Composite Resin.pptx

ORIGIN OF COMPOSITE…
Use of acrylic resin as restorative material due to
� Esthetic
� Insoluble in oral fluids
� Ease of manipulation
� Low cost

…ORIGIN OF COMPOSITE
Main drawbacks
� High polymerisation shrinkage
� Poor wear resistance
� High coefficient of thermal expansion
� Exothermic reaction causing pain

Introduction
� In an effort to improve the physical characteristics of unfilled
acrylic resins, Bowen of the National Bureau of Standards
(now called the National Institute of Standards Technology)
developed a polymeric dental restorative material reinforced
with silica particles.
� The introduction of this filled resin material in 1962 became
the basis for the restorations that are generically termed
composites.

� Composites are presently the most popular tooth colored
materials, having completely replaced silicate cement and
acrylic resin.
� Basically, composite restorative materials consist of a
continuous polymeric or resin matrix in which an inorganic
filler is dispersed.

� A compound of two or more distinctly different materials with
properties that are superior or intermediate to those of
individual components which are chemically bonded by
another interface.
Definition

� Acc to Phillips, Dental composite are highly cross –linked
polymeric materials reinforced by dispersion of glass
,crystalline,or resin filler particles and/or short fibers bound to
the matrix by silane coupling agents.

History
� During the first half of the 20th century ,silicates were only
tooth coloured aesthetic materials available for the cavity
preparation.
� Acrylics resins similar to those used for custom impression
trays and dentures replaced the silicates during the 1940s
and 1950s because of their tooth like appearance,
solubility in oral fluids, ease of manipulation and low cost.

� Unfortunately acrylics resin have poor wear
resistance ,they shrink severely during curing and they have
excessive thermal expansion and contraction.
� These problems were reduced somewhat by addition of quartz
powder to form a composite structure.
� The early composite based on PMMA were not very
successful ,in part because filler particles simply reduced
volume of polymer resin but were not bonded to resin.

� A major advance was made when Dr.Ray L.Bowen (1962)
developed a new type of composite material.
� Bowen’s main innovations were bisphenol A glycidy
methacrylate ,a dimethacrylate resin and an organic silane
coupling agent .

Indications
1. Diastema closure and Veneers
2. Class I and Class II
3. Inlays and Onlays
4. Core build up
5. Pits and fissure sealant
6. Repair of chipped porcelain restorations
7. Bonding of orthodontic brackets

According to Sturdevant
� Composites are usually divided into three types based
primarily on the size, amount, and composition of the
inorganic filler:
1) conventional composites,
2) microfilled composites, (0.01-0.04micro m)
3) hybrid composites (0.4-1 micro m)
Classification

� More recent changes in composite composition have
resulted in several other hybrid type categories,
⮚Flowable composite
⮚Packable composite
⮚Nanofilled composite (0.005 -0.01micro m)

According to filler particle size
MACROFILLERS ---- 10 TO 100 um
MIDIFILLERS ----- 1 TO 10 um
MINIFILLERS ----- 0.1 TO 1 um
MICROFILLERS ----- 0.01 TO 0.1 um
NANOFILLERS ----- 0.005 TO 0.01 um

According to phillips
� Traditional (large particle 1-50µm glass or silica)
� Hybrid (large particle 1-20µm glass,40nm silica)
� Hybrid (midifiller 0.1-10µm glass,40nm silica)
� Hybrid(minifiller/SPF 0.1-2 µmm glass, 40nm silica)

� Packable hybrid (midifiller/minifiller hybrid but with lower
filler fraction)
� Flowable hybrid (midifiller hybrid but with finer particle size)
� Homogenous microfill (40 nm silica)
� Heterogeneous microfill (40 nm silica, Prepolymerized resin
particles)

� Based on curing mechanism
� Class 1—self cured materials
� Class 2—light cured materials
◦ Group 1—energy applied intraorally
◦ Group 2—energy applied extraorally
� Class 3—dual cured materials

� Supplied as a kit containing
� Composite resin
� Etching liquid (37% phosphoric acid)
� Bonding agent
Supplied as

Components of dental composites or
restorative resin
� Matrix
� Fillers
� Coupling agents

Matrix
� Forms a continuous phase and binds with filler particles.
� It is made up of resin matrix- bis-GMA (Bisphenol A glycidyl
dimethacrylate) and UDMA( Urethane dimethacrylate
� form highly cross linked structure thus resistant to softening,
degradation of heat and solvents but is highly viscous.
� Addition of TEGDMA to reduce the viscosity of bis-GMA

� TEGDMA is the most common and comprises 10 to 35% of
most macrofilled composites and 30 to 50% of most
microfilled composites.TEGDMA is a smaller and more
flexible difunctional resin than Bis-GMA.
� The major disadvantages of this resin are that it is more brittle
and it undergoes more polymerization shrinkage than Bis-
GMA, shrinking about 5 to 9%.

