Composite Resin 1+2 Flashcards
when do you use direct filling materials?
- new dental caries
- abrasion/erosion
- failed restoration/ secondary caries
- trauma
ideal qualities of direct filling materials (11)
Mechanical – strength, rigidity, hardness
- Very important as need to be strong enough to withstand forces exerted on it
bonding to tooth / compatible with bonding systems
thermal properties
aesthetics
range of shades
radiopaque
handling / viscosity
anticariogenic
- glass ionomer cements
smooth surface finish/ polishable
low setting shrinkage
biocompatible
5 components of composite resin
- filler particles
- resin
- camphorquinone
- low weight dimerthacrylates
- silane coupling agents
what are filler particles?
Glass
Lots of variety – microfine silica – quartz – borosilicate glass – lithium aluminium silicate – barium aluminium silicate
% volume of filler particles in conventional composite
50%
% volume of filler particles in microfine (submicron) composite
25%
% volume of filler particles in fine composite
60-70%
% volume of filler particles in hybrid composite
70%
filler particle size in conventional composite
10-40um
filler particle size in microfine (submicron) composite
0.04-0.2um
filler particle size in fine composite
0.5-3um
filler particle size in hybrid composite
range
0.01-0.1um and 1-10um
greater % volume of filler particles means….
the harder the material
what composite resin is most commonly used in GDH?
hybrid composite resin
what is the monomer in resin?
BIS-GMA
- reaction product of bisphenol-A and glycidyl methacrylate
urethane dimethacrylates
what is a key characteristic of the monomer in resin of composite resin?
difunctional molecule
C=C bonds – facilitate crosslinking
- undergoes free radical addition polymerization
- Needed to take composite resin to hard rigid on curing
what activates 3. Camphorquinone?
blue light
photo initiator
- initiates free radical addition polymerisation of BIS-GMA
what increases viscosity in composite resin?
cross linking of BIS-GMA with other molecules due to photo-initiation
no all monomers react
what is the purpose of low weight dimethacrylates in composite resin?
- improve the material
- added to adjust viscosity & reactivity
Without can set too quickly - allow time to place and pack
- Slow down so more control
what is the purpose of silane coupling agent in composite resin?
- 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 glass and also bond to resin
intimate interface between the 2
- essential
uses of composites
- where aesthetics important
- Class III, IV & V permanent restorations
- Class II - limited occlusal wear
- labial veneers
- inlays, onlays - indirect technique
- cores
- modified forms as luting cements (some dual cured)
4 ways to classify composite
- filler type
- curing method (light or self)
- area of use (anterior, posterior or universal)
- handling characteristics
what type of composites can be used in an anterior location?
microfine (submicron)
hybrid
what type of composites can be used in posterior location?
heavily % filled - hybrid
what type of composites can be used in universal location?
submicron
hybrid
what are the 3 types of handling characteristics of composite resin?
condesable
syringeable
flowable
what is condensable composite like?
amalgam feeling
greater porosity
what is syringeable composite like?
good adaptation
less porosities
easy to apply
what is flowable composite like?
lower filler content
more shrinkage
difficult to apply
place for them - fibre ribbons
why do you want more filler particles per unit volume?
get a stronger, harder, more rigid composite resin
use a variety of filler particle sizes to get in between larger ones
10 effects of adding filler particles
- improved mechanical properties (strength, hardness, rigidity etc.)
- improved aesthetics
- glass reflects the light
- gives more of a tooth like appearance
- increased abrasion resistance
- less easy to scrape surface, make divots
- lower thermal expansion (still not perfect)
- lower polymerisation shrinkage (still a problem)
- less heat of polymerisation (BUT not negligible)
- some radiopaque
3 classes of composite curing
- self curing (two pastes)
- UV activation (obsolete, one paste)
- Light curing (blue light 440nm, one paste) Used most in GDH
2 different light sources for light curing composite resin
halogen - less efficient
LED
where is Camphorquinone peak absorption?
between 400 and 500nm
so ideally light cure is 450nm
6 advantages of light cure composite resin
- 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)
self cure has more voids/gaps so increased porosity
Light cured - smooth and uniform
Porosity is bad makes material more vulnerable to fracture
why is porosity bad in composite resin?
makes composite resin more prone to fracture due to increased voids/gaps
depth of cure
the depth to which the composite resin polymerises sufficiently,
- such that its hardness is about half that of the cured surface
what is the typical depth of cure of composite resin?
