Composites /certified fixed orthodontic courses by Indian dental academy

COMPOSITES

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION:
An era in dental restorative materials began in
1955, when Buonocore found that acrylic resin formed
acceptable

micromechanical

adhesion

with

dry

enamel that had been etched with phosphoric acid.
Many generations of restorative materials have
existed in the last five decades, and the modern
clinician may be overwhelmed when attempting to
make decisions as which material or technique must
be most appropriate in varying clinical situations.

When the best course of treatment, many factors
must be considered. These include the mechanics
of tooth preparation, including Black’s principles, the
physical properties of materials, esthetics of and
functional demands on the completed restoration,
and factors such as patient health, oral hygiene,
diet, quality and quantity of saliva and motivation.
In the current age of adhesive dentistry or
microdentistry, conservation of tooth structure is
paramount. Rather than using extension for
prevention as a treatment guideline, emphasis is
now placed on restriction with conviction. The
advent of composite resin restorative materials has
led the way towards achieving this goal

DEFINITION:

Oxford dictionary – Composite n. a thing made
up of several parts
Origin Latin componere ‘put together’
 Skinner:
Skinner defined the composite “as a
compound of two or more distinctly different materials
with properties that are superior to or intermediate to
those of individual constituents.
 Philips and lutz: Resin based restorative materials
are defined as 3 dimensional combinations of at least
two chemically different materials with a distinct
interface.
 John F. Mc Cabe:
A composite materials is a
product, which consists of at least two distinct phases
normally formed by blending together components
having different structures and properties.

Karl Leinfelder:
The term “composite” originated in the field of
material science. From a physical or mechanical
point of view a composite is a material consisting of
two or more components that are chemically bonded
together to provide overall properties superior to
those of either constituent. The number of natural
and man made composites is unlimited. Bone, which
is an example of a natural composite consists of
collagen and calcium appetite. The Collagen
component is soft but strong. Calcium appetite on
the other hand is hard and brittle. As a composite
bone can withstand many types of mechanical
stresses. Fibre glass is an example of man made
composite of Glass fibres in a resin matrix.

Mosby’s dental dictionary :
Defines a dental composite a resin used for
restorative purposes and usually formed by reaction
of an ether of Bisphenol-A (an epoxy molecule ) with
acrylic resin monomers , initiated by a benzoyl
peroxideamine system , to which is added as much
as 75% inorganic filler ( Glass beads or rods , lithium
aluminium silicate , quartz and tricalcium phosphate)

HISTORY:
Tooth coloured restorative materials have
increasingly been used to replace missing tooth
structure and to modify tooth colour and contour, thus
enhancing facial esthetics. During the first half of the
20th century, silicates were the only tooth coloured
esthetic materials available. Although silicates release
fluoride, they are no longer used to restore permanent
teeth because they severely Erode and discolour
within a few years (<2yrs ). Acrylic resins similar to
those used for custom impression trays and dentures
(PMMA based ) replaced the silicates during late
1940’s because of their tooth like appearance,
insolubility in oral fluids, ease of manipulation and low
cost.

Unfortunately, these acrylic resins also have poor
wear resistance and they shrink severely during
curing, which causes them to pull away from the cavity
walls and produce leakage along margins. Their
excessive thermal expansion and contraction cause
further stresses to develop at the cavity margins when
hot or cold beverages and foods are consumed.
These problems were overcome by the introduction of
composites by addingan inert filler to the unfilled
acrylic resins. In 1955, MICHAEL BUANOCORE
introduced the concept of bonding acrylic to teeth by
acid etching.

In 1962, Dr.RAPHAEL BOWEN of ADA research
unit at the national Bureau of standards began
experiments on reinforcing epoxy resin with filler
particles.deficiencies in epoxy resin such as slow
cure and tendency to discolour stimulated him to
work on combining the advantages of epoxy resin
and acrylates i.e. the reaction product of bisphenol A
and a glycidyl methacrylate, which has been
abbreviated as Bis-GMA.These two discoveries
revolutionized the application of composites in
restorative dentistry.


COMPOSITION:
These are the structural components in dental resinbased composites:
Matrix – A plastic resin material that forms a
continuous phase and binds the filler particles.
Filler – reinforcing particles and / or fibres that are
dispersed in the matrix.
Coupling agent – bonding agent that promotes
adhesion between filler and resin matrix.

Composites contain other components in addition
to these primary constituents.
An activator-initiator system required to convert
resin paste from a soft moldable filling material to
a hard durable restoration.
Pigments-help to match colour of tooth structure.
Ultra violet (UV) absorbers and other additives
improve colour stability.
Polymerization inhibitors extend storage life and
provide increased working time for chemically
activated resins.

RESIN MATRIX: (continuous phase)
Most dental composites use a blend of aromatic
and/or aliphatic dimethacrylate monomers such as
Bis-GMA, one of the most widely used ingredients,
Triethylene gycol dimethacrylate (TEGDMA) and
Urethane dimethacrylate (UDMA). UDMA, Bis-GMA,
and TEGDMA are widely used resin matrix ingredients
that form highly cross-linked polymer structures in
composites and sealant materials.

Because Bis-GMA and UDMA have almost
five times the molecular weight of methyl
methacrylate,

the

density

of

methacrylate

double-bond groups is approximately one-fifth as
high

in

these

monomers,

which

reduces

polymerization shrinkage proportionately. The
use of a dimethacrylate also results in extensive
cross-linking, which increases the strength and
rigidity of the polymer.