� A fourth resin-system called silorane results from the reaction
between oxirane and siloxane molecules.
� This resin-system shrinks less than Bis-GMA or urethane
dimethacrylate systems. Silorane systems reduce shrinkage.,

Fillers
▪ Reinforcement of matrix resin resulting in increased hardness
strength and decreased wear
▪ Reduction in polymerization shrinkage
▪ Improved workability by increase in viscosity
▪ Reduction in water sorption
� Reduction in thermal expansion and contraction
� Improved workability by increasing viscosity

� Improved workability by increasing viscosity
� Reduction in water sorption, softening and staining
� Increased radiopacity and diagnostic sensitiviy through
incorporation of strontium, barium, glass.
� Important attributes of fillers that determine the properties and
clinical application of composites are
� Filler loading
� Size of particles and its distribution
� Shape of fillers
� Radiopacity
� Refractive index

� Common filler particles are crystalline quartz; pyrolytic silica
(such as in Aerosil®, Degussa Corp., Ridgefield Park, New
Jersey); and glasses such as lithium aluminum silicate, barium
aluminum silicate, and strontium aluminum silicate.
� Quartz and heavy-metal glass are commonly used fillers in
conventional macrofilled composites
� Silica nanoparticles
� Fluoride releasing fillers—ytterbium trifluoride,

Coupling agents
� Coupling agents are used to help bond resin matrix and filler
particles together; they are also sometimes called adhesives.
� Commonly used coupling agents are epoxy, vinyl, and methyl
silanes.
� The single most commonly used silane in dental composites
is 3-(methacryloyloxypropyl) trimethoxysilane (Union
Carbide).

� Most silanes are difunctional molecules that, in theory, can
ionically bond to the inorganic filler particles and
simultaneously chemically bond to the organic matrix.
� In reality, silanes probably work mostly by reducing the surface
tension between the inorganic filler and organic matrix. In
simple terms, they act like a soap that increases the resin wetting
of the filler.

� Functions of coupling agents—
� Improve the properties of the resin through transfer of stresses
from the more plastic resin matrix to the stiffer filler particles
� Prevent water from penetrating the resin-filler interface
� Bind the fillers to the resin matrix thereby reducing the wear.

Initiators and Activators Of Polymerization
� Initiation systems start the polymerization process through
the formation of a free radical, a compound with a reactive
unpaired electron.

Chemically Activated Resins
Supplied as two pastes
� Benzoyl peroxide (initiator)
� Aromatic tertiary amine activator (e.g N,N-dimethyl-p-
tolvidine)

Light –Activated Resins
� The first light-activated systems were formulated for UV
light to initiate free radicles.
� Today UV light cured composites have been replaced by
visible blue light-activated systems with greatly improved
depth of cure, controllable working time.
� The free radical initiating system consists of photosensitizer
and amine initiator in a paste.

� As long as these two components are not exposed to light
,they don’t react.
� Exposure to light in blue region (468nm) produces an excited
state of photosensitize–react with amine–form free radicle.
� Camphoroquinone –commonly used, absorbs blue light (400-
500nm)

Inhibitors and stabilizers
� To prevent premature resin polymerization, compounds such
as 4-methoxyphenol (MEHQ) and 2,6-di-tert-butyl-4-methyl
phenol or butylated hydroxytoluene (BHT) are generally
added in amounts of about 0.01%.
Function
� Extend storage lifetime for all resins
� Ensure sufficient working time.

Color stabilizers
� Chemically cured composites may contain compounds such as
benzophenones, benzotriazoles, or phenylsalicylate that absorb
ultraviolet (UV) light and act as color stabilizers.
� These materials are not found in the UV light-polymerized
systems because they can inhibit polymerization.

