Composite Flashcards
What are the components of a composite resin?
Filler particles
Resin
Camphorquinone
Low weight dimethacrylates
Silane coupling agent
What is the resin found in composite?
Bis-GMA.
What reaction occurs in composite resins?
Free radical addition polymerisation.
What is the purpose of Camphorquinone?
Activated by blue light- initiates the free radical addition polymerisation of BIS-GMA>
What is the purpose of the silane coupling agent?
Allows a good bond between filler particle and resin.
- preferentially binds to glass and resin.
What is flowable composite?
Lower filler content, more shrinkage.
What is meant by the term depth of cure?
Depth at which material hardness is about 80% that of the cured surface.
What is the typical depth of cure?
2mm- increments should not be anymore than 2mm deep.
What happens if you have an increment greater than 2mm?
Under-polymerised base- poor bonding to the tooth and the restoration fails.
What are the clinical requirements of a large posterior cavity?
High YM, high strength, high abrasion resistance.
What is the purpose of acid etching enamel?
Removes the smear layer and roughens the enamel surface.
Allows unfilled resin to key into it.
What are the advantages of composite?
Bonds directly to tooth- reduces polymerisation contraction stress
Aesthetics
Radiopaque
Command cure
Conservation of tooth tissue during preparation
Support for remaining tooth tissue
Low thermal conductivity
What are the advantages of composite bonding directly to the tooth surface?
Reduces polymerisation contraction stress.
Minimise cavity design.
Stress is spread over the contact area- reduces risk of fracture and microleakage.
What are the disadvantages of composite?
Not as strong as amalgam
- compressive strength and tensile strength.
No as hard as composite.
Thermal expansion is poor- expands more than enamel nd dentine.
Why is it important to avoid cavosurface margins in areas of occlusal contact?
Likely to interfere with marginal integrity.