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FILLER PARTICLES:
(dispersed phase)
The primary purposes of filler particles are to
strengthen a composite and to reduce the amount of
matrix material.
Several important properties of dental composites are
improved by increased filler “loading” (volume
fraction):
Reinforcement of the matrix resin, resulting in
increased hardness, strength, and decreased wear;
reduction in polymerization shrinkage;
reduction in thermal expansion and contraction;
improved workability by increasing viscosity (liquid
monomer plus filler yields a paste consistency);

reduction in water sorption, softening, and staining;
and increased radiopacity and diagnostic sensitivity
through the incorporation of strontium (Sr) and barium
(Ba) glass and other heavy compounds that absorb xrays.
Filler particles are most commonly produced by
grinding or milling quartz or glasses to produce
particles ranging in size from 0.1 to 100μm.
Submicron silica particles of colloidal size (~0.04μm),
referred to collectively as microfiller or individually as
microfillers, are obtained by a pyrolytic or precipitation
process.

In these processes, a silicon compound (e.g,SiCl4)
is burned in an O2 and H2 atmosphere to form
macromolecule
chains
of
SiO2.
These
macromolecules are of a colloidal size and constitute
the inorganic filler particles. Composites are classified
on the basis of the average size of the major filler
component. In addition to filler volume level, other
important factors that determine the properties and the
clinical application of the resultant composites include
the filler size, size distribution, index of refraction,
radiopacity, and hardness of the filler.
Quartz has been used extensively as a reinforcing
filler, particularly in the early versions of dental
composites. It has the advantage of being chemically
inert and yet also very hard, making it abrasive as well
as difficult to grind into very fine particles.

However, this hardness also makes quartz
composites difficult to polish and potentially
abrasive to opposing teeth or restorations. Socalled

amorphous

silica

has

the

same

composition and refractive index as quartz, but it
is not crystalline and not as hard, thus greatly
reducing the abrasiveness of the composite
surface structure.

Types of fillers used 

Quartz



Fused silica



Aluminum silicates



Barium glasses



Boro silicates



Glasses



Lithium aluminum silicate, pyrogenic silica



The latest filler used is zirconium



Zinc and yttrium glasses



Hydroxyapatite


COUPLING AGENTS: (interfacial phase)
It is essential that filler particles be bonded to the
resin matrix.This allows the more flexible polymer
matrix to transfer stresses to thehigher modulus
(more rigid and stiffer) filler particles. The bond
between the two phases of the composite is
provided by a coupling agent. A properly applied
coupling agent can impart improved physical and
mechanical properties and inhibit leaching by
preventing water from penetrating along the fillerresin interface.


Although titanates and zirconates can be used
as

coupling

agents,organosilanes

such

as

γ-

methacryloxypropyl trimethoxysilane are used most
commonly. In the presence of water, the methoxy
groups (-OCH3)are hydrolyzed to silanol (-Si-OH)
groups that can bond with other silanols on the filler
surfaces by formation of a siloxane bond (Si-O-Si).
The

organosilane

methacrylate

groups

form

covalent bonds with the resin when it is polymerized,
thereby completing the coupling process.

ACTIVATOR-INITIATOR SYSTEM:
Both monomethacrylate and dimethacrylate
monomers
polymerization

polymerize

by

mechanism

the

initiated

addition
by

free

radicals. The free radicals can be generated by
chemical activation or by external energy activation
(heat, light, or microwave).

CHEMICALLY ACTIVATED RESINS:
Chemically activated products are supplied as
two pastes, one of which contains the benzoyl
peroxide (BP) initiator and the other an aromatic
tertiary amine activator (e.g, N, N-dimethyl-ρtoluidine).When the two pastes are mixed together,
the amine reacts with the BP to form free radicals,
and additional polymerization is initiated. Today,
these materials are mainly used for restorations and
large foundation structures (buildups) that are not
readily cured with a light source.

LIGHT-ACTIVATED RESINS:
Light-curable dental composites are supplied as
a single paste contained in a light-proof syringe. The
free radical initiating system, consisting of a
photosensitizer and an amine initiator, is contained
in this paste. As long as these two components are
not exposed to light, they do not interact. However,
exposure to light in the blue region (wavelength of
~468nm)

produces

an

excited

state

of

the

photosensitizer, which then interacts with the amine
to

form

free

radicals

that


initiate

addition

Camphorquinone (CQ) is a commonly used
photosensitizer

that

absorbs

blue

light

with

wavelengths between 400 and 500nm. Only small
quantities of CQ are required (0.2 wt% or less in the
paste). A number of amine initiators are suitable for
interaction with CQ, such as dimethylaminoethyl
methacrylate (DMAEMA), which is also present at
low levels, that is approximately 0.15 wt%.

INHIBITORS:
Inhibitors are added to the resin system to
minimize or prevent spontaneous or accidental
polymerization of monomers. Inhibitors have a strong
reactivity potential with free radicals. If a free radical
is formed, for example, by brief exposure to room
lighting when the material is dispensed, the inhibitor
reacts with the free radical faster than the free
radical can react with the monomer.

This prevents chain propagation by terminating
the reaction before the free radical is able to initiate
polymerization.

