Glass Ionomer Cements

Definition: Glass ionomer cement (GIC) is a water-based, tooth-coloured dental restorative cement formed by an acid-base reaction between glass powder and an aqueous polyalkenoic acid. GICs chemically bond to tooth structure, release fluoride, and are commonly used for minimally invasive and paediatric restorative procedures.

What are GICs made from?

GICs are an acid-base reaction cement made by mixing:

1. Powder: Calcium fluoro-aluminosilicate glass particles with strontium

• Calcium fluoride - reduce fusion temperature, increase the strength of the set cement due to early cross-linking of ions, therapeutic effects from fluoride release (anticariogenic, antibacterial)

• Silica - a silaceous gel forms providing strength, rigidity, and transparency

• Aluminium oxide - Modifies the how easily ions are released adjusting the setting time, can increase the compressive strength of the set cement with stable aluminum-polyacrylate bonds forming

2. Liquid: Polyalkenoic acid

• Polyacrylic acid (used in earlier conventional GICs)

• Copolymers of acrylic acid with maleic acid or itaconic acid (copolymers used in modern GICs)

• Tartaric acid is often included to improve working time and handling

When mixed the acid dissolves the outer layer of the glass, releasing ions that form a hard, tooth-bonded matrix. There are 3 stages:

1. Dissolution - acid attacks the glass surface, releasing ions (Ca²⁺, Al³⁺, F^-)

2. Gelation and hardening - Ions cross-link with polyalkenoate chains forming a hard matrix

3. Hydration - continued water uptake strengthens the cement over 24 hours

Tooth - GIC interaction

• Chemical adhesion occurs to mineralized enamel and dentine via ionic bonding.

• Micro-mechanical interlocking is enhanced by mild surface conditioning.

Clinical uses:

• Restorations: Class I, II, V, and cervical lesions.

• Luting agent: crowns, bridges, orthodontic bands.

• Base or liner: under composite or amalgam restorations or in sandwich restorations.

• Paediatric dentistry: atraumatic restorative treatment (ART).

• Root caries: fluoride-releasing restorative option.

How to do a GIC restoration:

1. Condition tooth.

2. Mix powder and liquid (or use capsule). Tip: mix gently to avoid air bubbles

3. Place cement into cavity. Tip: avoid over-drying the tooth

4. Allow initial set; contour and protect from moisture.

5. Apply varnish or resin coating if needed.

6. Allow at least 24 hours for full maturation