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19 Cards in this Set
- Front
- Back
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Define RBC |
At least 2 distinct phases formed by blending together components which have differing structures and properties |
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3 parts |
1. Resin (Dimethacrylate Monomer - BisGMA + TEGDMA/UDMA) 2. Filler (Silica particles/Glass/Quartz) 3. Coupling agent (Silanes) |
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Function of Resin |
- Chemically active component |
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What inhibitor prevents premature polymerisation |
hydroquinone |
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How is the monomer -> polymer |
radical addition |
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Filer particle size determines |
- resistance to abrasion - surface hardness - aesthetics - surface roughness - compressive strength - Viscosity - radiopacity |
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Function of the coupling agent |
binding of resin(hydrophobic) and filler(hydrophilic) |
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How does the coupling agent form the linkage |
binds via methacrylate group (c=c) to to the resin and via condensation rxn to the filler (OH group) |
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significance of the coupling agent |
Binds resin and filler so that when the composite is subjected to stresses - the energy can be evenly distributed throughout the composite reducing the likelihood of creep and fracture of restoration as stresses usually concentrated at the resin matrix |
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Early composites were chemically cured using which chemical |
camphoquinone - source of free radicals |
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what wavelength is appropriate for composite polymerisation |
450-490nm |
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polymerisation shrinkage depends on |
- type of resin used ( higher MW - less shrinkage) - how much of it remains in its unpolymerised for - Filler particle concentration and size |
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how to avoid polymerisation shrinkage |
- incremental filling (shrinkage occurs towards the cavity wall not away from it)
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Types of composites |
- Conventional (10-20 microns) - Microfilled (0.01-0.1 microns) - Hybird (10-20 micron of particles and 0.01-0.05 microns of colloidal silica) |
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Conventional |
- large filler particle size 20-50microns - plucking - poor surface finish - wear as resin is preferentially removed - dull appearance of surface due to filler particles |
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Microfilled |
-small particle filler size -0.01-0.1 microns - smooth surface finish when polishes - 50% overall filler loading with silica - difficult to obtain high filler loading as thee is more resin required to wet the surface area of the small filler particles (Inc viscosity, limits filler content) - how to overcome? Prepolymerised silica particles that increase the filler loading and minimize viscosity. - anterior restorations |
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Hybrid |
- large filler particles: 10-20 microns - small amount of colloidal silica (0.01-0.05 microns) - efficient filler loading - increased mechanical properties - decreased shrinkage - increased wear resistance - increase in surface roughness not as pronounced |
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microfilled hybrid |
- glass particle filler <1-3 microns - colloidal silica - 0.05 microns - highly polished surface finish - bond between matrix and filler particle is weak so not suitable for stress bearing areas - anterior restorations |
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problems with composite |
- moisture control - not adherent by nature, need a bonding agent - polymerisation shrinkage on set - loss of anatomical wear due to shrinkage - dissolution and breakdown of resin |