After

all

of

the

inhibitor

is

consumed, chain propagation begins. A typical
inhibitor is butylated hydroxytoluene (BHT), which is
used in concentrations on the order of 0.01 wt%.
Thus inhibitors have two functions: they extend the
storage lifetime for all resins and they ensure
sufficient working time.

DUAL-CURE RESINS:
One way to overcome limits on curing depth and
some of the other problemsassociated with light curing
is to combine chemical curing and visible-light curing
components in the same resin. So-called dual-cure
resins are commercially available and consist of two
light-curable pastes, one containing benzoyl peroxide
(BP) and the other containing an aromatic tertiary
amine. When these two pastes are mixed and then
exposed to light, light curing is promoted by the
amine/CQ combination and chemical curing is
promoted by the amine/BP interaction. Dual-cure
materials are intended for any situation that does not
allow sufficient light penetration to produce adequate
monomer conversion, for example, cementation of
bulky ceramic inlays.

Curing lamps
Most curing lamps are hand held devices that
contain the light source and are equipped with a
relatively short, rigid light guide made up of fused
optical fibres.Four types of lamps may be used for
photoinitiation process.
QTH lamps. QTH lamps have a quartz bulb with
a tungsten filament that irradiates both UV and white
light that must be filtered to remove heat and all
wavelengths except those in the violet blue range
(~450to500 nm).the intensity of the bulb diminishes
with use, so a calibration meter is required to
measure the output intensity.





LED lamps. Using a solid-state ,electronic
process, these light sources emit radiation only in
the blue part of the visible spectrum between 440
and 480 nm,and they do not require filters.LEDs
require low wattage ,can be battery powered
,generate no heat ,and are quiet because a cooling
fan is not needed.Althougfh they produce the
lowest intensity radiation, new technology is rapidly
overcoming this limitation.
PAC lamps. They are high intensity light curing
units. PAC lamps use xenon gas that is ionized to
produce a plasma . the high intensity light is filtered
to remove heat and to allow blue light
(~400to500nm)to be emitted.
Argon laser lamps. Argon laser lamps have the
highest intensity and emit at a single wavelength.
lamps currently available emit ~490nm.

Precautions of using curing lamps
The light emitted by curing units can cause retinal
damage if a person looks directly at the beam for an
extended period of time or even for short periods in
case of lasers. To avoid such damage ,never look
directly into the light tip and minimize observation of
reflected

light

for

longer

periods.

Protective

eyeglasses and various types of shields that filter the
light are available for increased protection for both
clinical personnel and patients.

CLASSIFICATION OF COMPOSITES:
I. The commonly used is the simplest classification given
by Skinner:
Traditional or conventional composites
8-12 µ.m
Small particle filled composites
1-5 µ. m
Microfilled composites
0-04 –0.9 µ. m.
Hybrid composites
0.6-1 µ. m


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II Philips and Lutz classification:
According to the mean particles size of the major
fillers Traditional composite resins: (5.30 µ m earlier, 1.5µ
m current)
Hybrid composite resins: (1.5 µ m. earlier, 0.05-0.1µ
m. current)
Homogeneous microfilled composites: 0.05-0.1 µ.m
Heterogeneous micro filled composites: 0.05-01, 125 µ.m
III Classifications based on inorganic loading:
a. Heavy filled materials – 75% of inorganic loading
by wt.
b .Lightly filled material –66% of inorganic loading by
wt.

IV. Based on method of curing
1. Chemical cured
2. Light cured
3. Heat cured
4. Dual cured
V Classification based on area used
Anterior composites
Posterior composites

VI.GENERATIONS OF COMPOSITE
RESTORATION (Marzouk)
A. First Generation composites
Consist of macro-ceramic reinforcing phase.
Has good mechanical properties.
Highest surface roughness
B. Second Generation composites
Consists of colloidal and micro-ceramic silica.
Low strength
Unfavourable coefficient of thermal expansion
Wear resistance better than first generation
Best surface texture.



C. Third Generation composites
Hybrid composite [combination of macro and
micro (colloidal) ceramics]
Ratio of75:25
Good surface smoothness and reasonable
strength
D. Fourth Generation composites
Hybrid composite (heat-cured, irregularly
shaped, highly reinforced composite macroparticles with micro (colloidal) ceramics].
Comparatively better surface characteristics and
mechanical properties

E. Fifth Generation composites
Hybrid composite (heat-cured, spherical, highly
reinforced composite macro. particles with micro
(colloidal) ceramics].
Improved workability
Surface texture and wear is similar to second
generation composites
Physical and mechanical properties similar to fourth
generation composites
F. Sixth Generation composites
Hybrid composite [agglomerates of sintered micro
(colloidal) ceramics and
micro-ceramics]
Highest percentage of reinforcing particles
Best mechanical properties
Wear and surface texture similar to fourth generation
Least polymerization shrinkage

VII. Classification according to Bayne and
Heyman:

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Category
Megafill
Macrofill
Midifill
Minifill
Microfill
Nanofill

Particle size
- 1-2 mm
- 10-100 µ.m
- 1-10 µ.m
- .01-.1µ. m.
- 0.04-0.4
- .005-.01 µ.m.


