Physical Properties of Orthodontic Materials

PHYSICAL PROPERTIES OF
ORTHODONTIC MATERIALS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


PHYSICAL PROPERTIES OF
ORTHODONTIC MATERIALS


INTRODUCTION



Metals are very remarkable materials.
Their ability to be rolled into sheets as thick as
the hulls of ships or as thin as gold and
aluminum foil, to be drawn into wire cables
supporting bridges or into fine strands, onehalf the thickness of a human hair, for delicate
electronic instruments, to be softened with
heat and hardened by cold working.



Metals resist wear and corrosion; they conduct
heat and electricity, they are generally
inexpensive.


Atomic arrangements for
metallic materials


In general, materials can be subdivided into
two categories according to their atomic
arrangements. In crystalline material there is a
three dimensional periodic pattern of the
atoms, whereas no such long-periodicity is
present in noncrystalline materials, which
possess only short-range atomic order.




There are seven crystal systems, with lattice
parameters. (The three dimensional arrangement of
lines that can be visualized as connecting the atoms
in undisrupted crystals, is called a lattice.)



Inherently, a space lattice is a geometric construct
wherein each point has identical surroundings.
Crystal structures of real material are based upon
space lattices, where there is a single atom or a
group of atoms at each space lattice point.




Crystal System
Cubic
Tetragonal
Orthorhombic

Rhombohedral
(Trigonal)
Hexagonal
Monoclinic

Space Lattice
Simple cubic
Body-centered cubic
Face-centered cubic
Simple tetragonal
Body-centered tetragonal
Simple orthorhombic
Body centered orthorhombic
Face-centered orthorhombic
Base-centered orthorhombic
Simple rhombohedral
Simple hexagonal
simple monoclinic
Base-centered monoclinic

Triclinic

Simple triclinic

It is most convenient to visualize the crystal structures
of metals in terms of their unit cells, where a unit cell
is the smallest portion that can be repeated in three
dimensions to produce the crystal structure.
Crystal  combination of unit cells, in which each
cell shares faces, edges or corners with the
neighboring cells
Unit cells for the simple cubic are a) Body-centered cubic, b) Facecentered cubic, and c) Hexagonal close-packed.

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

The hexagonal close-packed (hcp) structures can be
considered as formed from two interpenetrating
simple hexagonal structures.
It can be seen that, while nickel and chromium have
body centered cubic and face centered cubic
structures, respectively, all temperatures below their
melting points, iron and titanium have crystal
structures that depend upon temperature.



Grains  microns to centimeters



Grain boundaries
Atoms are irregularly arranged, and this leads
to a weaker amorphous type structure.
Alloy  combination of crystalline (grains)
and amorphous (grain boundaries)
Decreased mechanical strength and reduced
corrosion resistance

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Stages in the
formation of metallic
grains during the
solidification of a
molten metal
Polycrystalline- each
crystal - grain

Structure of metallic materials


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Crystals or grains of metals and alloys are composed
of billion upon billion of atoms regularly arranged in
a space lattice.
When stress is first applied, the space lattice is
slightly distorted out of shape, but returns to its
original position upon release of the stress. This
deformation is called elastic strain.
Whenever a crystal deforms, its lattice is distorted.
As the deformation increases, so does the distortion.
Simultaneously, the number of atomic dislocation
increases, disrupting the path of the sliding or
twinning planes produced by stress.



various defects  slip planes -along
which dislocation occurs


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

To prevent breakage, a softening step
(annealing) must be added to render the
distorted, cold material, strain free. Each alloy
has a specific recrystallization and annealing
temperature at which the grains, forcibly
reduced by cold work, can enlarge to allow
further processing. Thus annealing causes a
sharp drop in tensile strength.
Metals made of large grains are weak, the
smaller the grains, the more the intergranular
boundaries that oppose the planes slip.

ANNEALING:
Recovery
Recrystallization

Grain Growth


Before Annealing
Recovery – Relief of stresses
Recrystallization – New grains from
severely cold worked areas
-original soft and ductile condition
Grain Growth – large crystal “eat up”
small ones-ultimate coarse grain
structure is produced

Austenite:
This form presents as the face-centered
cubic crystalline structure in iron and steel, or the
body-centered cubic structure in nickel-titanium
alloys, at higher temperatures.
Appropriate cooling of nickel-titanium alloys can
induce a transformation to a close-packed hexagonal
martensitic phase. The transformation from
austenitic to martensitic and vise versa is what gives
alloys such as Ni-Ti the characteristic properties of
shape memory and superelasticity.





Martensitic:
This form presents as a body-centered
cubic phase in stainless steels, or a monoclinic,
triclinic or hexagonal crystalline structure in Ni-Ti
alloys. The martensitic phase of nickel titanium
exists at lower temperatures and is characterized by
high ductility. It is formed as a result of quenching
or cold work austenitic phase.

Physical properties
Mechanical
properties

Physical
properties

Tensile
Strength
Compressive
Shear
Elasticity Elastic modulus

Resilience
Ductility
Percentage
Plasticity
elongation
Electrical and
Yield
Electrode strength
Electrochemical
potential
properties
Electrical
Thermal
resistivity
properties

Basic properties of elastic materials
The elastic behavior of any material is defined in
terms of its stress-strain response to an external
load. Both stress and strain refer to the internal
state of the material being studied.
 Stress: When an external force or load is applied
to a solid body, an internal force equal in
magnitude and opposite in direction is set up in
the body. This internal force divided by the area
over which it acts is called stress.
 The basic types of stresses produced in dental
structures under force are tensile, compressive,
and shear.





