Composites
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In what ways does composite have ideal properties?
• Mechanical (strength, rigidity, hardness) • bonding to tooth/ compatible with bonding systems • thermal properties • aesthetics • radiopaque • handling/ viscosity • anticariogenic • smooth surface finish/ polishable • biocompatible
What are the components of composite resin?
• filler particles • resin • camphorquinone • low weight dimethacrylates • silane coupling agent
Name some of the types of filler particles?
• microfine silica • quartz • borosilicate glass • lithium aluminium silicate • barium aluminium silicate
what are the percentage volumes of filler particles in conventional, microfine, fine and hybrid composite resins? what is significant about this?
conventional - 50% microfine - 25% fine - 60-70% hybrid - 70% - (hardest/strongest/ most rigid material (?))
what are the monomers used in resin?
• BIS-GMA (most common I think). Reaction product of bisphenolA and glycidyl methacrylate • urethane dimethacrylates
What are the key characteristics of composite resin monomers
• difunctional molecule (C=C bonds which facilitate crosslinking) • undergoes free radical addition polymerisation
How do you activate camphorquinone?
by blue light
what does camphorquinone do?
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)
What degree of resin is converted by camphorquinone?
35-80%
What effect do low weight dimethacrylates have
added to adjust viscosity and reactivity
What does the silane coupling agent do?
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
describe filler particle coupling
methoxy groups hydrolyse to hydroxy groups react with absorbed water ro -OH groups in filler http://nersp.nerdc.ufl.edu/~soderho/E05.htm
Where are composites used?
• 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)
What are the different ways composites can be classed by?
• 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
How does composite develop
• filler particles • curing (activation) • particle/resin bonding
What is the effect of adding filler particles?
• 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
What are the differences in composite curing development between self, UV and light curing?
self (2 pastes) UV activation (obsolete, one paste) light curing (440nm, one paste)
how do self curing composites generate free radicals
benzoyl peroxide and aromatic tertiary amine
how do light curing composites generate free radicals?
camphorquinone and blue light (430-490nm)
What is the key issue surrounding light sources for curing composite resin?
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
What is better halogen or LED
LED - matches with camphoquinone absorption to produce the most efficient optical excitation at 450-470nm
What are the advantages of light curing systems?
• 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)
What are the advantages of light curing systems?
• 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)
Where is most of the blue light absorbed? Why is this relevant?
close to the surface (around 1mm) composite resin nearest the surface sets the most readily and becomes hard