Traditional Composites
The traditional composites have comparatively large
filler particles. This category was developed during the
1970s and modified slightly over the years. These
composites are also referred to as conventional or
macrofilled composites. Because these materials are
no longer widely used, the term traditional is more
meaningful than is conventional. The most commonly
used filler for these materials is finely ground
amorphous silica and quartz. Although the average
size is 8 to 12 μm, particles as large as 50 μm may
also be present. Filler loading generally is 70 to 80 wt
% or 60 to 70 vol% exposed filler particles, some quite
large, are surrounded by appreciable amounts of the
resin matrix.

A major clinical disadvantage of traditional
composites is the rough surface that develops
during abrasive were of the soft resin matrix,
thus exposing the more wear resistant filler
particles, which protrude from the surface.
Finishing of the restoration produces a
roughened surface, as does tooth brushing and
masticatory wear over time. These restorations
also tend toward discoloration, undoubtedly
caused in part by the susceptibility of the rough
textured surface to retain stain.

Small-Particle-Filled Composites
To improve surface smoothness and retain or
improve the physical and mechanical properties
of traditional composites, inorganic fillers are
ground to a size range of 0.5 to 3μm, but with
a fairly broad size range distribution. This broad
particle size distribution facilitates a high filler
loading, and small-particle-filled (SPF)
composites generally contain more inorganic
filler (80 to 90 wt% and 65 to 77 vol%) than
traditional composites. This is particularly true
for those composites designed for posterior
restorations.
This category of composite generally exhibits
superior physical and mechanical properties.

Microfilled Composites
The problems of surface roughening and low
translucency associated with traditional and
small particle composites can be over come
through the use of colloidal silica particles as
the inorganic filler. The individual particles are
approximately 0.04 μm (40 nm) in size. This
value is one tenth of the wavelength of visible
light and 200 to 300 times smaller than the
average particle in traditional composites. The
concept of the microfilled composite entails the
reinforcement of the resin by means of the filler;
yet these composites exhibit a smooth surface,
similar to that obtained with the unfilled direct
filling acrylic resins.

Hybrid Composites
This category of composite materials was developed in
an effort to obtain even better surface smoothness
than that provided by the small particle composites,
while still maintaining the desirable properties of the
latter. As the name implies, hybrid composites contain
two kinds of filler particles. Most modern hybrid fillers
consist of colloidal silica and ground particles of
glasses containing heavy metals, constituting a filler
content of approximately 75 to 80 wt%. The glasses
have an average particle size of about 0.4 to 1.0 μm.
Colloidal silica represents 10 to 20 wt% of the total
filler content. In this case, the microfillers also
contribute significantly to the properties.

The smaller filler particle size, as well as the
greater amount of micro fillers, increase the
surface area. Thus the overall filler loading is
not as high as it is for some of the SPF
composites.
Because of their surface smoothness and
reasonably good strength, these composites
are widely used for anterior restorations,
including Class IV sites. Although the
mechanical properties of hybrid composites
generally are somewhat inferior to those SPF
composites, the hybrid composites are widely
employed for stress bearing, posterior
restorations.

PHYSICAL PROPERTIES
Working and Setting times
For light cured composites, initiation of polymerization
is related specifically to the application of the light
beam to the material; about 75% of the
polymerization takes place during the first 10 minutes.
The curing reaction continues for a period of 24 hours.
Not all of the available unsaturated carbon double
bonds react; studies report that about 25% remain
unreacted in the bulk of the restorations. If the surface
of the restoration is not protected from air by a
transparent matrix, polymerization is inhibited, the
number of unreacted carbon double bonds may be as
high as 75% in the tacky surface layer. Although the
restoration can be finished with abrasives and is
functional after 10 minutes, the optimum physical
properties are not reached until about 24 hours after
the reaction is initiated.

For most composites that are initiated by visible light,
there is a critical time period after dispensing of the
paste onto a paper pad during which fresh composite
flows against tooth structure at an optimum level.
Within 60 to 90 seconds after exposure to ambient
light, the surface of the composite may lose its
capability to flow readily against tooth structure, and
further work with the material becomes difficult.
Florescent lights labeled “gold” can be substituted to
provide unlimited working time for light cured
composites.
The setting times for chemically activated composites
range from 3 to 5 minutes. These short setting times
have been accomplished by controlling the
concentration of initiator and accelerator.

Polymerization shrinkage
Free volumetric polymerization shrinkage is a direct function of
the amount of oligomer and diluent, and thus micro hybrid
composites shrink only 0.6% to 1.4%, compared with shrinkage
of microfilled composites of 2% to 3%. This shrinkage creates
polymerization stresses as high as 13 MPa between the
composite and tooth structure. These stresses severely strain
the interfacial bond between the composite and the tooth,
leading to a very small gap that can allow marginal leakage of
saliva. This stress can exceed the tensile strength of enamel
and result in stress cracking and enamel fractures along the
interfaces. The potential for this type of failure is even greater
with microfilled composites, in which there is a much higher
volume percent of polymer present, and polymerization
shrinkage is greater. The net effect of polymerization shrinkage
can be reduced by incrementally adding a light cured composite
and polymerizing each increment independently, which allows
for some contraction within each increment before successive
additions.

Thermal Properties
The thermal expansion coefficient of composites
ranges from 25 to 38 X 10-6/oC for composites with
fine particles to 55 to 68 x 10-6/o C for composites
with microfine particles.
Thermal stresses place an additional strain on the
bond to tooth structure, which further compounds the
detrimental effect of the polymerization shrinkage.
Thermal changes are also cyclic in nature, and
although the entire restoration may never reach
thermal equilibrium during the application of either hot
or cold stimuli, the cyclic effect can lead to material
fatigue and early bond failure. If a gap were formed,
the difference between the thermal coefficient of
expansion of composites and teeth could allow for the
percolation of oral fluids.

