on their chemical behavior on dentin. Comparison of the shear bond strength of RMGIC to a resin composite using different adhesive systems: An in vitro study.
An infectious disease requires a microbial agent, a susceptible host, and substrate that promotes growth of the infectious agent.
In Group A, composite was bonded to unset GIC employing a strong (pH 1) self-etch primer was used. The rationale behind the technique is to make the most of the physical and esthetic properties of each material as it combines the dentin-adhesion and fluoride release of glass ionomer as well as the aesthetics and polishability of resin. The infectious agents are Streptococcus mutans followed by an increase in lactobacilli species. Loss of tooth structure results from metabolism of carbohydrates by bacteria and the release of lactic acid as a byproduct.1,2 The traditional approach to treatment of even a small carious lesion is wide surgical excision. This results in removal of sound tooth structure both to gain access to the lesion and to obtain retention for the restoration. The margins of the cavity were placed in so-called caries-free zones that were more accessible to plaque removal by brushing.3 Limited areas of demineralization required the same amount of tooth structure removal as more advanced lesions. Results: Statistical analysis performed with one way analysis of variance and Tukey's test showed that the bond strength of composite to unset GIC was significantly higher for the mild self-etch primer group.
The clinical technique described by Mount [4] suggests etching the initially set GIC for 15 s prior to placing a layer of resin bond to develop a mechanical bond between the two materials. Tooth preparation further increased the risk of subsequent pulpal involvement in a pulp already affected by the carious process.4 The available restorative materials were not adhesive and required the cavity preparation to have a shape that promoted retention. In addition, energy dispersive x-ray (EDX) analysis was used to determine the composition of various structural phases identified by FE-SEM along the GIC-bonding agent interfaces. However, failure occurred due to sensitivity to moisture and the progressive loss of the GIC. The advent of adhesive restorative materials that were also capable of sealing the interface between the restoration and the tooth changed traditional concepts regarding tooth preparation. Further, bioactive materials capable of promoting the repair of tooth structure have changed how a carious lesion is treated.5 It has now been recognized that tooth structure can remineralize and heal. This could be attributed to the difference in the setting reactions between dental composites and conventional GICs. Research has indicated that a carious lesion can be reversed if it has not progressed to cavitation.5 Further, fluoride decreases susceptibility of the tooth to the development of caries. These approaches les-sen the chance for subsequent adverse outcomes, including pulpal involvement and tooth fracture.4 MINIMALLY INVASIVE DENTISTRY AND GLASS IONOMERS   The outer surface of teeth is constantly under biochemical assault. A clinician can employ a glass-ionomer adhesive system after the initial set of GIC or a self-etch primer over the unset GIC.
Clinically the latter technique would be more useful as it not only do away with the etch and rinse procedure, but also saves valuable clinical time as it can be employed immediately after the placement of GIC in the cavity.A self-etch approach involves either a two- or one-step application procedure. Depending on etching aggressiveness, they can be subdivided in to strong, intermediary, and mild self-etch adhesives. Fragile, demineralized enamel on occlusal surfaces may fracture due to stress on the teeth. Interprox-imal lesions are not exposed to the same occlusal forces and are more amenable to remineralization. At enamel, the resulting acid etch pattern resembles a phosphoric-acid treatment following an etch and rinse approach. In the presence of free fluoride ions, remineralization involves the formation of fluorapatite. It also modifies the surface energy of enamel and impedes the attachment of plaque to the tooth surface.
Mild self-etching adhesive systems generally have a pH of approximately 2, and induce only a shallow partial demineralization no deeper than 1 μm in dentin. Fluoride inhibits bacterial metabolism by diffusing hydrogen fluoride from the plaque into the bacteria. Micromechanical interlocking is obtained through hybridization of the microporous hydroxyapatite-coated collagen network. Fluoride in the bacteria interferes with bacterial metabolism and decreases the adherence of bacteria to hydroxyapatite.7 Fluoride in the water supply and toothpaste has been shown to reduce the prevalence of caries. The null hypothesis tested was that the pH of self-etching bonding agents has no effect on shear bond strength. The fluoride released from the glass ionomer aids in the formation of fluorhydroxyapatite on adjacent tooth structure. This will not prevent new carious lesions, but renders the adjacent tooth structure more resistant to demineralization.6 COMPOSITION AND PHYSICAL PROPERTIES OF GLASS IONOMERS   Conventional glass ionomers were developed by Wilson and Kent in 1974.


