Composite Resin Flashcards
What are composite?
A solid formed from two or more distinct phases that have been combined to produced properties superior to or intermediate to those of individual constituent.
Uses of composite ? 7
- Direct or indirect restorative material
- Fiber reinforced composite posts
- Luting agents
- Core build up in post endodontics restoration
- Pits and fissure sealants
- Bonding of orthodontics brackets
- Splinting of mobile teeth
Basic composition?
- Matrix- continous phase
- Filler- dispersed phase
- Coupling agents
Other constituents of composite?
- Activator-initiator
- Pigments
- inhibitors
- UV absorbers
What is dental resin based composite?
Dental resin based composite is structure composed of three major components : a highly cross-linked polymeric matrix reinforced by a dispersion of glass, mineral or resin filler particles and/or short fiber bound to the matrix by coupling agents.
What is resin matrix?
The resin matrix in most dental composite is based on a blend of aromatic and/or aliphatic dimethacrylate monomers such as bis-GMA and urethane dimethacrylate (UDMA)to form highly cross-linked,strong, rigid and durable polymer structures.
Most widely used resin matrix?
- Aliphatic / aromatic dimethyl acrylate monomers-Bis-GMA
- TEGDMA
- UDMA
Most recently used resin matrix?
Silorane monomers
Example of high density monomers?
- BISGMA
2. UDMA
advantages of high density monomers.
- Low polymerisation shrinkage due to large molecular volume of this monomer
- High cross linking improved properties
- High strength and rigidity
Disadvantages of high density monomer?
Due to high density these monomers are viscous and difficult to manipulate
How to overcome the high density monomers viscosity?
TEGDMA(dilutent monomer) + BISGMA(viscous) -> decrease viscosity ->easy to manipulate and paste like consistency
Functions filler
- Improve the mechanical properties
- Decrease polymerisation shrinkage
- Decreases thermal expansion and contractions
- Decrease water sorption
- Radioopacity
- Control of workability/viscosity
Examples of fillers?
- Quartz
- Silica
- Glasses with heavy metals
- fluoride releasing fillers
Properties of quartz?4
- chemically inert
- very hard and difficult to grind
- difficult to polish
- abrades opposing tooth
Properties of silica? 2
- less harder than quartz
- non crystalline structure
Properties of glasses with heavy materials?4
- radio opaque
- less inert
- slowly leach out
- shorter lifetime
Characteristics of fluoride releasing fillers
- ability to release fluoride
- Ytterbium trifluoride and Ba-Al-fluorosilicate
Effect of filler size and distribution?
- the composite properties are improved to a great extent by increasing the filler loading
- this can be achieved by particle and distribution
Filler size and aesthetics
Larger particles> scattering of light> opacity> decreasing curing depth > rough surface texture > stains, plaque
Small particle > less scattering light > less opacity > increase curing depth > smooth surface texture > higher aesthetics
Classification by filler particles size
- Macrofilled
- Small (fine) particle composite
- Midfilled
- Minifilled
- Microfilled composite
- Hybrid composite
- Nanofilled composite
What is the function of coupling agents?
- These bond the filler particles to the matrix
- improves properties of resin
- prevent leaching
How coupling agents improves properties of resins?
They improve properties of resin by transferring stresses from plastic resin matrix to stiff filler particles
Most commonly used coupling agent?
Organosilanes-gamma methacryloxypropyl trimethoxysilane
What is the used of activation/initiations system?
Both monomethacrylate and dimethacrylate polymerise by the addition polymerisation mechanism initiated by the free radicals. Free radicals can be generated by chemical activation or by external energy activation.
Most common photoinitiator?
Camphorquinone
Characteristics of camphorquinone?
- most common photoinitiator
- absorbs blue light
- 400-500nm range
How visible light activates?
- initiator reacts with amine activator
- form free radicals
- initiates addition polymerisation
Types of polymerisation mechanism?
- Chemically activated
2. Light activated
How chemically activated resins supplied?
Chemically cured composites are supplied as two pastes, one of which contains the benzoyl peroxide initiator and the other an aromatic tertiary amine activator.
Mechanism of chemically activated resin
-when the two paste are mixed together the amine reacts with the benzoyl peroxide to form free radicals and addition polymerization is initiated.
How the addition polymerisation occurs?
1. Induction A. Activation B. Initiation 2. Propagation 3. Chain transfer 4. Termination
Advantages of chemically cured composite?
- Convenience and simplicity
- Long term storage stability
- Manipulation of working / setting time by varying proportion
- Degree of cure equal through out if mixed properly
- Marginal stress build up during curing is much lower than for photocured due to slower cross linking
Disadvantages of chemical cured composites
- Mixing causes air entrapment leading to porosity which might weaken the material and increase staining
- Aromatic amine accelerators oxidise and turn yellow with time-colour instability
- Difficult to mix evenly
Two types of light used in light cured resins
- UV light
2. Visible light
Characteristics of uv light cured
- used before
- limited penetration of light into resin
- lack of penetration through the tooth structure
- caused damage to retina
What kinds of paste in light cured?
Single paste
What contain in the single paste of visible light cured composite ?
-photoinitiator
A. Camphorquininone-0.2 wt %
B. Dimethyl aminecethyl metacrylate 0.15 wt %
- amine accelator
How polymerisation occurs in light cured composite?
- Exposure to light(400-500nm)
- Excites photosensitizer
- Photosensitizer reacts with amine
- Free radical formed
- Addition polymerization starts
Advantages of light cured composites?
- no mixing needed
- no aromatic amine accelerator , thus greatly improved colour stability
- ‘command’ setting (upon exposure to an intense blue light). This means that working time is controlled, at will , by the clinician
- small increment of composite can be polymerised at a time allowing the use of multiple shades within a single restoration and accommodations for shrinkage within each increment as opposed to bulk shrinkage
Disadvantages of light cured composite?
- limited cure depth :necessary to build up in layers of about 2mm
- marginal stress buildup during curing is much higher in self cured resin
- mildly sensitive to normal room illumination
- special lamp is needed to photo initiate curing
- poor lamp accessibility in posterior and interproximal areas,require extra exposure time
- darker shades require longer exposure time
Factors involves in photocuring?
1. Curing lamps A. LED lamps B. QTH lamps C. PAC lamps D. Argon laser lamps 2. Depth of cure and exposure time 3. Safety precautions
Amounts of photon absorbed by initiators depend on
- wavelength
- light intensity
- exposure time
Curing depth should be kept
2-3mm
Exposure time depend on
Intensity of curing unit
-higher the intensity lesser the exposure time
