Miscellaneous properties of Composites Flashcards
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
What is an advantage of PAC light curing units
has a 1-3 second cure time
What are some disadvantages of the PAC light curing units
- Rapid conversion of resin causes high shrinkage stress
- Expensive
What do PAC light curing units use for a light source
Xenon gas ionised
Advantages of the Argon Laser light curing unit
- High energy
- Highest intensity
Disadvantages of the Argon Laser light curing unit
- Emits light at a single wavelength (~490nm)
- Very expensive
Advantages of Composites
- Great aesthetic results
- Less tooth tissue removed
- Command set, can cure when you want
Describe polymerisation shrinkage of composites and what problems it causes
2-3% vol. shrinkage as a result of double bonds converting to single bonds
- Marginal adaptation
- breakdown of bonds to tooth tissues
- results in recurrent caries
Describe water shrinkage of composites and the problems it can cause
The glass filler adsorbs water on to its surface.
This can cause unreacted monomer and highly soluble fractions in the composite to be released and this leaves a space that fills with water. This absorbed water affects wear resistance and colour stability
Describe different types of composite staining
- Marginal - debris penetrates the gap between the restoration and tooth tissue = staining
- Debris becomes trapped in spaces due to the surface roughness of the composite
- Bulk discolouration of the 2 paste amine cured systems
Describe how composite wear can occur and what effects it has on aesthetics
- Abrasive, fatigue and corrosive wear
- With time the resin matrix wears and the filler particles protrude through the surface giving the material a dull appearance
Name some general disadvantages of composites
- Does not adhere intrinsically to enamel and dentine
- Incremental so takes longer
Name some biocompatibility problems of composites
Composite components and breakdown products are released into the mouth.
Uncured resin can leach out and can lead to cytotoxic and delayed hypersensitivity reactions
Bisphenol A based monomers can also cause oestrogen effects
How does oxygen affect curing of the resin
It inhibits the cure of the resin surface and causes the air and resin interface to have a sticky surface.
What is the benefit of the sticky resin/air interface
Each increment of resin will bond well
What problems does oxygen inhibition present and how is this solved
- Final increment surface will be sticky
- Use a clear matrix strip and then overfill and polish
How does silorane resin overcome the problem of high polymerisation shrinkage
Uses ring opening monomers that open and then bond and this limits shrinkage (<1%)
What are the beneficial properties of silorane resin
Low shrinkage
Low water absorption
Mechanical properties “within the range of other composites”
AY BAWS CAN I HABE DE NOTE PLZ
Silorane requires an alternative silane for filler treatment so clinicians had to find another bonding agents to bond the hydrophobic resin to the tooth surface
What are the benefits of current bulk fill restorative composites
- One step placement - no incremental placements
- Has excellent adaptation without additional expensive dispensing devices
- Stress relief to enable up to 5mm depth of cure
What monomers are used in bulk fill restorative composite composition
AUDMA - aromatic dimethacrylate
AFM - Addition-fragmentation monomers
DDDMA - 1,12-dodecanediol dimethacrylate
UDMA - Urethane dimethacrylate
What happens at methacrylate groups of composite monomers
this is usually where polymerisation occurs
