Composite - Light Curing Process Flashcards
What type of light is used to cure composite and why
LED light
The LED spectral output overlaps the peak of camphorquinone’s absorption spectrum
What are the advantages of using light curing systems
Extended working time
On-demand curing
Restoration needs less finishing and polishing
Composite can have higher volume of filler particles
Less waste
Why must composite be laid in increments
Most of the blue light is absorbed close to the surface so composite nearest the surface sets the most readily
What is depth of cure
The layer thickness you can apply while ensuring the composite is cured adequately
Describe the ISO 4049 depth of cure
Test involves curing a cylinder of composite then scraping away the unpolymerised layer at the bottom
The remaining cylinder length, L, is measured and the depth of cure is defined as half of this length
Describe the hardness ratio depth of cure
Hardness is measured at various depths of the composite resin
Each hardness value measured is compared to the top surface’s hardness value giving a hardness ratio
The depth of cure according to this is the depth at which the hardness is 80%
What are the cons of the ISO 4049 depth of cure
Depth used to be defined as x, not x/2
Depths were rounded up to the nearest mm
What is the typical depth of cure
2mm
What occurs if too large an increment is used during a composite restoration
Results in an underpolymerised base - soggy bottom
Poor bonding to tooth causing early failure
What are the claims of depth of cure for BULK-FILL composites
Up to 6mm
What are the photo-initiators for BULK-FILL composites
Lucerin and camphorquinone
How are BULK-FILL composites cured
Using UV and blue light due to the different optical absorption spectrum of the photoinitiators
What are the potential problems of light curing
Any mismatch between curing light spectrum and materials absorption can lead to insufficient curing which may lead to the dentist overexposing it to try and cure it
If composite is protruding from the cartridge it may be illuminated by a dental light which may trigger polymerisation prematurely
There will be polymerisation shrinkage which may cause fracture or microleakage
Light output may vary after prolonged use
Why may light curing cause danger to the patient
Exothermic reaction so head is released which conducts to adjacent enamel and dentine
Research suggests there may be up to a 16C increase in temperature
5.5C rise is accepted as causing potentially irreversible trauma to the pulp
Blue light may illuminate patient’s soft tissues and cause thermal trauma
Why may light curing cause damage to the clinical staff
Ocular damage to the retina is possible - use safety shields or glasses
