Glass Ionomer Cements Overview

Glass Ionomer Cements (GICs)

• GICs are acid-base cements.
• Supplied as a powder and liquid mixture.
• Used for restorations and cementing restorations.

Classification of GICs (According to Use)

• Type I: Luting: Used to cement crowns, bridges, and orthodontic brackets.
  • Characterized by low powder-to-liquid ratio (P/L), thin film thickness, and rapid set.
  • Commercial brands include Ketac Cem (3M ESPE, Meron (VOCO), Riva luting (SDI), Medicem (Promedica).
• Type IIa: Esthetic Restoration: Used for aesthetic restorations.
  • Characterized by high P/L and good aesthetics.
  • Requires coating within 24 hours to protect from moisture.
  • Commercial brands include Ketac Fil (3M ESPE), Riva Self Cure (SDI), and Medifil (Promedica).
• Type IIb: Reinforced Restoration: Used for reinforced restorations.
  • Characterized by high P/L and good mechanical properties.
  • Has early resistance to moisture contamination.
• Type III: Lining or Base: Used as a liner or base.
  • Characterized by low P/L for lining and high P/L for base.
  • Commercial brands include Vitrebond (3M ESPE), Composeal & Medibond (Promedica), and Fuji lining LC (GC).

Advantages of GICs

• Chemical bond: Bonds to tooth structure.
• Fluoride release: Releases and recharges fluoride, making it anti-cariogenic.
• Biocompatibility: Acceptable biocompatibility.
• Aesthetics: Good aesthetic appearance.
• Dimensional stability: Good dimensional stability (shows 3% contraction if properly manipulated).

Disadvantages of GICs

• Low mechanical properties: Lower mechanical strength compared to other restorative materials.
• Water sensitivity: Water sensitivity, especially within the first 24 hours of mixing.

Modifications of GICs

• Mode of supply:
  • Capsule: Loaded with correct powder-liquid ratio (P/L) and mixing time to maximize restoration properties. Dispensing through a gun allows better adaptibility.
  • Water settable cement: The acid (polyacrylic acid) is freeze-dried and added to the powder of the GIC. The mixing liquid is pure water or an aqueous solution with tartaric acid. This formula has an extended working time.
  • Paste-paste formula: Supplied in a dual-tube clicker dispenser. Some brands use a spatula, while others use a mixing tip for dispensing. Commercial brands with paste-paste formulas are available.
• Composition:
  • Metal modified: Reinforcement of glass ionomer cement through sintering with a precious metal (e.g., silver) to the powder of GIC. Improved mechanical properties, but reduced aesthetics, fluoride release, and adhesion. Used in posterior pediatric molars and as a core material.
  • Resin modified: Addition of hydrophilic resin monomer (e.g., HEMA) to conventional GIC. Involves acid-base and polymerization reactions (chemical, light, or dual-cured methods). Improved mechanical properties, reduced water sensitivity, faster working time, and improved aesthetics.
  • Highly viscous (packable): Similar to conventional GIC but with reduced alkali ions in exchange for trivalent ions. Leads to increased crosslinking of the glass ionomer matrix resulting in enhanced properties.
  • Zinc reinforced: Conventional GIC with added zinc to the glass particles. Zinc rapidly releases into the matrix, leading to better cross-linking properties. Lower mechanical properties than RMGIC and HVGIC, but with higher fluoride release.
  • Polyacid modified composite resin (Compomer): Modification of composite resin with glass ionomer component as filler. Light-cured composite material. Releases less fluoride than glass ionomer, has no tooth adhesion, and lower mechanical properties than composite resin (but higher than GIC).
  • Nano-ionomer: Modification of RMGIC with zirconia/silica nanofillers and nanoclusters. Shows comparable properties to RMGIC.
  • Zirconomer (White Amalgam): Made by incorporating zirconia particles with conventional glass ionomer. Shows improved mechanical properties due to transformation toughening of zirconia particles. Available in opaque and translucent forms (improved form with additional nano-zirconia particles).
• Modifications of Coating:
  • Coating is needed due to early water sensitivity.
  • Water is the reaction medium.
  • Loss/absorption of water weakens the matrix, so coating is essential.
  • Multiple coating materials are available (e.g., cocoa butter, bonding agents, varnishes, and nanofilled coatings).
  • Commercial examples include Fuji coat LC, final varnish LC (VOCO), and Copal varnish (Promedica).

This quiz covers the various types and classifications of Glass Ionomer Cements (GICs), focusing on their specific uses and characteristics. Learn about Type I, IIa, IIb, and III GICs, their applications in dental restorations, and the importance of powder-to-liquid ratios. Test your knowledge on this essential dental material.