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.
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
What is the effect of adding filler particles to composite?
Improved mechanical properties (strength, hardness, rigidity)
Improved aesthetics
Increased abrasion resistance
Lower thermal expansion (still needs improvement)
Lower polymerisation shrinkage (still needs improvement)
Less heat of polymerisation
Some radiopaque
What are the advantages of light cure composite?
On demand set - extended working time Less finishing Immediate finishing Less waste Doesn't require mixing two pastes - higher filler levels, less porosity
What problems occur when you use compostie increments greater than 2mm?
Underpolymerised base ‘soggy bottom’
Early failure of restoration
What are the problems that can arise from using light cured composite?
Light cure/material mismatch - overexposure
Premature polymerisation from dental lights
Optimistic depth of cures
Polymerisation shrinkage
Ocular damage for blue light - safety shields/glasses
What are the properties of microfine composite?
Smaller particles - smoother surface, better aesthetics for longer period
Inferior mechanical properties
What are the properties of conventional composite resin?
Good strength
Good hardness
Problems with finishing & staining due to soft resins and hard particles
What are the properties of hybrid composite?
Compromise between conventional and microfine
Strength and hardness - less than conventional, but more than microfine
Smoothness - better than conventional, but worse than microfine
How is composite bonded to tooth?
Enamel - acid etch technique
Dentine - dentine/universal bonding systems
What is the bond strength of composite to tooth?
Dentine - 40MPa
Enamel - 40MPa
What are the benefits of a dental material that bonds to tooth?
Reduces microleakage
Minimises cavity design - no need for retention/undercuts
Stress transfer - restoration does not have to withstand full stress (transferred to tooth and bone)
Is composite resin anticariogenic?
Generally not but some products claim to be
GIC is so can be used as a liner
When would you use flowable composite?
In very small occlusal cavities
Used as a liner in deep cavities to allow good adaption of the material to the cavity floor
Is composite biocompatible?
Generally OK
Increasing concerns about resin (Bis-GMA) in general - when not all the monomer is polymerised
What caries risk should a patient be to allow use of composite resin?
Low caries risk
