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Dental Materials Y2 > Miscellaneous properties of Composites > Flashcards

Miscellaneous properties of Composites Flashcards

1
Q

What is a composite

A

Two or more materials put together with each contributing to the overall properties

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2
Q

Name some of the uses of composites

A 
Filling Materials
Luting Agents
Indirect Restorations
Endodontic Post and Cores
Fissure Sealants
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3
Q

What are most composites cured using

A

Light

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4
Q

Describe the reaction of light curing

A
  • A tertiary amine (DHPT) and light initiator (camphorquinone) in the composite only react under blue light.
  • A polymerising reaction takes place when a light source is directed on to the paste
  • The tertiary amine reacts with the light initiator under blue light to form free radicals, which then start the addition polymerisation
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5
Q

What are the advantages of Light Cured Composites

A
  • Single Component System
  • Less Decolouration
  • Minimal Porosity (due to no mixing of pastes)
  • Virtually command set
  • Rapid Polymerisation
  • Thin inhibited layer
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6
Q

What are the disadvantages of light cured composites

A
  • Light sensitive during application
  • Retina damage
  • Limited depth of cure
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7
Q

Why do light cured composites have limited depth of cure

A

Light is refracted as it enters and doesn’t penetrate very well

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8
Q

How is the limited depth of cure in light cured composites overcome

A

The composites must be cured in 2mm increments

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9
Q

What do the mechanical properties of a polymers/composites depend on

A

On how much of the monomer is converted to polymer (via free radical polymerisation)

One wants high degree of conversion of C=C bonds

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10
Q

What are the degrees of conversion for light, self and heat cured composites

A

Light cured = 65-80% of double bonds react
Self cured = 60-75%
Heat cured = >90%

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11
Q

What wavelength of light do visible light activated (VLA) composites cure at

A

450-500nm. depending on the activator/initiator system

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12
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

Need to have quality light source to ensure you use the right wavelengths so you need to check the light output at regular intervals

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13
Q

What should you make sure you do when you light cure a composite

A
  • Tip of light source must be close to the surface of the restoration
  • Light tip mustn’t be contaminated
  • Must cure for manufacturers recommended time and no less
  • Large restorations - no fanning, curing spots must overlap
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14
Q

What about the composite will tell you how long it will take to cure

A

obvs the manufacturer’s ting

but also the darker the shade the longer it’ll take

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15
Q

What do all light cured composites contain as a source for free radicals

A

an alpha-di-ketone (initiator) or an amine (activator)

e.g. DHPT and camphorquinone

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16
Q

What light wavelengths can activate camphorquinone

A

460-480nm

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17
Q

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

A

Tungsten

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18
Q

What light does the quartz-tungsten-halogen light curing unit emit

A

UV and white light that is filtered

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19
Q

Name a major advantage of the quartz-tungsten-halogen light curing unit

A

Very wide band width between 400-500nm, most photo-initiators react in this range

20
Q

What is the main disadvantage of the quartz-tungsten-halogen light curing unit

A

Heats up a lot so must cool it and every time you use it the bulb life decreases along with its efficiency

21
Q

Name some of the advantages of using a Light emitting diode (LED) light curing unit

A
  • Cordless
  • Less lateral heat production
  • long lasting source
  • requires low wattage
  • Ultra energy efficient
22
Q

Name a disadvantage of LED light curing units

A

Has a narrow emission spectrum (460-480nm), newer versions have increased emission range

23
Q

What kind of light does a Plasma Arc (PAC) light curing unit emit

A

High intensity filtered white light and allows blue light emission

24
Q

What is the emission range of a PAC light curing unit

A

400-500nm

25
Q

What is an advantage of PAC light curing units

A

has a 1-3 second cure time

26
Q

What are some disadvantages of the PAC light curing units

A
  • Rapid conversion of resin causes high shrinkage stress

- Expensive

27
Q

What do PAC light curing units use for a light source

A

Xenon gas ionised

28
Q

Advantages of the Argon Laser light curing unit

A
  • High energy

- Highest intensity

29
Q

Disadvantages of the Argon Laser light curing unit

A
  • Emits light at a single wavelength (~490nm)

- Very expensive

30
Q

Advantages of Composites

A
  • Great aesthetic results
  • Less tooth tissue removed
  • Command set, can cure when you want
31
Q

Describe polymerisation shrinkage of composites and what problems it causes

A

2-3% vol. shrinkage as a result of double bonds converting to single bonds

  • Marginal adaptation
  • breakdown of bonds to tooth tissues
  • results in recurrent caries
32
Q

Describe water shrinkage of composites and the problems it can cause

A

The glass filler adsorbs water on to its surface.

This can cause unreacted monomer and highly soluble fractions in the composite to be released and this leaves a space that fills with water. This absorbed water affects wear resistance and colour stability

33
Q

Describe different types of composite staining

A
  • Marginal - debris penetrates the gap between the restoration and tooth tissue = staining
  • Debris becomes trapped in spaces due to the surface roughness of the composite
  • Bulk discolouration of the 2 paste amine cured systems
34
Q

Describe how composite wear can occur and what effects it has on aesthetics

A
  • Abrasive, fatigue and corrosive wear
  • With time the resin matrix wears and the filler particles protrude through the surface giving the material a dull appearance
35
Q

Name some general disadvantages of composites

A
  • Does not adhere intrinsically to enamel and dentine

- Incremental so takes longer

36
Q

Name some biocompatibility problems of composites

A

Composite components and breakdown products are released into the mouth.

Uncured resin can leach out and can lead to cytotoxic and delayed hypersensitivity reactions

Bisphenol A based monomers can also cause oestrogen effects

37
Q

How does oxygen affect curing of the resin

A

It inhibits the cure of the resin surface and causes the air and resin interface to have a sticky surface.

38
Q

What is the benefit of the sticky resin/air interface

A

Each increment of resin will bond well

39
Q

What problems does oxygen inhibition present and how is this solved

A
  • Final increment surface will be sticky

- Use a clear matrix strip and then overfill and polish

40
Q

How does silorane resin overcome the problem of high polymerisation shrinkage

A

Uses ring opening monomers that open and then bond and this limits shrinkage (<1%)

41
Q

What are the beneficial properties of silorane resin

A

Low shrinkage
Low water absorption
Mechanical properties “within the range of other composites”

42
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

Silorane requires an alternative silane for filler treatment so clinicians had to find another bonding agents to bond the hydrophobic resin to the tooth surface

43
Q

What are the benefits of current bulk fill restorative composites

A
  • One step placement - no incremental placements
  • Has excellent adaptation without additional expensive dispensing devices
  • Stress relief to enable up to 5mm depth of cure
44
Q

What monomers are used in bulk fill restorative composite composition

A

AUDMA - aromatic dimethacrylate
AFM - Addition-fragmentation monomers
DDDMA - 1,12-dodecanediol dimethacrylate
UDMA - Urethane dimethacrylate

45
Q

What happens at methacrylate groups of composite monomers

A

this is usually where polymerisation occurs

Dental Materials Y2 (13 decks)

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