Water sorption
The water sorption of composites with fine
particles (0.3 to 0.6 mg/cm2) is greater than
that of composites with micro fine particles (1.2
to 2.2 mg/cm2), because of the lower volume
fraction of polymer in the composite with fine
particles. The quality and stability of the silane
coupling agent are important in minimizing the
deterioration of the bond between the filler and
polymer and the amount of water sorption. It
has been postulated that the corresponding
expansion associated with the uptake of water
from oral fluids could relieve polymerization
stresses.

Solubility
The water solubility of composites varies from
0.01 to 0.06 mg/cm2. Adequate exposure to the
light source is critical in light cured composites.
Inadequate polymerization can readily occur at
a depth from the surface if insufficient light
penetrates. Inadequately polymerized resin has
greater water sorption and solubility, possibility
manifested clinically with early color instability.


Color and Color stability
Change of color and loss of shade match with
surrounding tooth structure are reasons for replacing
restorations. 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. Discoloration can also occur by
oxidation and result from water exchange within the
polymer matrix and its interaction with unreacted
polymer sites and unused initiator or accelerator.
Color stability of current composites has been studied
by artificial aging in a weathering chamber (exposure
to UV light and elevated temperature of 70oC) and by
immersion in various stains (coffee/tea,
cranberry/grape juice, red wine, sesame oil).
Composites are resistant to color changes caused by
oxidation but are susceptible to staining.

Clinical Properties
Depth of Cure (light-cured Composites)
Maximum intensity of the light radiation beam is
concentrated near the surface of a light cured
composite. As the light penetrates the material, if is
scattered and reflected and loses intensity. A number
of factors influence the degree of polymerization at
given depths from the surface after light curing. The
concentration of photo-initiator or light absorber in the
composite must be such that it will react at the proper
wavelength and be present in sufficient concentration.
Both filler content and particle size are critical to
dispersion of the light beam. For this reason,
microfilled composites with smaller and more
numerous particles scatter more light than micro
hybrid composites with larger and fewer glass
particles. Longer exposure times are needed to obtain
adequate depth of cure of microfilled composites.

The light intensity at the resin surface is a critical
factor in completeness of cure at the surface and
within the material. The tip of the light source must be
held within 1 mm of the surface to gain optimum
penetration. More opaque shades reduce light
transmission and cure only to minimal depths (1
mmm). A standard exposure time using most visible
light is 20 seconds. In general, this is sufficient to cure
a light shade of resin to a depth of 2 or 2.5 mm. A 40
second exposure improves the degree of cure at all
depths, but it is required to obtain sufficient cure with
the darker shades. Application of the light beam
through 1 mm or less thickness of tooth structure
produces a sufficient cure at shallower depths, but the
hardness values obtained are not consistent.

Because the light beam does not spread
sufficiently beyond the diameter of the tip at the
emitting surface, it is necessary to “Step” the
light across the surface of large restorations so
that entire surface receives a complete
exposure. Larger tips have been manufactured
for placement on most light curing units
However, as the light beam is distributed over a
larger surface area, the intensity at a given
point is reduced. Use a longer exposure time
of up to 60 seconds when larger emitting tips
are used.

Radiopacity
Modern composites include glasses having
atoms with high atomic numbers, such as
barium, strontium, and zirconium. Some fillers,
such as quartiz, lithium-aluminum glasses, and
silica, are not radiopaque and must be blended
with other fillers to produce a radio opaque
composite. Even at their highest volume friction
of filler, the amount of radiopacity seen in
composites in noticeably less than the exhibited
by a metallic restorative like amalgam. The
microhybrid
composites
achieve
some
radiopacity by incorporating very finely divided
heavy metal glass particles.

Aluminum is used as a standard reference
for radiopacity. A 2 mm thickness of dentin is
equivalent in radio opacity to 2.5 mm of
aluminum, and enamel is equivalent to 4 mm of
aluminum. To be effective, a composite should
exceed the radio opacity of enamel, but
international standards accept radiopacity
equivalent to 2 mm of aluminum. Amalgam has
a radiopacity greater than 10 mm of aluminum,
which exceeds all the composite material
available.

Wear Rates
One problem with composites is the loss of
surface contour of composite restorations in the
mouth, which results from a combination of
abrasive wear from chewing and toothbrushing
and erosive wear from degradation of the
composite in the oral environment.
Wear of posterior composite restorations is
observed at the contact area, where stresses
are the highest. Interproximal wear has also
been observed.

Ditching at the margins within the composite
is observed for posterior composites, probably
resulting
from
inadequate
bonding
and
polymerization stresses.
Currently accepted
composites for posterior applications require
clinical studies that demonstrate, over a 5 year
period, a loss of surface contour less than 250 μm
or an average of 50 μm per year of clinical service.
Products developed as packable or laboratory
composites usually have better wear resistance
than micro filled or flowable composites

Biocompatibility of Composites
The chemical insult to the pulp from composites
is possible if components leach out or diffuse
from the material and subsequently reach the
pulp. Adequately polymerized composites are
relatively biocompatible because they exhibit
minimal solubility, and unreacted species are
leached in very small quantities. From a
toxicological point of view, these amounts
should be too small to cause toxic reactions.
However, from an immunological point of view,
under extremely rare conditions, some patients
and dental personnel can develop an allergic
response to these materials.

