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BDS2 - DMS > Composite Resins > Flashcards

Composite Resins Flashcards

1
Q

Under what conditions may a composite restoration be placed into a tooth? (4 points)

A
  • New dental caries
  • Abrasion/erosion
  • Failed restoration/secondary caries
  • Trauma
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2
Q

What are the 5 things contained within composite resins?

A
  • Glass filler particles
  • Resin
  • Camphorquinone (photo initiator)
  • Low weight dimethacrylates
  • Silane coupling agent
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3
Q

The filler particles within amalgam can have various types of glass in them. What are 5 examples of these?

A
  • Microfine silica
  • Quartz
  • Borosilicate glass
  • Lithium aluminium silicate
  • Barium aluminium silicate
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4
Q

What is the particle size and % volume for <i>conventional</i> composite resin filler particles?

A

Particle size = 10-40um

% volume = 50

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5
Q

What is the particle size and % volume for <i>Microfine</i> composite resin filler particles?

A

Particle size = 0.04-0.2um

% volume = 25%

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6
Q

What is the particle size and % volume for <i>Fine</i> composite resin filler particles?

A

Partical size = 0.5-3um

% volume = 60-70%

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7
Q

What is the particle size and % volume for <i>Hybrid</i> composite resin filler particles?

A

Particle size = Range (0.01-0.1um and 1-10um)

% volume = 70%

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8
Q

What monomers are used in the resin of composite resins? (2 examples)

A
  • BIS-GMA - reaction product of bisphenol-A and glycidyl methacrylate
  • Urethane dimethacrylates
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9
Q

What are the key characteristics of monomers in composite resins? (2 points)

A
  • Difunctional molecule (essential for the cross linking that will be needed for the polymerisation reaction)
  • Undergoes free radical addition polymerisation
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10
Q

What is Camphorquinone activated by?

A
  • Blue light (curing light)
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11
Q

What type of molecules does Camphorquinone produce and what do they do?

A
  • Produces radical molecules (that are electrically charged)

- These initiate free radical addition polymerisation of BIS-GMA which leads to chan ges in resin properties

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12
Q

Camphorquinone causes a degree of conversion of resin. What percentage or conversion can it facilitate?

A
  • 35-80% (the rest is unreacted monomer)
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13
Q

Why are low weight dimethacrylates added to composite resins? (2 points)

A
  • Added to adjust viscosity and reactivity

- Slows down the setting of the material

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14
Q

Why is a silane coupling agent used in composite resins? (3 points)

A
  • Good bond between filler particle and resin is essential
  • Normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
  • A coupling agent is used to preferentially bond to the glass and also bond to the resin
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15
Q

What are 7 uses of composites?

A
  • Where aesthetics are important
  • Class III, IV and V permanent restorations
  • Class II - limited occlusal wear
  • LAbial veneers
  • Inlays, onlays - indirect technique
  • Cores
  • Modified forms as luting cements (some dual cured)
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16
Q

How would you classify composites? (3 points)

A
  • Filler type
  • Curing method (light cured or self cured)
  • Area of use:
  • Anterior - microfilled, or submicron hybrid
  • Posterior - Heavily filled
  • Universal - Submicron hybrid
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17
Q

How can you classify a composite in terms of handling characteristics? (3points)

A
  • Condensable
  • Syringeable
  • Flowable
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18
Q

What is meant by a condensable composite?

A
  • ‘amalgam’ feeling - greater porosity

- (one that yo can pack into a cavity in a similar way to amalgam)

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19
Q

What are the characteristics of a syringeable composite? (3 points)

A
  • good adaption, less porosities and easy to apply
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20
Q

What are the characteristics of a flowable composite? (4 points)

A
  • Lower filler content
  • More shrinkage
  • Difficult to apply
  • Place for them - with fibrous ribbons
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21
Q

What are the effects of adding filler particles to composite resins? (7 points)

A
  • Improved mechanical properties
  • Increased aesthetics
  • Increased abrasion resistance (less easy to break the surface)
  • Lower thermal expansion (still not perfect)
  • Lower polymerisation shrinkage
  • Less heat of polymerisation
  • Some radiopaque
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22
Q

How many pastes are in a self curing composite?

A

2 pastes

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23
Q

How many pastes are in a UV activation composite resin?