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Complex stresses: It is very difficult to

induce a single type of stress in the body. For
example, when a wire is stretched, it becomes
longer suggesting that there is a tensile stress.
But a wire, which becomes longer, will also
becomes thinner. This means that there is a
compressive stress also in it. This is called
complex stresses and is an engineering
principle called Poisson’s ratio.
A material fractures in the area of maximum
stress concentration.



Strain: when a material is subjected to a force

or load, there is a equivalent stress induced in
the material. This internal stress brings about
change in dimension and shape of the material.
This change in dimension is usually measured
by change in length.
Change in length
Strain =
Original length

Elastic Properties

Stress

Wire returns back to
original dimension when
stress is removed

Elastic Portion


Strain

Hooke’s law: states that in an elastic
deformation, the stress is directly proportional
to strain.
 Elastic limit: It is the greatest limit upto
which an object can be stressed so that it will
recover or return to its original dimension,
when the load is withdrawn.
Only upto a point of stress or limit the elastic
can undergo Elastic Deformation. Beyond this
point, it undergoes a plastic or permanent
deformation.





Proportional limit: It is defined as the greatest
stress, the material will sustain without a
deviation from the Hooke’s law or
proportionality of stress to strain. Upto this
point, the stress and strain are proportional.
This is the proportional limit.
Beyond this point, the strain will not be
proportional to stress.



Yield strength: It is the point of stress at

which the material undergoes a SLIGHT but
permanent deformation or offset. Yield
strength is slightly more than the proportional
limit and for practical purposes the same as
proportional limit. It is sensitive to work
hardening.


Young’s Modulus or Modulus of
Elasticity: is an inherent property of the

material and cannot be altered appreciably by
heat treatment, work hardening, or any other
kind of conditioning. This property is called
structure insensitivity.

Elastic Properties

Stress

Yield strength

0.1%

Proportional Limit
Elastic Limit


Strain

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Ultimate tensile strength : If a material

continues to have more and more weight
applied to it, it will eventually break. If the
material is being stretched, the stress at
breakage is called the ultimate tensile strength.
When many metals are stressed above their
proportional limits, they undergo a process
called work hardening, and actually become
stronger and harder.



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Toughness: this is the entire area under the
stress – strain curve is a measure of the energy
required to fracture the material.
Resilience: The area under only the elastic
region of the stress-strain curve is a measure of
the ability of the material to store elastic
energy.


Stress

Elastic Properties
Ultimate Tensile
Strength


Fracture Point

Strain



Formability - amount of permanent
deformation that the wire can withstand
without breaking



Indication of the ability of the wire to take the
shape



Also an indication of the amount of cold work
that they can withstand

Stress

Elastic Properties

Yield strength
Proportional limit

Resilience

Formability


Strain

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Flexibility
large deformation (or large strain) with
minimal force, within its elastic limit.
Maximal flexibility is the strain that occurs
when a wire is stressed to its elastic limit.
Max. flexibility = Proportional limit
Modulus of elasticity.



Brittleness –opposite of toughness. A brittle
material, is elastic, but cannot undergo plastic
deformation. eg: Glass



Fatigue – Repeated cyclic stress of a
magnitude below the fracture point of a wire
can result in fracture. This is called fatigue.


Stiffness / Load deflection Rate


Magnitude of the force delivered by the appliance
for a particular amount of deflection.

Low stiffness or Low LDR implies that:1) Low forces will be applied
2) The force will be more constant as the appliance
deactivates
3) Greater ease and accuracy in applying a given
force.


Strength


Yield strength, proportional limit and ultimate
tensile/compressive strength



Kusy - force required to activate an archwire to a
specific distance.



Proffit - Strength = stiffness x range.



Range limits the amount the wire can be bent,
Stiffness is the indication of the force required to
reach that limit.



The shape and cross section of a wire have an
effect on the strength of the wire.


Range


Distance that the wire bends elastically, before
permanent deformation occurs (Proffit).



Kusy – Distance to which an archwire can be
activated- working range.



Thurow – A linear measure of how far a wire or
material can be deformed without exceeding the
limits of the material.

Springback


Kusy -- The extent to which a wire recovers its
shape after deactivation



Ingram et al – a measure of how far a wire can
be deflected without causing permanent
deformation. (Contrast to Proffit yield point).




Large springback



Activated to a large extent.



Hence it will mean fewer archwire changes.



Ratio – yield strength
Modulus of elasticity


Elastic Properties

Stress

Point of arbitrary clinical loading
Yield point

Range

Springback

Strain

Physical properties of
orthodontic wires
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The force required for the tooth movement has
always highlighted the importance of “Light
continous force.” (JIOS 2002; 76-88)
Metallic orthodontic wires are manufactured by
series of proprietary steps, typically involving
more than one company.
Initially the wire is cast in the form of an ingot,
which must be subjected to successive
deformation stages, until the cross section
becomes sufficiently small for wire drawing.



Moreover, the surface roughness of the wire,
which has a clinically significant effect on the
arch wire bracket sliding friction, varies
considerably among the various products and
is generally greater for the beta-titanium and
nickel titanium wires.




