DENTAL COMPOSITES
One of the basic requirements of aesthetics in
dentistry is to restore anterior teeth and any
extraorally conspicuous aspects of posterior teeth
with a material that has the same color, shade and all
visual perceptions as that of the adjacent tooth
structure while keeping them unchanged in function
Since the birth of dentistry there has been a
continuous attempt to formulate a material and
technique with such aesthetic requirements.besides
having the expected biocompatibility to behave in the
oral environment
INTRODUCTION
 Silicate cement was the first transcluscent direct
filing material to be introduced in 1871.
• Used extensively to restore carious lesions in
anteriors
• But use diminished because of solubility
problems, discoloration, loss of contour, surface
crazing, and lack of adequate mechanical
properties
 Acrylics were developed in Germany in 1930s.
• They were low molecular weight polymers and
lacked the reinforcement provided by the filler
particles.
• The early clinical failures of acrylics were related
to high polymerization shrinkage, high coefficient
of thermal expansion and lack of abrasion
resistance resulting in marginal leakage, pulp
injury, recurrent caries, color changes and
excessive wear.
• Thus the Poly Methyl Methacrylate based resins
were not so successful
 In an effort to improve the physical properties of unfilled
resins Ray C. Bowen introduced a polymeric dental
restorative material reinforced with silica particles in
1962.
 This became the basis for restorations and are termed as
COMPOSITES.
 They are often termed as Dental Composites, Composite
Restorative Materials, Filled Resins,Composites
resins,Resin composites, Resin Based Composites, Filled
Composites
COMPOSITE REFINEMENTS
Reviewing the last 50 years.
Dentin-Bonded
Unbonded
Composites
Composites
3c, 2c, 1c
Dentin Bonding System
Acid-Etching and
Enamel Bonding
1950
1960
Original
Development
1970
1980
1990
PACKABLES
MIDIFILL
Composites
MIDIFILL
Composites
Midi-HYBRID
Composites
2010
NanoHYBRID
COMPOSITE
FLOWABLES
MICROFILL
Composites
MACROFILL
Self-Cured
Composites
2000
CONTROLLED
SHRINKAGE
Prototypes
Mini-HYBRID
Composites
SELF-CURED
UV-CURED
VLC-CURED
[QTH, PAC, Laser, LED]
DEFINITION OF COMPOSITE
Phases and Interfaces
INTERFACE
INTERFACE
Enamel
Surface
Unfinished
Composite Surface
INTERFACE
Finished
Composite Surface
INTERFACE
Etched
Enamel Rods
INTERFACE
Voids at
Margins
Silicate
Reinforcing Filler
COMPOSITE
Crosslinked
Resin Matrix
50 v/o filler = 75 w/o filler
DEFINITION
 COMPOSITES are defined as a compound of two
or more distinctly different materials with
properties that are superior or intermediate to
those of individual constituents.
 DENTAL COMPOSITES are highly cross linked
polymeric materials reinforced by dispersion of
glass, crystalline or resin filler particles and/or
short fibres bound to matrix by silane coupling
agents
 Examples of natural composites are tooth enamel
and dentin.In enamel, enamelin represents the
organic matrix whereas in dentin the matrix
consists of collagen both of which having filler as
hydroxyapatite crystals.
COMPOSITION
 Composites involve a dispersed phase of filler particles
distributed with a continuous phase (Matrix phase)
 Composites consist of
• Organic phase (continuous phase) – resin matrix
• Inorganic phase (dispersed phase) – filler particles
• Interfacial phase coupling agent
Organic Phase
•
1)
2)
3)
4)
5)
It consists of :
Monomers
Activator Initiator system
Inhibitors
UV light absorbers
Pigments and Opacifiers
Monomers
• They are either aromatic or aliphatic diacrylates
• Bisphenol A-Glycidyl methacrylate (Bis-GMA),
Urethane dimethacrylate (UDMA),Triethylene
glycol dimethacrylate (TEGDMA) are most
commonly used in dental composites
• In high molecular monomers particularly BisGMA is extremely viscous at room temperatures.
• The use of diluent monomers is essential to attain
high filler levels and to produce a paste of
clinically usable consistencies which are mostly
low molecular wt less viscous TEGDMA
Monomers
• Binds filler particles together
• Provides “workability”
• Typical monomers
– Bisphenol A glycidyl methacrylate (Bis-GMA)
O
CH2=C-C-O-CH2CH-CH2O
CH3
OH
CH3
-C-
O
OCH2CHCH2O-C-C=CH2
CH3
OH
CH3
– Urethane dimethacrylate (UEDMA)
O
O
CH3
CH3
O
O
CH2=C-C-O-CH2CH2-O-C-NHCH2CH2CHCH2-C-CH2-NH-C- OCH2CH2O-C-C=CH2
CH3
CH3
CH3
– Triethylene glycol dimethacrylate (TEGMA)
O
O
CH2=C-C-O-CH2CH2-OCH2CH2 OCH2CH2O-C-C=CH2
CH3
CH3
• Unfortunately TEGDMA or other
such low molecular wt substances
increase polymerization shrinkage a
factor that limits the amount of low
molecular wt dimethacrylates used
in composites
• Polymerization converts an
aggregate of freely flowing
molecules to rigid assembly of cross
linked polymer chains ie.those held
by Van der waal’s forces get bound
by covalent bonds.
• This in turn leads to volumetric
shrinkage creating unrelieved
stresses in resin after it has gelled
leading to micro leakage but Bis
GMA and UDMA have 5 times
molecular wt methacrylate so
density of methacrylate double
bonds is 1/5th as high in these
monomers so less polymerization
shrinkage.
Activator Initiator system
• Methyl methacrylates and dimethacrylates
polymerize by the addition polymerization
mechanism initiated by free radicals generated by
chemical activation or by external energy
activation (light or heat)
• Basically there are three types of systems
described
o Chemically activated resins: Supplied in the form
of two pastes which contains Benzoyl peroxide as
initiator and a tertiary amine activator ( N- N
dimethyl –p- tolueidine.
• When two pastes are spatulated the amine reacts
with the benzoyl peroxide to form free radicals
and addition polymerization is initiated
• Mainly used for restorations and build ups that are
not readily cured with light source
o Light activated resins : The first light activated
system used UV light to initiate free radicals now
replaced by visible light activating systems
• Available as a single paste containing a
photoinititor molecule and an amine activator
which on exposure to light of correct wave length
(approx 468 nm) react to form free radicals that
initiate addition polymerization
• Commonly used photoinitiator is
camphoropuinone at level of 0.2 wt % and Amine
accelerator is 0.15 wt % dimethylaminoethyl
methacrylate
o Dual cure resins : Contains initiators and
accelerators that light activation followed by self
curing
Inhibitors
• To minimize or prevent
the spontaneous
polymerization of
monomers, inhibitors are
added to the resin system.
• These inhibitors have a
strong reactive potential
with free radicals
• A typical inhibitor is
butylated hydroxytoluine
in a concentration of
0.001wt %
• They extend the storage
life times of all resins and
ensure sufficient working
times
Pigments and UV Absorbers
• Pigments
– metal oxides
• provide shading and opacity
• titanium and aluminum oxides
• UV absorbers
– prevent discoloration
– acts like a “sunscreen”
• Benzophenone
Optical Modifiers
• Composites must have visual coloration and translucency
that can simulate tooth structure.
• Shading is achieved by adding different pigments
• These consist of different metal oxides that are added in
minute quantities
• Titanium oxide and aluminium oxide in minute amounts (
0.001 wt % - 0.007 wt % ) are effective opacifiers
• Eg.Cl IV incisal area translucency of unmodified composite
may allow too much light to pas thru restoration so less light
reflected back so restoration appears too dark
• Darker shades and greater opacifiers decrease depth of light
curing ability which requires either increased exposure time
or taking a thin layer during curing ]
Color stabilizers (UV light absorbers)
• Decomposition of tertiary amine activator
occurs by the natural UV light , creating
discoloration.
• So UV light absorbers are added to
minimize color changes by oxidation
Inorganic Phase
• Incorporation of filler particles
into resin matrix significantly
improves the properties of the
matrix material.
