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COMPOSITES
Seminar byDr. M. SHANMUGARAJ
Postgraduate Student
DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS SRI RAMACHANDRA DENTAL COLLEGE AND HOSPITAL
CHENNAI
CONTENTS
INTRODUCTION AND DEFINITION
HISTORY
COMPOSITION
POLYMERIZATION
CLASSIFICATION
IDEAL REQUIREMENTS
PROPERTIES OF COMPOSITES
INDICATIONS
CONTRA INDICATIONS
ADVANTAGES
DISADVANTAGES
CLINICAL CONSIDERATIONS
MANIPULATION OF COMPOSITE
Acid etching
Resin bonding agents
RESIN BONDING TO ENAMEL
RESIN BONDING TO DENTIN
REVIEW ARTICLES
CONCLUSION
INTRODUCTION
Dental amalgam has been restorative material of choice for many
decades how ever, in recent years, there has been increasing awareness
about the safety of dental amalgam, mainly in respect to possible mercury
toxicity that may affect human health and the environment and people are
more conscious about esthetics.
As we know greatest assets a person can have is a smile that shows
beautiful natural or naturally appearing teeth. When teeth are discolored,
malformed, fractured there is often a conscious effort to avoid smiling.
These concerns have helped the dental profession to focus on the
need to develop alternative restorative materials that esthetically and with
out hazardous effects of Hg can restore the tooth back to form, function
and esthetics. There are 5 tooth colored restorative materials
Silicate cements
Unfilled resin
Filled resin
Alumino silicate polyacrylate cement
Porcelain
Dental composites have been considered acceptable restorative
material for anterior, application for many years. Their improved
mechanical properties, tooth color matching ability and lack of metallic
mercury have caused them to be promoted as an adjunct to or substitute
for dental amalgam in the restoration of posteriors.
DEFINITIONS:
The term composite refers to a three dimensional combination of at
least 2 chemically different materials with a distinct interface separating
the components.
The significance of the combination is that it provides properties
that are superior to those of individual components.
According to Anusavice: Composite material may be defined as a
compound of 2 or more distinctly different materials with properties that
are superior or intermediate to those of the individual constituents.
Examples of natural composite materials are tooth enamel and
dentin. The collagen is the matrix and the filler is hydroxyapatite crystals.
OTHER TERMINOLOGIES USED:
Composite resins, filled composites, composite restorative
material, filled resins, resin composite.
HISTORY:
In early 1950's the silicate cement and unfilled resins were the 2
most commonly used materials for esthetic purpose.
However, Paffenberger etal1938 stated that silicate cements were
prone to acidic decay and required replacement after 4-5 years.
And unfilled resins, based on MMA show
Excessive shrinkage during hardening
Insufficient stiffness
Excessive coefficient of thermal expansion compared to tooth
structure (Tylman 1946, Paffenberger et a1 1953)
Because of these shortcomings, it leads to development of better
materials.
Epoxy resins were known to harden at room temperature with little
shrinkage, has good color stability, good adhesion to most solid surfaces.
But could be used only for indirect method and not for direct method.
Since no curing agents for these epoxy resins were available, to bring out
quick hardening reaction of the resins. It was necessary to invent a hybrid
monomer, prepared from epoxy resin but having methacrylate ester
groups.
Bowen 1956, made attempts to add fillers to enhance the good
esthetic appearance. In 1956 itself a molecule having 2 epoxy groups was
reacted with 2 equivalents of methacrylic acid in presence of a catalyst
and polymerization inhibitor to obtain a dimethacrylate that otherwise
resembled epoxy resin.
The same monomer was later on synthesized by bis-phenol A and
glycidyl methacrylate. The acronym "Bis-GMA" provided a label easier
to use than the proper name of2, 2- bis (4(2-hydroxy-3-methacryloxy
propoxy) phenyl] propane.
Advantages of this monomer
1. Rapid polymerization under oral conditions.
2. 1/3rd polymerization shrinkage in comparison to MMA (due to larger
molecular weight)
To reduce the coefficient of thermal expansion of these resins, use
of fillers was suggested by PAFFENBERGER in 1953.
A maximum volume of inorganic filler can be attained by utilizing
spherical reinforcement particles combined with intermittent size
distribution of these particles (l964, Bowen). However, spherical particles
reduces the interfacial area between the filler and polymer and there is
extra preparation cost.
One of the next improvements was development of spherical glass
fillers having refractive index that matches the refractive index of
polymeric phase. This improves the translucency of composites.
Silica, Barium oxide, Boric oxide and aluminium oxide were added
to yield radiopacity by Bowen and Cleek, 1972.
Dr. Michael Buonocore, 1955 first discovered the effect of
phosphoric acid on enamel, which made the surface rough and porous
thereby receptive to bonding of Polymerizable resin.
Lots of researchers worked on the "acid etch technique" like
Silverstone (1974) and Chow and Brown (1973) to figure out the correct
concentration of phosphoric acid used.
With the advent of visible light a great evolution came in the
composite system. Camphorquinone was added as a photo initiator in
conjunction to an amine in the resin. After this, another major
advancement came with the invention of the Dentin bonding agents.
FUSAYAMA (1980) have made significant contribution to the research
literature in the area of adhesive bonding agents.
COMPOSITION OF COMPOSITE RESIN:
Basically composite restorative material consists of the continuous
polymeric or resin matrix in which inorganic filler material is dispersed.
Dental composite resins are complex materials and contain
An organic resin component
(Resin component that forms the matrix)
Principal monomers
Diluent monomers
Inorganic filler
Coupling (interfacial) agent, to unite the resin with the filler.
Initiator system, to activate the setting mechanism.
Pigments
Polymerization inhibitors.
U. V stabilizers.
RESIN COMPONENT
Composite resins vary in their resin component but all the
variations are diacrylates
1. BIS-GMA (Bisphenol-A glycidyl dimethacrylate):- it is a high
viscosity aromatic monomer synthesized by Bowen in the USA in
1960s. Disadvantage does not bond to tooth structure effectively &
high water sorption.
