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BDS 2: Dental Materials > Miscellaneous Properties of Composites > Flashcards

Miscellaneous Properties of Composites Flashcards

1
Q

Under what conditions do DHPT and camphorquinone react?

A

Both only react under the presence of blue light

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2
Q

What 2 general substances are needed during a light cure reaction?

A
  • Tertiary amine

- Light initiator

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3
Q

Explain how light can cause filling materials to set?

A

The tertiary amine reacts with the light initiator, under blue light to form free radicals, which then start off the addition polymerisation reaction.

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4
Q

Advantages of light cured composites? (6)

A
  • Single component system
  • Less decolouration
  • Minimal porosity (no mixing of pastes)
  • Virtually command set
  • Rapid polymerisation
  • Thin inhibited layer
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5
Q

Disdvantages of light cured composites? (3)

A
  • Light sensitive during application (direct sunlight could start off reaction)
  • Retina damage
  • Limited depth of cure
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6
Q

What does limited depth of cure of a dental composite mean?

A

Light can only cure 2mm of composite at a time so if a big cavity is present can only cure in 2mm increments

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7
Q

What wavelength do composites cure between?

A

450-500nm

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8
Q

What is the maximum light output used for camphorquinone

A

460-480nm

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9
Q

What are 4 things to consider when carrying out a light cure

A
  • 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
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10
Q

What can happen to light when it hits a composite? (3)

A
  • Reflected
  • Scattered
  • Absorbed
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11
Q

Which shades of composites take longer to cure?

A

Darker shades

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12
Q

What were the earlier light curing units based off? (2)

A
  • UV light

- Benzoin methyl ether

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13
Q

What are modern light curing units based off?

A

Visible light Activated (VLA)

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14
Q

What is the most common light curing unit used today?

A

Quartz-Tungsten-Halogen light curing unit

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15
Q

What is the filament used in a Quartz-Tungsten-Halogen light curing unit?

A

Tungsten filament

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16
Q

What is the alternative for a Quartz-Tungsten-Halogen light curing unit?

A

Light Emitting Diode (LED) light curing unit

17
Q

What are some of the advantages of a LED light curing unit? (4)

A
  • Low lateral heat production
  • Long lasting light source
  • Requires low wattage
  • Typically cordless
18
Q

How long does a Plasma-Arc (PAC) light curing unit take to cure?

A

Claims 1-3 sec cure

19
Q

What is a disadvantage of a Plasma-Arc (PAC) light curing unit?

A

Bulbs are very expensive

bulbs >$600

20
Q

What are the 3 main advantages of composites?

A
  • Good aesthetic results
  • Less tooth tissue removed
  • Sets on command if light cured
21
Q

What 2 substances can be used as composite lining materials?

A
  • Calcium Hydroxide

- Glass ionomer cements

22
Q

Which substance cannot be used as a composite lining material?

A

Eugenol based materials as it inhibits setting

23
Q

What can shrinkage of a composite potentially lead to?

A

Rapid progression of caries at the margin

24
Q

What component causes a water uptake in composites?

A

Glass filler adsorbs water on its surface

25
Q

Which bond can be hydrolytically broke down by water in a composite?

A

Hydrolytic breakdown of bond between filler and resin

26
Q

What features can be compromised by adsorbed water in composites? (2)

A
  • Wear resistance

- Colour stability (staining)

27
Q

Where on the composite does staining most occur?

A

Margin between restoration and tooth

28
Q

What is the benefit of oxygen inhibition for composites?

A

Oxygen and resin interface results in a sticky resin surface which will allow placement of next composite increment

29
Q

How can you counteract the problem of a sticky composite surface? (3)

A
  • Use a clear matrix strip then cure so oxygen doesn’t get through but light does
  • Overfill and polish
  • Some clinicians apply bonding agent
30
Q

What are the advantages for silorane composites? (2)

A
  • Low polymerisation shrinkage

- Low water absorption

31
Q

Why was silorane removed from the market? (2)

A
  • High cost

- Requires alternative bonding agent

32
Q

What are some benefits of Bulk fill restorative composites? (4)

A
  • One step placement
  • 5mm depth of cure
  • Excellent sculptability
  • Available in capsule or syringe delivery in 5 shades
33
Q

What are;

Class I restorations?
Class II restorations?

A
  • Restorations that are less than 4mm deep

- Restorations that are 5mm deep

34
Q

Setting times for bulk fill;

Class I restorations?
Class II restorations?

A
  • 20 seconds from occlusal surface

- 10 secs from each tooth surface

BDS 2: Dental Materials (13 decks)

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