Opacifiers
� Opacity is controlled by adding titanium dioxide pigments,
and color is achieved by adding metal oxides of iron, copper,
magnesium, and others.
� To increase the opacity, manufacturer adds titanium dioxide
and aluminium oxide to composite in only minute amounts
(0.01-0.007 wt%) as these are highly effective.

Curing systems
Autocure systems
� Autocure systems generate small amounts of heat during
curing and do not need a light source.
� Their disadvantages include:
(1) a long setting time,
(2)voids in the final restorative (voids caused by mixing
typically account for 3 to 10% of the volume, inhibiting
polymerization and increasing surface roughness),
(3) a higher probability of long term discoloration after
placement.

Chemical Activation
� Referred to as cold curing or self curing.
� In chemically activated systems, the chemicals that initiate
polymerization are usually separated into two pastes. When
the pastes are mixed, polymerization starts.

Ultraviolet light-activated systems
� The first light-activated systems, introduced in 1970, used UV
light.
� The first product was the Nuva System developed by LD Caulk,
which also introduced acid etching.
Advantages
� Rapid cure
� Indefinite working time, because no setting occurs until the light
source is applied
� less composite waste.

Disadvantages
1. curing units require a 5-minute warm-up period,
2. depth of light penetration is 1 to 2 mm at best,
3. maintaining the light at 100% efficiency is difficult,
4. UV radiation can cause corneal burns.
5. the loss of UV efficiency cannot be determined by looking
at the unit.

Visible light-activated systems
� Over the past 25 years, many visible light-cured composite
resins and curing units have been introduced.
� Advantages
1. Materials can be manipulated longer and still have a shorter
curing time (20–40 seconds or less vs. minutes for autocured
composites),
2. earlier finishing,
3. better color stability
4. no lamp warm-up time
5. less chance of voids and air bubble incorporation
6. less waste of materials
7. use of halogen bulbs, which maintain constant blue light
efficiency for 100 hours under normal use.

Disadvantages
1. possible eye damage (retinal burns with visible light
systems),
2. a maximum depth of light penetration of about 3 mm,
3. heat generation that could harm the pulp, and
4. the high purchase and maintenance costs of curing lights.

� The mechanism of visible light-curing uses a diketone, most
commonly, camphoroquinone.
� When this photoinitiator absorbs blue light, the molecule
forms a free radical and starts the polymerization process.

Difference between chemically cured
and light cured composite
Chemical Cure Light Cure
Polymerization is central Polymerization is pheripheral
Curing in one phase Curing is in increment
Sets within 45 seconds Sets only after light activation
Less working time More working time
More internal porosity less internal porosity
Less color stability more color stability

Types of Lamps used for Photoinitiator Curing
1)LED lamps( Light Emitting Diode)
� light source emit radiation only in the blue part of the
visible spectrum between 440 and 480nm
� Don’t require filters
� Have a long life of 10000 hrs.
� Their low power consumption makes them easily portable.
� High cost

2)QTH lamps (Quartz Tungsten Halogen)
� Have quartz bulb with a tungsten filaments that irradiate both
uv and white light that must be filtered to remove heat and all
wavelength except those in violet –blue range(400 to 500nm)

Disadvantages
� Halogen bulb has life on an average of 50 hrs.
� The bulb reflection and filter degrade over time due to
production of high temperature-reduction in light output –
depth of cure.

3)PAC lamps(plasma Arc Curing)
� Use xenon gas that is ionized to produce a plasma.
� The high –intensity white light is filtered to remove heat and
to allow (400 to 500nm) blue light to be emitted.

4)Argon laser lamps
� Have the highest intensity and emit at a single wavelength.
� Lamps currently available emit 490 nm.
� More expensive

5. PAC
� Faster cures and greater depth of cures
� Generate intense white light by ionizing xenon gas to produce
plasma
� Filters required

� The total amount of resin polymerized depends on several
factors:
1. Transmission of light through the material
2. Shade of resin
3. Amount of photoinitiator and inhibitor present
4. Curing time
5. Intensity of light
6. Type of light
7. Thickness of resin
8. Distance from light

Configuration factor
� The c-factor (configuration factor) is a term used for the ratio of
the number of walls bonded to unbonded.
� As the c-factor increases, ramp, step, and pulse curing become
effective ways of reducing marginal openings and cuspal strain
from polymerization shrinkage