Inadequately cured composite materials at
the floor of a cavity can serve as a reservoir of
diffusible components that can induce long
term pulp inflammation. This situations is of
particular concern for light activated materials.
If a clinician attempts to polymerize too thick a
layer of resin or if the exposure time to the light
is inadequate (as discussed previously), the
uncured or poorly cured material can release
leachable constituents adjacent to the pulp.

The second biological concern is associated
with

shrinkage

of

the

composite

during

polymerization and the subsequent marginal
leakage. The marginal leakage might allow
bacterial in growth, and these micro organisms
may cause secondary caries or pulp reactions.
Therefore the restorative procedures must be
designed to minimize polymerization shrinkage
and marginal leakage.

Bisphenol A, a precursor of Bis-GMA has been
shown to be a xenoestrogen .BPA and other
endocrine disrupting chemicals (EDC’S) have been
shown to cause reproductive anomalies ,especially
in the developmental stages of fetal wildlife.
Although the effect on humans are still unclear,
testicular cancer, decreased sperm count,
hypospadias (displacement of urethral meatus)have
been seen as a result of
exposure to
EDCs.Controversy surrounds this issue because it
is unclear how much BPA or BPA-DM is released to
the oral cavity and what dosage is enough to affect
human health.

Composites for posterior restorations
Direct Posterior Composites
Amalgam has long been the direct filling material of
choice for restoration of posterior teeth. Its attributes
are ease of placement, good mechanical properties,
excellent wear resistance, and the unique
characteristic of being “self-sealing” (i.e. reducing
leakage within marginal gaps as the restorations
ages.) however, the increasing demand for aesthetic
dentistry and the concern of some individuals
regarding the potential toxicity of mercury has resulted
in an increased interest and frequency in use of
composites for Class I and Class II restorations.

Requirement of Posterior composites:
Aesthetics: the colour match to the natural tooth
should be as close as possible
Optical properties: The R.I of composite should
be similar to that of the R.I of the enamel (1.5)
Hardness value of the filler particles must not be
higher than that of hydroxy appetite crystal
which in 3.39 Gpa
Young’s modulus - the value of Young’s modulus
should be equal to or less than that of dentin

Compressive strength should be more than that of
enamel (348 Mpa) & dentin (297 Mpa)
Occlusal wear should be comparable to a attritional wear
rate which is 39 µ m/year
Radiopacity should be greater than that of enamel is
198%
One of the most commonly faced problem with posterior
composite in that of occlusal wear and poor fracture
resistance to occlusal loading and polymerization
shrinkage.


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Advantages:
Hg free
Thermally non-conducive
Bonding to the tooth structure
Tooth coloured
Disadvantages:
Technique sensitive
Contouring and wedging for proximal contact
is difficult in case of direct restoration
Gap formation at interface due to shrinkage
E.g. – Solitaire (3 M), Surefil (Densply),
Enamel pyramid, Alert, dentin pyramid etc.

Indication for Posterior composites:
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

All Class I and Class II cavities.
Patients allergic or sensitive to mercury
Patients who are afraid of possible mercury toxicity
Patients who demand aesthetics even in posterior
teeth
Contraindications for Posterior Composites:
Where moisture control is not possible
Proximal step of Class II cavities below gingival
margin. In this situation, not only does placement of
composites become difficult, but moisture control
from gingival tissues is difficult, if not impossible to
control.
If lack of time for placement is a factor.
If cost is a factor.

Packable Composites
Compared with amalgam, the technique of composite
placement is far more time consuming and
demanding. Because of the highly plastic, pastelike
consistency in the procured state, composites cannot
be packed vertically into a cavity in such a way that
the material flows laterally as well as vertically to
ensure intimate contact with the cavity walls. A
solution to this problem is offered by resin composites
with filler characteristics that increase the strength and
stiffness of the uncured material and that provide a
consistency similar to that of lathe-cut amalgams.
The so called packable and condensable composites
form two special categories of hybrid composites.
These materials were introduced in the late 1990s to
provide resin composites that enable clinicians to
apply techniques similar to those used for amalgam
restorations.

The packable /condensable characteristics
derive from inclusion of elongated, fibrous, filler
particles of about 100 μm in length, and / or
textured surfaces that tend to inter lock and
resist flow. This causes the uncured resin to be
stiff and resistant to slumping, yet moldable
under this causes the uncured resin to be stiff
and resistant to slumping, yet moldable under
the force of amalgam –condensing instruments
(“Plugger”).
At the present time these materials have not
demonstrated any advantageous properties or
characteristics over the hybrid resins, other
than being somewhat similar to amalgam in
their placement technique.

Indirect Posterior Composites
Indirect composites for fabrication of onlays are
polymerized outside the oral environment and luted to
the tooth with a compatible resin cement. Indirect
composite inlays or onlays reduce wear and leakage
and overcome some of the limitations of resin
composites.
The potential advantage of these materials is that a
somewhat higher degree of polymerization is attained,
which improves physical properties and resistance to
wear. The polymerization shrinkage does not occur in
the prepared teeth, so induced stresses and bond
failures are reduced, which reduces the potential for
leakage. Further more, these resins are repairable in
the mouth and they are not as abrasive to opposing
tooth structure as ceramic inlays.