A

one paste

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24
Q

How many pastes are in a light cure composite resin?

A

one paste

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25
Q

What happens in self cure composite activation?

A

Benzoyl peroxide + aromatic tertiary dentine -> free radicals

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26
Q

What happens in light cure composite activation?

A

Camphorquinone + blue light (430-490nm) -> free radicals

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27
Q

What are the advantages of light curing systems? (6 points)

A
  • Extended working time i.e. on demand set
  • Less finishing
  • Immediate finishing
  • Less waste
  • Higher filler levels (not mixing two pastes)
  • Less porosity (not mixing two pastes)
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28
Q

When light curing where is most of the light absorbed and what effect does this have?

A
  • Most of blue light is absorbed close to the surface

- Composite resin nearest the surface sets the most readily and becomes hard

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29
Q

What is meant by the ‘ depth of cure’?

A
  • The depth to which the composite resin polymerises sufficien tly (such thaqt its hardness is about half of that of the cured surface)
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30
Q

What is the typical depth of cure of a composite resin?

A
  • 2mm
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31
Q

What does the depth of cure indicate to use when building a restoration?

A
  • Indicates increment thickness to use

- Increment > 2mm results in a under-polymerised base which causes poor bonding to the tooth and early failure

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32
Q

What do bulk fill composites have as well a Camphorquinone?

A
  • Lucerin initiator (requires UV light)
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33
Q

What is UV and blue light needed to polymerise bulk fill composite material fully

A

= As contains both Lucerin initiator and Camphorquinone which have different optical absorption spectrums

34
Q

What lab test is used to test bulk filled composites?

A
  • Curing light positioned at several points

- Use hardness tests to verify if material at 4mm depth has cured fully

35
Q

What are the disadvantages for the lab test for bulk fill composites? (5 points)

A
  • Can curing light be positioned the same as in a lab test
  • Can optical rod be placed adjacent to tooth/composite
  • Does all blue light illuminate material
  • Will the composite polymerise fully
  • What impact does ‘stray’ blue light have on soft tissue
36
Q

What are the potential problems of using light cure? (5 points)

A
  • Light/material mismatch - overexposure
  • Premature polymerisation from dental lights - avoid exposure
  • Optimistic ‘depth of cure’ values (use small increments - 2mm max)
  • recommended setting time too short
  • Polymerisation shrinkage - affects bond to tooth, potential for fracture or microleakage
37
Q

What are the factors that could make a potential problem with setting times being too short? (5 points)

A
  • Light used
  • Light/material distance
  • Contamination or damage to light guide
  • Timer accuracy
  • Variations in light output
38
Q

What type of reaction is light curing?

A
  • Exothermic
  • Release of heat in resin material
  • Heat conducts to adjacent enamel/dentine
39
Q

What kind of light beam does light curing have?

A
  • A divergent light beam

- Beams through transparent optical rod and then diverges

40
Q

Modern light curing devices tend to be brighter/more intense. What is the theory behind this?

A
  • Idea is more intensity accelerates curing, reducing the exposure duration needed
41
Q

Unless the optical rod of a curing light is ALWAYS close to the composite resin, what may happen?

A
  • SOME blue light may illuminated the patient’s soft tissues which may cause thermal trauma
42
Q

What should you use with a curing light to prevent ocular damage?

A
  • Use orange safety shields or glasses
43
Q

Are composite resins typically strong and rigid?

A
  • Yes
44
Q

What are the requirements of a composite resin used for a large posterior cavity? (3 points)

A
  • High strength
  • High YM
  • High abrasion resistance
45
Q

What are the requirements of a composite resin used for a deciduous tooth with a large pulp? (3 points)

A
  • Strong in thin section
  • Wear = wear of tooth
  • Other properties more important - bonding, microleakage
46
Q

What are the properties of conventional composite resins?

A
  • Strong but problems with finishing and training due to soft resins and hard particles
47
Q

What are the properties of microfine composite resins? (2 points)

A
  • Smaller particles - smoother surface better aesthetics for longer period
  • But inferior mechanical properties (elastic limit and YM)
48
Q

What do hybrid composite resins usually compromise between ?

A
  • Originally compromisebetween conventional and microfine composites
49
Q

What is meant by the term ‘hardness’?