1. Polymerization Shrinkage
� Composite material shrink while hardening. This is referred to
as polymerisation shrinkage
� 1.67 to 5.68% of total volume
� Depends on the resin to filler ratio
� Ranges from 0.6-1.4% in composites with higher filler content
to 2-3% with lower filler content
� Tensile stresses of 130kg/cm2

� The defects produced by polymerization contraction are
the following:
• Open margins and white lines around margins.
• Debonding and open margins.
• Enamel cracking, especially when using strong
bonding agents and acid-etching techniques.
• Cuspal deflection, especially in well bonded
restorations.
• Marginal staining.
• Secondary caries, especially in patients using a lot of
sugar

To compensate the polymerization shrinkage
� Improving placement techniques
� Soft Start polymerization
� Stress breaking liner

� Clinical techniques to reduce polymerization shrinkage
include:
◦ Ramped curing
◦ Soft start
◦ Delayed curing
◦ Fabricating and curing the restoration extraorally on cast
thereby completing the polymerization before cementing

2. Linear Coefficient of Thermal Expansion:
� Coefficient of thermal expansion (LCTE) is the rate of
dimensional change of a material per unit change in
temperature.
� The LCTE for composites (28 to 45 ppm/°C) may be almost
three to four times greater than that for tooth structure.
� Matching thermal expansion coefficients between restoration
and tooth is a desirable quality. Teeth and restorations expand
and contract at different rates when patients eat or drink hot
and cold foods.

⮚The larger the mismatch between the thermal expansion
coefficient, the greater the likelihood of fluid percolation
down the margins. Leakage may result in marginal
staining or caries.
⮚The thermal conductivity should be low to reduce
transfer of excessive thermal stimuli to the pulp.

3.Water Absorption:
� All of the available tooth-colored materials exhibit some water
absorption.
� swells the polymer portion of the composite and promotes
diffusion and desorption of any unbound monomer.

� Water and other small molecules can plasticize the
composite and chemically degrade the matrix into monomer
or other derivatives.
� Materials with higher filler contents exhibit lower water
absorption values.

4. Wear resistance
� Wear resistance of composite materials is generally good.
While not yet as resistant as amalgam, the difference is
becoming smaller.
� Several mechanisms of wear are hypothesized on the basis
of clinical information for CFA wear on relatively small
posterior occlusal restorations.

The Hydrolysis theory
� The silane bond between the resin matrix and filler particle is
hydrolytically unstable and becomes debonded.
The Microfracture theory
� High modulus filler particles are compressed onto the adjacent
matrix during occlusal loading and this creates microfractures
in the weaker matrix.

The chemical degradation theory
� Materials from food and saliva are absorbed into the matrix,
causing matrix degradation and sloughing from the surface.
The protection theory
� The weak matrix is eroded between the particles.

� If the tooth preparation is narrow, then composites can be used
with little concern about wear.
� If the tooth preparation is wide, and/or is located in a molar
tooth (which is most frequently involved in masticating the
food bolus).
� Posterior composite wear 0.1 to 0.2 mm over 10 yr.

5. Flexural strength:
� Hybrid 80-160MPa
� Microfilled 60-120 Mpa
� Nanohybrids 180 Mpa
� Amalgam 90-130 Mpa
6. Compressive strength:
� Hybrid 240-290 MPa
� Microfilled 240-300 Mpa
� Nanohybrids 460 Mpa
� Amalgam 510 Mpa

7. Hardness:
� Determines the degree of deformation of a material
� Lower hardness than enamel and it depends on the amount and
type of filler used.
� Hybrid—60-117 KHN
� Microfilled– 22-80 KHN
� Amalgam—110KHN

8. Dimensional stability:
� Water absorption leads to a slow expansion—hygroscopic
expansion
� Starts 15 minutes after polymerization reaches equilibrium in
about 7 days

9. Surface Texture:
� The size and composition of the filler particles primarily
determine the smoothness of a restoration, as does the
material's ability to be finished and polished.
� Microfilled composites offer the smoothest restorative
surface, hybrid composites also provide surface textures that
are both esthetic and compatible with soft tissues.