2. Urethane dimethacrylate (UDMA) :- Oligomeric compounds they
either partially or completely replaces Bis-GMA.
3. TEGDMA (triethylene glycol dimethacrylate),
EGDMA (ethylene glycol dimethacrylate)
HEMA (hydroxy ethyl methacrylate):- low viscosity monomers are
incorporated to facilitate clinical handling.
There must be carbon- carbon double bonds at each end of the
monomer chain to allow polymerization and cross-linking.
FILLER PARTICLE
Addition of filler particles in to the resin matrix significantly
improves its properties.
1. Improves mechanical properties such as compressive strength,
modulus of elasticity and hardness.
2. Reduces water sorption and co-efficient of thermal expansion.
3. Contributes to aesthetics glass is able to reflect the color of the
surrounding tooth material.
4. Reduces the polymerization shrinkage
5. Less heat evolved in polymerization.
6. Gives radio-opacity if barium or strontium glasses are used.
Important factors with regard to filler clinical application of composites
are.
Amount of filler added.
Size of particles and its distribution
Index of refraction
Radiopacity
Hardness.
Particle size distribution in order to increase the filler loading of
the resin it is necessary to add the filler in a range of particle sizes. If a
single particle size is used a space will exist between the particles.
Smaller particles can then fill up these spaces.
Refractive index: for esthetics the filler should have a translucency
similar to tooth structure, in order to achieve good translucency refractive
index should closely match to that of the resin. Most glass and quartz
fillers have a refractive index of 1.5, which matches, with that of Bis
GMA and TEGDMA.
Types of fillers
Ground quartz
Colloidal silica
Glasses or ceramic containing heavy metal.
Quartz: Obtained by grinding/ milling quartz used in conventional
composites, chemically inert, very hard, difficult to polish, abrade
opposing tooth. Size O.I-100/lm.
Colloidal silica: Referred to as micro fillers and are obtained by a
pyrolytic precipitated process. Size of particles O. 04/lm or less added in
small amount 5 wt%.
Colloidal silica particles have a large surface area (50-300/lm2 per
gm) thus even small amount of filler thicken the resin. Their size is
smaller than wavelength of light so better polishing.
Ceramic containing heavy metals: these fillers provide radiopacity
refractive index 1.5 e.g. glasses are barium, zirconium (rarely), strontium
(rarely), zinc, and yttrium.
Not as inert as quartz
Alumina may also be used.
COUPLING AGENT:
The filler particles are treated with a silane-coupling agent to
produce a bond between the particles and the resin matrix.
Coupling agent used
- methacryloxypropyl trimethoxy silane ( organosilane)
Zirconates
Titanates
Loss of coupling releases particles and leads to surface break down.
Thus coupling agents
Improve physical and mechanical properties
Provide hydrolytic stability by preventing water from penetrating the
filler resin interface
It allows transfer of stress from (more flexible polymer to stiffer filler
particles).
INITIATOR SYSTEMS
Visible light activated systems
Single paste contains a two-component initiator system comprising a
diketone, and a tertiary amine. The photosensitive diketone, usually 0.2-0.7
% camphorquinone, absorbs the radiant energy of wavelength approximately
470nm (blue light). The diketone combines with the amine to from a
complex that breaks down to release free radicals, which then initiate
polymerization of the resin.
Chemically activated systems:
Supplied as two paste or powder liquid systems one part will contain
an initiator, benzoyl peroxide, and the other part a tertiary aromatic amine
accelerator ( N,N dimethyl P-toludine). Combination of the two parts will
yield free radicals which initiate polymerization of the resin.
Other systems
Dual activated composites have both a light activated and a
chemically activated initiating systems and are packaged as two pastes. The
light activation mechanism is used to initiate polymerization and the
chemical activation is relied upon to continue and complete the setting
reaction.
Polymerization
The free radicals, generated by the initiator systems, collide with the
carbon carbon double bonds of the monomer and pair with one of the
electron of the double bond leaving the other member of the pair free. The
monomer molecule itself then becomes a free radical and the process
continues only 75% of double bonds will be converted at best following
activation. In light activation 44% to 75% of double bonds will be converted
and depends on depth of cure. Where as in auto-activation even conversion
through out restoration to maximum 75%.
Most of the chemistry of the setting reaction and the consequent
contraction will take place within the first few seconds during light
activation and the remainder will complete within 2 days. Polymerization is
retarded in the presence of oxygen, which is taken up by the free radicals,
forms an air inhibited layer which is 1-20Jlm in thickness
LIGHT DEVICES
A number of light curing devices are manufactured. The light source
is usually a tungsten halogen bulb. The white light generated passes through
a filter that removes the infrared and visible spectrum for wavelength greater
than 500Jlm.
In some units the light source is remote and is transmitted to the site
of restoration through a light guide, which is a long flexible fiber optic cord.
There are also hand held light curing devices that transmit the light through
short light guide.
INHIBITORS
To minimize or prevent spontaneous polymerization of monomers
inhibitors are added to the resin systems. These inhibitors have a strong
reactivity potential with the free radial. They inhibit chain propagation by
terminating the ability of the free radical to initiate polymerization process.
Butylated hydroxy toluene is used in a concentration of 0.01 wt %
Optical modifiers: To match the appearance of teeth, dental composites must
have coloration (shading) and translucency that can simulate tooth structures
(i.e., dentin and enamel) shading is achieved by adding different pigments.
The optical modifiers usually used are metal oxides like
Titanium oxide
Aluminium oxide
Even sulfides
These are added in minute amounts 0.001-0.007 wt% as they are
effective opacifiers.
Color pigments are metal oxides
Cadmium/Gold- yellow.
Nickel- grey
Ferric- red
Copper- green
Tin- brown
UV stabilizers:
To prevent discoloration with age of composites, compound are
incorporated which absorb electromagnetic radiation. It also improves color
stability. E.g.,: 2-hydroxy-4 methoxy benzophenone.
