Miscellaneous Properties of Composites

Question 1

Under what conditions do DHPT and camphorquinone react?

Answer 1

Both only react under the presence of blue light

Question 2

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

Answer 2

• Tertiary amine

- Light initiator

Question 3

Explain how light can cause filling materials to set?

Answer 3

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

Question 4

Advantages of light cured composites? (6)

Answer 4

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

Question 5

Disdvantages of light cured composites? (3)

Answer 5

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

Question 6

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

Answer 6

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

Question 7

What wavelength do composites cure between?

Answer 7

450-500nm

Question 8

What is the maximum light output used for camphorquinone

Answer 8

460-480nm

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

• Reflected
• Scattered
• Absorbed

Question 11

Which shades of composites take longer to cure?

Answer 11

Darker shades

Question 12

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

Answer 12

• UV light

- Benzoin methyl ether

Question 13

What are modern light curing units based off?

Answer 13

Visible light Activated (VLA)

Question 14

What is the most common light curing unit used today?

Answer 14

Quartz-Tungsten-Halogen light curing unit

Question 15

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

Answer 15

Tungsten filament

Question 16

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

Answer 16

Light Emitting Diode (LED) light curing unit

Question 17

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

Answer 17

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

Question 18

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

Answer 18

Claims 1-3 sec cure

Question 19

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

Answer 19

Bulbs are very expensive

bulbs >$600

Question 20

What are the 3 main advantages of composites?

Answer 20

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

Question 21

What 2 substances can be used as composite lining materials?

Answer 21

• Calcium Hydroxide

- Glass ionomer cements

Question 22

Which substance cannot be used as a composite lining material?

Answer 22

Eugenol based materials as it inhibits setting

Question 23

What can shrinkage of a composite potentially lead to?

Answer 23

Rapid progression of caries at the margin

Question 24

What component causes a water uptake in composites?

Answer 24

Glass filler adsorbs water on its surface

Question 25

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

Answer 25

Hydrolytic breakdown of bond between filler and resin

Question 26

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

Answer 26

- Wear resistance | - Colour stability (staining)

Question 27

Where on the composite does staining most occur?

Answer 27

Margin between restoration and tooth

Question 28

What is the benefit of oxygen inhibition for composites?

Answer 28

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

Question 29

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

Answer 29

- Use a clear matrix strip then cure so oxygen doesn't get through but light does - Overfill and polish - Some clinicians apply bonding agent

Question 30

What are the advantages for silorane composites? (2)

Answer 30

- Low polymerisation shrinkage | - Low water absorption

Question 31

Why was silorane removed from the market? (2)

Answer 31

- High cost | - Requires alternative bonding agent

Question 32

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

Answer 32

- One step placement - 5mm depth of cure - Excellent sculptability - Available in capsule or syringe delivery in 5 shades

Question 33

What are; Class I restorations? Class II restorations?

Answer 33

- Restorations that are less than 4mm deep | - Restorations that are 5mm deep

Question 34

Setting times for bulk fill; Class I restorations? Class II restorations?

Answer 34

- 20 seconds from occlusal surface | - 10 secs from each tooth surface