10. Radiopacity:
� Most composites contain radiopaque fillers, heavy metal
atoms such as barium glass, to make the material radiopaque.
� Barium,zinc, boron ,zirconium,and yttrium ions are used

11. Biocompatibility:
� Concerns about biocompatibility of restorative materials relate
to effect on pulp from two aspects
1) the inherent chemical toxicity of the material
2) marginal leakage of oral fluids
a) Inadequately cured composite materials can release
leachable constituents adjacent to the pulp.
From long-term clinical studies there is no evidence of
any clinical problems resulting in pulp death or soft
tissue changes with the use of composite

b. Second biological concern is associated with the
shrinkage of the composite during polymerization and
marginal leakage.
Marginal leakage---bacterial ingrowth –secondary caries
or pulpal reactions.

c. Bisphenol A (BPA), a precursor of bis-GMA has been
shown to be xenooestrogen or a synthetic compound found
in the environment that mimics the effects of estrogen by
having affinity for oestrogen receptors.
� Although its effect on human being is unclear. Testicular
cancer, decreased sperm count have been seen as result to
exposure to Endocrine distributing chemicals.
� More recent studies have shown that BPA-DM should be
restricted for use in resin-based composites due to its potent
oestrogenic effect. However effect of BPA is negligible.

d. More cytotoxic than amalgam in vitro studies.
d. Have been shown to cause immunosuppression or
immunostimulation and to inhibit DNA and RNA synthesis

Traditional Composites(1970s)
� Conventional composites/macrofilled composite
� Contain approximately 75% to 80% inorganic filler by
weight.
� The average particle size of conventional composites in the
1980s was approximately 8 µm-12µm particles as large as
50 µm.
� Brand Name-Adaptic
� Filler-Ground amorphous silica and Quartz.
●70 to 80 wt% or 60 to 70 vol%

Properties
� >Hardness
� More resistant to abrasion
� Radiolucent

Clinical Consideration
� Rough surface during abrasive wear of soft resin matrix.
Before and After polishing

Microfilled Composites.
� In the late 1970s the microfilled, or "polishable," composites
were introduced.
� These materials were designed to replace the rough surface
characteristic of conventional composites with a smooth lustrous
surface similar to tooth enamel.
� Particle size are approx 0.04-0.4µm in size.

� Colloidal silica used as a filler.
� 50 wt %
� Brand Name-Heliomolar
Heloimolar HB
Gradio Direct Posterior

Microfillers are made from a
silicon dioxide smoke
or ash, called fumed silica
(commercially known asAirosil,
Degussa Corp., Ridgefield Park,
New Jersey) or by adding colloidal
particles of sodium silicate
to water and hydrochloric acid,
which produces
colloidal silica.

� In heterogeneous materials, the microfiller is compressed into
clumps by sintering, precipitation, condensation, or
silanization.
� The fumed silica resin is added to a heated resin at a
filler loading of approximately 70% by weight, more than
twice what is normally possible

� These filler particles, called pre polymerized resin fillers, are
then added to a non polymerized resin.
� Silica in cluster or agglomerate form, referred as homogenous
microfilled composites.

Properties
� Physical and mechanical properties are inferior to those of
traditional composite.
� Resin -40 to 80 vol% of restorative material
So, greater water absorption, higher coefficient of thermal
expansion, decreased elastic modulous

� In Class II and IV –potential for fracture
� Smooth surface-resin of choice for aesthetic restoration of
anterior teeth in cases Class III and Class V.

Hybrid Composites (end of 20th century)
� In an effort to combine the favorable physical and
mechanical properties characteristic of conventional
composites with the smooth surface typical of the
microfilled composites, the hybrid composites were
developed.
� 2 kinds of filler
◦ colloidal silica (10 to 20 wt.%)—0.04µm
◦ Ground particles of Glasses (0.4 to 1 µm) containing
heavy metals

� Filler Content- 75 to 80 wt %
� Brand Name-
◦ Herculite
◦ Aelite CS Posterior
◦ Prisma APH
◦ P-50

Properties
� Physical and mechanical properties range between traditional
and SPF composites.
� Superior to microfilled composite.
� Radioapoque (Filler – metal atoms)

� Due to their surface smoothness and reasonably good strength
widely used for anterior restoration including class IV sites.
� Also employed for stress bearing posterior restorations

Flowable Composites
� Flowable composites have lower filler content
� Modification of SPF and Hybrid composites
� Filler content—40-60 wt.%
� Ist Generation-Materials with lower filler content
� 2nd Generation-Materials with higher filler content

Properties
� Consequently inferior physical properties, such as lower wear
resistance and strength, when compared to more heavily filled
composites.
� Half stiffness of regular hybrids
� Greater polymerization shrinkage(3-5%)

� Use to form well adapted cavity base or liner especially in
Class II posterior
� Class V restorations and cervical lesions in gingival areas
� Pits and fissure sealants

Packable Composites For Posterior Restoration
(late 1990s)
• Also Called as Condensable Composite
• Packable composites are designed to be inherently more
viscous to afford a "feel’’ upon insertion, similar to that of
amalgam.
• Because of increased viscosity and resistance to packing,
some lateral displacement of the matrix band is possible.