A
  • relates to materials surface and its resistance to scratching
  • Indentation resistance
50
Q

What is meant by the term ‘abrasion’?

A
  • Removal of surface layers when two surfaces make frictional contact
51
Q

What affects can surface roughness have? (3 points)

A

Affects:

  • Appearance
  • Plaque retention
  • Sensation when in contact with tongue
52
Q

What are examples of factors affecting wear (material factors)? (5 points)

A
  • Filler material
  • Particle size distribution
  • Filler loading (% of filler that is there)
  • Resin formulation
  • Coupling agent
53
Q

What are examples of factors affecting wear (clinical factors)? (6 points)

A
  • Cavity size and design
  • Tooth position
  • Occlusion
  • Placement technique
  • Cure efficiency
  • Finishing methods
54
Q

What technique is used to bond composite to enamel?

A
  • Acid etch technique
55
Q

What system is used to bond composite to dentine?

A
  • Dentine/universal bonding systems
56
Q

What bond strength would you be expecting when bonding composite to dentine and enamel?

A
  • 40MPa
57
Q

What does good bonding of composite resins to tooth surfaces reduce? (3 points)

A
  • Reduce microleakage
  • Counteract polymerisation shrinkage
  • Good bond will reduce the likelihood of a gap between the restoration and the tooth
58
Q

Which is more resistant to abrasion: hybrid or microfilled composite?

A
  • Hybrid composite
59
Q

What is the elastic limit of a material?

A
  • The amount of stress the material can take and still go back to its original shape
60
Q

What is flexural strength?

A
  • The material’s ability to bend without obtaining any major deformities
61
Q

Which type of composite has a higher compressive strength: microfilled or hybrid?

A
  • Hybrid

- 300MPa compared to 260MPa of microfilled

62
Q

Which type of composite has a higher elastic limit: microfilled or hybrid?

A
  • Hybrid

- 300MPa compared to 160MPa of microfilled

63
Q

Which type of composite has a higher tensile strength: microfilled or hybrid?

A
  • Hybrid

- 50MPa compared to 40MPa of microfilled

64
Q

Which type of composite has a higher flexural strength: microfilled or hybrid?

A
  • Hybrid

- 150MPa compares to 80MPa of microfilled

65
Q

Which type of composite has a higher elastic modulus: microfilled or hybrid?

A
  • Hybrid

- 14GPa compared to 6GPa

66
Q

Which type of composite has a higher hardness: microfilled or hybrid?

A
  • Hybrid

- 90VHN compared to 30VHN of microfilled

67
Q

Is amalgam a better material than hybrid composite?

A

Yes, but not by much

68
Q

What is the thermal conductivity of composite?

A
  • Low - which is good
69
Q

What is the thermal expansion coefficient of composite?

A
  • High - which is poor
70
Q

Why should thermal conductivity of composite be low?

A
  • To avoid pulpal damage from hot and cold foods/fluids
71
Q

Why should the thermal expansion of composite resin be equal to that of teeth?

A

To reduce microleakage and gap formation

72
Q

What is the thermal expansion coefficient of composite resin?

A
  • Composite = 25-68ppm/degrees celcius
  • Enamel = 11
  • Dentine = 8
73
Q

Are composite resins radiopaque?

A
  • Some of them are
74
Q

What are important aesthetic properties for composite resins to have? (5 points)

A
  • Shade range
  • Translucency
  • Maintenance of properties over lifetime
  • Resistance to staining
  • Surface finish
75
Q

Are composites anticariogenic?

A
  • Generally NO

- BUT a few products claim to release fluoride

76
Q

Do composites have a high or low setting shrinkage?

A
  • Low
  • If minimise shrinkage then minimise the stress between the 2 tissues
  • Bonding techniques and clinical techniques help to minimise the impact of this
77
Q

What is the biocompatibility of composite resins?

A
  • Generally thought to be okay but increasing concern about resins in general (NB not all monomer is polymerised)
78
Q

When are you likely to place an RMGI? (2 points)

A
  • High caries risk patients

- Frequent attenders

79
Q

When are you likely to place a compomer? (3 points)

A
  • Medium caries risk patient
  • Caries under control
  • Regular attenders
80
Q

When are you likely to place a composite resin?

A
  • Low caries risk patients

BDS2 - DMS (14 decks)

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