Download Composite filling materials

Composite filling materials
TNT
Composition:
1. Organic matrix :
A. High molecular weight monomer (oligomer):
Bisphenol A-glycidyl mehtacrylate (BIS-GMA)
function
1-Less polymerization shrinkage
2-Less volatile.
3-More rapid hardening.
4-more cross linking
OR, urethane dimethacrylates(UDMA).
Function
-same as above +
5-lower viscosity
6-more ability for light curing
B. Lower molecular weight monomers (Diluent):
- Types:
1- Monofunctional: e.g. methyl methacrylate.
2- Difunctional: e.g. ethylene glycol dimethacrylate
functions
1-less polymerization shrinkage.
2-Less volatile
3-Less water sorption.
4-more cross linking
5-lower viscosity
2. Inorganic fillers (reinforcing fillers):
-it is some types of glasses as:
-quartz, borosilicate glass, lithium aluminum silicate, strontium, zinc glass
Effects of inorganic fillers on the properties:
1- Improve mechanical properties
2- improve esthetics
3- if barium or strontium glasses are used ..it gives radioopacity
4- decrease coefficient of thermal expansion.
5- decrease polymerization shrinkage.
6- decrease free monomer
7- decrease water sorption
1
Filler particle size and shape:
- Conventional contain large 20-30μm spherical particles then irregular
particles are developed due to better mechanical properties.
- Composite with large filler particles tend to be discolored rapidly due to
wear of the organic matrix, dislodgement of the filler particles leaving a rough
surface.
- Fine particles 0.5-3μm and microfine particles 0.04-0.2μm were developed ,
finally Hybrids containing mixture of fine and microfine .
- The microfine filler is added to oligomer of low viscosity then polymerized and
ground to particles 10-20μm in diameter, then added to oligomer to make further
paste, thus increase the inorganic filler to 32-50% by vol.
- microfine particles may be smaller than wave length of light giving lustrous
surface.
- Hybrid composite contain up to 70% filler by volume.
Classification of composite according to particle size, shape and distribution:
a. Conventional
b. Fine particles
c. Microfilled
d. Hybrid
Type
Range of
particle
size
% by
weight
of filler
General comments
Conventional
20-35
78
Difficult to polish. Abrasion of resin matrix
cause abrasion which may attract plaque.
Good mechanical properties.
Fine particle
0.5-3
70-86
Good mechanical properties. Superior
finishing and polishing than conventional.
Microfilled
0.04-0.2
25-63
Poor mechanical properties. Poor wear
resistance. More water sorption. Greater
polymerization shrinkage. Easily to attain
smooth surface which does not attract
plaque.
Hybrid
0.04 and
1-5
77-88
Has the benefits of both types of filler.
Or MACRO
2
3. Coupling agents:
- it is a compound which has ..organic group to react with…….
And has inorganic group to react with ………..
- the coupling agent used is called vinyl silane compound
- The function of coupling agent :
1- transfer the stress from the weak matrix to the stronger filler
2- Reduces early loss of the filler caused by penetration of water
between the resin and filler.
4. Initiator activator systems:
A- Chemical activation: “two phase system”
- One paste contain the initiator " benzoil peroxide "
- the other paste contains the activator " tertiary amine" which leads to better
color stability.
- Once the pastes are mixed, chemical activation begins by the reaction of
tertiary amine with the benzoil peroxide to produce free radicals which in turn
attack carbon double bonds causing polymerization.
B- Light activation: “light curing or photo initiated composite”
- Visible light waves “blue light wave of about 470 nm is used now instead of
ultra violet because the ultraviolet light has:
1- Limited depth of polymerization than visible light
2- Potential harmful effects as skin cancer and eye damage.
- Supplied as one paste system which contains a diketone such as benzil or
camphorquinone and an amine activator such as dimethylaminoethyl
methacrylate.
- On application of curing light, free radicals are generated to polymerize this
paste .
- The degree of curing depend on:
a. The characteristics of the light source e.g. new bulb gives high intensity.
b. The distance between light source and composite resin surface .
c. Time of exposure.
d. The initiator system absorption characteristics.
- 2 mm of composite can be polymerized in 10-20 seconds, so directing light from
both sides of anterior teeth or building up by layers is used to avoid
unpolymerized material which has reduced mechanical properties, poorer color
stability and greater susceptibility to stain.
C-dual cure
- Composite resin cement polymerize by both mechanisms are called dual cure
composite resin cements.
5. Polymerization inhibitors:
- an inhibitor is necessary to prevent hardening on storage.
- Hydroquinone was used, but cause discoloration of the material, so
nowadays monomethyl ether of hydroquinone is used .
3
6. ultraviolet stabilizers:
- To prevent discoloration of composite with age, compounds are added which
absorb electromagnetic radiation and improve color stability.
7. Pigments:
- Inorganic pigments are added in small amounts so the color of composite match
that of the natural tooth structure.
Properties:
1- Biological considerations:
- cause less pulp irritation than silicate and unfilled acrylics, but plaque can
accumulate on rough composite surface.
2- Solubility:
- composites have very low solubility due to polymerization which leads to more
cross-linked structure with less residual monomer.
3- Water sorption:
- Less due to the higher molecular weight and more cross-linkage
4- Thermal properties:
A- Thermal conductivity:
- Lower than those of metallic restoration and closely match those of enamel and
dentine, so provide good thermal insulation for the pulp.
B- Coefficient of thermal expansion:
- The higher the amount of organic matrix, the higher the linear coefficient of
thermal expansion
- the microfilled composite have the highest values for thermal expansion
“55-68x10-6”, so restorations from these composites will have greater change in
dimensions with temperature changes and more marginal leakage than fine and
hybrid composites.
5- Polymerization shrinkage:
- polymer. Shrinkage is proportional to organic matrix
so. fine particles composite shrink less than micro fine types (2-3%).
- This shrinkage creates polymerization stresses between the composite and the
cavity.
This stresses can lead to failure of bond between the composite and
tooth forming very small gap that allow marginal leakage of saliva
- Polymerization shrinkage can be reduced by:
a. incremental addition of light cure material and curing of each increment
independently
b. obtaining strong bond between the composite and enamel and dentine of the
cavity.
4
6- Mechanical properties:
- The compressive strength of microfine composite is less than that of
hybrid.
- The tensile strength of microfine composite is only half that of fine
composites.
- Modulus of elasticity of fine composites is two to three times that of
microfine.
7- Aesthetic and optical properties:
- Composite is a translucent material which can match the color of the
teeth.
- It can be radiopaque by adding high atomic number glasses as barium..
- wear may cause surface roughness, which lead to discoloration
- However microfine and hybrid types can take smooth surface finish for
long time.
8- Bonding and retention to tooth structure:
a. Bonding to enamel:
- bonding is obtained by mechanical interlocking to acid-etched enamel.
- After acid etching and washing of enamel, bonding agent is applied.
- Bonding agents usually consist of BIS-GMA or UDMA of low viscosity
b. Bonding to dentin:
- dentin bonding agent are now available. They usually consist of a
hydrophilic groups to improve wetting to dentin, and hydrophobic
groups to polymerize with composite.
- Bond strength of composite to dentin is less than for enamel.
- Recently single bonding agent has been introduced to be used for both
enamel and dentin. (Conditioner)
9-uses
1-anterior restoration
2-posterior restoration "hybrid type"
3-laminate veneers in anterior teeth
4-as resin cements and fissure sealants "the lower viscosity types " (UDMA and
EGDMA "
5