In general, an orthodontist should consider the
following aspects in the selection of wires:
force delivery characteristics, elastic working
range, ease of joining individual segments to
fabricate more complex appliances, corrosion
resistance and biocompatibility in the oral
environment and cost.


Requirements of an ideal archwire
(Kusy )
1.

Esthetics

7.

Resiliency

2.

Stiffness

8.

Coefficient of

3.

Strength

4.

Range

9.

Biohostability

5.

Springback

10.

Biocompatibility

6.

Formability

11.

Weldability

friction


Orthodontic archwires




Orthodontic wires, which generate the
biomechanical forces, communicate through
brackets for tooth movement, are central to the
practice of the profession.
Historically, gold alloy wires were first used in
orthodontic practice, although these noble
metal wires have minimal use currently
because of their much greater cost compared
to the popular base metal wires.



The gold alloy wire compositions were
generally similar to those of the type IV gold
casting alloys, and their modulus of elasticity
was approximately 100Gpa. Thus the gold
alloy wires had elastic force less than that for
stainless steel wires with the same crosssectional dimensions and segment lengths.


Stainless steel





Since 1950s stainless steel were used for most
orthodontic wires.
This continues to be the most popular wire
alloy for clinical orthodontics because of an
outstanding combination of mechanical
properties, corrosion resistance in the oral
environment, and cost.
The wires used in orthodontics are generally
American iron and steel institute (AISI) types
302 and 304 austenitic stainless steels. These
contained 17-25% chromium and 8-25%
nickel and the remaining were iron.

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The modulus of elasticity in tension for stainless
steel orthodontic wires, ranges from about 160 to
180 GPa.
The yield strength for the stainless steel archwires
shows a much wider variation than the elastic
modulus and to range from 1,100 to 1,500 MPa.
Heat treatment of these wires also causes
significant decrease in residual stress and modest
increase in resilience.





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The use of heat treatment to eliminate residual
stresses that might cause fracture during
manipulation of stainless steel appliances can
be important under clinical conditions.
Austenitic stainless steel can be rendered
susceptible to intergranular corrosion when
heated to temperatures between 400°c and
900°c, due to the formation of the chromium
carbides at the grain boundaries.
Since the stainless steel alloys must be heated
within this temperature range for soldering,
clinicians are cautioned to minimize the time
required for this process.



The stainless steel alloys used for orthodontic
wires are of “18-8” austenitic type. whereas
17-7 precipitation-hardenable stainless steel
alloy had higher yield strength in bending than
the commonly used stainless steel wire alloys.




The chromium in the stainless steel forms a
thin, adherent passivating oxide layer that
provides corrosion resistance by blocking the
diffusion of oxygen to the underlying bulk
alloy. About 12-13 wt% chromium is required
to impart the necessary corrosion resistance to
these alloys.


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Nickel ion release from the alloy surface causes
implications for the biocompatibility of these alloy.
X-ray diffraction has shown that austenitic stainless
steel orthodontic wires may not always possess the
single-phase austenitic structure that is based upon a
face-centered-cubic (fcc) arrangement of the iron
atoms.
In a two phase structure the austenitic was
accompanied by a body-centered cubic (bcc)
martensitic phase.





Formation of the martensitic phase resulted in
substantial reduction in the modulus of
elasticity, from about 200Gpa to about 150Gpa
for heavily cold worked alloys.
Extensive cold working can increase the yield
strength of austenitic stainless steels from
about 275 to 1100Mpa.




The modulus of resilience, represents the total
elastic biomechanical energy or spring energy
in the wire, is given approximately by
(YS)²/2E. This expression can be used to
estimate the changes in elastic spring energy
resulting from the heat treatment.




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For clinical purpose, heat treatment stainless
steel orthodontic appliances is to minimize
breakage rather than achieve significant
increase in resilience.
Heat treatment of stainless steel wires at
temperatures above 650°c must be avoided
because rapid recrystallization of the wrought
structure takes place, with deleterious effects
on the wire properties.

Cobalt-chromium-nickel wires




A cobalt-chromium-nickel orthodontic wire
alloy (Elgiloy) was developed during the
1950s by the Elgiloy cooperation (Elgin, IL,
USA).
This was originally used for watch springs, is
available in four tempers (levels of resilience)
that are colour-coded by the manufactures:
blue (soft), yellow (ductile), green (semiresilient), and red (resilient).





As with the stainless steel alloys, the corrosion
resistance of Elgiloy arises from a thin
passivating chromium oxide layer on the wire
surface.
Elgiloy blue alloy is very popular with many
orthodontists because the as-received wire can
easily be manipulated into the desired shapes
and then heat treated to achieve considerable
increases in strength and resilience.





The maximum yield strength for straight, 0.41
mm diameter, wire segments is obtained with a
heat-treatment temperature of about 500 °c.
This heat treatment causes complex
precipitation processes that substantially
increase the yield strength of the alloy.
Heat treatment of straight segment of Elgiloy
blue wire causes an increase of about 10% in
modulus of elasticity and about 20-30% in
yield strength.



Because of its “soft feel” (due to relatively low
YS) during manipulation, orthodontists can
mistakenly believe that as-received Elgiloy
blue wires have substantially lower elastic
force delivery than stainless steel wires. In
reality, the values of modulus of elasticity for
Elgiloy blue and stainless steel orthodontic
wires are similar.

