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BDS2 CDS Dental Materials Science > Clinical composites > Flashcards

Clinical composites Flashcards

ILO 1.6c: have knowledge of the chemical and physical properties as well as the clinical uses of a range of dental materials

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1
Q

when would you apply direct filling materials?

4

A
  • primary dental caries
  • failed restorations / secondary caries
  • abrasion / erosion
  • trauma
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2
Q

what are the ideal properties of direct filling materials?

10

A
  • mechanical - strength, rigidity, hardness
  • bonding to tooth
  • thermal properties
  • aesthetics
  • handling/viscosity
  • smooth surface finish / polishable
  • low setting shrinkage
  • radiopaque
  • anticariogenic
  • biocompatible
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3
Q

what makes up composite resin?

5

A
  1. filler particles - glass
  2. resin
  3. camphorquinone
  4. low weight dimethylacrylates
  5. silane coupling agent
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4
Q

what are the filler particles that make up composite resin?

A
  • microfine silica
  • quartz
  • borosilicate glass
  • lithium aluminium silicate
  • borium aluminium silicate etc.
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5
Q

what monomers are in the resin? what are the key characteristics?

2,2

A

BIS-GMA and urethane dimethacrylates
* difunctional molecule
* undergoes free radical addition polymerisation

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6
Q

what is camphorquinone?

3

A
  • activated by blue light
  • produces radical molecules which initiate free radical addition polymerisation of BIS-GMA
  • leads to changes in resin properties -stronger, more viscous
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7
Q

why are low weight dimethylacrylates added to composite resin?

A

adjusts the viscosity and reactivity, easier to manipulate

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8
Q

what is silane coupling agent added to composite resin?

A

bonds filler particles and resin

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9
Q

when would you use composite rather than other materials?

7

A
  • where aesthetics are important
  • class 3, 4, 5 permanent restorations
  • class 2 - limited occlusal wear
  • labial veneers
  • inlays, onlays - indirect technique
  • cores
  • modified forms as luting cements
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10
Q

what are good handling characteristics of composite resin?

3

A
  • condensable - greater porosity
  • syringeable - good adaption, lesser porosity, easy to apply
  • flowable - lower filler content, more shrinkage, difficult to apply
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11
Q

describe the size of hybrid filler particles

A

hybrid composites have filler particles of different sizes

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12
Q

what is the effect of adding filler particles to composite resin?

6

A
  • improved mechanical properties - strength, rigidity, hardness, abrasion resistance
  • lower thermal expansion
  • lower polymerisation shrinkage
  • less heat of polymerisation
  • improved aesthetics
  • some are radiopaque
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13
Q

how do different types of curing development for composite resins?

5

A
  • self curing - two pastes
  • UV activation - one paste
  • light curing - blue light, one paste
  • direct curing - in mouth
  • indirect curing / post curing - in lab
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14
Q

how do self curing composites set?

A

benzoyl peroxide + aromatic tertiary amine = polymerisation

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15
Q

how do light curing composites set?

A

camphorquinone + blue light (430-490nm)

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16
Q

what are the two light sources for curing composite resin? which is better and why?

A

halogen and LED
* difference in optical spectral range
* LED is better as it absorbs the same wavelengths as camphorquinone, especially at optical excitation

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17
Q

what are the advantages of light curing systems?

6

A
  • extended working time - command set
  • less finishing
  • immediate finishing
  • less waste
  • higher filler levels (not mixing 2 pastes)
  • less porosity (not mixing 2 pastes)
18
Q

where on composite is light absoprbed most?

A

close to the surface
* composite resin nearest the surface sets teh most readily and becomes hard

19
Q

describe the depth of cure ISO 4049

A
  • column of composite is light cured
  • soft composite is removed from bottom of column
  • hard composite is reached and no longer can be scraped
  • distance of hard composite is measured
  • distance is divided by 2
  • remaining distance is considered the depth of cure
20
Q

what does the depth of cure show?

