Direct resin composite

Dr. Passant El Sayed abd El Hameed

Lecturer at Dental Biomaterials Department
• Composite: mixture between two or more classes of materials.
• Dental composite Resin: is an esthetic restorative materials formed of
mixture of dispersed filler phase (e.g. silicate glass particles) dispersed
within a continuous matrix phase (e.g. acrylic monomer that is
polymerized during the application).
 Components
1)Organic Polymer Matrix (Resin matrix)
2) Inorganic Filler particles
3) Coupling Agent
4) Initiator activator system
5) Inhibitors
6) Pigments
1. Resin matrix:
• Bisphenol A glycidyl methacrylate (Bis GMA) nearly 75% and
urethane dimethacrylate (UDMA) which are extremely viscous.
They are diluted by adding TEGDMA (Triethylene glycol
dimethacrylate) nearly 25 %
2. Inorganic filler:
• Materials used as fillers : strontium glass, barium glass, quartz,
borosilicate glass, ceramic, silica, and prepolymerized resin.
• Advantages (Role of inorganic filler):
1. Reduction of polymerization shrinkage.
2. Increase mechanical properties as strength and abrasion
resistance.
3. Reduction of coefficient of thermal expansion→↓
Microleakage.
4. Less heat evolved during polymerization.
5. Good aesthetic qualities.
6. To give radio-opacity to diagnose recurrent caries.
3)Silane coupling agent:
• Provide chemical bond between filler particle and resin matrix,
so when stress is applied to composite, the stress can be
transferred from one strong filler particle to another.
• Organosilane is a bifunctional molecule ( X3-Si-R)
• (X3) siloxane end bonds to hydroxyl groups on silica fillers.
• (R) methacrylate end polymerizes with resin.
• This bond can be degraded by water absorbed by composite
during clinical use.
 4. Initiators and accelerators:
a) Chemically activated : benzoyl peroxide (initiator) reacts with a
tertiary amine (activator), forming free radicals, this starts the
polymerization process.
b) Light activated : Camphorquinone (photo initiator) reacts with
DMAEMA (dimethylaminoethylmethacrylate) or (Diketone)
(activator) forming free radicals, this starts the polymerization
process
• Camphorquinone is sensitive to 400-500 nm (peak is 468 nm).
Makes up 0.1%-1.0% of the monomer mixture.
C) Dual cured: that contain initiators and accelerators which allow
light activation followed by self-curing

Light cured composite

Dual cured composite.

Chemical cured composite
Setting reaction of self cure composite
Setting reaction of light cure composite
5. Inhibitors:
Prevents spontaneous polymer formation. Extends shelf life as
Hydroquinone
6.Pigments: Inorganic oxides commonly iron oxides, Metal oxides
provide shading and opacity as titanium and aluminum oxides this to
provide shading of composite.
7. UV absorbers: Prevent discoloration by oxidation and act like a
“sunscreen” as Benzophenone.
 Classification of Resin Composite
1.Accordying to filler particles :
a) Size of particle:
Macrofillers: 10-100 µm
Minifillers: 0.1-1 µm
Microfillers: 0.01-0.1 µm
Nanofillers : 001-.01 µm ( 1 nm =0 .001µm)
b) Shape of the particle.
c) Distribution of the filler
• MACROFILL COMPOSITES: 75-80%filler by wt., relatively large sized
particles (20-30 microns), rough surface that wears quickly, opaque. Not
used today.

• MICROFILL COMPOSITES: colloidal silica particles of very small size (35-

60% by wt.,) highly polished, good wear resistant in non-functional
areas.

• HYBRID COMPOSITES: high filler load (77-84% by wt.), a mixture of small

(2-4 microns) and very small ( 5%-15%, 0.04-0.2 microns) particles. Good
handling, relatively smooth surface but become rough with time, good
wear resistance and mechanical properties, suitable for stress area.
4.NANOFILL COMPOSITES:
• extremely small particles (1-100nm), Allows for:
1. High filler loading, good physical properties & polishability.
2. Will be more discussed in new trends section

5. NANOHYBRID COMPOSITE:
• Nano-sized particles mixed with microhybrids. Gradually become dull
after a few years because smoothness and wear is determined by the
size of the largest filler particles.
 2. According to method of activation

• Chemically activated→ a tertiary amine activate the initiator

(Benzoyle peroxide)

• Light activated → Visible light cured composite.

• Dual cure
 3. According to their applications
• Anterior composites

• Posterior composites (direct and indirect).

• Core build up

• Pit and fissure composites

 Packaging of Composites
• Light-cured composites: Various shades in syringes or capsules
that are made of opaque plastic material to protect composite
resin from exposure to light and thus provide adequate shelf life.
• Self-cured & Dual-cured composites : Packaged in syringes or
tubs of paste and catalyst and require mixing.
 Properties of Resin Composite
Physical properties:
1. Working and Setting Time:
• For light-cured composites: Initiation of polymerization is by
application of light about 75% of the polymerization occurs in
the first 10 minutes & continues for a period of 24 hours.
• The restoration surface is to be protected from air by a
transparent matrix.
• The optimum physical properties are not reached until about 24
hours after the reaction is initiated.
2. Polymerization Shrinkage :
• Free volumetric polymerization shrinkage creates polymerization
stresses between composite and tooth structure.
• These stresses lead to:
1. Strain the interfacial bond between the composite and the tooth,
leading to a very small gap that can allow marginal leakage of saliva.
Microleakage
2. This stress can exceed the tensile strength of enamel and result in
stress cracking and enamel fractures .
• The net effect of polymerization shrinkage can be reduced by:
I. Clinical procedures based approach:
1. ‘Soft start’ polymerization: means an initially weak radiation
level followed by a final cure with high radiation level. A slower
rate of conversion allows for better flow of the material, which in
turn decreases contraction stresses, leading to better marginal
adaptation

2. Incremental placement:
II. Materials based approach:
1. Use of stress breaking liners such as:
a. Filled Dentinal Adhesives.
b. RMGI (Resin modified glass ionomer).
c. Flowable composite.