POLYMERIZATION:
Two principal systems used to achieve polymerization are the
chemically activated system and light activated system. In the chemically
activated system, polymerization is accomplished with an organic peroxide
initiation and an organic amine accelerator. The initiator and accelerator
must be kept separately until just before the restoration is placed. Therefore
they are supplied as 2 pastes, with the initiator in one and accelerator in
other.
In light activated system, the composite is exposed to an intense blue
light. The light is absorbed by Diketone, which in the presence of an organic
amine starts the polymerization. Since, blue light is necessary to start the
reaction the diketone and amine can be supplied as a single paste, however it
must be protected from blue light until the dentist is ready to use it.
Reaction: Regardless of the system.
Dimethacrylate + Initiator + Accelerator [amine] + Treated inorganic or
[peroxide or reinforced fillers.
diketone +
blue light]
Most synthetic resins are polymers, which are formed by a process
known as polymerization. Polymerization begins with a single molecule
known as monomer, meaning one molecule or one mer. Many monomers are
joined to form one large molecule called polymer (many mers)
Composites undergo free radical addition polymerization:
Addition polymerization: This is a simple polymerization. Types:
Ring opening Polymerization.
Ionic polymerization.
Free polymerization.
Free radical polymerization reaction usually occur with unsaturated
molecules
Containing double bonds where "R" represents any organic group.
In this type of reaction no byproduct is formed. The reaction takes place in 3
stages.
Initiation.
Propogation.
Termination.
Initiation stage
0 0 0
R1_C- 0 -0 -C-R1-> 2R1 C -0 -> 2R1+ 2C02
Organic- peroxide (free radical)
R1 + CH2= CH - R1CH2CH
R R
The initiation stage is followed by rapid addition of other monomer
molecules to the free radical and the shifting of the free electron to the end
of the growing chain.
Propagation stage:
RICH2 - CH +CH2 = CH -> RI- CH2 - CH - CH2 = CH -> etc
R R R R
This propagation reaction continues until the growing free radical is
terminated. Free radical polymerization can be terminated by the presence of
any material which will react with the free radical thus decreasing the 'rate
of initiation. Eg., hydroquinone, eugenol, large amount of O2.
Formula of Bis- GMA
Strictly speaking Bis-GMA is not a monomer, it is an "Oligomer".
Lower molecular weight monomer such as TEGDMA are added to
reduce the viscosity and polymerization is accomplished using free radical.
Since the BisGMA has reactive double bonds at. Each end of the molecule
just as the added lower molecular weight monomers do, a highly cross
linked polymer is obtained.
The degree of conversion is 35% - 80%.
Termination stage: Free radical reacts with inhibitor and no free radical is
available for further propagation.
CLASSIFICATION:
According to Sturdevant
Composites are classified with respect to the components, amounts of
properties of their filler or matrix phases.
On the basis of matrix composition
Bis-GMA
UDMA
On the basis of polymerization method
Self curing I chemically cured, or 2 component systems: Amine
accelerators were used to increase polymerization rates (however,
contributed to discoloration after 3-5 years of intra oral service)
Ultraviolet light-curing: Used to initiate polymerization (curing units
which were required were of limited reliability and presented some safety
problems)
Visible light curing: Most popular today, but their success depends on the
access of high intensity light to cure the matrix material. If the composite
thickness exceeds 1.5 to 2mm, then the light intensity can be inadequate
to produce complete curing. In darker shades, filler particles and coloring
agents tend to scatter or absorb the curing light. Access to interproximal
areas is limited and requires special approaches to guarantee adequate
light curing energy.
Dual curing: Combining self-curing and light curing. The self-curing rate
is slow and is designed to cure only those portions that are not adequately
light cured.
Staged curing: Often composite finishing is complicated by the relatively
hard, fully cured material. By filtering the light from the curing unit
during an initial cure, it is possible to produce a soft, partially cured
material that can be easily finished. Afterwards, the filter is removed and
the dental composite curing is completed with full spectrum visible light.
Based on range of filler particle size range
I. Megafill -> contains megafillers- very large individual filler particle.
2. Macrofill-> contains macro fillers (10-100 m)
3. Midifill-> contains midi fillers (1-10 m)
4. Minifill -> contains minifillers (0.1-1 m)
5. Microfill -> contains micro fillers (0.01-0.1 m)
6. Nanofill -> contains nanofillers (0.005-0.01 m)
Composites with mixed ranges of particle sizes are called hybrids, and
the largest particle size range is used to define the hybrid type (e.g., minifill
hybrid as contains minifillers and microfillers).
If composite consists of filler and uncured matrix materials it is
classified as homogeneous. If it includes precured composite or other unused
filler, it is called heterogeneous.
LUTZ AND PHILLIPS CLASSIFICATION (1983)
Based on the filler particle size and distribution.
Type 1 : Macrofilled composite resin
Referred to as 'conventional' or 'traditional' composite.
Contains only macrofiller particles.
Because of particle size, they exhibit unacceptable wear, both
of itself and of the opposing tooth.
Type 2 : Microfilled composite resin
Fillers are amorphous Silica particles of 0.04 m average diameter.
Four different particle groupings have been developed to maximize
the filler loading while retaining acceptable clinical handling.
Homogeneous: Consists of directly admixed micro filler particles.
Splintered prepolymerised particles: Microfilled resin with optimal
filler loading is polymerized and then ground to form "filler
blocks" upto 80m in size. These 'filler blocks' or "prepolymerized
particles" are then incorporated into fresh resin containing
additional microfllier particles, ready for curing after placement
into a cavity. The results of this, technique are improved filler
loading and reduced polymerization contraction.
Spherical prepolymerised particles: Particles of selected size allow
optimal packing together.
Agglomerated micro filler complexes: The SiO2 micro filler
particles are sintered to a porous mass and then ground to form
coarse particles of agglomerated SiO2 upto 25m in size. These
are incorporated, with additional microfllier particles, into uncured
resin.