� The packable /condensable characteristics derive from
inclusion of elongated, fibrous, filler particles of about 100µm
in length and or textured surfaces that tend to interlock and
resist flow.
� This causes uncured resin to be stiff and resistant to slumping,
yet moldable under the force of amalgam –condensing
instruments.

� Twice the time required for amalgam placement is still
required.
� Despite manufacturers’ claims to contrary, packable
composite have not yet proven to be answer to the general
need for highly wear-resistant, easily placeable posterior
resins, low shrinkage and depth of cure greater than 2mm.
Indications:
� Class I and II cavities

Nanofilled Composite
� Contain filler particles extremely small .005-.01 micrometer.
� Nanoscientists have successfully manufactured
nonagglomerated discrete nanoparticles that are
homogeneously distributed in resin or coating to produce
nanocomposite.
� (Feltech O Universal Restorative).

� These products have superior strength, hardness, esthetic
appeal, excellent color density and high polish retention.
� When inorganic phases in an organic/inorganic composite
become nanosized, they are called nanocomposites.

� In mechanical terms, nanocomposites differ from
composite materials due to the exceptionally high surface to
volume ratio of the reinforcing phase and/or its exceptionally
high aspect ratio.

Nano-hybrid Composites
� Nano-hybrid composites are the newest addition to the
pantheon of composite filling materials.
� They are becoming popular, because they have superior
esthetic and wear characteristics, high polishability, and
superior handling characteristics.
� They are marketed as universal composites.
� Though nanocomposites have improved polishability,
nanohybrids are stronger than nanocomposites.

These composites have three types of filler particles.
1. Prepolymerized, finely milled, agglomerated nano-clusters-
modified silica particles
2. Larger, submicron-sized glass or silica particles in the range
of 0.4 micron.
3. Individual nano-sized particles, approximately 0.05 micron.
Disadvantage
� Not as esthetic as nanocomposite

Fiber Reinforced system
� The main advantage of fibers is that they have
excellent strength. Unfortunately, it is difficult to
efficiently pack the fibers or orient their direction.
� Fibres such as carbon, glass and polyethylene are
incorporated and are in u shaped.
� Small additions of fibers to regular fillers are effective
in improving properties. The limiting factor is that
fibers only may be used with dimensions greater than 1
µm because of the concerns for carcinogenicity of
submicron fibers such as asbestos.

Contraindications
� If the operating site cannot be isolated from contamination by
oral fluids, composite (or any other bonded material) should
not be used.
� If all of the occlusion will be on the restorative material,
composite may again not be the choice for use.

Advantages of composite resin
1. Esthetic
2. Conservative of tooth structure removal (less extension;
uniform depth not necessary; mechanical retention
usually not necessary)
3. Less complex when preparing the tooth
4. Insulative, having low thermal conductivity
5. Used almost universally
6. Bonded to tooth structure, resulting in good retention, low
microleakage, minimal interfacial staining, and increased
strength of remaining tooth structure
7. Repairable

Disadvantages of composite resin
1. May have a gap formation, usually occurring on root surfaces
as a result of the forces of polymerization shrinkage of the
composite material being greater than the initial early bond
strength of the material to dentin

2. Are more difficult, time-consuming, and costly (compared to
amalgam restorations) because:
• Tooth treatment usually requires multiple steps.
• Insertion is more difficult.
• Establishing proximal contacts, axial contours, embrasures,
and occlusal contacts may be more difficult.
• Finishing and polishing procedures are more difficult.

