What is the composition of GIC (Power/Liquid)?
Powder: Sodium aluminosilicate glass with 20% CaF, other minor additives
Liquid: Aqueous solution of:
- Itaconic acid + Acrylic acid
- Maleic acid + Acrylic acid
- Maleic acid copolymer
What is the setting reaction of GIC?
Acid base reaction between polyacrylic acid in liquid and calcium and aluminium ions in glass (powder) to form a polyalkenoate.
2 distinct phases: Dissolution and gelation
Dissolution:
- Surface of glass is attacked by polyacid, resulting in limited dissolution of glass with release of Ca2+, F- and Al3+ ions.
- Ca2+ released more readily than Al3+ ions. Al3+ diffuses through cement slower than Ca2+ ions but forms more stable complexes with F- than do Ca2+
- Ca2+ forms the matrix while Al3+ stabilises the matrix
Gelation:
- Initial set brought about by cross-linking of COO- with more mobile and readily available Ca2+ to form calcium polysalt
- Over the next 24h, a maturation phase occurs, dictated by Al3+; Al3+ salts are formed, leading to more rigid cross-linking between polyacid chain (this step is responsible for the initial sharp increase in physical properties)
What are the factors affecting the rate of setting of GIC?
- P:L (higher the P:L, faster the set)
- Glass composition (higher alumina:silica, faster the set as alumina is more reactive)
- Particle size (smaller the particle size, faster the set)
- Mixing temperature (higher the mixing temperature, faster the set)
- Addition of tartaric acid (dual effect on setting reaction: firstly inhibits gelation then accelerates setting reaction without compromising on working time )
What happens when GIC is exposed to air during its initial setting reaction ?
Dessication occurs, leading to crazing and cracking
What happens when GIC is exposed to water/moisture during its initial setting reaction?
Water contamination leads to opacity of restoration, decreased physical properties.
True or false: GIC has higher compressive strength than flexural strength.
True
What are the factors affecting the strength of GIC?
- P:L (lower P:L –> higher wear resistance, lower fracture resistance)
- Time (as cement matures, strength increases)
- Dessication decreases strength of cement
What are the properties of GIC?
- Biocompatible with pulp
- COTE similar to tooth
- High solubility during the initial setting reaction (must be protected with a varnish)
- Fluoride-releasing
- Adhesion to tooth structure via chemical bonding
What is the difference between RMGIC and GIC?
RMGIC: A hybrid material of GIC and resin that retains significant acid base reaction as part of overall curing process.
GIC: A cement that consists of a basic glass and acidic polymer that sets by an acid base reaction between these 2 components
What are the advantages of RMGIC?
- Rapid development of early strength
- Improved setting characteristics
- Sufficiently long working time that can be curtailed on command to a snap-set by light curing
- Resistance to water contamination (GIC faces the problem of water contamination, leading to decreased translucency in set cement and decreased physical properties)
- Possible to finish and polish immediately after light polymerisation
What are the advantages of using GIC over other restorative materials?
- Fluoride-releasing, cariostatic property
- Chemical bonding to tooth structure
- Conservation of tooth structure
- Similar COTE to tooth
- Biocompatible with pulp
What are the disadvantages of using GIC over other restorative materials?
- Low early mechanical strength
- Dessication during initial setting reaction retards reaction
- Exposure to moisture (both water loss and uptake) results in loss of translucency + decreased physical properties
- Poor flexural strength
What are the advantages of using RMGIC over other restorative materials?
- Resistance to water contamination
- Superior aesthetics: Improved translucency
- Higher early mechanical strength compared to GIC
- Possible to finish and polish immediately after light polymerisation
- Improved setting characteristics
- Long working time that can be curtailed on command to a snap set by light curing
- Improved adhesion to tooth structure
- Possible for chemical bonding to composite (Sandwich technique)
What are the disadvantages of using RMGIC over other restorative materials?
- Higher polymerisation shrinkage than GIC (~1%)
- Depth of cure is a problem
- Physical properties may degrade during long term exposure to moisture
