Composite Resin Flashcards
What is composite material?
A material which consists of at least two distinct phases. Principle phase is a matrix, whilst additional phases act as fillers.
In dental composite resin, there is a polymer matrix with ceramic filler.
List 4 problems with polymers
- Low mechanical properties
- Stress strain relationship is heavily temperature dependent
- High polymerization shrinkage
- High water sorption
What type of polymer is in dental composite resin?
Why is this polymer used?
Oligomer such as
bis-GMA or HEMA
and a diluent monomer.
Oligomer used so less shrinkage.
What is a diluent monomer put into composite for?
To increase fluidity, but does increase polymerisation shrinkage
Two examples of oligomers used in composite resin
Bis-GMA or HEMA
Example of an initiator in composite resin
BPO
Why are inhibitors included in composite resin
Increase shelf life
Three factors affecting composite light curing
- Pigments in composite (darker = longer)
- Activating energy
- Attenuation of light
5 advantages of adding fillers to composite
- Decrease polymerization shrinkage
- Decrease water sorption
- Decreasing coefficient of thermal expansion
- Improving the elastic modulus (so increased strength)
- Improving fracture toughness through crack deflection and tip blunting
2 ways to reduce poymerisation shrinkage of composits
- Fillers
- Control c factor (more shrinkage at bonding interface)
WHy is it important to have materials which matching coefficients of thermal expansion to the tooth
- Microleakage and secondary caries
- Failure of restorations
List 4 examples of composite resin fillers
- Quartz
- Pyrex
- Lithium aluminum silicate
- Partially stabilized zirconia
Two reasons why a coupling agent is required between filler and matrix
- To constrain thermal expansion
- To constrain deformation under sterss.
The mechanical strength of composites is determined by:
Mostly filler content
The wear resistance of composite resins is largely related to:
Size of filler particles and coupling agent