Using a combination of splintered prepolymerised particles in
combination with agglomerated micro filler complexes, inorganic filler
contents of upto 75% by weight can be achieved. Incorporation of ytterium
or zirconium can provide radiopacity but most micro filled composites are
radiolucent.
Type 3 : Hybrid composite resin
Often known as 'small-particle composites'
Contains combination of macrofiller particles with a proportion of
micro filler particles.
Probably the most commonly used composite resins.
Main variation is in the proposition and distribution of the various
particles of different sizes because they will control the ability to 'fill'
the resin and increase the percentage loading.
WILLEMS CLASSIFICATION:
Developed by Willems et al (1992), is more complex but provides
more information on mean particle size, filler distribution, filler content,
Young's modulus, surface roughness, compressive strength, surface hardness
and filler morphology.
Thus, it links the composition with a number of important clinical
characteristics and physical properties
Densified composites; midway filled
-Ultra fine midway- filled
-Fine midway-filled
Densified composites; compact filled
-Ultra fine compact- filled
-Fine compact-filled
Homogeneous microfine composites
Heterogeneous macro fine composites
- With splintered pre polymerised fillers
- With agglomerated pre polymerised fillers
- With spherical pre polymerised fillers
Miscellaneous composites
- With splintered pre polymerised fillers
- With agglomerated pre polymerised fillers
- With sintered agglomerates
- With spherical pre polymerised fIllers
Traditional composites
Fiber - reinforced composites
According to MARZOUK:
Depending on their chronological development
A) First generation composites
Consists of macro ceramic reinforcing phases in an appropriate resin
matrix
Disadvantage - highest proportion of destructive wear, clinically due
to dislodging of the large ceramic particles ---highest surface
roughness
B) Second generation composites
Colloidal and micro ceramic phases in a continuous resin phase
Exhibit the best surface texture of all composite resins
Wear resistance better than that of 1st generation due to the dimension
proximity of dispersed particles to dispersion matrix macromolecules,
and difficulty of engaging these minute ceramic particles in the
abrading element
Properties of strength and coefficient of thermal expansion are
unfavorable because of the limited percentage of rein forcers that can
be added without increasing viscosity beyond the limits of
workability.
C) Third generation composite
Hybrid composite in which there is a combination of macro and
micro (colloidal) ceramics as rein forcers, exists in a ratio of 75:25
in a suitable continuous phase resin.
Properties are somewhat of a compromise between the first and
second-generation materials.
D) Fourth generation composites: are also hybrid types, but instead of
macro ceramic fillers, these contain heat-cured, irregularly shaped, highly
reinforced composite macro-particles with a reinforcing phase of micro
(colloidal) ceramics.
These materials produce superior restorations, but they are very
technique sensitive.
Disadvantage: Exhibit the maximum shrinkage of all composite
restorations.
E) Fifth generation composites: hybrid composite in which the continuous
resin phase is reinforced with microceramics(colloidal) and macro,
spherical, highly reinforced, heat cured composite particles. Spherical shape
of the macrocomposite particles will improve their wettability and their
chemical bonding to the continuous phase of the final composite.
Surface texture and wear- comparable to that of 2nd generation composites.
Physical and mechanical properties similar to those of the 4th generation
materials.
F) Sixth generation: are hybrid types in which the continuous phase is
reinforced with a combination of micro (colloidal) ceramics and
agglomerates of sintered micro(colloidal) ceramics. This type shows highest
percentage of reinforcing particles of all composite. It has the best
mechanical properties. Wear and surface texture-> similar to -> 4th
generation exhibits the least shrinkage, due to the minimum amount of
continuous phase present, and also due to the condensable nature of these
materials.
Classification of resin based composite according to particle size by
PHILIPS
Category Average particle size (/lm)
Traditional composite 8-12
Small particle filled composite 1-5
Microfilled composite 0.04-0.5
Hybrid composite 0.6-1.0
ACCORDING TO CRAIG:
Classification of composite resins based upon fillers
Classification
Type I Description Particle sizes(m)
Class I Macro size particles 8-25
Class 2 Mini size particles 1-8
Class 3 Micro size particles 0.04-0.2
Class 4 Blends of classes 1 to 3 0.04-10
Type II
Class 1 Macro size reinforced particles in 10-20(organic)
Unreinforced resin matrix
Class 2 Macrosize reinforced particles in 10-20(organic)
Reinforced resin matrix 0.04-0.2(inorganic)
IDEAL REQUIREMENTS OF COMPOSITE RESIN:
Should have coefficient of thermal expansion closer to the LCTE of
enamel, less chance of creating voids or opening at the composite tooth
interface when temperature change occur. Improved composite have
LCTE 3 times to tooth structure.
Should not absorb water: materials with higher filler contents exhibit
lower water absorption values.
Polymerization shrinkage should be less- careful control of the amount
and insertion point of the material as well as acid etching the walls to
improve bonding, will reduce these problems
Should be wear resistant: filler particle size, shape and content affect the
potential wear.
Should have smooth surface texture: The size and amount of the filler
particles determines smoothness of the restoration.
Should be radiopaque: so that caries around or under a restoration can be
interpreted in a radiograph.
Should have higher modulus of elasticity (more MOE-7more rigid
material
-L-MOE-7 more flexible, can be used in class V)
Should be less soluble in oral fluids
Unfilled resin-bonding agents
Unfilled resin-bonding agents usually have chemistry similar to the
composite resin produced by. The same manufacturer and it is generally
recommended that brands should not be interred changed.
They have been diluted by additional monomers to provide lower
viscosity so that they will more readily wet the surface of acid etched enamel
or glass ionomer cement, thus improving adhesion.
PROPERTIES:
The type of resin matrix, the integrity of the silane coupling of the
resin matrix to the inorganic filler, the type and quantity of filler and the
filler particle size determine the properties of a composite resin.
