Miscellaneous properties of Composites Flashcards
(45 cards)
What is a composite
Two or more materials put together with each contributing to the overall properties
Name some of the uses of composites
Filling Materials Luting Agents Indirect Restorations Endodontic Post and Cores Fissure Sealants
What are most composites cured using
Light
Describe the reaction of light curing
- A tertiary amine (DHPT) and light initiator (camphorquinone) in the composite only react under blue light.
- A polymerising reaction takes place when a light source is directed on to the paste
- The tertiary amine reacts with the light initiator under blue light to form free radicals, which then start the addition polymerisation
What are the advantages of Light Cured Composites
- Single Component System
- Less Decolouration
- Minimal Porosity (due to no mixing of pastes)
- Virtually command set
- Rapid Polymerisation
- Thin inhibited layer
What are the disadvantages of light cured composites
- Light sensitive during application
- Retina damage
- Limited depth of cure
Why do light cured composites have limited depth of cure
Light is refracted as it enters and doesn’t penetrate very well
How is the limited depth of cure in light cured composites overcome
The composites must be cured in 2mm increments
What do the mechanical properties of a polymers/composites depend on
On how much of the monomer is converted to polymer (via free radical polymerisation)
One wants high degree of conversion of C=C bonds
What are the degrees of conversion for light, self and heat cured composites
Light cured = 65-80% of double bonds react
Self cured = 60-75%
Heat cured = >90%
What wavelength of light do visible light activated (VLA) composites cure at
450-500nm. depending on the activator/initiator system
AY BAWS CAN I HABE DE NOTE PLZ
Need to have quality light source to ensure you use the right wavelengths so you need to check the light output at regular intervals
What should you make sure you do when you light cure a composite
- Tip of light source must be close to the surface of the restoration
- Light tip mustn’t be contaminated
- Must cure for manufacturers recommended time and no less
- Large restorations - no fanning, curing spots must overlap
What about the composite will tell you how long it will take to cure
obvs the manufacturer’s ting
but also the darker the shade the longer it’ll take
What do all light cured composites contain as a source for free radicals
an alpha-di-ketone (initiator) or an amine (activator)
e.g. DHPT and camphorquinone
What light wavelengths can activate camphorquinone
460-480nm
What filament is used in the Quartz-Tungsten-Halogen light curing unit
Tungsten
What light does the quartz-tungsten-halogen light curing unit emit
UV and white light that is filtered
Name a major advantage of the quartz-tungsten-halogen light curing unit
Very wide band width between 400-500nm, most photo-initiators react in this range
What is the main disadvantage of the quartz-tungsten-halogen light curing unit
Heats up a lot so must cool it and every time you use it the bulb life decreases along with its efficiency
Name some of the advantages of using a Light emitting diode (LED) light curing unit
- Cordless
- Less lateral heat production
- long lasting source
- requires low wattage
- Ultra energy efficient
Name a disadvantage of LED light curing units
Has a narrow emission spectrum (460-480nm), newer versions have increased emission range
What kind of light does a Plasma Arc (PAC) light curing unit emit
High intensity filtered white light and allows blue light emission
What is the emission range of a PAC light curing unit
400-500nm
