Resin Composite Flashcards
What materials were used in:
a) 1950-1960s
b) 1960-1980s
a) 1950-1960s: Silicates, first tooth coloured restorative material
- setting reaction: acid base reaction between aluminosilicate glass and phosphoric acid
- releases fluoride, moisture sensitive, erosion prone, brittle
b) 1960-1980s: Acrylics, chemical set so working time was very limited
- setting reaction: free radical addition polymerisation reaction
List the stages of the free radical addition polymerisation of methyl methacrylate:
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- activation - when exposed to tertiary amine
- initiation - cleave carbon-carbon double bond when in contact with methyl methacrylate
- propagation - multiple units keep joining and joining and joining
- termination - chain attaches to impurity or free radical or further growing chain
What does the free radical addition polymerisation reaction mean for the clinician?
- material contracts on polymerisation
- reaction is exothermic
- tertiary amine not all used up - poor colour stability (clear/brown)
- must use correct P:L ratio
Compared to silicates, acrylics are less:
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- less prone to erosion
- less soluble
- less acidic
- less brittle
- exhibit lower thermal diffusivity
What did Knock and Glenn do and when?
When was composite formed and by who?
1951 - Knock and Glenn: introduced inert filler particles to reduce shrinkage, though successful in this regard, they weakened the material
1963 - Bowen: BIS GMA resin matrix, coupling agent and filler particles
What is a resin composite?
A combination of two chemically different materials with a distinct interface separating the components and having properties which could not be achieved by any of the components acting alone.
What are the components of resin composite matrix:
- resin matrix: generally based upon methacrylate or dimethacrylate monomers e.g. BIS GMA, Urethane dimethacrylate
- comonomers such as TEGMA: controls viscosity to facilitate manufacturers filler addition and clinical handling
- inhibitors: to prevent polymerisation reaction from occuring whilst product is in storage
Name some examples of inert fillers used in composite:
What must the filler be coupled with into the material?
- quartz
- silica
- glasses: aluminsilicates, boro silicate, barium oxide
A coupling agent, vinyl silane, which demonstrates good wetting
- characteristics of methacrylate, allowing it to react with the resin itself
- silane interacts and bonds with glass
Explain this graph:
Draw a graph to explain what happens with the addition of a filler to percentage volume setting:
As filler content increases, surface hardness increases.
How are resin composites set?
Activation of setting may be:
- chemical: powder/liquid form, paste/liquid form and encapsulated forms
- light cured: early years, UV light was used (health risks), today camphorquinone is used
What does camphorquinone do?
- yields the necessary free radicals to start the polymerisation
- becomes excited at wavelength: 460-480nm (visible blue light)
What do all resin composites contain?
What is the purpose of the coupling agent?
- resin: susceptible to shrinkage upon polymerisation
- filler: type, concentration, particle size and particle size distribution control properties of set
The coupling agent transfers stressed generated under loading from the rigid and brittle filler to the more flexible and ductile polymer matrix.
- filler may be regarded as a ‘shock absorber’
How are resin composites classified?
What are the types of resin composites according to ISO 4049?
Why is ISO 4049 relevant?
- according to method of activation: whether it is light or chemical
- according to filler particle size and how they are distributed within the set product
- handling characteristics: packable (highly viscous) or flowable (more fluid, less filler)
- intended clinical application: ISO 4049
Type 1 - restoration od cavities involving occlusal surfaces
Type 2 - all other polymer based restorative materials
To be on the market, material must conform with ISO 4049
Properties of resin composites:
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- biocompatible
- viscosity increases on leaving tube, work quickly
- exothermic set
- setting contraction - NOT towards light source
- thermal diffusivity matches dentine
Does cavity shape influence overall success of restoration?
What is the C-factor?
Why does it matter?
YES!
C-factor = number of bonded surfaces/number of un-bonded surfaces
COMPOSITE SHRINKS!
