Composites
On this page 7 sections
Composition
| Component | Function |
|---|---|
| Organic resin matrix | Main resin phase |
| Inorganic fillers | Improve strength and wear resistance |
| Coupling agent (silane) | Bonds filler to resin |
| Initiator | Starts polymerisation |
| Accelerator | Activates polymerisation |
| Pigments | Provide colour |
| Inhibitors | Prevent premature polymerisation |
Resin matrix
Common monomers:
- Bis-GMA
- UDMA
- TEGDMA
Filler particles
- Increase strength.
- Reduce polymerisation shrinkage.
- Reduce thermal expansion.
- Improve wear resistance.
- Improve handling characteristics.
Silane coupling agent
- Silane couples composite resin filler particles to the resin matrix.
- Polyacrylic acid is involved in GIC conditioning and chemical bonding to tooth structure.
Types of composites
| Type | Characteristics |
|---|---|
| Macrofilled | Large fillers, rough surface |
| Microfilled | Excellent polish, lower strength |
| Hybrid | Combination of filler sizes |
| Nanofilled | Small nanoparticles, good polish and strength |
| Nanohybrid | Combination of nano and larger fillers |
Polymerisation shrinkage
Associated with organic resin matrix.
This is because the monomers move closer together during polymerisation, causing volumetric contraction.
Important:
- Higher resin content generally means more shrinkage.
- Higher filler content generally means less shrinkage.
- Shrinkage can produce marginal gaps and microleakage.
- Incremental placement can reduce the effects of shrinkage.
Etching time
Remember the conventional clinical distinction:
- Enamel: approximately 15–30 seconds.
- Dentin: approximately 15 seconds.