• Fillers are important as they
 Reduce polymerization shrinkage
 Decrease water sorption and
coefficient of thermal expansion
 Improve compressive strength,
tensile strength and modulus of
elasticity
 Improves abrasion resistance
• Filler particles are most commonly produced by
grinding or miling quartz or glasses to produce
particles ranging in size from 0.1 – 100 um
• Silica particles of colloidal size approx 0.004 um
are referred collectively as microfiller ar obtained
by pyrolytic or precipitation process in which
SiCl4 is burnt in an O2 – H2 atmosphere producing
SiO2 macromolecules
• A distribution of filler particle sizes is important to
incorporate maximum amount filler into resin
matrix as if they are of uniform sizes there is space
between the particles
• Inorganic filler particles generally account for between 30
– 70 vol % or 50 – 80 wt % of the composites
• The amount of filler incorporated into the resin matrix
generally is affected by the relative filler surface area
• The surface area of colloidal particles is 50 – 400 m2/gm
which increases the viscocity so they contain only 20 – 59
vol % colloidal silica as inorganic filer component and
rest is pulverized precured resin organic filler particles
with size 5 – 20 um size
• To ensure acceptable esthetics, translucency of filer must
be similar to that of tooth structure and resin ie glasses
and quartz used for fillers have refractive indices of
approx 1.5 which enough to achieve sufficient
translucency
• The radiopacity of filer material is provided by a number
of glasses and ceramics that contain heavy metals like
Barium, Storntium, Zirconium
Coupling Agent
• Chemical bond
– filler particle - resin matrix
• transfers stresses
• Organosilane (bifunctional molecule)
– siloxane end bonds to hydroxyl groups on filler
– methacrylate end polymerizes with resin
CH2
Bis-GMA
OH
CH3-C-C-O-CH2-CH2-CH2-Si-OH
Bonds with resin
O
Silane
OH
Bonds with filler
Phillip’s Science of Dental Materials 2003
Interfacial phase
• It is important the filler particles are well bonded to resin
matrix to allow transfer of stresses from more flexible
polymer matrix to stiffer filler particles
• The bond between the two phases of composites is provided
by a coupling agent
• Organosilanes such as r- methacryloxypropyltrimethoxy
silanes are used most commonly.
• In hydrolyzed state the silanol groups of organosilanes bind
with silanols on the filler surface by the formation of
siloxane bond ( Si–O– Si)
• The methacrylate group of organosilane forms covalent
bonds with the resin when it is polymerized thus completing
the coupling process
CLASSIFICATION
• Composites are generally classified with
respect to the components, amounts
properties of filler particles or matrix phase
or by handling properties
• There are many classification schemes
given in many ways
According to filler particle size :
•
Category
Megafill
Macrofill
Midifill
Minifill
Microfill
Nanofill
Hybrid
Particle size
0.5-2 um
10-100 um
1-10 um
0.1 – 1 um
0.01-0.1 um
0.005-0.01 um
Mixed particle size range
Midi -filler 2 um
(beachball)
Mini -filler 0.6 um
(canteloupe)
Microfiller .04 um
(marble)
Nanofiller .02 um (pea)
Relative Particle Sizes
(not to scale)
Phillip’s classification based on mean
particle size
• Category
Conventional/Traditional
Small particle filled
Microfilled
Hybrid
Average particle size
8-12 um
1-5 um
0.004-0.4 um
0.6-1.0 um
Traditional (Macrofilled)
• Developed in the 1970s
• Crystalline quartz
– produced by grinding or milling
– large - 8 to 12 microns
• Difficult to polish
– large particles prone to pluck
• Poor wear resistance
• Fracture resistant
• Suitable for Class 3, 4 and 5
Microfills
• Better esthetics and polishability
• Tiny particles
– 0.04 micron colloidal silica
– increases viscosity
• To increase filler loading
–
–
–
–
filler added to resin
heat cured
ground to large particles
remixed with more resin and filler
Ground
polymer with
colloidal
silica (50 u)
Polymer
matrix
with
colloidal
silica
Microfills
• Lower filler content
– inferior properties
• increased fracture potential
• lacks coupling agent
• lacks radiopacity
• Linear clinical wear pattern
• Suitable for Class 3, 5
– exceptions with reinforced microfills
• Class 1 or 2
Small Particle
• 1 - 5 micron heavy-metal
glasses
• Fracture resistant
• Polishable to semi-gloss
• Suitable for Class 1 to 5
• Example: Prisma-Fil
Silane-coated
silica or glass
(1-5 u)
Polymer
matrix
Hybrids
• Popular as “all-purpose”
– AKA universal hybrid, microhybrids,
microfilled hybrids
• 0.6 to 1 micron average particle size
– distribution of particle sizes
Silane-coated
silica or glass
• maximizes filler loading
– microfills added
• improve handling
• reduce stickiness
Polymer
matrix with
colloidal
silica
Hybrids
• Strong
• Good esthetics
– polishable
• Suitable
– Class 1 to 5
• Multiple available
Table of Properties
Property
Traditional
Microfilled
Small Particle
Hybrid
Compressive strength
(MPa)
250-300
250-300
350-400
300-350
Tensile strength (MPa)
50-65
30-50
75-90
70-90
Elastic Modulus (GPa)
8-15
3-6
15-20
7-12
Coefficient of Thermal
Expansion (10-6/ºC)
25-35
50-60
19-26
30-40
Knoop Hardness
55
5-30
50-60
50-60
Phillip’s Science of Dental Materials 2003
FILLER PARTICLES
Schematic Examples
MEGAFILL
Different
Filler Particle
Sizes
MACROFILL
MIDIFILL
Not
Shown
HYBRID
(MIDIFILL)
MINIFILL
MICROFILL
NANOFILL
Not
Shown
HYBRID
(MINIFILL)
Mixtures
Of Filler
Sizes
Heterogeneous
MIDIFILL
Mixtures
Of Pre-Cured
Pieces of
Composite
Heterogeneous
MINIFILL
Heterogeneous
MICROFILL
HOW DO YOU MAKE FILLERS?
Not
Shown
Not
Shown
• Crushing, Grinding, Sieving
• Vapor Phase Condensation
• Sol-Gel Precipitation
Marzouk’s classification based on their
chronological development
 First generation composites : Consists of macroceramic
reinforcing phases in an appropriate resin matrix
Has highest mechanical properties in lab testing, highest
propertion of destructive wear clinically due to dislodging
of the large ceramic particles
 Second generation composites : With colloidal and
microceramic phases in a continuous resin phase
Best surface of all composite resins
Wear resistance is better than that of first generations due to
dimension proximity of dispersed filler particles to
dispersion matrix macromolecules and difficulty of
engaging these minute ceramic particles in abrading element
Third generation composites : Is a hybrid composite
in which there is a combination of macro and
microceramics as reinforcers in a ration of 75:25 in a
suitable continuous phase resin
The properties are somewhat of a compromise
between the first and second generation ones
Fourth generation composites : Hybrid cmposites
but instead of macroceramic fillers these contain
heat cured irregularly shaped highly reinforced
composite macroparticles with a reinforcing phase
of micro ceramics
 Fifth generation composites : They are hybried
system in which the continuous resin phase is
reinforced with microceramics and macro spherical
highly reinforced heat cured composite particles
The spherical shape of the macro composite particles
will improve their wettebility and their chemical
bonding to the continuous phase of the final
composite
 They are of hybrid types in which the continuous
phase is reinforced with a combination of
microceramics and agglomerates of sintered
microceramics
Exhibit highest percentage of reinforcing particles
and best mechanical properties
ADA Classifation
• ADA Type I Restorative :
Are typical of the older, unfilled restoratives
which are allowed to posses tensile strength as low
as 3480 psi and water sorption as high as 1.7
mg/cm2
• ADA Type II Restorative :
Are more modern highly filled composites
having tensile strength of 4390 psi or higher and a
maximum water sorption 0.7 mg/cm2
According to filler composition
• Homogenous : If the composites simply consists of filler
and uncured matrix material it is classified as homogenous
• Heterogeneous : If the composites consists of precured
composite or other unusual filler it is called heterogenous
Precured particles are generated by grinding cured
composites to 1-20 um sized powder
They become chemically bonded to new material and can be
finely finished
 If it includes novel filler modifications in addition to
conventional filers then it is called modified such as fiber
modified homogeneous minifill
According to matrix composition
• Bis phenol A Glycidyl methacrylate based
• Urethane dimethacrylate based
According to polymerization method
• Self cured / chemically cured / cold cured :
Cold curing is initiated by mixing two pastes
one of which contains BPO as initiator and
other a tertiary amine activator (N-N-dimethylp-toluidine)
Amine accelerator contributed todiscoloration
after 3-5 years
Air bubbles may be incorporated during
mixing leading to oxygen inhibition during
polymerization
• UV light curing : UV light is used to generate
free radicals.Presents some safety problems
and were replaced with visible light curing
systems
• Visible light curing : Supplied in a single
paste contained in a syringe
Free radical system contains an initiator
camphoroquinone and an amine activator
exposure to light of correct wavelength (468
nm) produces excited state of photoinitiator
and initiate addition polymerization
They provide increased working time and
exhibit greater color stability and less internal
porosity
If composite thickness exceeds 1.5-2mm
thickness then light intensity can be
inadequate to produce complete curing
especially with darker shades of composites
• The distance of light from resin should be 1 mm
or less at 90 degree angle
Various light curing units used are :
 Quartz/tungsten/halogen light curing system
 Plasma arc curing system
 Argon laser curing system
 Light emission diodes
• Factors that affect the efficeincy of visible light curing unit :
 Distance from light tip 1mm or less is ideal
 Dirty light tip can decrease wavelength below level
resulting in insufficient curing
 Age of bulb where light tips are used more bulbs should be
changed every 6 months or more
 Optical translucency of material :How well the material
allows the passage of light through outer surface to greatest
depth of material
 Refractive index has to do with the scatter of light within
material morel scatter enhances polymerization laterally but
inhibits depth of cure
Microfill : small numerous particles scatter more light
Hybrid : Larger fewer particles scatter less light
 Monomer system: High mol wt monomers have greater
degree of polymerization
• Dual curing : In order to overcome the problem of
curing light cured composite in inaccessible area dual
cured are used esp interproximal areas
This combines self curing and visible light curing
components in the same material
The self curing component rate is slow and is designed
to cure only those portions not adequately light cured
• Staged curing : By filtering light from the curing unit
during an initial curing it is possible to produce soft
partially cured material that can be easily finished
Afterwards the filter is removed and composite curing
is completed with full spectrum visible light
According to viscosity
• Flowable composites :
These are low viscosity materials that possess particle size
distribution similar to hybrid composite but reduced filler
content
They have inferior mechanical properties as compared to
standard hybrid composite
Viscosity allows them to be dispensed by as syringe for
easy handling
Recommended for cervical lesion , pediatric restorations
and other small low stress bearing restorations
• Packable composites :
They were developed to produce handling characterstics
similar to amalgam. Primarily used for class I and II
restorations
Have low polymerization shrinkage and low wear rate
According to the technique used
• Direct composites :
The tooth is prepared ,etched, bonding
adhesive applied and composite material is
directly inserted in to the mouth
• Indirect composites :
In order to overcome the disadvantages
of direct adhesive such as technique
sensitivity, anatomic form, polymerization
shrinkage and inter proximal contacts the
indirect composite resin were introduced
EVOLUTION OF CLASSIFICATIONS
• Composites generally are classified with respect to the
components, amounts, properties of their filler or matrix
phases or by their handling properties
• Almost all important properties are improved by using
higher filler levels except the problem that as filer content
is increased fluidity decreases
• Also highly filled compositions typically contain large
filler particles but this composition results in a rougher
finished surface
• The degree of filler addition is represented in terms of the
weight percent or volume percent of filler and since silica
fillers are 3 times as dense as acrylic monomer 75 wt %
filler is equivalent to 50 vol %.