A split Teflon mold (6 mm in diameter, 6 mm in height) was used to prepare glass ionomer cylinders (Fuji IX) of the dimension (6 mm in diameter, 3 mm in height). They combined ion-leaching glasses used in silicate cements with polycarboxylic acid polymers.8 Through improvements in the composition of the glasses and carboxylic acids and the incorporation of tartaric acid, these materials became suitable for different clinical situations.
A freshly mixed adper prompt self-etch liquid A and liquid B were applied over the unset GIC with a microbrush, using continuous rubbing with light pressure for 15 s. The addition of small quantities of light-polymerizable resin groups has improved physical properties, as translucency and water balance are more readily maintained.10,11   Figure 1. A chemical bond is formed between carboxyl ions in the glass ionomer and calcium in the tooth. Composite material was then added in increments to a height of 3 mm and each increment was light cured for 40 s.Group BCapsulated GIC was mixed for 10 s using capsule mixer and placed into the vertical mould.
AdheSE Primer was applied over the unset GIC with a microbrush, using continuous rubbing with light pressure for 15 s. The excess primer was dispersed and air dried with oil-free compressed air from an air syringe until the mobile liquid film disappeared. Composite material was then added in increments to a height of 3 mm and light cured for 40 s.Group CCapsulated GIC was mixed for 10 s using a capsule mixer and placed into the vertical mould. In addition to the chemical bond, the glass ionomer and the tooth maintain a physical union. Clearfil SE Primer was applied over the unset GIC with a microbrush, using continuous rubbing with light pressure for 20 s. The excess primer was dispersed and air dried with oil-free compressed air from an air syringe until it became a thin film. Composite material was then added in increments to a height of 3 mm and each increment was light cured for 40 s.Group DCapsulated GIC was mixed for 10 s using capsule mixer and placed into the vertical mould.
One coat SE bond applied in two consecutive coats over the unset GIC with a microbrush, using continuous rubbing with light pressure for 20 s. It is gently air dried with oil-free compressed air from an air syringe and light cured for 10 s. In addition, micromechanical pen-etration of the glass ionomer into tooth structure has been shown to occur12 (Figure 2). An understanding of the glass ionomer setting reaction is critical in obtaining the best clinical results and utilizing these materials in appropriate clinical situations.
FESEM was used to determine the effects of different pH environments on morphological characteristics of cured cement disks. The setting reaction is an acid-base reaction between polymeric carboxylic acid and basic fluoroaluminosilicate glass, and requires an aqueous medium in order for the ions leached from the glass to react with the polyacid moiety. The criteria for evaluation included the presence of cracks and micropores at the surface of the material. Only then is there sufficient replacement of silica by aluminum to render the network susceptible to acid attack, and this results in the release of simple and complex metal ions. This is the ion-leaching phase (H+ attacks the glass particles releasing Ca+2, Al+3, and F-). The glass ionomer sets and hardens by means of a transfer of the metal ions from the glass to the polyacrylic acid. Group B (intermediary strong self etch primer pH 1.4) showed significant bond strength from group A.
A silica gel layer is then formed at the interface between the cement matrix and the glass particles, as most of the metallic ions are lost.13 During this period of time, the material must be protected from dehydration because loss of water disrupts the cement structure. Group A (strong self etch primer pH 1) showed the least bond strength values.FESEM analysis showed morphological differences between the three samples. The calcium and aluminum ions diffuse into the polyacrylic liquid, forming polyacrylate (a cross-linked metallic salt).
Destruction of the material surface was evident in GIC with strong self-etch sample compared to other samples. When this salt begins to precipitate, gelation begins and continues until the cement is hard.
FESEM analysis revealed the presence of a large number of voids and cracks in GIC with strong self-etch sample [Figure 2].
Fluoride ion is also released from the glass particles, becoming available to nearby tooth surfaces and being released into saliva. Although microporosities were present, yet destructions like large cracks were not seen in GIC with mild self-etch sample [Figure 3]. Some materials also have a third reaction, specifically a chemically initiated reaction between free radical methacrylate and the polymer structure.11 There is a continuum of materials between conventional glass ionomers and light-cured composite resins.
