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BDS2 - dental material science > composite material > Flashcards

composite material Flashcards

1
Q

name 5 different restorative materials

A
  • composite resins
  • amalgam
  • glass ionomers
  • compomers
  • ceramics
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2
Q

when do you use direct filling materials

A
  • new dental caries
  • abrasion / erosion
  • failed restoration / secondary caries
  • trauma
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3
Q

what are the ideal properties of composite

A
  • mechanical
  • bonding to tooth / compatible with bonding systems
  • thermal properties
  • aesthetics
  • radiopaque
  • handling / viscosity
  • anticariogenic
  • smooth surface finish / polishing
  • low setting shrinkage
  • biocompatible
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4
Q

what traits are included in mechanical properties

A
  • strength
  • rigidity
  • hardness
    want it to be strong enough to withstand forces and be long lasting
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5
Q

what are the 2 main components of composite

A
  • glass ionomer particles
    > hard
  • resin material
    > soft
    > holds the particles together
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6
Q

what are the components of composite resin

A
  1. filler particles
  2. resin
  3. camphorquinone
  4. low weight dimethacrylates
  5. silane coupling agent
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7
Q

what is camphorquinone

A

the photo initiator

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8
Q

why is low weight dimethacrylates added

A

to improve the product

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9
Q

name filler particles in glass

A
  • microfine silica
  • quartz
  • borosilicate glass
  • lithium aluminium silicate
  • barium aluminium silicate
  • others
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10
Q

compare the particle size and % volume of different types of composite

A

conventional:
> Particle Size = 10-40um
> % volume = 50

microfine
> Particle Size = 0.04-0.2 um
> % volume = 25

fine
> Particle Size = 0.5-3um
> % volume = 60-70

hybrid
> Particle Size = range
> % volume = 70

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11
Q

what is meant by hybrid composite?

A

a mix of large particles and smaller sizes

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12
Q

what does more filler particles do to the material

A

increases the hardness of the material

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13
Q

what monomers are used in resins

A

> BIS-GMA
[reaction product of bisphenol-A and glycidyl methacrylate]

> urethane dimethacrylates§

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14
Q

what are the key characteristics of monomer

A

> difunctional molecule

  • C = C bonds
  • facilitate crosslinking (needed for polymerisation reaction)

> undergoes free radical addition polymerisation
[need composite to be cured to be a rigid, strong material with a hard surface]

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15
Q

what is camphorquinone activated by

A

blue light (curing light)

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16
Q

what does camphorquinone produce

A 
radical molecules (electrical charge)
these initiate free radial addition polymerisation of BIS-GMA [goes from the paste like material to undergo polymerisation and from the cross links so they end up a much stronger material]
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17
Q

what changes does the the camphorquinone product / reaction lead to in resin properties

A

> increased molecular weight
increased viscosity
increased strength
causes a degree of conversion of resin (35-80% unreacted monomer)

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18
Q

give an example of a low weight dimethacrylates

A

TEGDMA

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19
Q

why is low weight dimethacrylates added

A

to adjust viscosity and reactivity
to improve the material
[material would set too quickly without this being added so you would have no time to work in the patient’s mouth - allows more time as it slows it down a little]

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20
Q

why is silane coupling agent added

A

use to preferentially bond to glass and also bond to resin

a good bond between filler particles and resin is essential so this helps with that

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21
Q

what effect does water have on the bond between filler particles and resin

A

normally water will adhere to the glass filler particles and this prevents resin from bonding to the glass surface

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22
Q

name resin-filler particle coupling materials (unsure if this is even a q im not sure what i meant in my notes lol typical x)

A

> silane
eg methacryloxypropyltrimethoxysilane

> methoxy groups hydrolyse to hydroxyl groups react with absorbed water or -OH groups in filler

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23
Q

what are the uses of composite

A

> aesthetic importance
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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24
Q

what are the classifications of composite

A

> filler type
curing method
area of use
handling characteristics

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25
Q

what are the types of curing methods

A

> light cured

> self cured

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26
Q

what are the different areas of use for composite

A

> anterior

  • microfilled
  • submicron
  • hybrid

> posterior
- heavily filled

> universal
- submicron hybrid

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27
Q

what are the different classifications of the handling characteristics of composite