2mm
what will happen if increments are larger than 2mm?
under-polymerised base
‘soggy-bottom’
poor bonding to tooth -> early fracture
5 potential problems with light curing composite resins
- light / material mismatch – overexpose
- premature polymerisation from dental lights - avoid exposure
- optimistic” depth of cure” values
- recommended setting times too short
- polymerisation shrinkage - affects bond to tooth, potential for cuspal fracture, microleakage
factors that can cause issue for light cure composite - light/cure mismatch
don’t match the composite resin absorption spectrum - check right wavelength for your material
factors that can cause issue for light cure composite - premature polymerisation from dental lights
Background light contains blue light - can start to cause polymerisation so put cap back on material when not in use
factors that can cause issue for light cure composite as optimistic depth of cure values
product, shade, light exposure & intensity
use small increments - 2mm max
factors that can cause issue for light cure composite as recommended setting times are too short
product, light used, light/ material distance, contamination or damage to light guide, timer accuracy, variations in light output (e.g. over repeated use, between different units)
use > 30 s (more than suggested)
Inadvertently not aiming as should
- Recommend times can be less than desired due to inaccuracies in person
factors that can cause issue for light cure composite due to polyermisation shrinkage
Bonding between composite resin and tooth itself fails
- Ensure uniform behaviour
- use small increments - light from different angles
light curing safety points for patient
- Exothermic reaction
(Release of heat in resin material; heat conducts to adjacent enamel/dentine)
Divergent light beam and Modern devices brighter/more intense
- idea is more intensity accelerates curing, reducing exposure duration needed
BUT unless optical rod is ALWAYS close to the composite resin surface SOME blue light MAY illuminate patient’s soft tissues
- Beam passes through a transformed optical rod
- Diverges. Can hit soft tissues
causing Thermal trauma/ injury to patient
light curing safety for clinical staff
ocular damage
- use safety shields and/or safety glasses
what is the fracture stress for composite resin?
350MPa
- strong
what is the Elastic Young’s modulus for composite resin?
15GPA (15000MPA)
- high
- rigid
how does the properties of composite resin meet it’s clinical requirements?
Large Posterior Cavity needs High strength, high YM, high abrasion resistance
Deciduous (large pulp) needs to be strong in thin section
wear = wear of tooth (not amalgam)
- other properties more important - bonding, microleakage
characteristic properties of conventional composite resin
strong but problems with finishing and staining due to soft resins and hard particles
had large filler particles mean low quantity per volume poor finishing more likely to stain
characteristic properties of microfine composite resin
smaller particles - smoother surface better aesthetics for longer period
but inferior mechanical properties (Elastic limit & Young’s Modulus)
characteristic properties of hybrid composite resin
originally compromise between conventional & microfine
most modern composites are hybrids
improved filler loading and coupling agents have led to improvement in mechanical properties
what is hardness?
refers to material surface
- resistance to scratching
- indentation resistance
cannot be derived from stress strain curve
• not stress
hardness test
Indenter or made of stainless steel, has tapered point at end. Weight on top of indenter and leave on composite resin for set time.
