1
Q
In what ways does composite have ideal properties?
A
- Mechanical (strength, rigidity, hardness)
- bonding to tooth/ compatible with bonding systems
- thermal properties
- aesthetics
- radiopaque
- handling/ viscosity
- anticariogenic
- smooth surface finish/ polishable
- biocompatible
2
Q
What are the components of composite resin?
A
- filler particles
- resin
- camphorquinone
- low weight dimethacrylates
- silane coupling agent
3
Q
Name some of the types of filler particles?
A
- microfine silica
- quartz
- borosilicate glass
- lithium aluminium silicate
- barium aluminium silicate
4
Q
what are the percentage volumes of filler particles in conventional, microfine, fine and hybrid composite resins? what is significant about this?
A
conventional - 50%
microfine - 25%
fine - 60-70%
hybrid - 70% - (hardest/strongest/ most rigid material (?))
5
Q
what are the monomers used in resin?
A
- BIS-GMA (most common I think). Reaction product of bisphenolA and glycidyl methacrylate
- urethane dimethacrylates
6
Q
What are the key characteristics of composite resin monomers
A
- difunctional molecule (C=C bonds which facilitate crosslinking)
- undergoes free radical addition polymerisation
7
Q
How do you activate camphorquinone?
A
by blue light
8
Q
what does camphorquinone do?
A
produces radical molecules, these initiate free radical addition polymerisation of BIS-GMA which leads to changes in resin properties
(i.e. increased molecular weight, so increased viscosity, strength)
9
Q
What degree of resin is converted by camphorquinone?
A
35-80%
10
Q
What effect do low weight dimethacrylates have
A
added to adjust viscosity and reactivity
11
Q
What does the silane coupling agent do?
A
preferentially bond to glass and also bond to resin
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
12
Q
describe filler particle coupling
A
methoxy groups hydrolyse to hydroxy groups react with absorbed water ro -OH groups in filler
http://nersp.nerdc.ufl.edu/~soderho/E05.htm
13
Q
Where are composites used?
A
- where aesthetics 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)
14
Q
What are the different ways composites can be classed by?
A
- filler type
- curing method
1. light cured
2. self cured - area of use
1. anterior (microfilled or submicron hybrid)
2. posterior (heavily filled)
3. universal (submicron hybrid) - handling characterisitics
1. condensible - ‘amalgam feeling’
2. syringeable - good adaptation, less porosities, easy to apply
3. flowable - lower filler content, more shrinkage, difficult to apply, place for them with fibre ribbons
15
Q
How does composite develop
A
- filler particles
- curing (activation)
- particle/resin bonding
16
Q
What is the effect of adding filler particles?
A
- improved mechanical properties (strength, hardness, rigidity etc)
- improved aesthetics
- increased abrasion resistance
- lower thermal expansion (still not perfect)
- lower polymerisation shrinkage (still a problem)
- less heat of polymerisation (BUT not negligible)
- some radiopaque
17
Q
What are the differences in composite curing development between self, UV and light curing?
A
self (2 pastes) UV activation (obsolete, one paste) light curing (440nm, one paste)
18
Q
how do self curing composites generate free radicals
A
benzoyl peroxide and aromatic tertiary amine
19
Q
how do light curing composites generate free radicals?
A
camphorquinone and blue light (430-490nm)
20
Q
What is the key issue surrounding light sources for curing composite resin?
A
How well does the light source spectra match the absorption spectrum of the photoinitiator?
e.g. halogen vs LED
There is a difference in optical spectral range
21
Q
What is better halogen or LED
A
LED - matches with camphoquinone absorption to produce the most efficient optical excitation at 450-470nm
22
Q
What are the advantages of light curing systems?
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)
23
Q
What are the advantages of light curing systems?
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)
24
Q
Where is most of the blue light absorbed?
Why is this relevant?
A
close to the surface (around 1mm)
composite resin nearest the surface sets the most readily and becomes hard
25
what does 'depth of cure' mean?
the depth to which the composite resin polymerises sufficiently such that is hardness is about half that of the cured surface
26
what is the typical depth of cure?
2mm
27
what does the typical depth of cure mean for how we use composite
indicates increment thickness to use when building a resoration
28
what do increments of over 2mm result in?
under-polymerised base
"soggy bottom"
poor bonding to tooth--> early failure
29
When looking at manufacturers claims about depth of cure what do we have to be careful of
they often exaggerate depth of cure values
need to be wary that:
- their lab tests might not position curing light the same way we might
- can optical rod by placed adjacent to tooth/ composite
- does all blue light illuminate the material
- will composite polymerise (cure) fully?
- what impact does "stray" blue light have on soft tissue
- do any clinical tests of 4-6mm depth of cure actually work?
30
Potential problems of light curing? (and how to fix)
- light/ material mismatch (overexpose)
- premature polymerisation from dental lights (avoid exposure)
- optimistic "depth of cure" values. Product, shade, light exposure and intensity (use small increments, 2mm max)
- recommended setting times too short
(use over 30s)
- polymerisation shrinkage - affects bond to tooth, potential for cuspal fracture, microleakage (use small increments and light from different angles)
31
Safety issues for patient using blue light?