Flowable Composites
A modifications of the SPF and hybrid composites
results in the so called flowable composites. These
resins have a reduced filler level so as to provide a
consistency that enables the material to flow readily,
spread uniformly, and intimately adapt to a cavity form
to produce a desired dental anatomy. The reduced
filler makes them more susceptible to wear, but
improves the clinician’s ability to form a well adapted
cavity base or liner, especially in Class II posterior
preparations and other situations in which access is
difficult. Because of their greater ease of adaptation
and greater flexibility as a cured material, flowable
composites are useful in Class I restorations in
gingival areas.

Another application is in minimal Class I
restorations to prevent caries, when used in a
manner similar to the use of fissure sealants.
Flowable composites are also indicated for
applications in which there is poor accessibility
and little or no exposure to wear and for
applications in which excellent adaptation is
needed.

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Indications:
Sealing gingival floor of the proximal box of Class II
restorations.
Class V cavities
Small Class III cavities
First increment of all deep restorations to prevent
voids and porosities and to get good seal.
Small Class I cavities frequently referred to as
‘Preventive Resin Restorations’
Blocking out cavity undercuts during inlay, onlay and
crown preparations.
Contraindications:
Avoid on the surface of moderate to large
restorations because of its less wear resistance,
compared to viscous composites and compomers.

COMPOMERS
They are polyacid- modified resin composites.They
are similar to resin-modified glass ionomers in that
they contain all the major components of both polymer
based composites and glass ionomers,with the
exception of water. Water is excluded to prevent
premature setting of the material and also to ensure
that setting occurs only through a polymerization
reaction. limited acid-base reactions are believed to
occur once the material is exposed to ,and absorbs
,water. Although the name implies that the material
possesses a combination of characteristics of both
composites and glass ionomers,

These materials are essentially polymerbased composites that have been slightly modified
to take advantage of the potential fluoride
releasing behavior of glass ionomers.The
properties of compomers are superior to those of
traditional glass ionomers and resin-modified
glass ionomers,and in some cases, are equivalent
to those of contemporary polymer based
composites.Although compomers are capable of
releasing fluoride,the release sustained at a
constant
rate
and
anticariogenicity
is
questionable.





REVIEW OF LITERATURE:
Ralph W Phillips , David R Avery , Rita Mehra ,
Marjorie L Swartz and Robert J Mc Cune (1973)
Did a three year evaluation of class II amalgam and
composite
restorations. Except wear, composite
performed well in terms of marginal adaptation,
recurrence of secondary caries and discoloration.
Felix Lutz and Ralph W Phillips, (1983) Classified the
composites resins based on the manufacturing
technique, the average size and chemical composition
of filler and analyzed the performance of the different
types. They concluded that hybrid composite resins
can be considered in optimal combination of the well
tried traditional and the new microfiller composite resin
technology. If esthetics is the prime concern and
virtually undetectable restorations are desired,
microfilled resin systems, particularly light cured are
the materials of choice.

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

R.B. Joynt , G . Wiezkowski et al (1987) studied the
effect of composite restorations on resistance to
cuspal fracture in posterior teeth. They found prepared
unrestored teeth were weaker than restored. No
significant difference was noted in fracture resistance
between teeth restored with amalgam and with
composite resin.
Hideaki Shintani , Naoki Satou et al (1989) studied
two brands of the hybrid type posterior composite
resin placed in extensive occlusal cavities after
removal of only the caries detector stainable tissue ,
and application of a bonding agent showed no
adverse pulp reaction after four years and may be
considered suitable for posterior restorations whne
indicated.

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

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Frank Cougman , Fredrick Rueggrberg et al
(1995) reviewed the literature to arrive at
guidelines for optimal curing conditions ;
Attention should be paid to the signs of
degradation of the bulb , reflector and curing tip
of the curing lamp
Restoration to be light cured no greater than 2
mm increments, when using darker shades 1
mm is optimal .
Distance of the light tip to the restoration’s
surface should be kept within 6 mm to ensure
sufficient depth of cure .
Exposure time of 60 seconds is optimal if light
intensity id greater than 280 mW/ cm2



A. Versluis , W H Douglas et al (1996) evaluated the popular
belief that incremental technique reduces residual shrinkage
stress . in there study of various layering techniques they
concluded that incremental filling techniques increase the
deformation of restored tooth. The incremental deformation
decreases the amount of composite needed to fill a cavity. but
incremental filling methods may need to be retained for reasons
such as densification , adaptation , thoroughness of cure and
bond formation .



K D Jandt , R W Mills et al.(2000) studied the depth of cure
and compressive strength of dental composites cured with blue
light emitting diode and compared with the QTH lamps. The
conventional lamps cured significantly deeper, but both cured
deeper than required by ISO 4049 standards. The compressive
strengths were similar.With its inherent advantages, such a
constant power out over the life time of the diodes, LED’s have
great potential to achieve clinically consistent quality of
composite cure.



