Composite Resins Flashcards
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.