BIOCOMPATIBILITY
Response of the pulp
Cyto toxicity studies suggest polymerized resin as far as possible
causes minimum pulpal irritation. Incompletely cured resin may be due to
unpolymerised monomers or the surface active complexes formed between
the low molecular weight components of the light activated initiator
systems, is a potential hazard.
HEMA is hydrophilic and also strongly allergenic. It has been shown
that HEMA is able to transverse dentinal tubules and appear in the pulpal
tissue leading to allergic responses.
Fluorides have been added to composites to produce some
anticariogenic effect.
MICROLEAKA GE
The enamel surrounding the cavity is acid etched to allow generation
of a mechanical bond.
Some authorities recommend etching of the dentine as well, to
develop a further mechanical bond. However, etching the dentin removes the
smear layer and opens the dentinal tubules, allowing a positive dentinal fluid
flow and this leads to an increase in the wetness of the dentin surface. Also
should marginal leakage occur subsequently, the pathway to the pulp would
be more susceptible to, irritation.
Unless the marginal seal of the restoration can be guaranteed,
particularly on the root surface, there is a substantial risk of sensitivity,
caries and pulpal irritation resulting from lack of adaptation, micro leakage
and ingress of bacteria & their toxins.
It is therefore currently recommended that until reliable techniques
and materials are available for resin bonding to dentin, as a general rule.
Dentine should not be etched in vital teeth
A strong glass ionomer base should completely cover the dentin of all the
cavity walls before acid etching the enamel margins.
IRRITATION FROM ACTWATOR LIGHT
Light activation units generating intense visible light has the potential
to cause pulpal injury. Temperature rise of 0.5-10°C have been reported
through dentine measuring 1-2mm in thickness this may lead to pulp
damage. Prolonged exposure of the eye to the 470nm wavelength visible
light has the potential to cause damage to the retina.
RESPONSE OF THE GINGWAL TISSUES:
Clinical and laboratory evidence shows that tissue cells respond less
favorably to composite resin than to glass ionomer. Incompletely cured
resin, particularly in those materials with low filler content, appears to be a
tissue irritant. Also, in the absence of fluoride release, there is no resistance
to plaque formation on the surface of the composite resin restoration, so any
roughness or porosity will lead to accumulation of plaque
WATER SORPTION AND SOLUBILITY
Water sorption is higher for microfilled resins (1.5-2.0 mg/cm2) than
for hybrid and macro filled resins (0.6-1.1 mglcm2) because of the large
volume percent of resin.
A limited amount of water sorption may be beneficial to a newly
placed composite resin restoration because it will bring about a degree of
expansion and help to counteract setting contraction.
After completion of setting reaction solubility of the resin in relatively
low (0.01-0.06 mg/cm2). Depends on:
The type and amount of monomers and diluents. UDMA based materials
tend to show less sorption and solubility.
The proportion of filler to resin. The less heavily filled the resin, the
greater the proportion of matrix and therefore the greater the sorption.
The degree of polymerization if the curing time is reduced by 25% there
will be a two-fold increases in sorption and a four-fold to six fold
increase in solubility.
OPTICAL PROPERTIES
Although the visual perception of a restorative material and the
closeness of its shade to that of tooth structure is subjective, it can be
evaluated and predicted by objective testing, namely tests for refractive
index, opacity, transparency, translucency reflective ness, hue, value,
chroma and metamerism.
Transparency: is chiefly controlled by absence / presence of and type
of filler. That is why unfilled resins have high transparency.
Translucency depends mainly on type and nature of unreacted
particles of the original powder material or its filler. Composite have the
most appropriate translucency to that of tooth enamel.
Reflective ness: is mainly the product of surface texture. Smoother the
surface, more rays are reflected. Reflective ness is a major modifying factor
for any shade. It should be emphasized that saliva will impart certain
reflective ness on the surface of the tooth and material, that is why in
choosing a shade the tooth should be covered with saliva.
Hue, Value and "Chroma are products of the inherent coloration of
the material and the nature of incorporated pigments. Inorganic pigments
seem to produce the most stable and predictable coloration and shading.
DEGRADATION IN THE ORAL ENVIRONMENT
Surface of a composite resin in non-load bearing areas undergoes
degradation in response to chemical, physicochemical and thermal changes.
Softening and cracking of the surface enhances the effects of abrasion from
load bearing and may result in increased surface porosity.
Factors affecting rate of wear and degradation:
1. Unreacted methacrylate groups degrade more rapidly and may be leached
from the resin.
2. Hydrolytic degradation of barium or strontium glass filler may lead to a
build up of pressure at the resin filler interface resulting in crack formation.
3. Microfilled composites are less susceptible to hydrolytic degradation.
4. Water and chemical attack may cause breakdown of the silane coating and
failure of the bond between the resin matrix and the filler.
5. Rapid thermal changes may also cause breakdown of the silane coating.
Types of composite wear:
1. Wear by food (contact free area, or CF A wear)
2. Impact by tooth contact in centric (occlusal contact area, or DCA wear)
3. Sliding by tooth contact in function (functional contact area. Or FCA
Wear)
4. Rubbing by tooth contact inter proximally (proximal contact area or PCA
Wear)
5. Wear from oral prophylaxis methods (tooth brush or dentifrice abrasion)
Several mechanisms of wear have been hypothesized based on clinical
information. In general, the process of wear is envisioned with respect to
failures of the key components i.e., resin, filler and coupling agent.
Microfracture theory: Proposes that high modulus filler particles are
compressed onto the adjacent matrix during occlusal loading and this creates
micro fractures in the weaker matrix. With passage of time, these micro
fractures become connected and surface layers of the composite are
exfoliated.
Hydrolysis theory: The Silane bond between the resin matrix and filler
particles is hydrolytically unstable and becomes debonded. This bond failure
allows surface filler particles to be lost.
Chemical degradation theory: The materials from food and saliva are
absorbed into the matrix, causing matrix degradation and sloughing from the
surface.