Wire alloy
Austenitic
Stainless steel
CobaltchromiumNickel (Elgiloy)
Beta-titanium
(TMA)

Composition

Modulus of elasticity

YS

Springback

17-20% Cr, 8-12% Ni,
0.5% C. balance Fe

160-180

1100-1500

0.0060-0.0094 (AR)
0.065-0.0099 (HT)

40% Co, 20% Cr,
15%Ni, 1.8% Fe,
7%Mo, 2%Mn,
0.15% C, 0.04% Be.

160-190

830-1000

0.0045-0.0065 (AR)
0.0054-0.0074 (HT)

62-69

690-970

0.0094-0.011

34

210-410

77.8% Ti, 11.3% Mo,
6.6% Zr, 4.3% Sn.

Nickel-titanium 55% Ni, 45% Ti
(approx. and may
contain small amounts
of Cu or other elements)


0.0058-0.016



Another clinical use of Elgiloy blue wires is
fabrication of the fixed lingual quad-helix
appliance, which produces slow maxillary
expansion for the treatment maxillary
constriction or cross bite in the primary and
mixed dentitions.


Beta-Titanium Wires




A Beta-titanium wire for orthodontics is marketed
by the Ormco Corporation (Glendora, CA, USA).
The commercial name for this wire is TMA, which
represents “titanium-molybdenum alloy”.
The Beta-titanium wire was conceived for
orthodontic use about two decades ago by Burstone
and Goldberg, who recognized its potential for
delivering lower biomechanical forces compared to
the stainless steel and cobalt-chromium-nickel
alloys.



The elastic modulus for the beta-titanium
wires is approximately 40% that of the
stainless steel and Elgiloy blue wires. Because
of the much lower value of elastic modulus,
despite lower values for yield strength, the
beta titanium wires have significantly
improved values of spring back (YS/E), which
increases their working range for tooth
movement.





Another clinical advantage of the betatitanium wires is excellent formability, which
is due to their body – centered cubic structure.
(bcc)
The addition of molybdenum to the alloy
composition stabilizes the high-temperature
bcc beta-phase polymorphic form of titanium
at room temperature, rather than the hexagonal
closed-packed alpha-phase.





The x-ray diffraction pattern for a betatitanium (TMA) orthodontic wire shows a
single phase bcc structure, with the broadened
peaks and preferred crystallographic
orientation expected for a heavily cold-worked
alloy.
The slip-systems for dislocation movement for
the bcc crystal structure account for the high
ductility of the beta-titanium wires.



The Zirconium and zinc in the alloy
composition contribute increased strength and
hardness, and their presence avoids the
formation of an embrittling omega-phase
during wire processing at elevated
temperatures. This wire processing is
problematic because of the reactivity of
titanium, and there have been reports of TMA
archwires are susceptible to fracture during
clinical manipulation, despite the excellent
formability of the beta-titanium alloy.





Heat treatment by the orthodontist is not
recommended for the beta-titanium wires, heat
treatment of the alloy by the manufacturer
approximately 700-730°c followed by water
quenching.
Subsequent aging at approximately 480°c
results in precipitation of alpha phase and a
maximum of spring back for the TMA wires.





The next clinical advantage of beta-titanium is
that it is the only orthodontic wire alloy
possessing true weldability.
Another important feature of the beta-titanium
wires is their absence of nickel that is present
in the other three types of alloy types.




The beta-titanium wires are generally the most
expensive of the orthodontic wire alloys, but
the greater cost is considered by orthodontist
by the combined advantages of intermediate
force delivery and the excellent formability and
weldability when fabrication of more complex
appliances is required.


Nickel titanium wires






The pioneer for the development of nickel-titanium
wires for orthodontics was Anderson, who
published articles with colleagues advocating in the
early 1970s.
The first nickel-titanium orthodontic wire alloy
(Nitinol) was marketed in the Unitek Cooperation.
The generic name nitinol that is applicable to group
of nickel-titanium alloys originates from nickel,
titanium and the Naval Ordinance Laboratory where
the alloys were developed by Buehler and
associates.





The Nitinol orthodontic wire offered a
modulus of elasticity about 20% that of the
stainless steel wires, along with a very wide
elastic working range. This was evident when
the wire was tested in cantilever bending.
Two new superelastic nickel-titanium wires,
Chinese NiTi and Japanese NiTi were
introduced during the mid 1980s.





Heat treatment of the Japanese NiTi wires at
500°c was found to significantly alter the
super elastic force plateau that occurred during
unloading of three point bending test
specimens. It was also observed that heat
treatment at 600°c eliminated the superelastic
behavior.
The bending properties of nonsuperelastic
nickel-titanium wires are not affected by heat
treatments at 500°c and 600°c temperature
range.





In the early 1990s a NiTi orthodontic wire
alloy (Neo Sentalloy) with true shape memory
at the temperature of the oral environment was
introduced by GAC International, which had
an optimum combination of light force
delivery and springback under clinical
conditions.
X-ray energy-dispersive spectroscopic analysis
with the SEM suggests that commercial
orthodontic wires are generally titanium rich.





There are two major NiTi phases in the nickeltitanium wires. Austenitic NiTi has an ordered
bcc structure that occurs at high temperatures
and low stresses. Martensitic NiTi has been
reported to have a distorted monoclinic,
triclinic, or hexagonal structures, and forms at
low temperatures and high stresses.
The shape memory effect is associated with a
reversible martensite
austenite
transformation.