• Filler particles for the earliest composites averaged 10 to 20
um with many of larger particles as many as 50 um.
• With evolution of formulations towards better finishing
characteristics and greater resistance to wear, smaller and
smaller filler particles were used
• Since the early fillers were relatively large they were known
as macrofill materials.
• After early macrofill composites next generation had fillers
that were 8 t0 10 um in average size (midifillers) and were
originally designated fine particle sized composites to imply
improved finishing characteristics which soon replaced
silicates and direct filing resins and soon became known as
traditional or conventional composites
• The next step in evolution was to utilize 0.02-0.04 um
diameter particles to produce microfill composites
• They were also called fine finishing composites but smaller
filler size produced high viscosities in uncured mixes of BISGMA and TEGDMA which required the addition of greater
amounts of monomer diluents, along with a reduced overall
filler content to maintain workable consistencies
• To circumvent the viscosity problem two strategies were
developed.
 To blend precured microfill composite with uncured material
particles of which are generated by grinding cured composites
to a 1-20 um sized powder which in turn become chemically
bonded to the new material provide islands with better
properties and can be finely finished(heterogeneous microfills
 To sinter small filler particles into large but porous filler
particles impregnate them with monomer and add new particl
to microfill composite.Within the local region the materal is
highly filled and yet capable of being polished
• Although vast preponderance of fillers in composites fever
reinforced system are gaining interest due to the fibers
having excellent strength in primary fiber direction but
difficult to pack the fiber or orient their direction.
• Small additions of fibers to regular fillers are effective in
improving properties with a limiting factor to use fibers
with dimensions greater than 1 um for carcinogenicity
concerns for submicron fibers as asbestos.currently used of
diameters 5-10 um and lengths 20-40 um.
• Single crystals generally have symmetric shapes behaving
like fibers with an advantage that they are much stronger
than non crystalline or poly crystalline fibers.Best eg of
crystal modified composite is SiC single crystals but they
are colored so cant be used for esthetics but can be used
where strength is required
• With advances in control of filler sizes and to improve the
handling characteristics introduction of two types:
 Flowable : low viscosity materials that possess particle sizes
and size distributions similar to hybrids but with reduced
filler content allowing increased amount of resin to decrease
viscosity..Further classified as with low filler content used
as pit and fissure sealents and for small anterior restorations
and those with high filler content used for Cl I to V
conservative restorations.
 Packable (condensable) : To produce handling similar to
amalgam primarily for Cl I and II restorations.Composition
similar to traditional hybrids except less sticky and higher
viscosity than latter.
• In addition to inorganic or composite fillers it is possible to
add crystalline polymer fillers to supplement the traditional
fillers.They being stronger than amorphous polymer
material
• Two basic forms of silical fillers used in dental
compositions :
 Colloidal silica : precipitated from a liquid solution as
amorphous silica
 Pyrogenic silica : Precipitated from a gaseous phase as
amorphous particles
• For posterior composites also possible to place one or two
large glass inserts (0.5-2mm particles) into composites at
points of occlusal contact or high wear called
inserts(megafillers).They have demonstrated improved wear
resistance to contact area wear but do not totally eliminate
contact free area (CFA) wear
• After it was realized that highly filled microfills were
difficult to use composites were made with mixtures of
particles in the microfiller range to 2 to 5 um size allowing
high filler levels and permitted good finishing called hybrid
composites .Currently the principal particle size for newer
materials is in 0.1-1 um range called minihybrids
• New composites nano fillers particle size 0.005-0.01 um
which is below the wavelength range for visible light(0.02-2
um).Since these particles do not interact with visible light
they do not produce scattering or significant absorption.
• Non silicate based composites can be used for nano fillers
because they are effectively invisible.They do not
agglomerate in chains like silica filers and are so small they
fit between several polymer chains allowing very high filler
loading and still workable consistencies
NANOCOMPOSITES
What is all this “nano” stuff all about?
70% Midi-Hybrid 30%
Mini-Hybrid
Nano-Hybrid
MegaFiller
MacroFiller
MidiFiller
MiniFiller
MicroFiller
NanoFiller
100
10
1 mm
0.1
0.01
10-4
10-5
10-6
10-7
10-8
0.001 0.0001
METERS
100
10-1
10-2
10-3
1m
1 dm
1 cm 1 mm
1 mm
Dentinal Tubule
Width
IPS Target
Bacteria for Wear
Resistance
Standard
Dentistry
Reference
10-9
10-10
1 nm
1Å
Atomic
Dimensions
CURING OF RESIN BASED COMPOSITES
• Chemical Activation: Initial method of curing
initiated by mixing two pastes just before use.
During mixing it is impossible to avoid
incorporating air into the mix thereby forming pores
that weaken the structure and trap oxygen which
inhibits polymerization during curing
Also with chemical activation the operator has no
control over the working time after the two
components have been mixed
So both insertion and contouring must be completed
quickly once the resin components are mixed
Light activation
• Light activation is the currently used technique to cure the
resin based composites so it has to be discussed at a stretch:
• Advantages :
 Mixing not required so less porosity and staining and
greater strength
 An alliphatic amine as an activator so greater color stability
 Command polymerization on exp to blue light controls W.T
• Disadvantages :
 Limited depth of cure ie 2mm or less
 Poor access in posterior and interproximal areas
 Variable exposure times with diff shades,longer exp times
for darker shades increases opacity
 Sensitivity to room illumination forming a crust or skin
IR
band-pass
filter
UV
band-pass
filter
INTENSITY
INTRAPULPAL HEAT,
GINGIVAL IRRITATION
UV
Visible
CQ
WAVELENGTH (nm)
•
•
•
•
•
•
Power Supply
Cycle Timer (Circuit Board)
Bulb / Reflector
Filter
Fan
Fiber-Optic Train
IR
•
•
•
•
•
Curing Lamps
Curing lamps are hand held devices that contain the light
source equipped with a short rigid light guide madeof
fused optical fibers
At present the most widely used light source is a quartz
bulb with a tungsten filament in a halogen environment
similar to those used in automobile head lights
Precisely power supply heats the tungsten filament in the
bulb the output of which depends on voltage control and
operational characteristics
Within the unit the light is collected by reflecting it from a
silverized parabolic mirror behind the bulb towards the
path down the fiberoptic chain to tip
So imp to keep the mirror surface clean as it heats during
operation and cools in between condenses vapors from
mercury,bonding system solvents or moisture in operatory
• So it should be cleaned with alcohol swabs or with methyl
ethyl ketone
• Of the light produced only 0.5 % is useful for curing most
of it being converted to heat at some point of time so to
minimize heat two band pass filters UV and infrared are
placed in path of light just before fiber optic system which
eliminate significant amount of unnecessary light and
convert it to heat within the unit for which a fan is placed to
dissipate the unwanted heat
• Light passed through fiber optic bundle is emitted from the
tip some of which is lost through the fiber optic system.Also
high intensity is observed from the center of the bundle.So
tip should be free of cured resin and if necessary cleaned
with rubber wheel on slow speed
• Curing light output is monitored directly with a built in
radiometer or by trial curing of composite.
