Glass Ionomer Restorations PDF

Glass Ionomer Restorations Glass Ionomer Cements (GIC) were introduced to dentistry in 1972 by Wilson and Kent. They were first marketed in Europe in 1975 and became available in the United States in 1977. The invention of GIC stemmed from previous fundamental studies on silicate cements and investi...

Glass Ionomer Restorations Glass Ionomer Cements (GIC) were introduced to dentistry in 1972 by Wilson and Kent. They were first marketed in Europe in 1975 and became available in the United States in 1977. The invention of GIC stemmed from previous fundamental studies on silicate cements and investigations where organic chelating acids were substituted for phosphoric acid in dental silicate cements. For this reason, glass ionomer cement has been characterized as a hybrid of dental silicate cement and zinc polycarboxylate cement. I. Conventional GIC GIC Powder: The powder consists of an acid-soluble calcium fluoroaluminosilicate glass similar to silicate, but with a higher alumina-silicate ratio that enhances its 1 reactivity with the liquid. Additives such as lanthanum, strontium, barium, or zinc oxide provide radiopacity. GIC Liquid: The liquid is an aqueous solution of polymers and copolymers of acrylic acid. Itaconic and tricarboxylic acids are added to 1. Decrease the liquid's viscosity. 2. Promote reactivity between the glass and the liquid. Tartaric acid is also present to improve handling characteristics and extend working time, although it accelerates setting time. Setting Reaction: The setting reaction is an acid-base interaction between the acidic polyelectrolyte and the aluminosilicate glass, occurring in three distinct but overlapping phases: 2 1. Ion Leaching Phase: This phase initiates upon mixing the powder and liquid. The polyacid attacks the glass particles (leaching) upon mixing, releasing cations such as Ca²⁺ and Al³⁺. 2. Hydrogel Phase: in this phase, calcium ions are rapidly released. These ions react with the acid and cross-link with polyacrylic acid, forming calcium bridges to create a calcium polycarboxylate gel with embedded non-reacted glass. Water plays a crucial role in GIC setting, acting as the initial reaction medium and gradually hydrating the crosslinked agents to form a stable gel structure resistant to moisture contamination. Clinical Tip: Freshly mixed cements left exposed to ambient air without protection will craze and crack due to desiccation. Water contamination at this stage can lead to dissolution of the matrix, releasing cations and anions into the surrounding areas. 3. Polysalt Gel Phase This phase occurs at the final set. Continued attack by hydrogen ions leads to delayed release of Al ions from the silicate glass as AlF ions, which deposit in the preformed matrix to form a water-insoluble Ca-Al-Carboxylate gel. The strength of the cement is provided by these Al ions. 3 Adhesion  Proper wetting of the tooth surface is facilitated by applying fresh cement, owing to the hydrophilic nature of both the cement and tooth surface. Adhesion rapidly develops through the formation of hydrogen bonds between the free carboxyl groups of the cement and bound water on the tooth surface.  Adhesion of glass-ionomer cements involves a true chemical bond, with ionic bonds forming between the carboxylate groups on the polyacid molecules and calcium ions on the tooth surface. Fluoride release Fluoride released from glass-ionomer cements into demineralized dentin penetrates deeply into the underlying dentin at concentrations of about 5000 ppm. Aqueous fluoride concentrations as low as 600 ppm have been shown to inhibit fluoride- resistant Streptococcus mutans bacteria. 4 Classification of GICs Traditional classification (Based on application)  Type I—Luting cements  Type II—Restorative esthetic or reinforced cements  Type III—Liner or Base Classification of GICs according to the clinical use  Type I—For luting cements  Type II—For restorations  Type III—Liners and bases  Type IV—Fissure sealants  Type V—Orthodontic cements  Type VI—Core build up 5 Indications of GICs  Restoration of permanent teeth (Class V, Class III, small Class I tooth preparations, Abrasion/Erosion, Root caries).  Restoration of deciduous teeth (Class I – Class VI tooth preparations, Rampant and nursing bottle caries).  Luting or cementing (Metal restorations: Inlay, onlay, crowns. Nonmetal restorations: composite inlays and onlays, Veneers, Pins and posts, Orthodontic bonds and brackets).  