In some cases an intermediate R-phase having
a rhombohedral crystal structure may form
during this transformation process.



For the superelastic nickel-titanium alloy,
complete transformation to austenite occurs
only slightly above the temperature of the oral
environment





In 1994 Ormco Cooperation introduced a new
orthodontic wire alloy, copper NiTi which is
available in three temperature variants of 27 °c,
35°c, and 40°c. The shape memory behavior is
reported by the manufacturer to occur for each
variant at temperatures exceeding the specified
temperature.
For example, the 27°c variant would be useful
at for mouth breathers; the 35°c variant is
activated at normal body temperature; and the
40°c variant would provide activation only
after consuming hot food and beverages.



In the recent studies 27°c copper NiTi wire
alloy contain a single peak on both the heating
and cooling curves, indicating direct
transformation from martensitic to austenite on
heating and form austenite to martensite on
cooling, without an intermediate R-phase. In
contrast, the 35°c copper NiTi and 40°c copper
NiTi wire alloys exhibited two overlapping
peaks on heating, corresponding to
transformation from martensite to R-phase
followed by transformation from R-phase to
austenite.





Element analysis using SEM have indicated
that the three Copper NiTi variants have very
similar compositions of approximately 44%
nickel, 51% titanium, and slightly less than 5%
copper, and 0.2-0.3% chromium.
Kusy, has reported that copper Ni-Ti contains
nominally 5-6 wt% copper and 0.2 – 0.5 wt%
chromium. The 27°c C variant contain 0.5%
chromium to compensate for the effect of
copper in raising the Af temperature above
that of the oral temperature, and the 40°c C
variant contains 0.2% chromium.

Nickel-titanium open and closed coil
springs




Super elastic nickel titanium alloy wires and springs
introduced the concept of applying a super-elastic
unloading curve that could potentially deliver a
more constant force.
Springs differ from archwires in that; springs are
necessarily subjected to an additional manufacturing
procedure of winding, which might effect their
mechanical properties. Another difference is that,
the forces applied to springs include torsional and
tensional components in addition to bending force.





Advantages of the compression and tensile
springs made of nickel-titanium are: a
minimum of permanent deformation and
possibility of a more constant force during
unloading.
The closed coil nickel titanium springs are
used for space closure; open coil nickel
titanium springs are mainly used for opening
space to unravel the teeth for molar
distalization.



Miura et al (AJODO 1988) subjected Japanese
nickel-titanium closed and open coil springs to
tensile and compression tests respectively. Springs
of various lumen sizes, wire size, and different pitch
was used in the study. It was observed that the
lumen of coil springs remained constant, the load
value of the super elasticity increased as wire
diameter increases.



When the diameter remained constant, the load
value of super elastic activity increased, as the
lumen of the coil became smaller. It was also
shown that the open coil springs showed a
more constant load value of super elasticity
when compared to closed coil springs.



Ryan (BJO 1995), compared the force
characteristics of different commercially
available open and closed coiled nickel
titanium springs. He stated that the super
elastic nickel titanium coil springs possess
superior properties than other springs.






Barwart ( AJODO 1996) in a study examined
the effect of temperature change on the force
delivery of nickel titanium closed coil springs.
The springs were heated and cooled between
20°c and 50°c, while held in constant
extension.
Load values were found to increase with rising
temperature. The force measured at 37°c was
about twice as high as at 20°c. Immediately
after the temperature started to drop, a rapid
decrease in the force occurred to levels below
those found at raising temperatures.



Angolkar et al (AJODO 1992) conducted an
in-vitro study on closed coiled springs of
different length, and lumen in stainless steel,
cobalt chromium nickel and nickel-titanium
alloys. They showed that all the springs
demonstrated loss of force over a time period.
Most spring showed a major force reduction in
first 24 hours to 3 days. Nickel-titanium
springs showed least force decay and it was
observed that increase in lumen size reduced
the force delivery, and an increase in the wire
size, increased the force delivery.





Effect of lumen size on force characteristics :
Jebby Jacob, Divakar Karanth, K. Sadashiva
shetty. (JIOS 2002)
Findings of this study on open coil springs
revealed that, as the size of lumen increased,
the force delivered decreased for a given
diameter. In case of large size lumen a
decrease in force value and increased range of
super elastic activity is seen. These findings
confirm the findings of Miura et al.




Effect of wire diameter on force characteristics :
In springs with a constant lumen size, as the
diameter of the wire increased, the force
delivered increased minimally. The super elastic
activity range was almost the same. These
findings slightly differed from the studies of
Chaconas et al (1984) who observed that, with a
constant lumen size, an increase in wire diameter
produced an increase in force at a given
activation.





When the closed coil springs of different
diameters were compared, it was found that
larger diameter spring produced significantly
higher force levels. It was also found that as
the wire increased, force levels also increased
drastically.
Studies on Japanese nickel titanium springs by
Miura et al (1988) showed that, the load value
of super elastic activity increased in proportion
to increase in diameter of wire.

Effect of spring length on force characteristics :
The length of the spring has a great effect on the
load deflection rate. A shorter spring stiffer
than a larger spring of same dimensions. As
the length of the open coil spring increased,
initial force delivered was high, but the range
of super elastic activity increased significantly.
Shorter springs delivered more force than longer
springs.