Protection theory: The weak matrix is eroded between the particles.
Microprotection : Filler particles are much harder than the polymer
matrix, thus resist wear very well. If filler particles are closely spaced, then
they shelter the intervening matrix polymer.
As in micro filled composites, although they have low filler content,
they show very good contact free wear resistance as the particles are very
small and therefore the inter-particle spacing is very small.
Macroprotection : Composite restorations with relatively narrow
cavity preparations minimize food contact and provide sheltering of the
restoration.
COLOUR STABILITY: In the oral environment composite resin may
undergo extensive surface staining, intrinsic colour change or both.
Maximum water sorption will take place in the first 7-10 days after
placement and strong staining agents such as tea; coffee or cola drinks may
be incorporated into the surface to a depth of 3-5 m. In the longer term
surface porosity or roughening of the surface by wear or clinical degradation
may lead to the incorporation of stains from drinks and food stuffs.
Intrinsic colour change may occur in both chemically activated and
light activated composite resins. Chemically activated composites become
yellowish within 1-3 years, as a result of oxidation of excess amine from the
initiator system and may require replacement.
Visible light activated composites lighter in colour and may become
more translucent during placement and curing. Further lightening may occur
over the next 24-48 hrs; probably caused by the decomposition of the
camphoroquinone. In the long term, light activated composites are relatively
colouring stable, provided that the resin in adequately cured.
POLYMERISATION CONTRACTION:
Composite resins undergo a substantial amount of polymerization
contraction during setting and it may affect the adhesion between the
restoration and the tooth.
Volumetric contraction for
Macrofiller containing materials (hybrid and macro filler composites
1-25%) and for micro filled composites 2-3.5% for light activated materials,
60% of the total contraction occurs with in 60 seconds after photo initiation,
prolonging the activation time from 30-60 seconds will increase the total
contraction because the material closest to the total activator light sets first,
the contraction will be towards the light, thus tending to pull the resin away
from the cavity walls.
With chemically activated composites, the contraction develops more
slowly and evenly with a tendency to draw towards the center of the
restoration the result is some what less stress at the restoration tooth
interface with a degree of concavity developing on any free surface.
Polymerization contractions effects adaptation to dentin, marginal
adaptation and marginal seal. In the larger cavity, with weakened cusps,
there is a potential for cusp deformation leading to post-restoration
sensitivity and even fracture at the base of a cusp.
So incremental technique that is placing material in layers of 2mm
thickness can reduce this problem and use of GIC as base, this will reduce
the total quantity of composite required and thus amount of shrinkage.
MECHANICAL PROPERTIES
1. Hardness: The knoop hardness number is the usual measure for surface
hardness of composite resins.
Hybrid and macro filled composites 35-65 kg/mm2 . 24%
surface hardness of a restoration can be increased by
additional curing after final completion of occlusal
adjustment and finishing procedures.
2. Rigidity: The modulus of elasticity indicates the stiffness of a material. .
Microfilled composites 4-8 Gpa.
Hybrid and macro filled composites 8-19 Gpa.
More heavily loaded composites have higher values have almost same
stiffness as that of dentine (18.5 Gpa) but substantially less rigid than
enamel (82.5 Gpa).
3. Fracture toughness:
This is a measure of the energy required to propagate a crack within
a material; that is, it indicates resistance to crack growth. More
heavily loaded composites and those with coarser particles have
greater fracture toughness.
Microfilled composites 0.7-1.2 MNm-1.5
Small particle 0.9-1.3MNm-1.5
Larger particle, hybrid and macro filled 1.4-2 MNm-1.5
Fiber reinforced composite 3MNm-1.5
Fracture toughness tends to reduce overtime in the oral environment
because of water sorption and degradation.
4. Creep: Creep measures progressive permanent deformation behaviour
under occlusal loading. Microfilled composites exhibit greater creep because
they contain a greater proportion of resin matrix than other types. There may
also be deformation of any pre-polymerized particles (filler blocks).
Absorption of water increases creep.
5. Strength: Measuring the strength characteristics of composite resins, such
as ultimate compressive strength and tensile strength, is of uncertain clinical
relevance. However, testing the transverse strength, by applying bending
forces to a beam of composite, may be useful. It ranges from 45 Mpa to 125
Mpa with micro filled showing lowest values.
6. Thermal properties: The thermal coefficient of expansion for complete
resins is substantially greater than for the crown of a tooth.
Natural tooth: 11.4 X 10-6 /0
Amalgam 25 X lO-6/0
Hybrid and macro filled composites 30-40 X lO-6/0
Microfilled composites 60 X 10-6/ °c
Thermal diffusivity indicates the ability of the material to respond to
transient thermal stimuli.
7. Radiopacity: Radiopaque composite resin restorations enable the clinician
to detect secondary (recurrent) caries, particularly at the gingival margins of
proximal restorations. The radiopacity of composite resins is stable in an
aqueous environment and does not decline. Radiopacity of dental materials
is measured against aluminium in a standard range of thickness.
INDICATIONS FOR COMPOSITES:
1. For esthetically pleasing restorations, class I, II, III, IV and V.
2. Areas of minimal masticatory loading.
3. As a provisional restoration in teeth with doubtful prognosis.
4. Only used for supra gingival lesions.
5. Incisal angle involvement.
6. Used in areas of erosion and abrasions lesions, where teeth are very
sensitive and cavity preparation may increase that sensitivity.
7. In a badly broken down tooth prior to end/ortho/perio treatment.
8. As a treatment restoration to create a tooth or occlusal pattern and specific
configurations to test its compatibility with surrounding tissues and to allow
correction of any discrepancies before replicating them in permanent
restoration.
9. For provisional splinting
10. In case of midline diastema closure
11. As a core material
CONTRAINDICATIONS
Composites are generally not recommended under the following
conditions.