Noboru Ebi , Satoshi Imazato et al (2001) studied
inhibitory effects of resin composites containing
bactericide – immobilized filler on plaque
accumulation. In experimental composite containing
immobilized bactericide at 2.83% was prepared by the
incorporation of antibacterial monomer 12 –
methacryloloxydodecylpyridinium bromide (MDPB)
into a prepolymerised resin filler, and elution of
antibacterial components and inhibition of invitro
plaque accumulation by streptococcus mutans was
determined.The experimental composite had
reproducible inhibitory effects against plaque all
though it showed no elution of unpolymerised MDBB.
The plaque inhibitory effect was found to depend upon
the ability to inhibit attachment , glucan synthesis and
growth of bacteria on its surface .



Raul W. Arcis , Manuel Toledano et al (2002) studied
the mechanical properties of visible light cured resins
reinforced with hydroxyapetite . The surface of the
hydroxyapetite particles was modified using a coupling
agent (citric, maleic acrylic or methacrylic acid).The
addition of 50 to 60 wt % of hydroxyapetite particles to
the unfilled monomer lead to the increase of both
Young’s modulus and surface hardness of the
material., while the flexural strength decreased.



H H Xu , G E Schumacher et al (2003) studied the
effect of continuous – fiber performed reinforcement
dental resin composite restorations . Glass fibers were
sialinzed , impregnated with a resin cured and cut to
form inserts for tooth cavity restorations . Substational
improvement in flexural strength toughness and
stiffness were achieved.



Sanjukta Deb , Harminder Shemi et al (2003)
conducted a study to investigate the effect of
plasma arc light using a 3 s and a step cure
regime on the properties of 4 dental restorative
materials and compared it with properties
resulting form halogen light curing of the same
materials. Plasma step cure and halogen curing
were found to yield composites with superior
properties in comparison to 3 s plasma cure
suggesting that a step cure resin is preferred
method, when a plasma light unit is used

CONCLUSION
Today composites have come a long way from
the early used unfilled resins .New research
and development in these materials have made
it possible to overcome their initial drawbacks
such as poor color stability, excessive wear,
microleakage strength of these materials
Composites with their various applications have
encroached into all fields of dentistry, for
prevention as pit and fissure sealants and block
out resins , for strengthening of teeth in
periodontal splints , as orthodontic retainers, in
fixed prosthodontic and restorative dentistry.

Esthetic dentistry has emerged taking the inherent
advantage of composites which can produce
outstanding results. Diastema closures, cosmetic
mockups, cover up of stains can all be done in a
single sitting. With the development in indirect resin
systems they have come to challenge ceramics , the
most popular of the esthetics restorative materials till
date.Packable composites have literally replaced
amalgam as esthetic posterior restorations.
With all this inherent advantages and vast
applications composites have become the restorative
material to look out for the present millennium.

REFERENCES:
1.Inhibitory effects of resin composite containing
bactericide – immobilized on plaque accumulation.
Noboru Ebi , Satoshi Imazato, Yuichiro Noiri ,
Shigeeyuki Ebisu . Dental mat. 17 (2001) 485 – 491
2. Mechanical properties of visible light cured resins
reinforced with hydroxyapetite for dental restorations .
R W Arcis , A Lopz , Macipe , M Toledano , E Osorio ,
R Rodriguez – Clemente , J Murtra , M A Fanovich , C
D Pascual Dental mat. 18 (2002) 49-57
3. A comparative studies of the properties of the dental
resin composites polymerized with plasma and
halogen light. S Deb , H Shemi Denatl mat. 19 (2003)
517 – 522
4 Continuous fiber reinforcement of dental resin
composite restorations . H H Xu , G E Schumacher , F
C Eichmiller , R C Peterson, J M Antonucci , H J
MuvllerDental mat. 19 (2003)

5. Depth of cure and compressive strength of dental
composites cured with blue light emitting diodes. K D Jantt
, R W Milles , G B Blackwell , S H Ashworth ,
Dental mat. 16 (2000) 41 – 47
6. Does an incremental filling technique reduce
polymerization shrinkage stress? A Versluis , W H
Dougles , M Cross , R L Sakaguchi J Dent. Res. 75 ; 871
– 878
7. Classification and evaluation of composite resin systems .
Felix Lutz and R W PhilipsJ Prosthet. Dent. 50 , 4, 480488 (1983)
8 . Effects of composites resin restorations on resistance to
cuspal fracture in posterior teeth. R B Joynt , G
Wieczkowski Jr, R Klockwski , E L Davis J Prosthet. Dent
57 , 4 , 431- 435 (1987)
10. Clinical significance of polymerization shrinkage of
composite resins . J R Boaush , K D Lange , C L Davidson
, A Peters , A J DeGeee J Prosthet. Dent 48 ,1 , (1992)

11. Clinical evaluation of two posterior composite resins
retained with bonding agents.Hideaki Shintani , Naoki
Satou , Jumko Satou, J Prosthet. Dent 62 , 627 – 632
(1989)
12. Philips Science of dental materials 11 th edition – K
J Anusavise
13. Restorative dental materials 11 th edition - Robert G.
Craig
14. Sturdevants art and science of operative dentistry 4
th edition – T M Roberson
15. Dental materials properties and selection - William J
O’Brien
16. Adhesive metal free restorations – D Dietschi, R
Specafico
17. Esthetics dentistry – B G Dale , K W Aschheim
18. Clinical restorative materials and techniques – K F
Leinfelder, J E Lemons

19 . The dental clinics of North America Oct’
1983
20 The dental clinics of North America July 1993
21 The dental clinics of North America Jan ‘ 2001
22 Oxford concise dictionary
23. Mosby’s dental dictionary


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