Glass Ionomer Cement

Glass Ionomer Cement

Glass Ionomer Cement:

• Glass ionomer cement was first reported by Wilson and Kent in 1972.
• These are adhesive tooth-colored anti-cariogenic restorative
  materials.
• These cements have the combined properties of silicate cement and polycarboxylate cement.
• It was named glass ionomer because the powder is glass and the settling reaction and adhesive bonding to the tooth structure is due to the ionic bond.

Classifiation/Types of GIC:

1. Traditional Classification (Based on application):

• Type I: Luting cement
• Type II: Restorative cement
• Type II.1: Restorative aesthetic
• Type II.2: Reinforced materials (Fuji IX, Fuji II LC)
• Type III: Liner or Base.

GIC In Dentistry

2. Newer Classification:

• Type I: Luting cement
• Type II: Restorative esthetic or reinforced cement
• Type III: Liner or base.

3. Classification (Based on use):

• Type I: Luting cement
• Type II: Restorative cement restorative aesthetic

4. Reinforced materials (Fuji IX, Fuji II LC):

• Type III: Lining cement
• Type IV: Fissure sealant
• Type V: Orthodontic cement
• Type VI: Core Build-up cement.

Application / Uses Glass Ionomer Cement:

• As anterior, aesthetic restorative material for class III cavityFor eroded areas and class V cavities
• As a luting agent for restoration and orthodontic brackets
• As liners and bases
• For core build-up
• To a limited extent as pit and fissure sealants.
• Intermediate restorative material.

Properties Of Glass Ionomer Cement

Composition of Glass Ionomer Cement:

Powder:

The powder is an acid-soluble calcium floroalumino-silicate glass.

Liquid:

Setting Reaction of Glass Ionomer Cement: 

• Leaching: When the powder and liquid are mixed together, the acid attacks the glass particles. Thus calcium, aluminum, sodium, and fluoride ions leach out into the aqueous medium.
• Calcium cross-links: The initial set occurs when the calcium ions cross-link the polyacrylic acid.
• Aluminum cross-links: In the next phase, the aluminum also begins to cross-link with polyacrylic acid chains.
• Sodium and fluoride ions: These ions do not take part in the cross-linking. Some of the sodium ions may replace the hydrogen ions in the carboxylic groups. The rest combine with fluoride to form sodium fluoride which is uniformly distributed within the cement.

Uses Of Glass Ionomer Cement

• Hydration: Water plays a very important role in the cement. Initially, it serves as the medium. Later it slowly hydrates the matrix, adding to the strength of the cement.
• Silica gel sheath: The unreacted glass particle is sheathed by a silica gel. It is formed by the leaching of ions (Ca²⁺, Al³⁺, Na⁺, F^–) from the outer portion of glass particles.

Structure of Set Cement: The set cement structure is composed of an agglomeration of unreacted powder particles surrounded by a silica gel sheath and embedded in a matrix of hydrated calcium and aluminum cross-linked polyacrylic gel.

Properties of GIC:

• Mechanical Properties:
  • Compressive strength: Compressive strength of restorative
  • GIC is 150MP Compressive strength of luting GIC is 85 MP
  • Tensile strength: For luting GIC it is 6.2 MPa and for restorative GIC it is 6.6 MP
  • Hardness: It is less hard than silicate and composite. It is 49 KHN.
  • Fracture toughness: Type II GICs are inferior in fracture toughness.
  • Modulus of elasticity: It is 7.3 GPa
  • Wear resistance: GICs are most susceptible to toothbrush abrasion and occlusal wear.

• Solubility and Disintegration: Initial solubility due to the leaching of intermediate products is high. The complete setting reaction occurs in 24 hours, so it is recommended that cement should be protected by saliva in the mouth. For the luting type of cement solubility in water is 1.25% wt, while for the restoration type of cement, solubility is 0.4% wt.
• Adhesion: GIC adheres well to enamel and dentin. The shear bond strength of GIC is 3 to 5 MPa
• Esthetics: In esthetics, GICs are inferior to silicate cement and composites. GICs lack translucency and have rough surface textures. GICs can stain with time.