1. Improper isolation of operating site.
2. All occlusal contacts will be on composite material
3. Heavy occlusal stresses
4. Deep subgingival areas that are difficult to prepared or restore.
5. Poor oral hygiene.
ADVANTAGES OF COMPOSITES
Good esthetics.
Conservation of tooth structure.
Improved resistance to microleakage.
Strengthening of remaining tooth structure.
Low thermal conductivity.
Completion in one appointment.
Economic - less expensive compared to gold or porcelain.
DISADVANTAGES
Highly technique sensitive.
Higher coefficient of-thermal expansion than tooth structure. -7 Low
modulus of elasticity.
Biocompatibility of some components unknown.
Limited wear resistance in high stress areas.
MODE OF SUPPLY
I. Composite resins may be supplied in one of the six systems.
Chemically cure.d paste- paste system.
Each paste contains - monomer of the continuous phase.
- the dispersed phase treated particles.
One phase contains the initiator and, the other contains activator
and coloring agents.
II. Chemically cured or photocured paste - liquid system.
Liquid contains- monomer of the dispersion phase resins accelerator
(activator and photon energy absorber and convertor)
Powder contains- polymer of the dispersion phase particles of the
dispersed phase initiator and coloring agents.
III. Chemically cured or photocured paste- liquid system
Paste contains- the monomer, the particles, initiator and coloring
agent.
Liquid contains- monomer- activator or u-v/ visible light energy
absorber and a convertor to activate decomposition of the initiator.
When these both are mixed the benzoyl peroxide will be decomposed
chemically or by application of visible or u.v light and this will
precipitate the polymerization of the continuous phase.
IV. Photo cured one paste system: The system is available in varying
viscosities. With rest of the constituents it also contains energy
absorber of uv/visible light rays, which direct the energy to
decompose the initiator and start polymerization.
V. Photocured one liquid system: Consists of high viscosity liquid,
contains all the ingredients found in one paste system, but with lower
percentage of reinforcing phase. It is usually used in intricate areas of
a cavity preparation where high wettability is needed.
VI. Chemiacally cured three or four part system.
o Main powder contains polymer, dispersed phase particles, coloring
agents.
o Liquid part is monomer
o Third part - Initiator
o Fourth - accelerator
sometimes first and second parts are supplied together.
CLINICAL CONSIDERATIONS:
Depth of cure: Failure to light activate a composite resin to the full
depth of the restoration effects success and longevity of the restoration.
A variety of factors influence effective depth of cure.
Degree of cure decreases with increasing depth
Increased time of exposure to the light increases depth of cure. A 40
second cure will penetrate deeper than a 20 second cure.
The more heavily filled the resin and the larger the particle size the
greater depth of cure.
Microfilled resins will cure to a depth of 2-3mm, where as hybrid resins
may be cured to a depth of 4-5mm.
Lighter shades of material are cured to greater depth.
Materials that are more translucent are cured to greater depths.
Light activator units vary in their light output over time as well as with
power fluctuations the efficiency of these units should be checked
frequently.
Polymerization continues at a significant rate for 20 minutes after
activation and then more slowly for at least 1 day.
The tip of the light source should be placed as close as possible to the
restoration and should never be more than 4mm away.
Curing through tooth structure will reduce the depth of cure to the same
extent as curing through a composite resin of similar opacity.
Marginal defects related to occlusal loading.
Four types of occlusal margin defects have been identified in relation
to composite resin restorations.
Surface fracture of excess composite resin material
Crevice formation- ditching, marginal fracture
Voids or porosities-incorporation of air between restoration and tooth
during placement.
Wear progressive exposure of the axially directed cavity wall.
Coarse composites usually exhibit wear at the margins.
Hybrid tends to chip (crevice formation) as well as wear Microfilled exhibits
chipping and surface fracture of -/fracture toughness, tensile strength and
elastic modulus and high polymerisation contraction and thermal coefficient
of contraction.
Incrententalbuild-up
Polymerization contraction induces stress of approximately 17Mpa at
the restoration tooth interface that may disrupt the mechanical interlocking
which has been induced by acid etching and applying bonding agent.
A light activated composite resin cures first at the surface closest to
the activating light and shrinks away from other regions incremental
placement entails placement of the composite in small quantities in selected
areas of the cavity and then directing the light activating unit in such a way
that, while curing the resin will shrink towards the tooth structure rather than
away from it.
Selection of an activator light
There can be considerable variation in the efficiency of an activator
light and the strength of the light output will decline with time. Some
manufactures provide a meter built on to the machine to test intensity. A
minimum intensity of about 300 mw/cm2 is necessary to ensure an adequate
cure in 40 seconds for the average increment of composite resin, the tip of
the light should be at least 10mm in diameter and must be kept clean.
Selection of Matrix band :- To allow optimal light activation of the initial
increments of composite resins it is desirable to use a translucent matrix.
Several types are available, precontoured etc. Bitene ring can be used with
sectional matrices.
Placement of a wedge:
In case of a proximal lesion, where contact has to be rebuilding, a
strong wedge is necessary to gain separation between the teeth as well as to
avoid an overhang. If both proximal surface of the same tooth are to be
restored with the one restoration, build only one side a time.
Use of a light-transmitting wedge
There are plastic wedge available with built-in light reflection core
designed to assist in directing light into the inter proximal areas during the
initial stages of curing, shrinkage towards the gingival margin occurs.
POST-RESTORATION SEQUELAE
Placement of a light-activated composite resin restoration may have several
outcomes
A symptom free tooth
Tooth that is sensitive to loading: There may be an intact
enamel margin seal but
Incomplete seal of the dentinal tubules. Movement of dentinal fluid
along the tubules (in response to occlusal loading of a weakened tooth) may
then stimulate sensory receptors.
Tooth sensitive to thermal and sweet stimuli: lack of seal at the
enamel or dentinal margins and unsealed dentinal tubules.
tooth with fracture of cusps caused by polymerization contraction in a
weakened tooth. The clinical options to minimize these problems
when large composite resin restorations are to be placed include.