• Most modern units have a radiometer as part of it which
measures the no of photons per unit of area per unit of time
but does not discriminate the light energy that is matched
toinitiator.Generally QTH lamps have an output of 400 to
800 mW/cm2 and should not fall below 300 mW/cm2
• Shifting from a standard 11mm diameter tip to a small 3mm
tip increases the light output 8- fold.This increases the
chance that heat produced will raise the temperature of the
restoration and surrounding dentin to dangerous
levels.Increase more then 5 to 8oC causes cell death
• Ideally tip should be adjacent to the surface being cured but
this would cause tip to get contaminated by material being
cured.The intensity of light striking the composite is
inversely proportional to the distance from tip to composite
surface .So ideal is tip within 2mm of the composite to be
effective which may not be possible due to anatomy or
distance into prep extensions create geometric interference
• Distances of 5-6 mm are also encountered in fact distances
beyond 6mm for QTH lamps output may be less than one
third at tip so to permit closer approximation of the light to
composite Light transmitting wedges for interproximal
curing and light focusing tips for access to proximal boxes
• Smaller tips are very useful but may require more light
curing cycles to cover the same amount of cured area
• Filler particles tend to scatter light and darker colorants
absorb the light so no more than 1.5-2 mm increments be
light cured at a time.Smaller particles in range of 0.1-1um
interfere most with the light and maximize scattering.
• The intensity of the tip output generally falls off from the
center to edges producing a bullet shaped curing pattern
which may produce inadequate curing in regions as
proximal box line angles of Cl II restorations
• Most light curing requires a minimum of 20 secs for
adequate curing under optimal conditions of access.To
guarantee adequate curing has occurred it has become
common to post cure for 20 to 60 secs (curing again after
completion of the recommended curing procedure which
may improve surface layer properties like wear resistance
• Typical curing cycles of 20 secs are laborious and interests
in much shorter ones is strong
• Lamps with increased intensities opening the possibility of
reduced exposure times and greater depth of cure
• But light absorption and scattering in composites reduces
the power density and degree of conversion (DC)
exponentially with depth of penetration
• DC is measure of percentage of carbon-carbon double
bonds that have been converted to single bonds to form a
polymeric resin
 The higher the DC better the strength, wear resistance, and
many other properties.A DC of 50-60 % for BIS-GMA
implies that 50-60 % of the methacrylate groups have
polymerized.
 This does not imply that 40-50 % monomer molecules are
left in resin because of one of the two methacrylate groups
per dimethacrylate could still have reacted and could be
covalently bonded to polymer forming a pendant group
however conversion is controlled by many factors
 Total DC within resins does not differ between chemically
activated and light activated having same monomer
formulations.
 Conversion values of 50-70% are achieved at room
temperature for both types
 DC is related to intensity of light and duration of exposure
decreasing considerably with depth
 A curing light may only produce a 55 % degree of cure at
1mm into composite and even less at greater depths
 The boundary between between somewhat cured and
uncured material is called the depth of cure and is of 5mm
for light Vita shades (A2 or A3)of material in which tip is
close to composite but in cases of poor access or darker
shades it is less and so materials placed and cured in
increments of 1.5-2mm and for darkest increments of 1mm.
 Light is also absorbed and scattered as it passes through
tooth structure especially dentin causing incomplete curing
in critical areas as proximal boxes so while attempting to
cure through tooth structure exposure time should be
increased by a factor of 2 to 3
• High intensity curing involves combination of increased
light output and a narrowed wavelength range for output
using more discriminating band pass filters or other means
• This goes well if initiator is coincident with the wavelength
range of the light source
• Heat is an important problem with this system.They do not
produce the same type of polymer network during curing
• Rapid polymerization produces more stresses and weakens
the bonding system layer against tooth structure As at
beginning only some monomer is consumed and system is
still a viscous liquid but as it progresses net volume
decreases and as long as it is liquid it deforms but as DC
reaches 10-20% the network creates a gel and beyond this
gel point shrinkage creates strain on network and
attachment area to bonding system, the stresses being
relieved afterwards but are deleterious at the time of curing
because of effects on restoration marginal walls
• Light curing influences the initiation process(of the 4 steps
:activation,initiation, propagation,termination)
• Increased light intensity increases the amount of effective
activation and subsequent number chains started.
• However there is a practical point at which it is no longer
useful to encourage activaiton
• The stages in polymerization occur quickly already.
• Activation and initiation occur in less than a second
• Early propagation rates are extremely fast 100000 to
1000000 reactions per second.
• So increased light intensity is useful only to push the degree
of conversion to high levels deeper within a material
• However amount of unreacted material is important as it
may diffuse out of system
• Current composites have two or more principal monomers
and they do not coreact equally.
• TEGDMA constitutes most of the unreacted monomer
• Keeping this in view many things have been attempted in
terms of technique and the armamentarium used for
composite restorations
 One way to overcome limits of curing depth and other
problems with light curing is to go for dual cure resins
consisting of two light curable pastes one having BPO and
other containing an aromatic tertiary amine.When they are
mixed and exposed to light, light curing is promoted by
amine/CQ combination and chemical curing by amine/BPO
interaction esp in situation that does not allow sufficient
light penetration eg cementation of bulky ceramic inlays
 Also extraoral heat or light can be used to promote a higher
level of cure eg. A chemical or light cured composite can be
used to produce an inlay on a tooth or die This can be cured
directly within the tooth or on die and transferred to an oven
where it receives additional heat or light curing
• Reduction of residual stresses :
In case of chemical cured resins internal pores act to relax
residual stresses that build up during curing(pores enlarge
during hardening and reduce the concentration of stresses at
margins).Also slower curing rate of chemical activation
allows a larger portion of shrinkage to be compensated by
internal flow among the developing polymer chains before
formation of extensive cross linking
• But for the light cured resins two approaches:
 By altering the chemistry and/or composition of resin
system which is more desirable and intensive research
efforts are currently going to develop resins with low
shrinkage and low TE
 Clinical techniques designed to offset the effects of
polymerization shrinkage:
 Incremental build up and Cavity configuration: attempts to
reduce the so called C-Factor which is related to cavity
preparation geometry and is represented by ratio of bonded
to non bonded surface areas.
Residual polymerization stress increases directly with this
ratio.During curing shrinkage leaves bonded cavity surfaces
in a state of stress and nonbonded free surfaces(ie those that
reproduce the original external tooth anatomy) relax some
of the stress by contracting inward toward the bulk of
material
A layering technique in which the restoration is built up in
increments curing one layer at a time effectively reduces
polymerization stress by minimizing the C-factor ie thinner
layers reduce bonded surface area and maximize nonbonded
surface area thus minimizing the associated C-factor
Thus incremental build up overcomes both limited depth
of cure and residual stress concentration but adds to time
and difficulty of placing a restoration
 Soft Start,Ramped curing and Delayed Curing:
Another approach is an initial low rate of polymerization
thereby extending the time available for stress relaxation
before reaching the gel point which is accomplished by a
soft start technique in which curing begins with low
intensity and finishes with a high intensity allowing high
initial level of stress relaxation during early stages and it
ends at max intensity once gel point has reached
This drives the curing reaction to the highest possible
conversion only after much of the stress has been relieved
Variations in this technique include ramping and delayed
curing
o Ramping means the intensity is gradually increased or
ramped up during exposure.This ramping consists of either
stepwise,linear or exponential modes.
