L15 Resin Composites 2 Flashcards
(56 cards)
What is the role of filler?
Reduces polymerisation shrinkage
Reduces coefficient of thermal expansion
Improves mechanical properties
Increases elastic modulus
Provides radiopacity
Adjusts handling
Controls translucency and aesthetics
How does filler reduce polymerisation shrinkage?
More filler means less resin means less shrinkage
But can still be enough to generate sufficient stress at the interface to cause gaps
Compare the TEC of the resin monomer and the tooth
Expansion at different rates is unwanted. Resin thermal properties do not match the tooth. Monomer - 80ppm/0C, enamel - 11ppm;0C, glasses - 8ppm/0C
Which mechanical properties does filler improve?
Fracture toughness and overall strength
How does filler increase elastic modulus?
Increases stiffness and reduces flexibility of the polymer. Creates appropriate wear resistance.
What does filler making resin more radioopaque mean?
It is harder to spot on radiographs than amalgam
(Zirconia is added to help this)
What are the indications of using a relatively large filler?
You have a higher SA and a differential wear rate - filler does well at resisting wear but the resin matrix wears away quicker, reacting a rough surface where the fillers can fall out of.
What is the issue with acid-modified resin?
Self adhesive properties with acid modified resin with low pH becomes very hydrophilic. Will soak up a lot of moisture and degrade quicker, reserved for adhesive.
What are the issues with light curing?
Cannot place more than a certain amount to cure because you won’t get effective light transmission through the material.
What can be filled more overcoming the light cure issues?
Bulk fill
What is the order and development of light-curing units?
Self-cured, UV, visible light
Order in development of fillers
Microfilled, hydrids,munivsersal flowables and packables, microhybrids, nano filled and nanohybrid
Order in development of resins
Low-shrinkage, self-adhesive, bulk-fill
How has particle size of fill restorative resins changed over time?
Decrease in average particle size range since the introduction of RBCs
Filler particle sizes manipulated to achieve desired mechanical and physical properties
In hybrid resin composites, how are properties optimised?
Filler packing. To increase load, use a range of filler sizes so smaller ones will fill inside the gaps if the larger ones, so a distribution of sizes.
How would you increase viscosity of a resin composite?
Increase amount of filler or decrease amount of resin
When might a flowable composite be used?
Likely used to line a cavity not on an occlusal surface as it will likely have less filler and have less wear resistance than a higher viscosity type.
What are the key aspects of curing efficiency?
Degree of conversion, cross-linking
Depth of cure
Shrinkage and shrinkage stress
Mechanical properties - strength characteristics, modulus
Trapped radicals, residual monomer
What is degree of conversion and how is it optimal for curing efficiency?
The degree to which you’ve converted monomer to polymer units - want to maximise this and not have excess uncured material
How does depth of cure affect curing efficiency?
DC with depth? Not only amount of cross-linking creating, but how much is created with depth.
How does shrinkage affect curing efficiency?
Stress generation is more critical. Gaps can cause secondary infection.
How might trapped radicals and residual monomer be formed, from curing efficiency?
Consequences of monomer elation
Always be some residual monomer
Why is there a limited depth of cure?
Due to filler particles placed in the way, because of the pigments that are incorporated into the composite, photo-initiator has to absorb some of the light to create the polymerisation reaction. Surface reflection.
What affects absorption of light?
Photoinitiator chemistry
Pigments