3. Are more technique sensitive because the operating site must
be appropriately isolated and the placement
� Of etchant, primer, and adhesive on the tooth structure
(enamel and dentin) is very demanding of proper technique
4. May exhibit greater occlusal wear in areas of high occlusal
stress or when all of the tooth's occlusal contacts are on the
composite material.
5. Have a higher linear coefficient of thermal expansion,
resulting in potential marginal percolation if an inadequate
bonding technique is utilized

� Adhesion, or bonding, is the joining together of two objects,
by means of a glue or cement
� True adhesion involves chemical bonds between the materials
being joined
� Dental adhesives are commonly used to form a thin layer
between tooth substance and a restorative material
Adhesion to tooth structure

� Acid selectively dissolves the tooth structure to provide
retention for the restoration
� Also known as conditioners
� 37% phosphoric acid
Conditioning/Etching

• Conditioning of dentine is done:-
1. To remove the smear layer
2. To demineralise the peritubular and intertubular
dentine partially to enhance the bonding
• The different conditioner used in dentistry are 10% maleic
acid, citric acid, EDTA, polyacrylic acid etc
• Supplied in clear or colored gel / liquid or in syringe form

Smear layer:
� This are debris of mineralized collagen matrix
� Consists of inorganic material such as tooth structure such as
enamel and dentine debris
� Organic materials such as coagulated proteins, saliva, blood
cells and microorganisms

Etching of enamel:
� Increases the surface area
� Etched enamel has high surface energy—allows the resin to
wet the tooth surface better and penetrate into micro porosities
—when polymerised forms resin tags—forms mechanical
bond to the enamel
� Creates microporosities by discrete etching the enamel

Types of etching pattern:
� Type I.
Partial demineralisation of enamel rods
� Type II
Partial demineralistion of interrod substance
� Type III
A combination of the above

Type I etching pattern
Type II etching pattern
Type III etching pattern

Etching the dentin:
� Removes the smear layer and partially opens the dentinal
tubules
� Provides modest etching of the intertubular dentin

1. Surface of the tooth is cleaned with pumice
2. The surface is etched with 37% phosphoric acid for 15 secs
3. The acid is thoroughly washed with stream of water for 15
sec and air dried.
4. A frosty white appearance is seen in enamel indicating a
proper etching
5. Bonding agent is applied over the tooth surface and cured
for at least 20 secs
6. The composite is then placed in increments
Bonding of composite resin with enamel

1. Conditioning of the dentine with a mild acid for 15 secs
2. The etchant is removed by rinsing
3. The surface is dried not dessicated using cotton pelledget
4. Application of primer and (dentine bonding agent) from
1-6 coats followed by curing for 20secs
5. Application of dentine adhesive and cured for 20 secs
6. Placement of composite
Bonding of composite resin with dentin

� Primers contain hydrophilic monomers dissolved in solvents
such as acetone, ethanol or water which are able to
penentrate the etched dentine and infiltrate the collagen
mesh to form the hybrid layer
� It has both hydrophillic component as well as hydrophobic
component.
� The hydrophilic component is required to wet the moist
conditioned dentine and the hydrophobic group to ensure
bonding with restorative material
Primers

� They are HEMA( 2 hydroxyethyl methacrylate) and 4
META( 4- metha cryloxyethyl trimellitate anhydride
dissoved in acetone or ethanol.
1. Use of primer increases wettability of the dentin surface
1. Increases the bonding between resin and tooth structure

� The adhesive resins is a low viscosity unfilled resin or
sometimes semifilled resin which flow easily and
combines with the primer to form a RESIN REINFORCED
HYBRID LAYER AND RESIN TAGS
� Ideally the bonding agents should be hydrophilic to displace
water and there by wet the surface—penetrate into the
porosities in dentin and react with the organic / inorganic
components
� Should contain both hydrophilic and hyrophobic parts
Dental Adhesives

Composition
� Bonding agents are often methacrylates with some volatile
carrier and solvent like acetone.
� They also contain some diluent monomers, most typically
HEMA and TEGDMA, but occasionally UDMA.

Bonding systems
� Modern dental bonding systems come either
a. as a “three-step system”, where the etchant, primer, and
adhesive are applied sequentially;
a. as a “two-step system”, where the etchant and the primer are
combined for simultaneous application;
a. as a “one-step system”, where all the components should be
premixed and applied in a single application.