o Delayed curing means restoration is initially incompletely
cured at low intensity and then the clinician sculpts and
contours the resin to correct occlusion and later applies a
second exposure for the final cure , the delay allowing
substantial stress relaxation to take place.The longer the
time available for relaxation lower the residual stress
 In addition to the normal QTH lamps other types with high
intensity curing rate have been introduced with an intention
to decrease the curing time :
 PAC lamps : uses a xenon gas that is ionized to produce a
plasma.The high intensity white light is filtered to remove
heat and to allow the blue light to be emitted
 Argon laser lamps : Have highest intensity and emit at a
single wavelength. Lamps currently available emit light 490
nm
Curing depths equivalent to that of a 500 mW/cm2 QTH
lamp(2mm at 40 sec) have been demonstrated using an
exposure time of 10 sec with PAC lamps and 5 sec with
argon laser lamps
PROPERTIES OF COMPOSITES
•
•
•
•
PHYSICAL PROPERTIES
THERMAL PROPERTIES
MECHANICAL PROPERTIES
CLINICAL PROPERTIES’
PHYSICAL PROPERTIES
Working and Setting time :
• For light cured composites initiation of polymerization is
related specifically to application of light beam to material
• About 75% of polymerization occurs during the first 10
mins while the curing reaction continues for a period of 24
hours.Remaining 25% of available carbon double bonds
remain unreacted in the bulk
• If surface is not protected from air by transparent
matrix,polymerization is inhibited
• Although restorations can be finished and are functional
after 10 mins but optimum properties achieved 24 hours
after reaction is initiated
• Within 60-90secs after exposure to ambient light the surface
looses its capability to flow readily against tooth structure
POLYMERIZATION SHRINKAGE
SHRINKAGE (%)
5
50% Filler
25% Bis-GMA
25% TEGDMA
65%
Conversion
4
3
Porosity Formation
2
(Internal Contraction)
15-25% =
Gellation
Bond Stretching
(External Contraction)
1
Flow
0
0
25
50
75
CONVERSION (%)
100
Polymerization Shrinkage :
• Composites shrink during hardening referred to as
polymerization shrinkage
• It produces internal stresses and causes pulling away of the
material from the cavity walls
• Most composites only can be practically cured to levels of
55-60% degree of conversion of reactive monomer sites
• In early stages,there are limited no of polymer chains and
they are not well connected but with 20% conversion
polymer network is sufficient to create a gel where the
system changes from behaving like a liquid that can flow to
a solid that has increasingly stronger mechanical properties
• So during the first 20% the shrinkage is accommodated by
fluid changes in dimension of system
• But after the gel pointshrinkage produces both internal
stresses within the network and stress along all the surfaces
of system
• Bounded surfaces of enamel and dentin may undergo some
local stress which could reduce the strength of the recently
forming bonding layer.Unbounded surfaces will
distort,when possible,to accommodate the stresses
• In early 80s when composites were less highly filled and
bonding systems were not as reliable or strong it was
possible that shrinkage stresses form composite curing
actually dislocated the newly bonded surfaces and created
marginal openings
• The consequences of this process were first analyzed by
Feilzer and others and described in terms of the ration
(Configuration factor or C-factor)
• C-factor:
 It is the ratio of bonded surfaces to the unbonded surfaces in
the tooth preparation
 It ranges typically for dental restorations form 0.1 – 5.0 with
higher values >1.5 indicating more likelihood of high
interfacial stresses.
 Light cured composites develop higher stress than auto
cured analogues further high with higher energy curing light
 Newer dentin bonding systems are designed thicker gto be
stress relieving so typical wall stresses on during curing
may actually be only 1-2 Mpa within acceptable range
 Stresses both within cured composite and along walls
appear to be relived in few hours accelerated by water
absorption
 Recently strong interest in oxirane & oxitane chemistry as a
method of designing controlled shrinkage composites
THERMAL PROPERTIES
Linear coefficient of thermal expansion :
• It is rate of dimensional change of material per unit change
in temperature
• The closer the LCTE of material to the LCTE of enamel,the
less chance there is for creating voids or opening at the
junction of the material and tooth
• LCTE of Tooth structure is ppm / oC
Unfilled resin is 72 ppm / oC
Composites 28-45 ppm / oC
• LCTE of composite is approx. 3 times that of tooth structure
• During extreme intraoral temperature changes and times
significant stresses are generated at the tooth restoration
interface where the composites are micromechanically
bonded
• If the interfacial bond fails microleakage may
produce unesthetic staining, pulpal sensitivity due to
dentinal fluid flow, pulpal irritation due to diffusion
of bacterial endotoxins and predisposition towards
recurrent caries
• Intraoral temperature changes of 20 to 30 oC that
involve only 20-30 secs may be insufficient to
produce significant temperature change in either
tooth structure or composites
• The more is the resin matrix higher is LCTE
Water sorption :
• It is the amount of water that a material absorbs over time
per unit surface area or volume
• Water absorption swells the polymer portion of the
composite and chemically degrades matrix into monomer or
other derivatives
• Materials with higher filler content exhibit lower water
sorption value.Those with fine particles have greater value
than those with microfine particles
Water solubility :
• It is loss of weight per unit surface area or volume due to
dissolution or disintegration of material in oral fluids over
time at a give temperature
• The value varies from 0.01-0.06mg/cm2
• Inadequately polymerized resin has greater solubility
manifested clinically by color instability.
MECHANICAL PROPERTIES
Strength :
• Compressive strength and tensile strength of composite is
higher than silicate and ASPA
• The flexural strength of various composites are similar
Modulus of elasticity :
• It is the stiffness of the material.A material having a higher
modulus is rigid conversely that having lower value is more
flexible.
• The microfill composite with greater flexibility may
perform better in Cl V restoration than a more rigid hybrid
• Particularly true fo Cl V restorations with heavy occlusal
forces where stresses concentration exists in cervical area
Bond strength :
• The bond strength of composites to etched enamel
and dentin is typically between 20 and 30 Mpa
• Composites can be bonded to existing composite
restoration, ceramics and alloys when the surface is
roughened and primed appropriately
• Bond strength to treated surfaces are typically
greater than 20 Mpa
CLINICAL PROPERTIES
Degree of conversion :
• It is the measure of the percentage of consumed carbon
carbon double bonds
• It is related to both the intensity of light and duration of
exposure
• It decreases considerably with depth into a composite
material
• Most composites can practically be cured only to level of
55-65 %
• The vast majority of current composite employ
camphoroquinone as a photoinitiatior and it absorbs photons
of light energy predominantly at 474 nm
• Most light curing requires min of 20 secs for adequate
curing and for complete curing post curing of 20-60 secs
CHEMICAL PROPERTIES
Curing Light
3. DEPTH-OF-CURE
0 mm
1
2
65%
3
4
45%
25%
1. DEGREE-OFCONVERSION
2. SHAPEOF-CURE
Z100
FACTORS AFFECTING CURE
Equipment + Procedural + Restorative Factors
•
•
•
•
•
•
•
•
•
Bulb frosting or degradation
Light reflector degradation
Optical filter degradation
Fiber-optic bundle breakage
Light-guide fracture
Tip contamination by resin buildup
Line voltage inconsistencies
Sterilization problems
Infection control barriers
Procedural
Factors
•
•
•
•
•
•
Light tip direction
Access to restoration
DISTANCE from surface
Size of tip
Tip movement
TIME of exposure
Restoration
Factors
•
•
•
•
•
Restoration thickness
Cavity design
Filler - amount and size
Restoration shade
Monomer ratios
Curing Equipment
Factors
Check Fiber Optic Tips
Clean Reflector
Check Bulb
and Reflector
Wear resistance :
• It refers to material’s ability to resist the surface loss as a
result of abrasive contact with opposing tooth
structure,restorative materials,food bolus or tooth picks
• The wear of composite is affected by :
Filler particle size,shape and content
Location of restoration in dental arch
Occlusal contact relationship
• Types of wear
 Wear by food (Contact free area wear /CFA)
 Impact by tooth contact in centric(Occlusal cont. area wear)
 Sliding by tooth contact in function(Funct. cont. area wear)
 Rubbing by tooth contact interproximally
 Wear from tooth brush or dentifrices
COMPOSITE WEAR
5 Wear Types:
CFA = food bolus wear
OCA = impact wear
FCA = sliding wear
PCA = sliding wear
TBA = abrasive wear
1st Premolars
30%
40%
100%
FOOD BOLUS
60%
2nd Premolars
1st Molars
2nd Molars
• Theories of wear in CFA are :
 Microfracture theory : The filler particles are compressed
into adjacent matrix during the occlusal loading and this
creates a microfracture in weaker matrix with passage of
time these microfractures become connected and surface
layer of composite exfoliates
 Hydrolysis theory : It proposes that the silane bond between
the resin matrix and filler particles is hydrolytically unstable
and becomes debonded.The bond failures allow surface
filler particles to be lost
 Chemical degradation theory : Material from food and
salive are absorbed onto the matrix causing degradation and
sloughing from the surface
 Protection theory :
o Proposes that the weak matrix is eroded between the
particles
o Wear can basically occur due to improper case
selection,inferior material used and insufficient operator’s
skill
o Large extensive posterior composites that have total
occlusal contact are more prone to fail
o Composite restorations that are relatively narrow in its
preparation minimizes food bolus contact and provide
sheltering for the restoration called Macroprotection theory
o Filler particles are much harder than resin matrix thus
sheltering the intervening matrix called Microprotection
theory
o Microfills are most wear resistant formulations
WEAR (CFA, mm)
Wilder AD, May KN, Bayne SC, Taylor DF, Leinfelder KF.
17-year clinical evaluation of UV-cured composite resins
in posterior teeth. J Dent Res 1996; 75: 173, Abstr 2100.