Effect of static, simulated oral environment :
The load deflection rate of open coil springs
showed minor changes over 4 weeks in static
simulated oral environment.
It was noticed that for an open coil spring of
9mm length at given activation the force level
decreased from week 0 to week 2, but
surprisingly the force level regained at week 4
to that of week 0.



Summary and conclusion: the force
characteristic of the open and closed coil
springs were concluded as :
As the size of lumen increased, the force
delivered by the open spring decreased.
Increase in the wire diameter increased the force
level in both open and closed coil spring.
Closed coil spring of smaller diameter from
“Ultimate Arch Forms” showed good range of
super elastic activity.



As the length of open coil springs was increased, the
range of super elastic activity increased
significantly. In case of closed coil springs, shorter
springs exhibited wide super elastic range.
Closed coil springs of similar dimension from
different manufactures showed the variation in their
properties.
The ideal spring for clinical situation should be the
one with optimum force level and with greater range
of super elastic activity. Open coil springs with large
lumen size and length and smaller diameter would
meet these criteria. Closed coil spring with shorter
length and the smaller diameter showed good super
elastic range.

Property

Stainless steel

Cobalt-chromium-

Beta-titanium (TMA)

Nickel-titanium

Nickel (Elgiloy Blue)
Cost

Low

Low

High

High

Force

High

High

Intermediate

Light

Low

Low

Intermediate

High

Formability Excellent

Excellent

Excellent

Poor

Ease of

Can be soldered.

Can be soldered

Only wire alloy that

cannot be

Joining

Welded joints

Welded joints must

has true weldability.

Soldered or

delivery
Elastic
Range
(springback)

must be
reinforced with

be reinforced with

welded.

solder

solder
ArchwireBracket

Lower

Lower

Higher

Higher

Orthodontic brackets


The original treatment approach utilized a slot
attached to a stainless steel band that was
cemented to the tooth, and early attempts to
modify this attachment resulted in wide base
surfaces on to which a slot was soldered. This
appliance was then bonded to the tooth with
epoxy resin. In the late 1970s the direct
bonding to the enamel was widely accepted as
a standard procedure to replace banding.





The next stage of bracket evolution included
modification of the base design to provide
higher bond strength with adhesives, while
concurrent efforts focused on decreasing the
bracket surface.
The bracket manufacturing process employed
mechanical deformation or wrought processing
technique to fabricate these appliances.





Early commercially available aesthetic product
included both plastic brackets fabricated from either
poly crystalline or single crystal alumina.
The thicker profile of the initial ceramic brackets
caused slight discomfort for some patients.








In describing bracket evolution, it is important to
include the introduction of the self ligating bracket.
This was the result of an effort to develop a reliable
appliance that would maintain steady force levels
during activation while providing decreased
frictional resistance and optimum three dimensional
control of the tooth movement.
Important characteristic of these appliances
documented through both in vitro and vivo studies is
the potential elimination of cross-contamination
through the avoidance of elastomeric ligature.

Metallic brackets






The morphology of the base of the stainless steel
brackets, which is composed of metal mesh, yields
adequate adhesive bond strength values to enamel.
Gwinnett and his colleagues, determined the
optimum mesh size for increased bond strength.
Recent investigations were not able to identify any
differences in the bond strength between
conventional bracket bases with more condensed
mesh configurations.

Advance in metallic brackets




Despite the clinically sufficient bond strength
provided by conventional metal brackets, some
attempts have focused on increasing the
strength of the bracket-adhesive interface.
Droese and Diedrich have introduced the
plasma-coated metal bracket bases having a
variety of mesh design as well as ceramic
bracket bases. They reported that the
enormously increased active surface area of
the base resulted in much greater interlocking.





For metal brackets, the non-mesh, plasma-sprayed
bases had tensile adhesives bond strengths similar to
those of unsprayed bases.
There was alarming reports on the corrosion
potential of the AISI type 316L austenitic stainless
steel alloy. This alloy contains – 16-18% Cr, 1014% Ni, 2-3% Mo and maximum of 0.03% C, the
“L” designation refers to the lower carbon content
compared to type 316 stainless steel.





Although the 316L stainless steel bracket alloy
has performed well clinically, some corrosion
of this material may be identified in the form
of discoloration of the underlying adhesive
layer.
Maijer and Smith have attributed this effect to
the diffusion of corrosion products from the
bracket base to the adhesive, noting also the
potential for enamel discoloration.

Aesthetic brackets





Appliances fabricated from alumina and zirconia
ceramics, as well as a variety of plastic brackets.
A 2205 stainless steel alloy that contains half the
amount of nickel found in the 316L, alloy has been
recently proposed by Oshida, Moore and their
colleagues.
The 2205 stainless steel alloy has a duplex
microstructure consisting of austenitic and deltaferritic phases, and is harder than the 316L alloy
when coupled with NiTi, beta-titanium, or stainless
steel archwires.



Matasa measured the microhardness values of
the metallic brackets to obtain information
about the relative strengths of the bracket
alloys, it was found that the 316L alloy had
much lower hardness compared to the
precipitation hardening 17-4 stainless steel
bracket alloy, although the former had
significantly higher corrosion resistance.


Plastic brackets


The first plastic brackets were manufactured
from unfilled polycarbonate and introduced
during the early 1970s. But, unfortunately
these brackets had a tendency to undergo creep
deformation when transferring torque loads
generated by archwires. To alleviate this
problem ceramic reinforced, fiberglassreinforced, and metal slot-reinforced
polycarbonate brackets were introduced.