First generation dental adhesive
� Silane coupling agents were used
� contain acidic group to react with the mineral portion
specifically the calcium in hydroxyappetite
� The first marketed product contain glycophospheric acid
dimethacrylacate
� High polymerization shrinkage
� High coefficient of thermal expansion

� Introduced in late 1960s early 1970s
� it was an attempted to bond chemically to either inorganic or
organic components of dentin
� But they produced only limited bond strength (5-6 mpa).
� Materials tried were:- halogen phosphoric acid esters of Bis-
GMA, NPG-GMA, PHENYL-P
Second generation:-

� Third generation attempted to deal with smear layer and dentinal
fluid
� They employed two approaches:-
Modification of smear layer to improve its property
Or
Removal of smear layer without disturbing smear plugs that
occlude the dentinal tubules.
� The idea was to avoid aggressive etching of dentin because it
cause pulpitis
Third generation (1990s):-

Third generation used acids like:-
⮚ 2% nitric acid
⮚ 2.5% maleic acid with HEMA
⮚ 10% citric acid with 3% ferric chloride
⮚ 10% phosphoric acid
⮚ Generally include 4 steps:
1. Application of dentine conditioner
2. Application of primer(DBA)
3. Application of adhesive( unfilled resin)
4. Placement of resin based composite

� Developed in 1990s and was available in multiple bottles
� Etching with phosphoric acid required
� Light and dual cured formulations are available.
� ETCHANT:- Phosphoric acid, citric acid/ calcium chloride,
oxalic acid/ aluminum nitrate.
� PRIMER:- NTG-GMA/BPDM,HEMA/GPDM,4META
� ADHESIVES:- Bis-GMA,TEGMA
� SOLVENT:- acetone, ethanol/water.
Fourth generation:-

� 4th generation dentin bonding agents are based on total
removal of smear layer and plugs
� Resin tags were produced in dentinal tubules and these
extension into dentin contributed to the retention of restorative
resin
� This is called the total etch technique
� To the date most widely used bonding system

Hybrid layer:
� Infiltration of adhesive monomers into the filigree of collagen
fibers
� Penetration of adhesive monomers into micro- and macro
porosities and subsequent polymerization
� Resin infiltrated/reinforced layer or hybrid layer at the
interface between dentine and resin

� These are simplified version of fourth generation
� In fifth generation bonding agents, primer and adhesives are in
same bottle.
� Etching and rinsing are required
� ETCHANT:- Phosphoric acid,
� PRIMER:- PENTA, Methacrylated phosphonates
� SOLVENT:- acetone, ethanol/water.
� These agents are inferior to fourth generation bonding agents
in terms of bond strength.
Fifth generation:-

� These includes self etching primers where the etchant and
primer are in one bottle and adhesive resin in another bottle.
� Manipulation is easy, show good bond strength to dentin but
not to enamel
� Etching and rinsing not required
� Primer applied first then adhesive.
� ACIDIC PRIMER ADHESIVE:- Methacrylated phosphates
� SOLVENT:- Water
Sixth generation(mid 1990s):-

� One bottle- no mixing required.
� Etching and rinsing not required
� Light cured formulation
� Useful for direct applications with light cured restorative
material.
� ACIDIC PRIMER ADHESIVE:- Methacrylated phosphates
� SOLVENT:- Water
Seventh generation(early 2000s):-

Ideal requirements of dentin bonding agents:
� High bond strength to dentin .
� Provide bond strength to dentin similar to that of enamel.
� Biocompatibility to dental tissue including the pulp.
� Minimize microleakage at the margins of the restorations.
� Prevent recurrent caries and marginal staining.
� Easy to use and minimally technique sensitive.
� Good shelf life.
� Be compatible with a wide range of resins.
� Non toxic and non sensitizing to the operators or patients.
� Bonding agents should seal the tooth surfaces from oral
fluids.

� Best done after 24 hours
� Can be started 15 minutes after curing
� Initial contouring done with knife or diamond stone
� Final with rubber impregnated abrasives or rubber cups with
polishing pastes or aluminium oxide disks.
Finishing and polishing:

Conclusion
� It is apparent that current composites have
significantly improved clinical performance
compared with their predecessors, especially in
posterior teeth and in stress bearing areas on
anterior teeth.
� Nowadays, composites have unquestionably
acquired a prominent place among the filling
materials employed in direct techniques.

� Their considerable esthetic possibilities give rise to
variety of indications and on the other hand it also
conserve tooth structure.
� Nonetheless, it should not be forgotten that they are
highly technique-sensitive, hence the need to apply
with high cautions.

References
� Sturdevant’s Art and Science of operative dentistry
� Phillips
� Marzouk
� Tooth coloured Restoratives by Harry.F.Albers

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