300
MACRO
PROTECTION
R2 = 0.99
ENAMEL
LATE
WEAR
200
MIDDLE
WEAR
100
MICRO
PROTECTION
1
2
5
10
EARLY
WEAR
20
TIME (years)
SC Bayne
Surface texture :
• Restoration close to the gingival tissues requires surface
smoothness for optimum gingival health
• Size and composition of filler particles determines the
smoothness of restoration
• Midifill composites with larger particles show more surface
roughness than microfill having smaller filer size particles
Radio opacity :
• Aesthetic restorative materials should be sufficiently
radiopaque so that the radiolucent margin of recurrent caries
around or under the restoration can be more easily detected
• Most composites contain radiopaque filer such as Barium
glass to make the material radiopaque
Fluoride release :
• Conventional composites lack fluoride releasing abilities
• Fluoride releasing composites are available containing some
filler particles with releasable fluoride, long tem fluoride
release is quite low
• Incorporation of inorganic fluoride has resulted in increased
fluoride release but with creation of voids in matrix as the
organic fluoride leaches out
• Dispersion of leachable glass or soluble fluoride salts into
polymer matrix water soluble diffusion of fluorides from the
composite into local environment.Most of fluoride is during
the setting reaction with a small long term fluoride release
• Addition of organic F salts like Methacrylol fluoride –
Methyl methacrylate acrylic amine –HF salt, t- butylamine
ethyl methacrylate HF and recently terbutyl ammonium
tetrafluoroborate
CLINICAL CONSIDERATIONS
Color matching
Interfacial staining and secondary caries
Wear
Marginal integrity
Fracture
Post operative sensitivity
Color matching :
• Color matching not only depends on initial color match but
also on relative changes that occur with time.Both
restoration and tooth structure change color with age
• Assessment is made with tooth properly
hydrated.Temporarily drying the tooth structure makes it
appear lighter and whiter in color because of dehydration of
enamel
• With time chemical changes in matrix polymer makes
composite to appear more yellow which is accelerated by
exposure to UV light,oxidation,and moisture.
• Self cured ones under go more yellowing while newer
visible light cured systems containing high filler contents
and are modified with UV absorber and antioxidants
making it more resistant to color change
• However tooth structure undergoes a change in its
appearance over time because of dentin darkening from
aging.Aged tooth appears opaque and darker yellow.Dentin
is more likely to change color more rapidly most rapidly
during middle age (35 to 60 years)
• Bleaching which is very popular complicates the process of
trying to establish and maintain good color match of an
anterior restoration .If bleaching occurs as a treatment of
fixed duration restorative procedures should be postponed
until after teeth have assumed a stable lighter shade
(probably after 2 weeks).Bonding done 48 hrs after bleach
• Also gradual transition in color and translucency between
restoration and tooth structure.This goal is accomplished by
beveling the enamel, which blends the color difference
associated with margin over approx 0.5-1mm rather than
making it abrupt
Interfacial staining and secondary caries :
• Marginal leakage leads to accumulation of subsurface
interfacial staining that is difficult to remove and creates a
marked boundary for the restorative appearance
• Proper beveling and etching of enamel results in good
resistance to interfacial staining.
• As long as margins are well bonded and no marginal
fractures occurs resistance to secondary caries should be
good
• Most secondary caries occurs along proximal or cervical
margins where enamel is thin, less well oriented for
bonding, difficult to access during the restorative procedure
and potential subject to flexural stress as well.Rarely
secondary caries are evident along margins on occlusal
surfaces or non cervical aspects of other surfaces
Wear :
• The principal concern for posterior composites is that
occlusal wear could occur at a high rate and continue over
long periods of time, exposing underlying dentin and
leading secondary caries or sensitivity
• Evidence of composites actually wearing to point of
exposing underlying dentin is only minimal and after many
years of service worn restorations can be repaired simply by
rebonding a new surface onto the old composite to replace a
worn or discolored surface
Marginal integrity :
• It is very good under most circumstances.Clinical
appearance is affected by the nature of margin.Butt joint
margins emphasize composite wear more than beveled
margins.
• Butt joint margins of well bonded margins of well bonded
restorations wear more slowly and create meniscus
appearance against the enamel
• However as beveled margins wear thinner edges of material
are produced that are more prone to fracture
Fracture :
• Bulk fracture of posterior is rare
• Microfill composites are more prone to fracture at occlusal
contact areas
Post operative sensitivity :
• Causes of post operative sensitivity are :
 Operative trauma:Deep cavity preparation with excessive
dry cutting at ultra high speed
 Previous insults:Cumulative effects of repeated episodes of
pulpal irritation may often results in chronic to sub acute
pulpal inflammation and final necrosis
 Undercure: of either composite material or protective base
may result in skin effect a hard fully cured outer layer and a
relatively soft under cured inner layer
 Hyper occlusion :If a high spot is left on composite
restoration the tooth will become hypersensitive within a
few days
 Polymerization contraction : May place the cusps under
tension thereby disturbing fluid balance in dentinal
tubules.Same shrinkage may draw the base away form the
dentinal interface thus resulting in a contraction
gap,microleakage and subsequent bacterial invasion causing
post operative pain and sensitivity
Indications of composites
 Aesthetic restorations of Class I,II,III,IV,V,VI cavities
 Foundation or core build ups
 Sealants and conservative composite restorations
 Aesthetic enhancement procedures
 Partial veneers
 Full veneers
 Tooth contour modifications
 Diastema closure
 Cement for indirect restorations temporary restorations
 Periodontal splinting
Contradictions of composites
In areas of heavy occlusal stresses
Sites that cannot be isolated
In patients who are allergic or sensitive to
composite resin
Advantages of composites
• Aesthetic restoration
• Conservation of tooth structure (as less extension,uniform
depth not necessary,mechanical extension not required)
• Less complex when preparing tooth
• Insulative, low thermal conductivity
• Used almost universally
• Bonded to tooth structure resulting in good retention, low
microleakage, minimal interfacial staining and increased of
remaining tooth structure
• Repairable
Disadvantages of composites
• Gap formation occurs on root surfaces due to forces of
polymerization shrinkage of composite being greater than
initial bond strength of material to dentin
• More difficult, time consuming, costly than amalgam
• Tooth treatment usually requires multiple steps
• Insertion is more difficult
• Establishment of proximal contacts,axial
contours,embrasures,and occlusal contacts more difficult
• More technique sensitive
• Exhibits wear in areas of high occlusal stress or when all
contacts are on compostie
• High LCTE resulting in marginal percolation if improper
bonding technique is used
Extended applications for composites
•
•
•
•
•
•
Anterior veneers
Porcelain bonding
Core build up
Posterior restorations
Orthodontics
Pit and fissure sealants
Anterior veneers :
• Application of anterior cosmetic veneers to mask hypoplasia
or discoloration has become an integral part of dentistry
• Composites placed in a thin layer over etched enamel and
sculpted to provide enhanced tooth form or esthetics
• Lower viscosity composites for direct application against
etched enamel have been developed which is diff to control
• Those with filler content less than 20 wt% formulated with
opacifiers added iv a variety of shades to block out stained
enamel
• Tinted composites with added color modifiers are also
available in varied shades such as yellow,brown,blue,black
and pink to provide characterization for an anterior veneer
• These shade modifiers are all photoinitiated and although
they require additional exposure to light, can be cured as
they are applied to gain desired esthetic effect
• By layering these composites either under or between
applications of composites life like color characteristics can
be developed
• Labial veneers can also be made indirectly on a model with
newer materials in which the degree of polymerization can
be increased with higher energy light sources,vaccum
chambers,and applied heat.Then the prefabricated veneer is
luted to the etched enamel surface with a lower viscosity
composite cement.
• Weakest portion of the bonded interface is the bond
between the precured composite veneer and freshly applied
composite cement which may leak and require repair
Porcelain bonding :
• Porcelain bonding systems have been developed to lute
indirect anterior veneers to etched enamel and also to place
a composite restoration that replaces fractured porcelain
• When broken porcelain is being repaired the interface must
be roughened to increase surface texture and to create some
mechanical locking
• These lasted for short periods frequently as they were
generally in full incisal function and those with least use
had best prognosis
• Porcelain veneers can be bonded to enamel with similar
techniques and a low viscosity composite cement which is
more successful as a larger surface area of porcelain is
available and is generally roughened by a HF treatment
during fabrication
Core build ups :
• Modifications have been made to alter the viscosity and the
setting time of highly filled composites to formulate core
materials that will closely adapt to pins and posts
• They are usually chemically initiated so that they can be
inserted with a syringe enclosed in a metal or celluloid
crown form or matrix and cured in bulk.This is why these
materials have slightly prolonged working time
(approaching 2 mins) and a relatively quick snap set
• Since they are highly filled composites they provide
optimum resistance to deflection forces and shear stresses
• Also highly colored or opaque materials so that there will be
a visible interface at the composite-tooth junction during
final cavity preparation
Posterior restorations :
• Indications:
 Primary indication is aesthetics
 Need for conservative preparations but not used for cuspal
coverage or better not to use for restorations exceeding 1/3rd
the buccolingual width of the tooth
 Use of composites to decrease thermal conduction
• Many composite formulations for posterior applications like
one is microfine filler sintered into macrosized particles to
improve wear resistance while another has hydrophobic
resin matrix to reduce water sorption with the hope that
failure of silane coupling agent be reduced
• The packable/condensable composites introduced in late
1990s derive from inclusion of elongated fibrous filler
particles of about 100 um in length and/or textured surfaces
•
•
•
•
•
that tend to interlock and resist flow
This causes the uncured resin to be stiff and resistant to
slumping yet moldable under force of amalgam condensing
instruments(pluggers).