McLean14 proposed a classification for these new materials: (1) The unqualified term glass ionomer cement should be reserved exclusively for a material consisting of an acid-decomposable glass and a water-soluble acid that sets by a neutralization reaction.
However, this system was advocated only to be applied on dentin alone, and therefore required clinically selective-enamel etching in a separate step.
The current self-etch adhesives provide monomer formulations for simultaneous conditioning and priming of both enamel and dentin. Most common self-etch adhesives involve two application steps with the self etch primer followed by an adhesive resin, resulting in two-step self-etch adhesives. Some are very similar to traditional glass ionomers and cure by a traditional acid-base reaction. Recently, one-step self-etch or so-called all-in-one adhesives combining the conditioning, priming and the application of an adhesive resin into a single application have been marketed.Besides, on the basis of the number of application steps, self-etch adhesives should also be subdivided into mild, intermediary strong, and strong self-etch adhesives, depending on their pH and thus etching potential. At the other end of the spectrum are materials that cure mainly as a result of light-activated polymerization.
Materials that are more composite in nature have increased thermal expansion and demonstrate less fluoride release. The materials that are more glass ionomer in nature have low thermal expansion and high fluoride release. They require a conditioner for maximum adhesion that is rinsed off before the restoration is placed.15   Figure 4. Elemental analysis of GIC with mild self-etch showed similar ion concentration to that of set GIC without any bonding agent and FESEM showed few microporosities without any destructions like large cracks as seen on GIC with a strong self-etch sample. Based on organic chemistry, when there is only a mild acid attack, there will be minimal flushing of ions, and hence salt crumps formation will be minimal. With stronger acids there will be more neutralisation of the cations and formation of salt crumps (crusts) which is a weaker structure and fragile form, thereby resulting in a weaker bonding.
These materials were originally developed for use in regions of the world where dental services are limited.11,16 They are utilized following spoon excavation of a tooth.
FESEM analysis provided direct visibility of the changes at the material surface like the presence of a large number of voids and cracks that could have resulted in increased bond failure.


The area is then isolated as best as possible, and the restorative material is condensed into the tooth with finger pressure.
The higher viscosity and improved physical properties are achieved by the addition of polyacrylic acid to the powder, a finer grain-size distribution, and modifications to the chemical treatment of the glass powder to allow the incorporation of more powder into the liquid. These materials are adhesive and demonstrate fast setting times, high compressive and tensile strength, surface hardness, and fluoride release.
These characteristics allow their use in patients with a high caries rate as bases and for emergency repair of fractured cusps (to cover exposed dentin and sharp margins; Figure 4), as interim restorations, and as final restorations in nonstress-bearing areas. The surgical approach to cavity preparation requires removal of all carious tooth structure.
Excessive removal of tooth structure could result in the need for endodontic therapy if the pulp chamber was breached. If, however, glass ionomers are used as the transitional restoration after removal of infected dentin, microleakage can be eliminated because of glass ionomers' adherence to enamel and dentin via ion exchange. Ion exchange between the glass ionomer and the de-mineralized dentin allows the dentin to remineralize. If there is uncertainty that the dentin has remineralized, the entire glass ionomer restoration can be removed and the area examined prior to placing the final restoration. It should be noted that "compomers," or polyacid-modified resin composites, unlike true glass ionomers, do not contain water, and the setting reaction does not involve an acid-base reaction. The amount of fluoride released is lower than traditional and resin-modified glass ionomers.10 In addition, glass ionomers have a greater capacity to be recharged. Exposure of fluoride-containing dental materials to fluoride rinses or fluoridated toothpastes provides a source that will replenish the fluoride in the dental material.10 The resin bonding agent that is utilized in adhesive restorations prevents fluoride from the compomer from being released. The weaker mechanical properties of these materials restrict their use to areas of minimal stress, such as class I, III, and V restorations in adult and primary dentition and small class II restorations in primary teeth. CLINICAL APPLICATIONS OF GLASS IONOMERS   In addition to the use of glass ionomers as restorations, clinical applications of these materials include use as a bonding agent, liner, base, core material, sealant, and for luting.
