Composite Resins
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What are the advantages of composite resin?
Good aesthetics Cavity prep allows conservation of tooth tissue Adheres/bonds to tooth with use of dentine bonding agents Low thermal conductivity Elimination of galvanism
What are the disadvantages of composite resin?
Polymerisation shrinkage Marginal integrity Changing shape and volume with temp change Post-op sensitivity Technique sensitivity Water sorption and hydrolytic breakdown
What is the failure rate of composite restorations?
Generally 1-3.4%
Describe cavity design for a composite restoration.
Cavosurface margin angle of 90 degrees. Avoid cavosurface MA in areas of occlusal contact. No mechanical retention required. Beveled margins. No unsupported enamel.
What is the hybrid layer?
An interface between conditioned dentine (smear layer removed) and adhesive resin forming a collagen/resin phase.
What type of dentine is most favourable for hybrid layer formation?
Primary dentine - open tubules
What type of dentine is unfavourable for hybrid layer formation?
Tertiary dentine - irregular structure, not as porous, much more mineralised Deeper dentine - wetter, more mineralised, more tubules Reactive dentine - fewer tubules, more mineralised, occluded tubules
What is polymerisation contraction stress?
When monomers polymerise they contract. This polymerisation occurs in the setting reaction of composite resin. This stress is enough to debond the material from dentine resulting in decreasing retention and increasing leakage.
What is configuration factor?
The ratio of the bonded surface area in a cavity to the unbonded surface area. So in an occlusal cavity it would be 4:1. In a MO cavity it would be 3:2
Generally how large should composite increments be to be sufficiently light cured?
2mm
What intensity of curing light should be used for 2mm composite increments?
Minimum 280-300mW/cm squared
What is the composition of composite resin?
Filler particles Resin Camphorquinone Low weight dimethyl methacrylates Silane coupling agent
What are the glass filler particles in CR made up of?
Glass particles of various sizes. Microfine silica, quartz, borosilicate glass, lithium aluminium silicate, barium aluminium silicate, others
What percentage of filler particles are found in conventional CR?
50% f.p.
What percentage of filler particles are found in microfine CR?
25% f.p.
What percentage of filler particles are found in fine CR?
60-70% f.p.
What percentage of filler particles are found in hybrid CR?
70% f.p.
What monomers are found in the resin component of CR?
Bis-GMA Urethane dimethyl methacrylates
What is the function of the resin component of composite resin?
Undergoes free radical addition polymerisation.
What is the function of the camphorquinone component of composite resin?
Activated by blue light. Produces radical molecules that initiate free radical addition polymerisation of Bis-GMA
What is the function of the low weight dimethyl methacrylate component of composite resin?
To adjust viscosity and reactivity e.g. TEGDMA
What is the purpose of the silane coupling agent?
Preferentially bonds to glass and resin, preventing water from adhering to the glass filler particle (if this occurred it would prevent resin from bonding to the glass surface) e.g. Y-methacryloxypropyltrimethoxysilane
What are the uses for composite resin?
Where aesthetics are important Trauma e.g. composite bandage, splint Restorations (class II, III, IV & V) Labial veneers Inlays, onlays Cores Modified forms - luting cement
How is composite classified?
Handling - condensible, syringable, flowable Area of use - dentine, enamel Curing method - self cured, light cured