20.03.2016
The ST series amalgamator adapts patented resonation absorption technique to minimize the noise. Your use of this website constitutes acknowledgement and acceptance of our Terms & Conditions. Excellent mechanical properties – high compressive strength, minimal abrasion, and excellent surface hardness. An infectious disease requires a microbial agent, a susceptible host, and substrate that promotes growth of the infectious agent. The filling material has good filling effects with low shrinkage and good sealing effect without looseness, falling off or breaking.
It is a ideal impression material of polymerized rubber which has characteristics as high strength, elasticity and nice flowability, plasticity, stable dimensions, good precision, and stable chemical properties etc. The infectious agents are Streptococcus mutans followed by an increase in lactobacilli species.
The vibration frequency is highest among same kinds of amalgamators up to 4300-4500RPM to ensure optimal mixture. 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. Containing active components of fluoride and strontium ions, it can emit fluoride ions constantly and so has anti-cavity function. 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.
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. 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. 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.
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. 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.
Fluoride inhibits bacterial metabolism by diffusing hydrogen fluoride from the plaque into the bacteria. 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 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.
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. 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. In addition to the chemical bond, the glass ionomer and the tooth maintain a physical union. 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.
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.


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. 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. The calcium and aluminum ions diffuse into the polyacrylic liquid, forming polyacrylate (a cross-linked metallic salt).
When this salt begins to precipitate, gelation begins and continues until the cement is hard. Fluoride ion is also released from the glass particles, becoming available to nearby tooth surfaces and being released into saliva. 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.
Some are very similar to traditional glass ionomers and cure by a traditional acid-base reaction. 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. 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. 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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