Hard material = small indentation
- need a high powered microscope to measure
abrasion
removal of surface layers when two surfaces make frictional contact
- Tooth grinds/slides along the opposing tooth surface (or restorative material at its surface).
happens if material is not hard
what does abrasion effect?
increased surface roughness
- not as attractive potential (notices by patient)
- increased plaque retention
- sensation when in contact with tongue (unpleasant)
what is lost first from composite resin when it is worn?
loss of resin first and then filler particles as wear continues
degree of roughness felt depends on size of filler particles
5 material factors affecting wear of composite resin
- filler material
- particle size distribution
- filler loading (% present)
- resin formulation (if resin is soft will abrade easily, relatively hard will resist abrasion more)
- coupling agent (bonding filer particle to resin)
6 clinical factors affecting wear of composite resin
- cavity size & design
- tooth position
- occlusion
- placement technique
- cure efficiency (if you don’t cure composite resin effectively will not form expected properties. Not as hard so wear quicker)
- finishing methods
how does enamel bond to composite resin?
acid-etch technique
how does dentine bond to composite resin?
dentine/universal bonding systems
summary of acid etch technique on enamel
- 30 % Phosphoric acid
- 20 secs
fill with unfilled resin (no filler particles)
then follow with composite resin on top
enamel to composite resin typical bond strength
40MPa
dentine to composite resin typical bond strength
40MPa
what causes micro-leakage?
gaps forming around composite
what is polymerisation shrinkage?
material placed pulls away from tooth surfaces it has been bonded to
- good bond will reduce this chance
composite resin cavity design
minimal (less tissue removal)
bond holds restoration in place
importance of good bond strength of composite to tooth in terms of stress transfer
forces acting on base are spread evenly and equally and good bond then restoration likely to last
what is stress transfer like when there is poor bond strength between composite and tooth?
poor bond and gaps/voids between composite resin and tooth tissue then stress force is not spread evenly as focuses on the voids.
Stress in these regions is great so more vulnerable to fracture
- restoration does not have to withstand full stress - stress transferred to tooth and bone
is hybrid composite or micro-filled composite more resistant to abrasion?
hybrid
higher compressive strength higher elastic limit stress higher tensile strength higher flexural strength double elastic modulus triple hardness
which has higher rigidity amalgam or composite resin?
amalgam - double Elastic modulus
thermal conductivity of composite resin is….
low
why is it advantageous that the thermal conductivity of composite resin is low?
avoids pulpal damage from hot and cold foods/fluids
- composite resin acts as insulator not a conductor
the thermal expansion coefficient of composite resin is….
high compared to enamel, dentine and amalgam
glass ionomer cement is closest to tooth tissue range
why is it disadvantageous that the thermal expansion coefficient of composite resin is high?
should be equal to the tooth to reduce microleakage
- want to expand and contract at same rate as natural tooth tissue
- this reduces void formation and microleakage
what is the advantage of some composite resins being radiopaque?
can be seen in X-rays
- see if any has fallen or been misplaced
- diagnose secondary caries easily
e.g. Clearfill Majesty ES-2 used in clinical skills
5 composite resins aesthetics positives
- shade range
- translucency
- maintenance of properties over lifetime
- resistance to staining
- surface finish
what does light curing give?
on demand setting
means can have mixing and working times adjusted to you
is there variation in composite resin viscosities?
yes
pick one that is suited to your working preferences and cavity
- some flow and some need packed
what is one of the most critical factors for patients?
aesthtics
so composite resins have a smooth polishable surface finish is good
- but technique sensitive can crystalise
what helps minimise the impact of setting shrinkage in composite resin?
bonding agents and clinical techniques (carefully places increments)
what happens to the non-polymerised monomers in the resin?
20% of monomers are captured in mass of composite resin
over time can be released
- irritates the surrounding tissue
10 properties that impact choice of material
- Mechanical
- Bonding
- Thermal
- Aesthetic
- Handling
- Surface finish
- Polymerisation shrinkage***
- Anticariogenic
- Biocompatible
- Radiopacity
what can polymerisation shrinkage lead to?
gaps/voids between restorative material and tooth
lead to micro-leakage and restoration failure
when is resin modified glass ionomer most likely to be used in clinical setting?
with high caries risk patients
frequent dental attenders
when is compomer most likely to be used in clinical setting?
with medium caries risk patients
caries is under control
regular dental attenders
when is composite resin most likely to be used in clinical setting?
low caries risk patients