Rough surfaces and blends of fibrous and particulate filler
produce a packable consistency and enable it to be used
At present they have not yet proven to be an answer to the
general need for highly wear resistant,easily placeable
posterior resins with low curing shrinkage and a depth of
cure greater than 2mm
It is still uncertain in dental profession whether a 250 um
loss of substance truly represents a clinically acceptable
restoration that adequately supports occlusal function.Also
the wear being greatest in occlusal functional contact
Limited to Cl-I,II in premolars with minimal B-L extension
• Indirect posterior composites:
 Indirect composites for fabrication of onlays are
polymerized outside the oral cavity and luted to the tooth
with a compatible resin cement which has been said to
reduce the wear and leakage and overcome some limitations
of resin composites
 Several different approaches for resin inlay construction:
o Use of both direct and indirect fabrication methods
o Application of light,heat,pressure,or a combination of these
o Combined use of hybrid and microfilled composites
 Fabrication process for direct composite inlays requires
application of a separating medium to the
tooth(glycerin,agar sol) resin pattern is then formed,light
cured and then removed.Rough inlay then exposed to light
for more 4 to 6 mins or heat activated at 100oC for 7 mins
after which the preparation is etched and the inlay is
cemented in to place with a dual cure resin and then
polished
 Composite systems are also available as indirect
products.Indirect inlay resins require an impression and
fabrication of inlay in lab,in addition to conventional light
and heat curing,lab processing may employ heat 140oC and
pressure 0.6Mpa ofr 10 mins.The potential advantage of
these materials is somewhat higher degree of
polymerization is achieved improving physical properties
and wear resistance
 Polymerization shrinkage does not occur in prepared teeth
and so induced stresses and bond failures are reduced which
reduces the potential for leakage.Also repairable in mouth
and not abrasive to opposing tooth structure like ceramics
Orthodontics :
• Lower viscosity filled composites are also being used for
the cementation of orthodontic brackets to the facial
surfaces of both anterior and posterior teeth.
• Enamel is acid etched in the usual manner and each bracket
is applied directly to the surface in the desired position
• High modulus fine composites resist stress better than
unfilled or microfine composites so most orthodontic
composites are fine particle or hybrid composites
Pit and fissure sealants :
• Pit and fissure sealants were first proposed in 1960s which
prevent tooth preparation and restoration techniques fro the
elimination of caries prone pits and fissures on occlusal
surfaces of teeth
• Pits and fissures that are not self cleansing are caries prone
• The objectives of these materials is to eliminate the
geometry that harbors bacteria and to prevent nutrients
reaching bacteria in base of pit and fissure
• Since they have modest wear resistance,contact area wear
and food abrasion may quickly wear it away from naturally
self cleansing areas where it is not needed although key
areas remain occluded
• The principal feature of sealant is adequate retention
• Sealant is applied only after gross debridement isolation and
acid etching of surfaces.And can’t be applied so precisely
that there is no excess extending onto self cleansing areas of
occlusal surfaces.
• So it is important the material is adjusted as needed
following placement so that it does not interfere with
normal occlusal contacts or disrupt occlusal paths,once
removed from self cleansing areas rest blocks the non
cleansing area
• Classification and History:
 They can be self curing and visible light curing
 Early ones were based on methyl methacrylates or
cyanoacrylates
 Most contemporary are unfilled or lightly filled and based
on difunctional monomers such as used for matrix of
composites
 Principal monomer of this system BIS-GMA is diluted with
lower mol wt species like TEGDMA to reduce the viscosity
with addition of colorants such as titanium dioxide
• Composition,Structure and properties :
 Primary clinical property is flow into small access
spaces:Penetration coefficient that is relative rate of flow in
a standard sized orifice.Penetration is a function of capillary
action and viscosity.
 If a site is well cleaned,etched,rinsed and dried than acrylic
monomer can wet the surface reasonable well even if the
opening is small it will draw the material by capillary action
if the viscosity is low long enough.
 Complete penetration is not absolutely critical only if the
neck region is occluded it is clinically acceptable
 Glass ionomers were explored for pit and fissure
applications but lacked sufficient abrasion resistance ,were
brittle and prone to fracture
 Traditional composites are not good sealants as they do not
penetrate into pits and fissures readily due to high viscosity
but instead useful in treating such caries
 Newer low viscosity versions composites,flowables have
been used for this purpose had good wetting,sufficient
flow,adequate abrasion resistance,god fracture resistance.
 Properties are like the resin matrix of composites.No
evidence that water sorption,chemical degradation,or other
events observed with composites detract from longevity of
these materials
 However one controversy of BIS-GMA degrading into BPA
which was found to be estrogenic although many flaws in
the report as misidentification of TEGDMA as BPA
 Also measured levels of monomer released from sealents
was unusually high but it was not noted that air inhibited
superficial layer of resin had not been removed by wiping
with cotton roll before sampling which is generally wiped
away or lost during the first few chewing strokes and this is
not the actual cured sealant material
• Clinical considerations:
 Prevention of occlusal caries at defects depends simply on
exclusion of bacteria or their nutrients
 Many say as long as pits and fissures remain completely
sealed there is 100% prevention of caries at those sites.
 The ideal time to apply sealants is soon after occlusal
surfaces erupt into the oral environment but with with
partial eruption difficult to maintain isolation (cotton
rolls/absorbent wedges)
 Sealants also have been applied to smooth surfaces to try to
eliminate caries but are abraded by food and/or brushes
 Another important consideration is degree to which children
and adolescents are susceptible to caries.The one who are at
greater caries risk are the most benifitted.Older patients with
decreased salivary flow are also good candidates
 Also used to repair or seal leaking or failing dental
restorations
 It is now accepted that sealants provide outstanding service
when done properly for very low costs.In societies
committed to dental care this is a core strategy for early
management of caries
FINISHING AND POLISHING
Original
rough
surface
SURFACE ROUGHNESS = Ra
Average up-and-down geometry =
20 mm
COARSE
finished
Significant
material
removal
New surface
approximates
abrasive size
2 mm
0.2 mm
FINE
finished
Polished
Fine grooves
Smearing and
burnishing to
smoothen surface
TWO CRITICAL FACTORS for Finishing and Polishing:
(1) Abrasive size
(2) Filler particle size
FINISHING OF COMPOSITES
• Optimum finishing and polishing of composite resins is
very important step in completion of restoration as residual
surface roughness can encourage bacterial growth leading to
myriad of problems including secondary caries,gingival
inflammation and surface staining
• The best possible finish is produced by not polishing the
surface at all at least for surfaces that have polymerized next
to matrix strip.The smoothest surface on a restoration on a
restoration can be obtained by curing the composite against
a smooth matrix strip which minimizes porosities as well as
the oxygen inhibited layer
• Three important factors affecting finishing and polishing:
Environment,Delayed vs Immediate finish,Type of material
 Environment refers to whether to perform in dry or wet
field.Some suggest dry field on a slow speed for better
visualization but it has been shown that the heat produced
disturbs the marginal seal and that structural and chemical
changes occur in restoration in dry field but some say dry
polish has no effect on hardness or surface structure.
o In a way it should be carried out in moderation in an
environment in which the margins are clearly discernible
and where minimal heat is generated.Water cooling during
grinding and finishing should ensure standard quality
 Elapsed time has too an effect as some say delaying the
finishing for up to 24 hrs because polymerization is
incomplete at placement although manufacturers
recommend that finishing be accomplished shortly after
placement.But studies indicate not much of a diff in both
o Thus for all practical purposes all composite restorations
should be finished and polished shortly after placement
during the same appointment although the finishing should
be delayed for approximately 15 mins after curing
 Several systems can be used for this purpose.Use of a
scalpel blade or any thin sharp edged instrument to remove
flash on the proximal areas is recommended although very
risky esp if trimming involves shearing in direction away
from gingival margin which can lead to debonding and
leakage.Trimming forces should be parallel or towards the
gingival tissue
o Coarse to ultrafine aluminium oxide discs produce the best
surface and minimal trauma.Tungsten carbide burs or fine
diamond tips used to adjust occlusal forces and blending
o Other systems extrafine polishing pastes,silicone resin
finishing devices,silicone carbide brushes and points
o The most important step in finishing and polishing is
application of a bonding agent or a surface sealer
o It is been widely documented that finishing and
possibly polishing is detrimental to composite
surfaces in that it introduces microcracks and
removes the most highly polymerized area of the
restoration
o Application of surface sealer or low viscosity resin
with letter or no filler ensures that surface porosities
are filled and microcracks are sealed which also
decreases microleakage by improving the marginal
seal of restorations
REPAIR OF COMPOSITES
• Composites may be repaired by placing new material over
the old one
• When a restoration has just been placed and polymerized it
may still have an oxygen inhibited layer of resin on the
surface.Additions of new composite can be made directly to
this layer because this represents an excellent bonding
substrate.A restoration that has just been cured and polished
may still have more than 50 % of unreacted methacrylate
groups to copolymerize with the newly added material
• As it ages fewer unreacted methacrylate groups remain and
greater cross linking decreases the ability of fresh monomer
to penetrate in matrix.Strength of the bond between the
original and new resin decreases with time elapsed between
polymerization and addition of new resin
• Also polishing exposes filler surfaces free from silane so
the filler surface area does not chemically bond to the new
composite layer.