Preventive restorations (Tunnel preparation and Pit and fissure sealants).  Protective liner under composite and amalgam.  Bonding agent.  Dentin substitute.  Core build-up. 6 Advantages of GIC  Inherent adhesion to tooth structure due to chemical bonding to enamel and dentin through ion exchange.  Biocompatible because large-sized polyacrylic acid molecules prevent the acid from eliciting a pulpal response.  Minimal shrinkage and good marginal seal.  Anticariogenic properties due to fluoride release, which can also be replenished through topical fluoride applications.  Requires minimal tooth preparation, making it easy to use on children.  Less technique-sensitive compared to composite resins. Limitations of GIC  Lower compressive strength compared to amalgam and resin composites.  Reduced wear resistance.  Susceptibility to water during the setting phase, affecting physical properties and aesthetics.  Opaqueness reduces aesthetic appeal compared to composites.  Requires moisture control during manipulation and placement. II. High Viscosity Conventional GICs Highly viscous glass ionomers are primarily beneficial for the atraumatic restorative treatment technique, serving as an alternative to amalgam for posterior restorations. In these cements, polyacrylic acid is finely ground to enable the use of higher powder-liquid ratios. 7 Advantages of Highly Viscous Glass Ionomers:  Fast setting  Low early moisture sensitivity  Low solubility in oral fluids  Finishing can be completed five minutes after placement Glass Hybrid In 2014, GC Corporation introduced EQUIA Forte®, the first glass-hybrid technology designed for stress-bearing Class II restorations. In 2019, the company launched the high-viscosity GIC EQUIA Forte® HT Fil, featuring enhanced translucency and suitable for stress-bearing and non-stress-bearing Class I and Class II restorations, as well as Class V restorations. This generation was reinforced with evenly dispersed ultrafine and highly reactive glass particles and optimized polyacrylic acid molecular weight, resulting in excellent mechanical properties usable in high load-bearing areas. III. Reinforced GICs The strength of GIC can be enhanced by modifying the chemical composition of the original glass powder through: 8 1. Disperse-phase Glasses: Strengthening is improved by preparing glass with a high amount of dispersed strengthening crystallites like corundum (Al2O3) and tielite (Al2TiO5). 2. Fiber-reinforced Glasses: Flexural strength is enhanced by adding alumina fibers, glass fibers, silica fibers, and carbon fibers. 3. Metal Reinforced GIC: Flexural strength is increased by incorporating metal powder or fibers. Notable examples include "Miracle mix," which combines amalgam alloy powders with GIC. 4. Cermet Cements: Metal and glass powders are sintered together to create a strong bond between the metal and glass, resulting in improved resistance to abrasion and higher flexural strength. IV. Resin-Modified GIC Introduced in 1988, resin-modified glass ionomer cements (RMGIC) were developed to address the limitations of conventional GICs. Resin-based bonding to tooth structure occurs via micromechanical and chemical mechanisms, forming ionic bonds between the carboxyl groups of RMGIC and calcium ions of enamel and dentin. RMGIC typically comprises around 80% GIC components 9 (fluoroaluminosilicate glass and polyacrylic acid) and 20% light-cured methacrylates. Advantages of RMGIC  Extended working time  Controlled setting  Good adaptation  Chemical adhesion to enamel and dentin  Fluoride release  Improved aesthetics  Superior strength characteristics Disadvantages of RMGIC  Shrinkage during setting  Limited depth of cure, particularly with more opaque lining cements. Forms:  Powder and liquid  Capsules containing premeasured powder and liquid with an angled nozzle  Paste dispensing system Setting reaction: The setting reaction involves a combined slow acid-base reaction and resin polymerization, with a dual mechanism (chemically induced and completed by light). 