Aesthetic Restorative Materials Flashcards
Direct Aesthetic Restorative Materials
Should be
radiopaque to enable detection of secondary caries, identification of overhang ledge and detection of incompletely filled cavities.
Lower initial pH in silicate cements , why ?
pulpal protection was required to minimize the irritation
Unfilled Acrylic Polymers, Early clinical failure of this material is ..
dimensional instability
(high polymerization shrinkage and thermal dimensional changes).
Unfilled Acrylic Polymers
Compositions:
Powder: polymethyl meth-acrylate, initiator benzyl
peroxide and pigment.
Liquid
Unfilled Acrylic Polymers
Disadvantage
cause pulpal irritation
Mechanical properties are poor.
Composite is
a combination of two or more chemically different materials
Composite Compositions
- Organic matrix .
- Inorganic filler.
- Coupling agent binds the inorganic filler to the organic matrix.
- Initiator activator system.
- Inhibitor.
- Ultraviolet.
- Pigments.
Organic matrix consist of
A. high molecular weight monomer (oligomer)
B. Diluents (lower molecular weight monomers)
high molecular weight monomer (oligomer)
1. bisphenol A-glycidyl methacrylate (BIS-GMA)
2. Urethane dimethacrylate (UDMA).
Oligomer product are superior to methyl methacrylate monomers by
- Lower polymerization shrinkage
- Lower volatility.
- More rapid hardening.
- Production of stiffer and stronger resin
The urethane dimethacrylates are superior to BIS-GMA by
I. lower viscosity.
II. Lower water sorption.
III. Greater toughness.
IV. Greater susceptibility to visible light curing
Diluents , These monomers are included in composite formulation to
reduce the viscosity , and to facilitate clinical manipulation.
Modification of resin composite have been made in order to
………of resin such as……
minimize polymerization shrinkage , Ormocers (organic modified ceramic)
Silorane (low shrinkage composite)
In this composite, polymerization occur by…..
ring opening polymerization
quartz.
Borosilicate glass.
Lithium aluminum silicate.
Barium aluminum silicate.
Strontium.
Colloidal silicate.
These elements contribute to
radiopacity
Role of inorganic filler
1- mechanical properties such as compressive strength,
modulus of elasticity and hardness .
2. Reduction in coefficient of thermal expansion.
3. Glass is able to reflect the color of surrounding tooth material
4. Reduction in polymerization shrinkage.
5. Less heat evolve
6. The composite is radiopaque if barium or strontium glasses are used.
Classification of composite according to filler
:
1. Smaller filler particles as fine particles (0.5-3µm).
2. Very small micro-fine particles (0.04-0.2µm).
3. Blend (hybrid) containing mixture of (fine and micro-fine).
4. Finally nano-filled composite (2-75nm)
Fillers are treated by…..
this compound has two functional group ……….and…..
silane coupling agent
an inorganic group that react with the filler
an organic group that react with the organic matrix
The use of coupling agent
- Improve the mechanical properties of composite by
transferring the stress from the weak resin to the stronger filler. - Reduces early loss of the filler caused by penetration of
water between resin and filler.
chemical activation: (two paste system) in two component chemically polymerized one paste contain …
initiator (benzyl peroxide), the other paste contains activator (tertiary amine).
Plastic spatula used instead of metal , Why ?
Metal spatula should not be used since they are easily abraded by the hard fillers of composite and cause discolouration
Blue visible light radiations are about
470nm
Initiator of chemical cured system is ….
And activator is …
Benzoyl peroxide
Tertiary amine
Initiator of Light-cured system is ….
And activator is …
camphorquinon , Aliphatic Amine
Disadvantages of light cure are
requiring build up layers of 2mm or less
Poor accessibility in certain posterior and interproximal areas
High cost
Factors effecting Depth of cure
- Shade of composites, darker the shade the longer the exposure time
- The intensity of light is inversely proportional to the distance (the source be held within 1mm from the surface)
- The time of exposure not be less than 40 second
- Each increment of the restoration 1.5-2 mm thick should be cure
before another layer - Filler size and filer concentration effecting light penetration
- The concentration of photoinitiator
Inhibitors
Hydroquionone, widely used but responsible for causing discoloration. Mono-methyl ether of hydroquinone is now used .
Classification according to particle size, shape and distribution
a. Fine composite.
b. Micro-fine composite.
c. Hybrid composite.
d. Nano composite.
Composite solubility
very low solubility , lower than the solubility of unfilled acrylic due to loss of residual monomer from acrylics .
Thermal conductivity of composite
lower than those for metallic
restoration, composite provide good thermal insulation for the dental pulp.
Composite materials undergo shrinkage during polymerization
, is direct function of
organic matrix
Polymerization shrinkage can be reduced by
- Incremental addition
- Obtain strong bond between composite filling and the enamel
- Composite inlay :polymerization of composite outside or inside pt. mouth
Aesthetic and Optical properties
can be radiopaque by addition of glasses (barium, strontium and zirconium)
Bonding is obtained by
mechanical retention to acid - etched
enamel.
Bonding agents usually consist of
BIS - GMA or UDMA
The most frequently used etchant is
37 % phosphoricacid
phosphoricacid MODE OF ACTION ON
ENAMEL
- It creates micro-porosities
- Etching increases the surface area
- enamel has a high surface energy, allowing the resin to wet the tooth
surface better and penetrate into the micro-porosities.
etchant When polymerized, it forms
resin “tags’ which
forms a micromechanical bond to the ename
EVOLUTION OF DENTIN BOND AGENTS THE VARIOUS GENERATIONS are
First generation , second and third generations had the
main problems:
1- They bonded to the loosely attached smear layer .
2-They did not contain a hydrophilic group, (E.g Scotch bond)
3- They showed low bond strength.
Fourth generation: Total etch technique, hybrid layer demineralization of the surface and
subsurface, followed by infiltration of monomers in to the collagenmesh
Fifth generation , bonding into :
two steps , the adhesive resin in one bottle but the etchant is in a
separate bottle
Six generation (self etching primer )
Seventh generation : Attempts to combine all three (etchant, primer and adhesive) selfetchingadhesive(SEA)(onestep)
Note : The disadvantages of sixth and seventh generation bonding
system are: Most of them have their bond strength values
are far inferior from the 4th and 5th generations.