A

> condensable

  • amalgam feeling
  • pack into cavity
  • greater porosity

> syringeable

  • good adaptation
  • less porosities
  • easy to apply

> flowable

  • lower filler content
  • more shrinkage
  • difficult to apply
  • less viscous
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28
Q

what is involved in composite development

A

> filler particles
curing (activation)
particle / resin bonding

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29
Q

what are the effects of adding filler particles

A

> improved mechanical properties

  • strength
  • hardness
  • rigidity

> improved aesthetics
- gives a real tooth like appearance

> increased abrasion resistance

> lower thermal expansion
- still not perfect

> lower polymerisation shrinkage

> less heat of polymerisation

> some radiopaque

30
Q

explain the composite curing developments

A

> self curing
- 2 pastes

> UV activation

  • obsolete
  • 1 paste

> light curing

  • blue light 440nm
  • 1 paste

> direct curing
- in mouth

> indirect curing / post curing
- in lab

31
Q

how does self curing composite activation work

A

benzoyl peroxide and aromatic tertiary amine

results in free radicals (break resin C=C bonds)

32
Q

how does light curing composite activation activation

A

camphorquinone and blue light (430-490nm)
results in free radicals (break resin C=C bonds)
the blue light activates the material which breaks the carbon bonds

33
Q

what are the light sources for curing composite resin

A

> halogen
[old style - have ordinary white light and a filter which allows the blue light to pass through]

> LED
This is most efficient

34
Q

what are the advantages of light curing systems

A

> extended working time

  • on demand set
  • can pack / place the material the way you want to before you activate it

> less finishing

> immediate finishing

> less waste

> higher filler levels

> less porosity

35
Q

what is the depth of cure for composite

A

the depth is which the composite resin polymerises sufficiently such that is hardness is about half of that cured surface
typically 2mm
indicates increment thickness to use when building a restoration

36
Q

can you cure increments greater than 2mm

A

no
by definition you wont have polymerised that material accurately
soggy bottom

37
Q

what are the different problems with light curing

A

> light / material mismatch

  • overexposure
  • dont match up to the composite resin absorption spectrum (need to use correct blue light for the material)

> premature polymerisation from dental lights

  • avoid exposure
  • careful with operating light as it contains blue light in lower intensities

> optimistic depth of cure values
- small increments = 2mm max

> recommended setting times too short

  • timer accuracy
  • depends on light used
  • distance of light from material
  • use longer than 30 seconds (dont want to undercook)

> polymerisation shrinkage

  • affects bond to tooth
  • potential for cuspal fracture
  • microleakge
  • use small increments
  • light from different angles
38
Q

what needs to be considered with regards to the curing light and the patient

A

consider the patient’s safety
> exothermic reaction
- release of heat in resin material
- heat conducts to adjacent enamel and dentine
- there can be a 16 degrees rise in temperature (a 5.5 change is accepted as potentially irreversible traumatising dental pulp)

> modern devices are brighter / more intense
- idea is that more intensity accelerates curing, reducing exposure duration needed

  • optical rod must always be close to the composite resin surface or some blue light might escape and may cause thermal trauma to the patient’s soft tissues
39
Q

what needs to be considered with regards to the curing light and the clinical staff

A

> ocular damage
- dont look directly at the light on a regular basis

> use safety shields and glasses to protect eyes

40
Q

what are the clinical requirements of a large posterior cavity filled with composite

A
  • high strength
  • high young’s modulus
  • high abrasion resistance
  • can withstand biting forces
41
Q

what are the clinical requirements of filling a deciduous tooth with a large pulp with composite

A
  • strong in thin section
  • wear of tooth
  • other properties more important like bonding and microleakge
42
Q

what are the advantages and disadvantages of conventional composite

A
  • strong

- problems with finishing and staining due to soft resins and hard particles

43
Q

what are the advantages and disadvantages of microfine composite

A

smaller particles = smoother surface, better aesthetics for longer
but
inferior mechanical properties (elastic limit and young’s modulus)

44
Q

what are the advantages and disadvantages of hybrid composite

A

originally compromise between conventional and microfine

improved filler loading and coupling agents have led to improvements in mechanical properties

45
Q

can hardness be derived from a stress strain curve

A

no

hardness is no strength

46
Q

what does hardness as a property include

A
  • material surface
  • resistance to scratching
  • indentation resistance
    if you dont have a hard material it will experience abrasion or wear
47
Q

define abrasion

A

removal of surface layers when two surfaces make frictional contact

48
Q

how does abrasion happen to a restored tooth

A

Tooth grinds / slides along the opposing tooth surface (or restorative material at its surface)
Tooth surface is abraded - loss of material surface layers, roughened surface

49
Q

how affects does abrasion have on the tooth

A

> appearance - can be visible to the eye
plaque retention
sensation when in contact with tongue - unpleasant feeling

50
Q

explain the wear removal process with regards to composite

A

resin is initially removed
then when the glass filler particles are exposed then they are removed
different depths of roughness for the different particle sizes
> conventional = 80microns
> microfine = 10 microns

51
Q

what are the factors affecting wear of a material?