• Under the most ideal condition the addition of a silanate
bonding agent to the surface before the addition of new
composite,the strength of the repaired composite is less
than half the strength of the original material
Biocompatibility of composites
• The chemical insult to pulp from composites is possible if
components leach out or diffuse from the material and
subsequently reach to pulp.Adequately polymerized
composites are relatively biocompatible because they
exhibit minimal solubility and unreacted species are leached
in very small quantities
• Inadequately cured material at the floor of a cavity can serve
as a reservoir of diffusible components that can induce long
term pulp inflammation esp for light activated materials ie
too thick a layer cured for less of time leaving uncured or
poorly cured material
• Second concern is with shrinkage of composite during
polymerization and subsequent marginal leakage
• This leakage allows bacterial ingrowth and cause secondary
caries or pulp reactions
• Bisphenol A a precursor of bis-GMA has been shown to be
a xenoestrogen or a synthetic compound found in the
environment that mimics the effects of estrogen by having
an affinity for estrogen receptors
• BPA and other endocrine disrupting chemicals (EDC) have
been shown to cause reproductive anomalies especially in
developmental stages of fetal wildlife
• Although unclear in humans testicular cancer, decreased
sperm count,and hypospadias have been sen due to csp to
EDCs
• BPA has recently been shown to exhibit antiandrogenic
activity which may prove to be detrimental in organ
development and estrogenicity mainly related to BPA and
BPA dimethaacrylate (in vitro applied to cancer cells)
COMPOMERS
• They are defined as poly acid modified resins
• These materials are basically light cured, low fluoride
releasing composite resins
• The difference between composites and compomers is that
compomer monomer contains acidic functional group that
can participate in an acid base glass ionomer reaction
following polymerization of the resin molecule
• It consists of a paste of Ca, Al, F silicate glass fillers in
dimethacrylate monomer with acrylic acid like molecules
• They contain poly acid modified monomers with fluoride
releasing silicate glasses and are formulated without
water.Some compomers have monomers that provide F
release
• They are packaged as single paste formulations in compules
and syringes
• Setting primarily occurs by light cured polymerization but
an acid-base reaction also occurs as the compomer absorbs
water after placement and on contact with saliva.Water
uptake important for F transfer
• They require bonding agent to bond to tooth structure
• Indications :
 Cervical restorations
 Class III restorations
 Minimal Class I and II restorations
 Deciduous teeth restorations
 Geriatric restorations
 Miscellaneous restorative repair
CEROMERS
• Term ceromer stands for ceramic optimized polymer.
• It is an advanced composite that utilizes combinations of
ceramic fillers to provide unique handling,wear and esthetic
properties
• Consists of a paste containing barium glass,spheriodal
mixed oxide, Ytterbium trifluoride and silicone dioxide in
demethacrylate monomers
• They set by a polymerization of carbon carbon double
bonds of methacrylate.They must be bonded to tooth
• The properties of ceromers are similar to those of
composites and they exhibit F release lower than glass
ionomers or compomers
ORMOCERS
• It is an acronym for organically modified ceramics
• This class of material represents a novel inorganic-organic
copolymer in the formulations that allows for modifications
of its mechanical parameters
• This inorganic-organic copolymer are synthesized form
multifunctional urethane and thioether methacrylate
alkoxysilanes as sol-gel precursors
• Alkoxysilyl group of the same permit the formulation of an
inorganic Si-O-Si network by hydrolysis and
polycondensation reactions
• The methacrylate groups are available for photochemical
polymerization.Filler particles are 1-1.5 um in size and filler
content is 77% by wt and 61 vol%.
SMART COMPOSITES
• Class of composites was introduced as the product Ariston
pHc in 1998.It is an ion releasing composite material.
• It releases fluorine, hydroxyl and calcium ions as the pH
drops in area immediately adjacent to the restorative
material which is the result of active plaque which results in
a corresponding increase in release or functional ions
• They work based on newly developed alkaline glass filler
which reduces secondary caries at margins of restoration
produced by bacterial invasion.This results in reduced
demineralization and a buffering of acid produced by caries
forming micro orgs.
• Paste contains Ba,Al,F silicate glass fillers(1 um) with
ytterbium trifluoride,silicone dioxide and alkaline calcium
silicate glass(1.6 um) in dimethacrylate monomers
• Filler content 80 wt % or 60 vol% the use of an adhesive to
tooth is not recommended
• However the dentin should be sealed to reduce sensitivity
• The F release is lower than conventional glass ionomers but
more than that of compomers]
COMPOSITES WITH EXPANDING MONOMERS
• The primary cause of
failures of resin based
composites is
secondary caries
because of
polymerization
shrinkage of these
restorations
• Several approaches
being pursued to
reduce polymerization
shrinkage
• Composites containing expanding
monomers such as spiroorthocarbonates
were introduced in 1970s.It is believed that
low shrinkage results from expansion of
oxirane rings as it opens which partially
offsets the shrinkage associated with the
formation of covalent bonds as monomers
are linked during polymerization
• The difficulties with these materials has been in producing
sufficient ring opening expansion to offset the
polymerization contraction without reducing the extent of
cure
• Recently the system containing expanding monomers a
diepoxide monomer and a polyol has reduced
polymerization contraction stress compared to commercial
Bis-GMA/TEGDMA composites
• Various properties of epoxy polyol mixtures:
 Water sorption with these materials are slightly higher
 Cycolo polymerizable di and multifunctional oligomers
synthesized through the reaction of acrylates and
formaldehyde can produce resin with higher conversion and
lower shrinkage than acrylates
MONOMERS FOR ENHANCED DEPTH
OF CURE
• Use of monomer with high molecular weight such as
multiethylene glycol dimethacrylates have added benefits of
producing resins with enhanced cure
• Esterified multimethacrylate oligomers of poly
(isopropyllidenediphenol) have recently been synthesized
and mixed with TEGDMA to produce resin with reduced
polymerization shrinkage
• One commercial composite contains multifunctional
methacrylate monomers organically developed for the
indirect resin composite Artglass
• Addition of chain transfer agents such as propanal and
diacetyl increases the degree of conversion and cross
linking of Bis-GMA and UDMA resins from 80-90% to
98%
FIBER REINFORCED RESINS
• Fiber reinforced polymer resin has been available
for many years
• Silane treated glass fibers are commonly used as
plasma treated polyethylene often in woven form
• Unlike glass fibers polyethylene does not
appreciably raise the stiffness of the material
• They strengthen and toughen the composite for
single and multiple unit restoration
ANTICARIOGENIC MATERIALS
• Imazate developed an antibacterial monomer
MDPB(methacryloxydodecylpyridinium bromide) to be
added to dental resin
• This methacrylated monomercan polymerize assuring that
the antibacterial portion of the molecule is permanently
affixed to the resin matrix
• Composite containing MDPB has been shown to inhibit
growth of S.mutans and do not reduce the degree of cure
and other properties
• Recently an antibacterial material Halo was added at
concentration upto 1 wt% to a commercial composites and
showed antibacterial behaviour against S.mutans and
A.viscosus that lasted for upto 10 weeks
BIOACTIVE REMINERALISING COMPOSITES
• Calcium phosphate has been used as a filler to make
composites that serve as bioactive liner and bases to
enhance remineralization
• Though this composite provides sustained release of
calcium and phosphate ions they have low strength
and stability
• Recently bioactive polymeric composites based on
amorphous calcium phosphate but strengthened by
hybridization of fillers with glass forming elements
have been developed
Surface coating of polymer
• A thin clear polymeric material that could be coated
onto the tooth to inhibit plaque formation and
demineralization may be beneficial
• These coatings are made form copolymer of acrylic
acid and alkylmethacrylate such as
isobutylmethacrylate and a polysiloxane
• This copolymer is cross linked via pendant silane
group using tetraethylorthosilicate
FUTURE POLYMERS
• Evidence of molecular addition that enhances cure
and radiopacity (triphenylbismuth and other
brominated monomers)
• Memory polymers that could serve as inlay/onlay
materials that expand or contract to fit the prepared
tooth as a result of intraoral heating
• Lining,coating and restorative material that are self
adhesive to dentin
• Cationic initiated curing reaction on basic surfaces
• Biodegradable polymer scaffolds for carrying drugs,
cells and growth factors to tissue sites to repair or
close defects