Miscellaneous Properties of Composites Flashcards
Under what conditions do DHPT and camphorquinone react?
Only 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 paste mixing)
- Virtually command set
- Rapid polymerisation
- Thin inhibited layer
Disadvantages of light cured composites? 3
- Light sensitive during application (direct sunlight could start 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.
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 reaction
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-Tungsetn light curing unit?
Tungsten Filament
What are some advantages of a LED light curing unit? 4
- Low lateral heat production
- Long lasting light source
- Requires low voltage
- Typically cordless
How long does a Plasma-Arc (PAC) light curing unit take to cure?
Claims 1-3 Second cure
What is a disadvantage of PAC light curing unit?
Very expensive bulbs
>$600
What are the 3 main advantages of composites?
- Good aesthetics
- 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
What is the alternative for a Quartz-Tungsten Halogen light curing unit?
LED curing unit
Which substance cannot be used as a composite lining material?
Eugenol based materials, as they inhibit 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?
Bond between resin and filler
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 the next composite increment
What features can be compromised by adsorbed water in composites? 2
- Were resistance
- Colour stability (staining)
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 still 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
- Availible in capsule or syringe delivery in 5 shades
What are Class I restorations?
Restorations less than 4mm deep
What are Class II restorations?
Restorations that are 5mm deep
What are the setting times for Class I Bulk fill restorations?
20 seconds from occlusal surface
What are the setting times for Class II Bulk fill restorations?
10 Seconds from each tooth surface