1. Exothermic reaction
- release of heat in resin material, heat conducts to adjacent enamel/ dentine. Around a 16oC rise yet 5.5oC is accepted as potentially irreversibly traumatising to dental pulp
2. divergent light beam
3. modern devices brighter/ more intense (idea is more intensity accelerates curing, reducing exposure duration needed). Unless optical rod is always close to the composite resin surface, some blue light may illuminate patient's soft tissues causing thermal trauma
32
Safety issues for clinical staff using blue light?
- ocular damage
33
What is measured by youngs modulus?
measure of the ability of a material to withstand changes in length when under lengthwise tension or compression.
34
What are the clinical requirements of composite for a large posterior cavity?
- high strength
- high youngs modulus
- high abrasion resistance
35
What are the more important clinical requirements of composite in deciduous teeth
- strong in thin section
- wear = wear of tooth (?)
- other properties more important - bonding, microleakage
36
Properties of conventional composite?
strong but problems with finishing and staining due to soft resins and hard particles
37
Properties of microfine composite?
- smaller particles (smoother surface better aesthetics for longer period)
- but inferior mechanical properties (elastic limit and youngs modulus)
38
Properties of hybrid composite?
originally compromise between conventional and microfine
39
what composition are most modern composites? why?
hybrids
| - improved filler loading and coupling agents have led to improvement in mechanical properties
40
What indicates hardness?
- material surface
- resistance to scratching
- indentation resistance
41
What is abrasion?
removal of surface layers when two surfaces make frictional contact
42
Describe the hardness test
an indentor is placed with an 100g weight on top of composite resin. If it's hard it won't make much on an indent, if soft it will
43
What does abrasion result in?
loss of material surface layers, roughened surface
44
What does surface roughness affect?
- appearance
- plaque retention
- sensation when in contact with tongue
45
What is the surface roughness of conventional composite?
80um
46
What is the surface roughness of microfine composite?
10um
47
What material factors affect wear
- filler material
- particle size distribution
- filler loading
- resin formulation
- coupling agent
48
What clinical factors affect wear?
- cavity size and design
- tooth position
- occlusion
- placement technique
- cure efficiency
- finishing methods
49
what is the composite bond to tooth/ compatible with bonding systems like
generally okay but some mismatches have been reported
50
how do you apply the acid etch to enamel?
30% phosphoric acid
| 20 seconds
51
What does acid etch do to the surface of enamel
etches into it
52
What part of the composite binds into the grooves created by the acid etch
unfilled resin
| composite with the filler particles sits on top
53
What is the typical bond strength of composite on enamel (know this)
40MPa
54
What is the typical bond strength of composite on dentine (know this)
40MPa
55
What are the typical bond strength values dependent on
- surface preparation of tissue
- composite brand
- test method
56
What are the benefits of bonding to tooth surface?
- reduce microleakage
- counteract polymerisation shrinkage
- minimise cavity design (no need for retention undercuts)
- stress transfer (restoration doesn't have to withstand full stress - stress transferred to tooth and bone
a good bond will reduce likelihood of gap between restoration and tooth
57
What has better mechanical properties between microfilled composite and hybrid composite?
What about amalgam?
hybrid
amalgam beats both
58
what are the different mechanical properties
```
compressive strength
elastic limit stress
tensile strenght
flexural strength
elastic modulus
hardness
```
59
What thermal conductivity does composite have
low (which is good)
60
what thermal expansion coefficient does composite have?
high (which is bad)
61
why is it good that the thermal conductivity of composite resin is low?
to avoid pulpal damage from hot and cold foods/fluids
62
what is the ideal thermal expansion for composite
it should be equal to tooth, to reduce microleakage (on cold stimulus?)
(25-68ppm/oC)
63
Comment on aesthetic properties of composite
very good, range of shades
anterior: important
posterior: less important
important to gage patient's perceptions and expectations
- shade range
- translucency
- maintenance of properties over lifetime
- resistance to staining
- surface finish
64
comment on handling/ viscosity properites of composite
Light curing
- "on-demand" setting (but potential problems)
Mixing/ working times
- depend on specific material
viscosity
- some materials flow, others need to be packed (condensed) - adv/disadv depends on cavity
Should be user friendly
- but not at expense of other properties
65
is composite anticariogenic
generally no (a few products claim to release fluoride)
66
comment on the ability of composite to produce a smooth surface finish/ polishable?
can be good but product/ technique sensitive
67
Why is low setting shrinkage a problem?
polymerisation shrinkage still a problem as stresses develop at hard tissue surfaces (making de-bonding more likely)
68
How can we minimise the impact of polymerisation shrinkage?
bonding agents and clinical techniques help minimise impact of this
69
What is the biocompatibility of composite like?
generally thought to be ok but increasing concern about resins in general. Nb not all monomer is polymerised
70
after 8 years how does composite compare to amalgam in terms of failure rates
amalgam has a lower failure rate than all types of composite
71
what are the properties to consider which would affect your choice of material?
```
mechanical
bonding
thermal
aesthetic
handling
surface finish
polymerisation shrinkage
anticariogenic
biocompatible
radiopacity
```