Plastic brackets are generally made from
polycarbonate, but were subsequently found to
suffer from several problems. These included
distortion following water absorption, fracture,
wear, discolouration and an inability to
withstand the torquing forces generated by
rectangular wires. (Reynolds, 1975)




While the metal slot-reinforced polycarbonate
brackets appear to be capable of generating the
desired torque on teeth under clinical
conditions, problems have been reported with
the integrity of the slot periphery. Some of the
metal slots have a level of surface roughness
that may significantly effect archwire sliding
friction.





A beneficial consequence of the relatively low
elastic modulus of polycarbonate is that the
load applied during debonding of the plastic
brackets results in a peel-off effect.
Ceramic brackets have the advantages of
permanent translucency and greater strength.
Unfortunately they have the disadvantage of
brittleness and excessive bond strength.( Scott,
1988) and enamel damage on debonding
(Joseph and Russouw, 1990)





Attempts have been made to combine the best
properties of plastic and ceramic materials in a
single bracket. One approach has been the ceramic
filled plastic bracket. Although these brackets are
easier to remove from enamel than the ceramic
brackets, this is due to their significantly lower bond
strength.
A different approach has been taken by combining a
ceramic bracket with a polycarbonate laminate as
the bracket base. (Ceramaflex* brackets. TP
Orthodontics, Indiana).

Ceramic brackets






Most of the ceramic brackets are made of highpurity aluminum oxide, and the brackets are
available in both polycrystalline and single-crystal
forms.
Ceramic brackets fabricated from the polycrystalline
zirconium oxide were subsequently manufactured in
Australia and Japan.
Optical properties and strength are inversely related
to the polycrystalline alumina ceramics: the larger
the individual grains in the microstructure, the
greater is the ceramics translucency.





Heat treatment must be carefully controlled to
prevent grain growth that would degrade the
physical properties.
While the manufacturing process readily
allows alumina brackets to be molded to the
desired geometry, structural imperfections at
the grain boundaries or trace amounts of
sintering aids can serve as sites of crack
initiation under stress.



The single crystal alumina bracket contain less
impurities than are found in the polycrystalline
alumina brackets, which require the presence
of sintering aids during manufacturing. Single
crystal alumina has lower resistance to crack
propagation than does polycrystalline alumina.






Zirconia brackets have the possibility of
achieving much higher values of fracture
toughness than are possible for polycrystalline
alumina brackets.
Smooth bracket base surfaces should better
distribute the shear stresses over the entire
adhesive, while minimizing localized areas of
stress concentration.


Self ligating brackets






Self-ligating brackets result in greater patient
comfort, shorter treatment time, reduced chair
time, and greater precision and control of tooth
translation.
Self-ligating bracket design permit the use of
lighter force levels and impart lower frictional
forces compared with ligated brackets.
Friction during tooth translation is reduced
significantly, due to elimination of steel or
elastic ligatures.





Self-ligating brackets has been reported to
reduce the risk of percutaneous injury and the
potential for transmission of hepatitis B virus,
hepatitis c virus, or human immunodeficiency
virus for the orthodontist and the support staff,
self-ligation decreases the possibility of soft
tissue laceration and infection from the cut end
of ligature ties.
The elimination of tie – wings and other type
of food traps on some self-ligating bracket
designs significantly elevates the hygiene level
of all patents.

Frictional Resistance of the Damon SL Bracket
RUPALI KAPUR et al (JCO 1998)
 Twenty Damon SL self-ligating brackets and 20
Mini-Twin brackets were tested.
 All samples were .0225" X .030" maxillary first
premolar brackets with standard Andrews
prescriptions.
 Wires used were 55mm lengths of .018" X .025"
nickel titanium and .019" X .025" stainless steel.






Results
The Damon SL bracket showed significantly lower
kinetic frictional forces (p < .0001) than the Mini -Twin
bracket with both wires. With the nickel titanium wires,
the Damon SL brackets had a mean friction of 15.0g,
compared to 41.2g for the Mini-Twin brackets. With the
stainless steel wires, the Damon SL brackets produced a
mean friction of only 3.6g, compared to 61.2g for the
Mini-Twin brackets.


Comparison of self- ligated and ligated
brackets:
Ligation stability
Ligation
Force level
Friction
Sliding mechanism
Office visits
Treatment time
Esthetics
Patient comfort
Oral hygiene
Infection control
Instruments
Staff

Comparison behavior of 2205 duplex stainless
steel: (Jeffrey A. Platt) AJODO 1997The 2205 stainless steel is a potential orthodontic
bracket material with low nickel content (4-6wt
%) whereas the 316L stainless steel with a nickel
content (10-14wt%) is a currently used bracket
material.
Both were subjected to electrochemical and
immersion corrosion tests in 37°c, 0.9wt%
sodium chloride solution.






Electrochemical testing indicates that 2205 has
a longer passivation range than 316L.
When 316L is coupled with NiTi, TMA, or
stainless steel arch wire and was subjected to
the immersion corrosion test, it was found that
316L suffered from cervical corrosion. On the
other hand, 2205 stainless steel did not show
any localized cervical corrosion, although the
surface of 2205 was covered with corrosion
products, formed when coupled to NiTi and
stainless steel wires.