Reduction of the total bulk of composite resin by basing the cavity
with a substantial quantity of glass ionomer as a dentin substitute and
then replacement build up of composite resin.
Restoration using an indirect restoration ao7 a composite resin or
ceramic inlay.
MANIPULATION
The tooth to be restored is first cleaned with a mild abrasive agent.
Cavity is etched. The acid is rinsed off and the area is dried. An enamel or
dentin-bonding agent is applied and. polymerized. The cavity is then
restored with composite resin.
Acid etching: is a physical process that creates a microscopically
rough enamel surface, termed as 'enamel tags' or 'micropores'.
PROCESS:
Enamel surface is cleaned with pumice.
Washed and area dried with compressed air.
Etchant applied for 15-30 seconds, etchant can be in liquid or gel form.
Etchant used is 37% ortho phosphoric acid.
Etchant is rinsed away with water and the surface is dried with
compressed air. If the enamel is properly etched, it appears chalky or
frosty white.
Etching may dissolve the periphery of the enamel rods, or the core of
the rods, or both in different areas. If over etched, crystals (precipitate) can
form from the calcium and phosphate ions initially dissolved. Such
precipitated crystals can inhibit bonding.
Deciduous teeth need to be etched for a longer time than permanent
teeth. The enamel rods of deciduous teeth are less regularly arranged and a
longer etching time is required to obtain a surface with sufficient roughness
for bonding.
Resin-Bonding Agents:
It is essential to enhance the adaptation, retention and seal of
composite resins to enamel and to dentine (or glass-ionomer base) by the
prior application of a resin-bonding agent.
Resin- bonding to enamel:
Unfilled Resin bonding agent with low viscosity is used to seal the
interface between composite resins and etched enamel, thus developing a
form of micro mechanical retention. The resin flows into the micropore to a
depth of 1020 11m.
The following factors will influence the reliability of the bond.
Type and concentration of the etchant ideally 37% acid applied for a
minimum of15 seconds.
Viscosity of the bonding resin: logically a low viscosity resin will
penetrate further than one with a high viscosity.
Contamination of the enamel after etching:- particularly saliva, although
even moisture from exhaled air may reduce the efficiency of the bond.
Time between the resin application and curing allow a short time(1O-15
seconds) for the resin to soak into the enamel.
Pooling of resin bonding agent at the margins or internal angles
represents a weakness in the bond. Structure and condition of the enamel
at the cavo-surface margin. Microcracks, particularly in unsupported
enamel, and already fractured enamel reduces the efficiency. .
Resin- Bonding to dentine:
The goal of a resin-dentine bonding agent is to attach composite resin
to healthy dentine and to seal the dentine tubules against the entry of bacteria
and their toxins, also prevent both inward and outward flow of fluid from
either the oral environment or the pulp. Effective bonding prevents post-
restoration sensitivity, caries and loss of the restoration.
Principles apply to successful resin-dentine bonding
Dentine should be etched to remove smear layer and dentinal tubule
plugs using 37% orthophosphoric acid for 15 seconds.
Etching should be sufficient to demineralise the surface layer of both
intertubular and intratubular dentine, leaving collagen fibers exposed and
available for a mechanical interlock with the resin.
The surface should be thoroughly washed to remove all remaining
etchant. The surface should remain wet but not flooded.
Apply a hydrophilic primer to guide and facilitate penetration of the resin
adhesive around the exposed collagen fibers.
Apply the resin adhesive and cure.
Restore with composite.
Components of a resin-dentine bond
1. Hybrid layer (resin- dentine interdiffusion zone) a hydrophilic primer and
an adhesive bonding agent penetrate approximately 5f.lm around and into
partly and completely demineralized intertubular dentine on the cavity wall.
This layer provides a seal and, perhaps, a little retention for the resin-dentine
bond.
2. Resin tags: The primer and bonding agent form tags of resin, up to 100m
long, in the dentinal tubules. Micromechanical bonding on to the partly
demineralized walls of the dentinal tubules and the resin tags themselves
combine to provide most of the retention achieved by the resin-dentine bond.
3. Elastic bonding zone: The hybrid layer and the adhesive bonding agent
that covers it provide an "elastic cavity wall" or " shock absorber" that
assists the bond to resist stresses from polymerization contraction and
functional loading.
Techniques for insertion:
Chemically activated composites: The correct proportions of base and
catalyst pastes are dispensed onto a mixing pad and combined by rapid
spatulation with a plastic instrument for 30 seconds. Metal instruments
should be avoided as it may discolor the composite. Insert while it is still
plastic for better adaptation to cavity walls. It can be inserted with a plastic
instrument or syringe. Air inclusion can be avoided by wiping the material
into one side of the cavity, filling the cavity from bottom outwards.
The cavity is slightly overfilled. A matrix strip is used to apply
pressure for better adaptation and to avoid inhibition by air.
Light activated composites:
The light activated composites are single component pastes and
require no mixing. The working time is under the control of the operator.
The paste is dispensed just before use as exposure to operatory light
can also initiate polymerization. The material hardens rapidly, once exposed
to the curing light. The depth of cure is limited, so in deep cavities the
restorations must be built up in increments, each increment being cured prior
to insertion of the next one. Thus significant portion of polymerization
shrinkage is compensated. Voids should be minimized during inserting into
cavity.
To ensure maximal polymerization a high intensity light should be
used. The light tip should be held as close as possible to the restoration. The
exposure time should be no less than 40-60 secs. The resin thickness should
be no greater than 2-2.5 mm. Darker shades require longer exposure times,
as do resins that are cured through enamel. Microfilled resins also require a
longer exposure time.
Finishing and Polishing:
Finishing procedure can be started 5 mins. after mixing. The initial
contouring can be done with a knife or diamond stone. The final finishing is
done with rubber-impregnated abrasives or rubber cup with polishing pastes
or aluminium oxide discs.
The best finish is obtained when the composite is allowed to set
against the matrix strip.
