Miscellaneous Properties of Composites Flashcards
Under what conditions do DHPT and camphorquinone react?
Both only react under the presence of blue light
What 2 general substances are needed during a light cure reaction?
- Tertiary amine
- Light initiator
Explain how light can cause filling materials to set?
The tertiary amine reacts with the light initiator, under blue light to form free radicals, which then start off the addition polymerisation reaction.
Advantages of light cured composites? (6)
- Single component system
- Less decolouration
- Minimal porosity (no mixing of pastes)
- Virtually command set
- Rapid polymerisation
- Thin inhibited layer
Disdvantages of light cured composites? (3)
- Light sensitive during application (direct sunlight could start off reaction)
- Retina damage
- Limited depth of cure
What does limited depth of cure of a dental composite mean?
Light can only cure 2mm of composite at a time so if a big cavity is present can only cure in 2mm increments
What wavelength do composites cure between?
450-500nm
What is the maximum light output used for camphorquinone
460-480nm
What are 4 things to consider when carrying out a light cure
- Tip of light source must be close to surface of restoration
- Light tip must not be contaminated
- Must cure for manufacturers recommended time
- Curing spots must overlap for large restoration
What can happen to light when it hits a composite? (3)
- Reflected
- Scattered
- Absorbed
Which shades of composites take longer to cure?
Darker shades
What were the earlier light curing units based off? (2)
- UV light
- Benzoin methyl ether
What are modern light curing units based off?
Visible light Activated (VLA)
What is the most common light curing unit used today?
Quartz-Tungsten-Halogen light curing unit
What is the filament used in a Quartz-Tungsten-Halogen light curing unit?
Tungsten filament
What is the alternative for a Quartz-Tungsten-Halogen light curing unit?
Light Emitting Diode (LED) light curing unit
What are some of the advantages of a LED light curing unit? (4)
- Low lateral heat production
- Long lasting light source
- Requires low wattage
- Typically cordless
How long does a Plasma-Arc (PAC) light curing unit take to cure?
Claims 1-3 sec cure
What is a disadvantage of a Plasma-Arc (PAC) light curing unit?
Bulbs are very expensive
bulbs >$600
What are the 3 main advantages of composites?
- Good aesthetic results
- Less tooth tissue removed
- Sets on command if light cured
What 2 substances can be used as composite lining materials?
- Calcium Hydroxide
- Glass ionomer cements
Which substance cannot be used as a composite lining material?
Eugenol based materials as it inhibits setting
What can shrinkage of a composite potentially lead to?
Rapid progression of caries at the margin
What component causes a water uptake in composites?
Glass filler adsorbs water on its surface
Which bond can be hydrolytically broke down by water in a composite?
Hydrolytic breakdown of bond between filler and resin
What features can be compromised by adsorbed water in composites? (2)
- Wear resistance
- Colour stability (staining)
Where on the composite does staining most occur?
Margin between restoration and tooth
What is the benefit of oxygen inhibition for composites?
Oxygen and resin interface results in a sticky resin surface which will allow placement of next composite increment
How can you counteract the problem of a sticky composite surface? (3)
- Use a clear matrix strip then cure so oxygen doesn’t get through but light does
- Overfill and polish
- Some clinicians apply bonding agent
What are the advantages for silorane composites? (2)
- Low polymerisation shrinkage
- Low water absorption
Why was silorane removed from the market? (2)
- High cost
- Requires alternative bonding agent
What are some benefits of Bulk fill restorative composites? (4)
- One step placement
- 5mm depth of cure
- Excellent sculptability
- Available in capsule or syringe delivery in 5 shades
What are;
Class I restorations?
Class II restorations?
- Restorations that are less than 4mm deep
- Restorations that are 5mm deep
Setting times for bulk fill;
Class I restorations?
Class II restorations?
- 20 seconds from occlusal surface
- 10 secs from each tooth surface