Some materials such as Fuji Bond LC (GC America) are true glass iono-mers and can be used to bond direct placement composite res-ins.
Materials such as Scotch-bond Multipurpose (3M ESPE) incorporate glass ionomer technology that includes carboxylic acid groups to aid in the attachment to dentin. Glass ionomers have been utilized as a cavity liner (eg, Vitrebond [3M ESPE] and Fuji Lining [GC America], Figures 5 to 7). They provide a chemical bond to tooth structure, good pulpal response, and fluoride release. The chemical bond, the initial low pH, and fluoride release help to minimize bacterial invasion.17   Figure 8. Fuji IX is placed in the mesial fossa to reduce the bulk of composite and the resulting contraction stress. When enamel remains at the gingival margin, this area is usually sealed with a composite resin. The term "sandwich technique" refers to the use of a glass ionomer to replace the dentin and composite resin to replace the enamel (Figures 8 to 18).
The glass ionomer provides caries resistance, chemical ad-hesion to dentin, and remineralization capability, and by reducing the amount of composite that is needed, it reduces shrinkage. Glass ionomers have a stiffness that is much less than composite filling materials, especially hybrids. In addition, water absorption increases the volume of the base, which also serves to compensate for shrinkage. However, due to the ongoing reaction of glass ionomers, internal cracks can be repaired, and over time the glass ionomer actually increases in strength due to this continuous reaction, especially when it is in contact with water.18 The presence of a resin-rich, nonparticulate, amorphous interfacial transition zone exists in dentin bonded with resin-modified glass ionomer cement (RMGIC) and has been called the absorption layer. This is because of the movement of water in the maturing RMGIC when placed in contact with deep, moist dentin. The RMGIC may serve to act as a stress-breaking layer similar to that of a dentin adhesive layer used to relieve polymerization stress.19,20 The overlying composite will bond well to enamel and provides enhanced aesthetics and durability.
The major drawback associated with composite is the high shrinkage that occurs after light curing, which results in stress on the adhesive interface.11 In class II lesions, the glass ionomer can be placed as either an open (Figure 17) or closed sandwich (Figure 18). Glass ionomer used instead of composite in the cervical portion of the proximal box is an open sandwich. When enamel is present at the cervical margin, composite is bonded to this surface, and the glass ionomer is placed internally as a dentin replacement. Less micro-leakage has been demonstrated utilizing this technique as op-posed to conventional bonding in deep class II proximal boxes. However, these materials are strong under compressive forces but weak under tension and shear.17 If glass ionomers are used as core materials, a majority of the tooth should be present.
The ideal sealant should have a long-term bond to enamel, be cariostatic, be easy to apply, be free flowing so that it can penetrate narrow fissures, and have low solubility in the oral environment. Glass ionomers must be placed in fissures with an orifice wide enough to accommodate an explorer tip (excess of 100 µm, Figures 19 and 20). If the fissures are patent, then the sealant can be used successfully.24 CONCLUSION   The original concept of caries management involved the removal of all affected tooth structure and replacement by restorative material. Ideally, methods to prevent the disease or approaches to biological repair of a lesion should be developed.25 Prevention includes antimicrobial therapy, modification of the substrate via reduction in fermentable carbohydrates (decreasing sugar intake), and making the teeth more resistant to acid dissolution (use of fluoride).
Glass ionomer materials can provide a valuable addition to the dentist's restorative armamentarium. The ion exchange and diffusion-based union of material tooth structure inhibits microleakage and maintains the seal between the tooth and the restoration. Glass ionomers have been modified to improve their physical properties for different restorative applications. Trushkowsky is a fellow in the Academy of General Dentistry, the Academy of Dental Materials, the International College of Dentists, the American College of Dentists, and the Pierre Fauchard Academy. He wrote a chapter on direct composites in Esthetic Dentistry published by CV Mosby and a chapter on complex single-tooth restorations in Dental Clinics of North America. He has published more than 80 articles and abstracts in a variety of journals and magazines.Additionally, he is on the editorial boards of Contemporary Esthetics and Restorative Practice and Collaborative Techniques. He can be reached at (718) 948-5808 or This email address is being protected from spambots. Trushkowsky has received financial remuneration for providing consulting services to GC America.



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