A 
> filler material
> particle size distribution
> filler load
> resin formulation (if it is very soft it will wear easily but if it is hard then it will resist)
> coupling agent (affects bonding)
52
Q

what are the factors affecting wear clinically?

A 
> cavity size and design
> tooth position
> occlusion
> placement technique
> cure efficiency  (need to cure properly to get the properties you expect)
> finishing methods
53
Q

how do you bond composite to enamel?

A

acid etch technique

54
Q

how do you bond composite to dentine?

A

dentine / universal bonding systems

55
Q

what is the acid etch technique?

A

apply 37% phosphoric acid to the enamel surface for 20 seconds then wash off
this creates etches / gaps in the enamel that is then filled with unfilled resin

56
Q

what is the typical bond strength of enamel and dentine to composite

A

40MPa

dependent of surface preparation of tissue, composite brand and test method

57
Q

what does bonding to tooth substance do

A

> reduce microleakage

  • good bond will reduce the likelihood of gap between restoration and tooth
  • microorganisms can exist in these gaps and cause the restoration to fail

> counteract polymerisation shrinkage

> shear bond strength

> minimise cavity

  • no need for retention undercuts
  • bond holds restoration in place

> stress transfer

  • restoration does not have to withstand full stress
  • stress is transferred to tooth and bone
58
Q

what are the composite mechanical properties

A

there was a table w lots of numbers but i dunno how important it was to know ALL of them lol this is a reminder to have a littlee nosey at it but i personally dont think i’ll know it xoxo gossip girl

59
Q

what are the thermal properties of composite?

A

> thermal conductivity is low (this is good)

> thermal expansion coefficient is high (this is poor)

60
Q

explain thermal conductivity with composite

A

it is low
avoids pulpal damage from hot and cold foods and drinks
heat is transferred poorly so composite acts as a protector

61
Q

explain thermal expansion with composite

A

we want thermal expansion to be the same as the tooth to reduce microleakage
thermal contraction causes an ingress of saliva and bacteria
thermal expansion of dentine and enamel is roughly half of that of composite
this means composite tries to expand at twice the rate of the tooth which puts more stress on the bond making it more likely to fracture

62
Q

explain the aesthetic property of composite

A 
good
range of shades to match tooth colour
important in the anterior more than the posterior
translucency 
maintenance of properties over life time
resistance to staining
surface finish
63
Q

explain radiopaque as a property of composite

A

some are radiopaque not all
helps to diagnose secondary caries
ideal for looking for fragments that have come off or fracturered

64
Q

explain the handling / viscosity properties of composite

A

gives a choice on what material suits you / what you prefer to use

> light curing

  • demand setting
  • more time to work with material
  • problems w safety

> mixing / working times

> viscosity

  • variations
  • some materials flow
  • others need to be packed / condensed
  • advantage / disadvantage depends on cavity
65
Q

is composite anticariogenic

A

generally no

few products claim to release fluoride

66
Q

does composite give a smooth surface finish / is it polishable

A
  • can be good
  • technique / product sensitive
  • part of aesthetics
67
Q

what does low setting shrinkage have to do with composite

A

polymerisation shrinkage is still a problem as stresses develop at hard tissue surfaces (make debonding more likely)
bond agents and clinical techniques help minimise the impact of this

68
Q

what is the biocompatibility of composite

A
  • ok
  • increasing concern about resins in general
  • not all monomer is polymerised
  • over time the monomer can be released and irritate surrounding tissues
69
Q

list the properties of composite that affect choice of material

A 
mechanical
bonding
thermal
aesthetic 
handling
surface finishing
polymerisation shrinkage 
anticariogenic 
biocompatible 
radiopacity
70
Q

when would you use RMGI

A

high caries risk patients who are frequent attenders

71
Q

when would you use compomer

A

medium caries risk patients
caries under control
regular attenders

72
Q

when would you use composite resin

A

low caries risk patients

BDS2 - dental material science (13 decks)

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