composite resins Flashcards

1
Q

classification

A

filler particles - conventional, microfine or hybrid
setting - light or self-cure
area of use - anterior/posterior
handling - condensable/syringeable/flowable

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2
Q

composition

A
filler particles - glass
resin
camphorquinone
low weight dimethacrylates
silane coupling agent
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3
Q

ideal properties

A
mechanical - strength, rigidity, hardness
bonding to tooth/compatible with bonding systems
thermal
aesthetics
radiopaque
handling/viscosity
anticariogenic
polishable
low setting shrinkage
biocompatible
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4
Q

filler particles

A

control aesthetics
not involved in polymerisation
polymerisation shrinkage inversely proportional to filler loading

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5
Q

hybrid

A

range of filler particle sizes so can have higher %

  • better mechanical properties
  • less polymerisation shrinkage
  • less heat of polymerisation
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6
Q

camphorquinone

A

photoinitiator
activated by blue light
produces radical molecules
initiates free radical addition polymerisation of Bis-GMA
leads to changes in resin properties
- increased molecular weight so increased viscosity and strength
can add inhibitor (hydroquinone) to prevent premature polymerisation - shelf-life (0.1%)

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7
Q

resin - monomers used

A

Bis-GMA

urethane dimethacrylates

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8
Q

resin - monomer characteristics

A

difunctional molecule
C=C bonds facilitate X-linking
undergoes free radical addition polymerisation

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9
Q

unreacted monomer

A

potential to cause an allergic reaction

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10
Q

low weight dimethacrylates

A

e.g. TEGDMA
added to adjust viscosity and reactivity
because the resin monomers are highly viscous, adding any filler would make it too stiff

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11
Q

why is a silane coupling agent necessary?

A

good bond between filler particle and resin is essential

- but normally water adheres to glass filler particles, prevents resin from bonding to the glass surface

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12
Q

silane coupling agent

A

preferentially bonds to glass and also to resin
bonds hydrophobic resins to hydrophillic glasses
hydroxyl group bonds to glass
methacrylate group bonds to resin via C=C

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13
Q

flowable

A

lower filler content

  • more shrinkage
  • poorer mechanical properties
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14
Q

effect of adding filler particles

A
improved mechanical properties
improved aesthetics
increased abrasion resistance
lower thermal expansion
reduced polymerisation shrinkage
reduced heat of polymerisation
some radiopaque
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15
Q

curing development

A
self (2 pastes)
UV activation (obsolete, 1 paste)
light curing (blue light, 440nm, 1 paste)
direct curing
indirect/post curing (in lab)
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16
Q

advantages of light curing

A
extended working time
less finishing
immediate finishing
less waste
higher filler levels - not mixing 2 pastes
less porosity - not mixing 2 pastes
17
Q

light cure sources

A

halogen or LED

LED much more efficient - light source spectra matches camphorquinone absorption much better

18
Q

activation self-curing 2 pastes

A

benzoyl peroxide initiator

aromatic tertiary amine activator

19
Q

light-curing 1 paste

A
camphorquinone
blue light (430-490nm)
20
Q

activation

A

free radicals break resin C=C bonds

21
Q

hardness

A

most of blue light absorbed close to surface - where it sets most readily and becomes hard

22
Q

depth of cure

A

depth to which it polymerises sufficiently such that its hardness is about half that of the cured surface
2mm
increment thickness

23
Q

> 2mm

A

underpolymerised base

  • ‘soggy bottom’
  • poor bonding to tooth - early failure
24
Q

what do manufacturers do re depth of cure?

A

exaggerate it

25
bulk fill e.g. tetric ceram
different optical absorption spectrum - UV and blue light needed to polymerise (cure) fully lucerin initiator as well as camphorquinone
26
safety
exothermic reaction divergent light beam thermal trauma to STs staff - ocular damage
27
light curing potential problems
light/material mismatch - overexposure premature polymerisation from dental lights optimistic DOC values recommended setting times polymerisation shrinkage - micro leakage - use small increments
28
properties
``` biocompatible (but unreacted monomer) quite hard but some concerns for posterior strong rigid - high YM bonding good but technique dependent hybrid best mechanical properties thermal conductivity low - good as avoids pulpal damage TEC high - poor (micro leakage) good aesthetics - translucency some radiopaque not anticariogenic on demand set and polishable polymerisation shrinkage ```
29
conventional
strong but problems with finishing and staining soft resins and hard particles
30
microfine
smoother surface - better aesthetics for longer period reduce shrinkage stress inferior mechanical properties
31
wear
resin soft relative to hard filler particles - more wear | conventional - bigger filler particles so rougher surface
32
factors affecting wear - material
``` filler material particle size distribution filler loading resin formulation coupling agent ```
33
factors affecting wear - clinical
``` cavity size and design tooth position occlusion placement technique cure efficiency finishing methods ```
34
bonding to tooth surface
``` reduce microleakage counteract polymerisation shrinkage shear bond strength minimise cavity design stress transfer to tooth and bone - good bonding = no stress concentration areas ```
35
amalgam vs composite failure rate
amalgam much lower failure rate
36
Filtek silorane posterior composite
not methacrylate based - lower polymerisation shrinkage | no grey/white high stress areas in stress concentration map