A

the depth to which the composite resin polymerises sufficiently
* indicated increment thickness to use when restoring

21
Q

how deep can hybrid composites be cured? what happens when more composite is used?

A

2mm
* using >2mm increments results in under-polymerised base and poor bonding to tooth = early failure

22
Q

what is depth of cure defined as?

A

depth at which material hardness is about 80% of the cured surface

23
Q

describe this depth of cure profile

A
  • around 80% of material hardness of cured surface is around 12
  • if you read a hardness of 12 on the graph, the depth equivalent is around 1.5mm
  • so the depth of cure is <1.5mm
24
Q

what are the potential problems of light curing

5

A
  • light / material mis-match
  • premature polymerisation from dental lights
  • optimistic depth of cure values (too high)
  • recommended setting times too short
  • polymerisation shrinkage
25
Q

what are the differences between conventional, microfine and hybrid composites?

A
  • conventional = strong but problems with finishing and staining due to soft resins and hard glass filler particles
  • microfine = smaller particles so smoother surface for better aesthetics fro longer period but inferior mechanical properties
  • hybrid = compromise between conventional and microfine - improved filler loading and coupling agents have led to improvements in mechanical properties
26
Q

what is abrasion?

A
  • removal of surface layers when two surfaces make frictional contact
  • tooth grinds/slides along the opposing tooth surface or restorative material and the surface is roughened
27
Q

what does surface roughness affect?

3

A
  • appearance
  • plaque retention
  • sensation when in contact with tongue
28
Q

what happens when composite wears? what does the roughness depend on?

A
  • surface layer is removed so uneven surface and filler particle protrudes
  • roughness depends on size of filler particle in composite resin
29
Q

what material factors affect the wear of composite?

5

A
  • filler material
  • particle size distribution
  • filler loading
  • resin formulation
  • coupling agent
30
Q

what clinical factors affect the wear of composite?

6

A
  • cavity size and design
  • tooth position
  • occlusion
  • placement technique
  • cure efficiency
  • finishing methods
31
Q

what is the bond strength of composite resin to enamel and dentine?

A

40MPa

32
Q

what does a good bond to the tooth give rise to? what does a poor bond do?

2, 1

A
  • reduced microleakage and counteracts polymerisation shrinkage
  • transfers stress to tooth and alveolar bone
  • poor bond concentrates stress at different interfaces so more likely to fail
33
Q

what is the compressive strength, tensile strength, elastic modulus and hardness of amalgam and hybrid composite compared to dentine and enamel?

A
  • amalgam and composite have a higher compressive strength than enamel and dentine
  • amalgam and composite have a higher tensile strength than enamel and sometimes dentine
  • amalgam and comosite have a lower elastic modulus than enamel but higher than dentine but composite is similar to dentine
  • amalgam and composite are harder than dentine but less hard than enamel
34
Q

describe the ideal thermal conductivity of cmposite resins

A

should be low to avoid pulpal damage from hot and cold foods and drinks

35
Q

what is thermal diffusivity and what is ideal for composite resins?

A
  • how readily a material transmits heat when exposed to a short/transient stimulus
  • should be low and similar to dentine
36
Q

what is the ideal thermal expansion of composite resins? what are the thermal expansion values for enamel, dentine and other restorative materials?

A

should be equal to the tooth to reduce microleakage but it is high = poor

37
Q

why are composite resins good for aesthetics?

5

A
  • shade range
  • translucency
  • maintenance of properties over time
  • resistance to staining
  • surface finish
38
Q

how is the handling/viscosity of composite resins?

4

A
  • light curing - on demand setting
  • mixing, working time - depends on the material
  • viscosity - some flow and some need to be packed
  • user friendly
39
Q

when would you use resin modified glass ionomer clinically?

3

A
  • high caries risk
  • frequent attenders
  • anticariogenic - releases fluoride
40
Q

when would you use compomers clinically?

3

A
  • medium caries risk
  • caries under comtrol
  • regular attenders
41
Q

when would you use composite resins?

A

patients with low caries risk

BDS2 CDS Dental Materials Science (5 decks)

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