L14 Resin Composites 1 Flashcards
Direct chairside indications of resin based composites
Filling material, fissure sealant, cementation
Indirect lab clinical indications
Composite inlay, CAD/CAM crowns, fibre-reinforced bridge, 3D printing
What is dental resin composite made up from?
Organic resin matrix - 20-30 mass% for high viscosity paste
Inorganic glass filler (treated*) - 70-80 mass% for high viscosity paste
*coupling agent - amphiphillic molecule to provide chemical affinity
How are dental resin composites adjusted by the manufacturer?
Viscosity to make flowable composites
High viscosity composites for larger cavities etc
Why is PMMA a bad direct restorative?
It suffers from excess shrinkage and poor wear resistance
What is bisphenol-A the building block for?
Building block for many polymers, e.g., polyesters, polycarbonates, and epoxy
How and why is the structure of bisphenol A useful?
Steric hindrance (H-bonding) and no rotation about benzene
BPA polymer chain rigidity»_space; MA
Improves mechanical properties
What is the controversy around bisphenol-A?
Potential hormonal effects with the release of BPA if consumed in the human body. Part of plastics. Biocompatibility concerns.
But very small amounts of release with no evidence for harmful effect of it in the mouth.
What is Bowen’s resin?
BisGMA - Bisphenol A glycol dimethacrylate
Why is BisGMA a good restorative material (brief)?
It has multiple functional groups to create polymers and high density of cross-links for rigidity needed for a restorative material.
What is a thermoplastic?
More basic, linear, not as many cross-links, held together by entanglement and secondary bonds
What is thermoset?
Increase of cross-link density network
Structure of MMA
Linear structure
Entanglement
No cross links
Structure of BisGMA
Cross-linked
Entangle
Bulky monomer
Reduced polarity
Difunctional
Non-toxic
Cheap
Why can’t BisGMA be used by itself?
Because it is very viscous and hard to handle by itself. Must be admixed.
What is BisGMA add mixed with?
Add mixed - diluents
What are diluents?
Resins that will reduce the viscosity of the BisGMA and provide extra cross-links
Compare BisGMA with TEGDMA
BisGMA has high molecular weight, high viscosity, H-bonding and limited filler load
TEGDMA has low molecular weight, diluent (non-volatile), little steric hindrance
What other dental methacrylates are there?
HEMA, UDMA, 10-MDP
(do I need to know these?, gauge in lecture)
What do the other monomers have and vary in?
All have an MA group, vary in molecular weight and viscosity and hydrobicity
Resin matrix monomers
Usually BigGMA, UDMA or derivatives
Resin matrix diluent crosslinkers
TEGDMA
What does an inhibitor do in resin matrix?
Radical scavengers - help to stop any radicals formed from creating polymers before we want them to
Examples of inhibitors
Hydroquinone
Relevance of polymerisation chemistry in resin matrix
Polymerisation chemistry. Additives that allow the generation of radicals. Base/catalyst, photosensitiser.
How was resin matrix cured before light curing technology?
Chemical cure - 2 large composites (base and catalyst)
Why was mixing an issue for chemical cure of resin matrix?
Mixing is an issue because quantities and ratios have to be correct and it might trap air in the process.
Is UV light dangerous?
Ionising and damaging for DNA
What light do we use to cure?
High intensity blue light, around 470nm, not UV
What else must be used with the light?
Co-initiator is needed which acts as a hydrogen donor enabling efficient activation and generation of radicals
How has the light source developed?
Halogen
Specific (single) diode emitting a much narrower wave-band of light - efficient
Hand-held battery-operated lights - less degradation than in the past
Multiple diodes
Advantages of visible light during
No mixing - eliminates operator induced variability, reducing porosity
Increased working time
Improved colour stability
Improved mechanical properties
Command set
Why is an interface needed to connect the filler and resin?
Interface needs to be connected between the filler and resin to create a strong interface.
Why is a strong interface needed?
Inorganic component is the hard component compared to soft resin. So need to increase mechanical properties to slow down crack propagation within the material, improving fracture toughness. Without a strong interface means the crack occurs around the surface.
What is silane?
An amphiphillic molecule
What might silane do?
Accelerate water uptake in this region
Lead to interfacial degradation and bulk fracture
What does the inhibitor in resin matrix do?
Helps improve shelf life and ambient light stability (e.g., HQ)
Are resin based composites hydrophilic or hydrophobic?
Hydrophobic
Is hydrophobic or hydrophilic better for placing a material?
Hydrophobic is not good for when placing as if means you need moisture control. Hydrophilic will uptake and absorb the water.