2. Development of new monomers with less polymerization shrinkage.

3. Thermal properties:
The thermal expansion coefficient of composites is higher of enamel &
dentine.
Effect of thermal stresses:
1. Place an additional strain on the bond to tooth structure.
2. Thermal changes are also cyclic → material fatigue, early bond failure &
marginal percolation of oral fluids
4.Water Sorption :
• Swells the polymer portion of the composite and degrade the matrix
into monomer and other derivatives.
• Silane coupling agent is important in minimizing the deterioration of
the bond between the filler and polymer and the amount of water
sorption.
5. Solubility:
• Inadequately polymerized resin has greater water sorption and
solubility.
• During the storage of composites in water, the leaching of inorganic
ions can be detected.
6. Color and Color Stability:
• Change of color and loss of shade-match with surrounding tooth
structure.
• Discoloration can occur by:
1.Oxidation
2. Water exchange within the polymer matrix and its interaction with
unreacted polymer sites and unused initiator or accelerator.
3. Stress cracks within the polymer matrix and partial debonding of
the filler to the resin as a result of hydrolysis tend to increase opacity
and alter appearance.
 Mechanical Properties
• As the overall filler content increases, the physical, chemical, and
mechanical properties generally improve.
• As a result, fine-particle and hybrid composites have higher
compressive and tensile strengths as compared to microfilled
composites.
 Clinical Properties
1) Wear:
• Factors that contribute to wear
1. Increased filler volume : Wear resistance is increased by decreasing the
size of the filler particle
2.Degree of polymerization
3.Coupling agent: The absence of a silane coupling agent at the matrix-filler
interface reduces wear resistance by about half.
4. Method of finishing: Wear resistance decreases with the use of carbide
or diamond finishing burs which weaken the surface .
2)depth of cure:
• Factors affecting depth of cure
1) Type of composite such as polymerization reaction never completes,
Degrees of conversion ranges between 60% to 75% which is higher in light
cured than chemical cured type.
2) High quality & intensity of light source increases depth of cure
3) Technique of light tip placement which should be held within 1 mm & for
standard exposure time of 20-40 seconds.
3. biocompatibility:
1. Residual monomer molecules have shown a moderate degree of cytotoxicity on
pulp tissue, even in low concentrations.

2. Postoperative sensitivity may be a consequence of debonding between dentin

and the composite at the cavity floor possibly expressing irritants or bacterial
toxins into dentinal tubules.

3. Pulpal protection is recommended in deep parts of the cavity preparation.

4. Components of composites are known allergens.

4) Radiopacity :
• Some fillers, such as quartz, lithium-aluminum glasses, and silica, are
not radiopaque and must be blended with other fillers e.g. barium and
zirconium oxides to produce a radiopaque composite.
 Manipulation
Placement :
1. Interim restorations containing eugenol are not recommended.
2. The use of cavity varnish is not recommended .
3. Deep preparations may require the placement of a glass-ionomer or
resin-modified glass-ionomer liner or base over the dentin.
4. Generally, enamel and dentin are etched for 15 seconds using a 35% to
50% phosphoric acid solution or acid gel.
5. A transparent matrix band is sometimes placed for the purpose of
contouring the restoration.
•
 Single-paste system (light-cured composite)
• Curing depth is 2mm for 20 to 40 seconds
• Advantages:
1. Infinite working and short controlled setting time.
2. No mixing is needed, so less chance of incorporation of air into mix.
3. Less waste of material.
4. Less amount of finishing required.
5. Polymerization shrinkage is compensated in layering technique.
• Disadvantages:
• Contraction occurs toward the light source.
• Time consuming layering technique with maximum depth of 2 mm
 Two paste system (chemical-cured composite)
• Advantages:
1. Reaction occurs almost uniformly throughout the material.
2. Curing is not generally dependent on the thickness of restoration.
3. Easy manipulated.
• Disadvantages:
1. Shorter working time
2. Air may be incorporated during mixing, producing porosity or voids
3. The polymerization shrinkage is towards the center of the cavity leading
to marginal leakage.
 Light Curing Units
1. Quartz-Tungsten-Halogen light curing units:
• Light sources have quartz halogen bulbs with tungsten filament.
• The intensity of the bulb decreased with use, produces heat.
2. Light Emitting Diodes:
• Emit radiation in the blue part of visible spectrum 440-480 nm and do not
require any filters and do not produce any heat or sound.
3. Plasma Arc Curing Lamps:
• These lamps use xenon gas that is ionized to produce plasma, which is a
high intensity white light.
• Filters needed to remove heat and to allow blue-light to be emitted.
4. Argon Laser Lamps
• It produces the highest intensity of light with a wavelength of ~ 490 nm.
• Indications for dental resin composite:
1. Anterior restorations
2. Posterior restorations
3. preventive resin
4. conservative class 1 or 2

• Contraindications for dental resin composite:

1. Large posterior
restorations
2. Bruxism
3. Poor isolation