9 Glass Ionomer Restoration

Glass Ionomer Restoration (2)

• Glass ionomers (GIC) are classified by composition, chemistry, and clinical use.
• Compositional forms include polyacid mixable, water mixable, and mixed.
• Polyacid mixable GIC has the poly-acid as an aqueous solution (liquid) that may gel over time.
• Water mixable GIC has components separated; the poly-acid is freeze-dried and added to the powder. A liquid of distilled water or tartaric acid is used.
• Mixed GIC uses a combination, where part of the poly-acid is freeze-dried and the rest is aqueous.
• Chemical forms include conventional, resin-modified (hybrid), highly viscous (for atraumatic restorative technique), and nanoionomer (improved esthetics and polish).
• Conventional GICs set through an acid-base reaction and are sensitive to moisture. They require sealing and should not be finished immediately after placement (at least 48 hours). They have short working times and extended setting times. Some are metal reinforced (Cermet cement).
• Resin-modified GICs (hybrid ionomers) contain water-soluble methacrylate monomers (HEMA) in an aqueous solution of polyacrylic acid. They can set via acid-base or photo-polymerization reactions(dual cure).
• Resin modification decreases moisture sensitivity and allows immediate finishing
• Resin modified GICs have advantages of decreased moisture sensitivity, no water-proof seal needed after placement, ability to finish immediately, faster setting, less water sensitivity, and high color stability.
• Resin modified GICs have more shrinkage, less fluoride release, and reduced ability to bond to tooth substrate. HEMA monomer can cause pulp inflammation and temperature changes during polymerization are drawbacks. Water uptake by HEMA can cause fracture in all-ceramic crowns when using hybrid ionomer.
• Clinical applications include fissure sealant, bases, and restorations.
• Indications include Class V carious, erosive, or abrasive lesions; pit and fissure sealants; Class I and II restorations in primary teeth; luting cement; core buildup; and root surface caries.
• Contraindications include low tensile strength and brittleness and low resistance to wear in Class I and II restorations.
• Cavity preparation generally does not require retentive features, as the cement adheres well and only needs to be placed where decay is.
• Manipulation involves dispensing and mixing; placement; and contouring and finishing.
• Glass ionomer cements are available commercially in two forms: encapsulated (mechanical mixing) or powder and liquid (hand mixing).
• Dispensing ensures consistent powder/liquid ratio.
• Cavity requires pretreatment with a conditioner (10-20% polyacrylic acid) for 10-20 seconds, and thorough 20-30 second wash and light drying.
• Contouring and polishing can be performed after 48 hours or up to one week. Fine diamonds and aluminum oxide discs are used. Light-cured GICs can be contoured and polished immediately.