10 Clinical steps A. Conditioning of the prepared surface: To enhance the adhesion of GIC to tooth structure, various conditioning agents have been employed, with polyacrylic acid being the most commonly used conditioner. B. Restorative Procedures: Following mixing, GIC is applied using a cement carrier for placement into the prepared tooth. To optimize the restoration and minimize voids, the use of a matrix is recommended. Excess material is promptly removed, and final contouring is carried out. For chemically cured glass ionomers, the matrix is kept in place until the cement begins to harden initially. However, with light-cured glass ionomers, photoactivation can be utilized to expedite the setting process. C. Finishing and Polishing: The surface of GIC is susceptible to both moisture and desiccation. It is advisable to postpone finishing and polishing of glass ionomer cements during the initial cement setting phase. Ideally, this should be delayed for at least 24 hours after placement to allow the restoration surface to achieve ionic equilibrium with the environment. 11 D. Surface Protection Since GIC show sensitivity to both moisture contamination and surface desiccation, the newly placed restoration should always be protected immediately after matrix removal so as to prevent water exchange. It can be done with the help of resin bonding agent, cocoa butter, petroleum jelly or varnish ―Coat. Tunnel GIC Restoration A tunnel preparation is created to remove proximal caries by accessing through the occlusal surface while preserving the marginal ridge. Indications:  Recommended for teeth with a life expectancy of up to 5 years, such as deciduous teeth or mobile teeth in geriatric patients.  Suitable for incipient proximal lesions of posterior teeth.  Ideal for patients with low caries risk. Clinical Steps:  Thoroughly assess the tooth to identify the location and extent of caries. Take a bitewing radiograph to ensure the access area does not involve any pulp horn.  Isolate and dry the tooth targeted for restoration with a tunnel preparation.  Position a wedge beneath the carious proximal area. 12  Using a round bur, penetrate the occlusal surface of the tooth. The bur entry should be 2 mm inside the marginal ridge, at a 45° angle to the carious lesion.  Once the enamel is penetrated, employ a spoon excavator to eliminate the caries. Measure the lesion depth with a periodontal probe. Expand the preparation using a tapered fissure bur.  Proceed to remove the caries by cutting into the proximal lesion and eliminate the wedge to assess the preparation's extent.  Upon confirming complete caries removal, apply a matrix band and wedge on the proximal surface to prevent overhanging restorations and injury to the gingiva.  Utilize the restorative material and condense it from the occlusal surface, ensuring there are no voids.  Remove the wedge and matrix, and carry out the final finishing and polishing of the restoration. 13 14 3. Atraumatic Restorative Treatment (ART) This technique involves removing carious lesions using hand instruments like spoon excavators, followed by restoring the cavities with high-viscosity GIC. ART enables restorative procedures in areas without electricity and sophisticated dental equipment. 15 Sandwich Technique The term "sandwich technique" involves a laminated restoration utilizing glass ionomer to replace dentin and composite resin to replace enamel. Advantages:  The open sandwich technique, applied in deep Class II preparations where the cervical margin lacks enamel, has demonstrated enhanced resistance to microleakage and caries compared to resin bonding at dentin margins.  Improved strength, aesthetics, and finish of composite resins.  Fluoride release from GIC.  Reduced bulk of composite resins results in less polymerization shrinkage.  Reduction in the number of composite resin increments required, saving time.  The use of GIC eliminates the need for acid etching of dentin, thus reducing postoperative sensitivity caused by incomplete sealing of etched dentin.  Positive pulpal response due to the biocompatibility of GIC. 16 Disadvantages:  Technique sensitivity.  Time-consuming. Clinical Steps:  Isolate the tooth for preparation.  Prepare the tooth with cavosurface margins involving a dentin butt joint.  Condition the prepared tooth using polyacrylic acid for optimal adhesion of GIC.  Fill the prepared tooth with freshly mixed fast-setting GIC.  Acid etching of GIC is only necessary if the restoration has been in place for some time and is fully matured. If the GIC is freshly placed and immature, bonding can be achieved by simply washing the GIC surface, as water causes washout of the GIC matrix around the filler particles, creating a microscopically rough surface for composite attachment.  Apply a dentin bonding agent to the prepared tooth surface for optimal adhesion and cure it for 20 seconds.  Place composite and cure according to the manufacturer's recommendations. Finish and polish the restoration. 17 18 19