Types Of Glass Ionomer Cement

• Biocompatibility: Pulmonary response to GIC is mild. Type II glass ionomer cement are biocompatible. Luting type GIC is more acidic
• Anticariogenic Properties: GIC releases fluoride in amounts. Since GIC is adhesive in nature it has the potential for reducing infiltration of oral fluids at the cement tooth interface and prevent secondary caries.

Advantages of  Glass Ionomer Cement:

• Mechanical properties are good.
• Adhesion: It adheres well to the enamel and dentine. GIC bonds chemically to the tooth structure.
• Esthetics: They are tooth-colored restorative materials so can use as an anterior restorative material.
• Biocompatibility: Pulmonary response is mild.
• Anti-cariogenic properties: It releases fluoride and continues to do so over an extended period of time.
• Thereby preventing secondary caries.
• GIC is the best restorative material for children due to its good marginal integrity.

Disadvantages of  Glass Ionomer Cement:

• Its hardness or wear resistance is less than composite.
• Fracture toughness is inferior to composite.
• Solubility: The initial solubility is high due to the leaching of intermediate products.
• GIC is extremely sensitive to air and water during setting, so requires protection during setting.

Manipulation of Glass Ionomer Cement:

The steps involved in the manipulation of glass ionomer cement are:

• Preparation of tooth surface
• Manipulation
• Protection of cement during setting
• Finishing

Uses Of Glass Ionomer Cement

Preparation of Tooth Surface:

• The tooth should be clean for effective adhesion of cement.
• The smear layer present after cavity preparation which tends to block of the tooth surface should be removed to achieve adhesive bonding.
• This is achieved by pumice wash and polyacrylic acid.
• For conditioning apply 10% polyacrylic acid for l0 to l5 seconds and then rinse with water for 30 seconds.
• Very deep areas of the preparation should be protected by a dab of calcium hydroxide.
• After conditioning and rinsing, the surface is dried but not desiccated. It should be kept free of contamination with saliva or blood, as these will interfere with bonding

Manipulation: Proportioning and Mixing:

• Powder: Liquid ratio should be 3: l by weight. A low P/L ratio reduces mechanical properties and increases the chances of cement degradation.
• Manual mixing: The powder and liquid are dispensed just before mixing.
  • A cool and dry glass slab is used as it allows all the powder to be incorporated into the mix and yet maintain its plasticity.
  • Here the spatula used for mixing is agate or plastic.
• Divide the powder into two equal increments.
  • The first increment is incorporated into the liquid rapidly with the stiff-bladed spatula to produce a homogenous milky consistency.
  • The remainder of the powder is then added. The mixing is done in a folding method in order to preserve the gel structure.
  • Mixing time should be of 45 seconds. The mix is immediately packed into
    the cavity with a plastic instrument.

Types Of Glass Ionomer Cement

• Mechanical mixing: GIC supplied in capsule form containing preproportioned powder and liquid is mixed in an amalgamator which is operated at a very high speed. The capsule has a nozzle, so the mix can be injected directly into the cavity.

Protection of Cement During Setting:

Glass ionomer cement is extremely sensitive to air and water during settling. So, immediately after placement into the cavity, a preshaped matrix is applied to:

• To protect the cement from the environment during the initial set.
• To provide maximum contour so that minimal finishing is required.
• The matrix is removed after 5 minutes. Immediately after removal, the cement surface is again protected with:
• A special varnish supplied by the manufacturer or
• An unfiled light-cured resin bonding agent or Cocoa butter.

Finishing of Cement During Setting:

• Trim the excess material and the cement from the margins.
• To avoid ditching hand instruments are preferred to rotary tools.
• If required further fishing is done after 24 hours.