Considering corrosion resistance, 2205 duplex
stainless steel is an improved alternative to
316L for orthodontic bracket fabrication, when
used in conjunction with titanium, its alloys, or
stainless steel wires.








Shear, torsional, and tensile bond strengths of
ceramic brackets using three adhesive filler
concentrations: Alan J.Ostertag et al (AJODO 1991)
210 bovine teeth were bonded with one of three
ceramic brackets using a 30%, 55%, or 80% filled
adhesives.
The brackets were debonded with a shear, torsional,
or tensile force to test the bond strength and the site
of bond failure.







No significance was found in the shear, torsional, or
tensile bond strength of each ceramic bracket type in
relation to changes in the adhesive filler
concentration. However, there was a trend toward
increased bond strength with increasing filler
concentration.
The mechanically retained ceramic bracket showed
greater shear bond strength and maximum shear
bond strength in torsion than the chemical or
chemical/mechanically retained ceramic bracket.
The failure site was at the bracket-adhesive
interface.





Corrosion of orthodontic bracket bases : R. Maijer
and D.C. Smith.: AJO January 1982.
Recently attention was focused on the development
of black and green stains in association with directly
bonded stainless steel brackets. 12 clinical cases of
staining were studied. After intraoral photography of
the stains, the brackets were removed for
examination.





Multiple voids were observed at the resin-bracket
interface, especially at the periphery. Considerable
deterioration of the alloy base and mesh structure
was observed in the void areas.
Findings suggested that the presence of voids,
together with poor oral-hygiene, led to corrosion of
the type 304 stainless steel and formation of colored
corrosion products which can result in enamel
stains. Thus use of improved corrosion resistant
stainless steel is recommended.

Alternatives to ceramic brackets: the tensile bond
strengths of two Aesthetic brackets compared Ex
vivo with stainless steel foil-mesh bracket bases :
S. Arici and D. Regan. BJO 1997.
The mean tensile/peel bond strength were evaluated
for three types aesthetic brackets (a ceramicreinforced bracket and two generations of a
ceramic/polycarbonate combination bracket). These
were found to be significantly lower than the mean
tensile/peel bond strength of a conventional foilmesh stainless steel bracket base.







Failure of the ceramic-reinforced
polycarbonate brackets occurred
predominantly by fracture of the tie wings
during testing.
With the ceramic/polycarbonate combination
brackets, the majority of the specimens failed
due to separation of the ceramic and
polycarbonate parts of the bracket.


The fracture strength of ceramic brackets :
Daniel A. Flores et al; (AO 1989).
The fracture strength of different ceramic
bracket under different surface conditions and
ligation methods using a torsional wire
bending force were compared.
Five different bracket types (two polycrystalline,
two single-crystal, and one metal) were tested
using elastic and wire ligation.
Results showed a significant difference between
bracket types and surface conditions.





Non-scratched single-crystal brackets had higher
fracture strengths and slightly higher fracture
loads than polycrystalline brackets. However,
single crystal brackets were significantly
adversely affected by surface damage, while
polycrystalline brackets were not significantly
affected by surface damage.


Elastomeric ligatures and chains






Elastomeric products are used in orthodontics as
ligatures and as continous modules (chains) for the
engagement and retraction of teeth.
The elastomeric modules were first introduced to
orthodontics three decades ago and have gained
almost universal acceptance by the profession.
Due to the force degradation exhibited by the
elastomeric chains, over the past decade there has
been increasing interest in self-ligating brackets.

Elastomeric ligatures and chains are poly urethanes,
which are thermosetting polymers possessing a
structural unit formed by step-reaction
polymerization.
General properties of electrometers: by Billmeyer,
 when stretched rapidly, elongations greatly in
excess of 100% can be achieved, with no major loss
of energy.









The highest values of tensile strength and
stiffness are obtained after full stretching.
Upon removal of the tensile force, a rapid
contraction occurs, since the polymer structure
has a strong tendency to return to its original
condition.
Full recovery takes place as long as the tensile
force does not exceed the elastic limit,
demonstrating the high resilience of these
materials.





Riley et al (1979) determined that steel
ligatures generated more friction than elastic
ligatures, particularly when plastic brackets
were used.
Kusy et al (1988) used laser spectroscopy to
study surface roughness of orthodontic wires.
Among the 4 wire-alloys that are commonly
used in orthodontic practice, stainless steel
appeared the smoothest, followed by cobaltchromium, beta-titanium and Nickel-titanium.
Kusy cautioned that surface roughness and
friction in orthodontic appliance systems have
yet to be correlated.





Schumacher and Bourauel (1990) conducted a
series of experiments to find the friction forces
affected by the ligation technique. They
inferred that friction is determined by the sort
of ligature and the way of ligation and not by
the dimensions of different archwires.
Sims and Waters (1993) compared self –
ligating and two other type of ligations. The
placing of figure of “8” tie increased friction
than self ligating brackets, because the self
ligating brackets apply less frictional contact
to the arch wire than conventional ties Siamese
brackets.

Conventional ligatures:
clinician prefer to use these materials over the
0.20mm to 0.36mm stainless steel ligature wires for
several reasons, including the ease of application,
potential for fluoride release, patient-friendly nature,
aesthetic appearance and decreased force delivery.
This force been found to reach the levels achieved
with stainless steel ligatures in twin brackets were
the extension of the elastomer is maximized because
of the large size of the bracket.





Taloumis et al have reported the force decay of
variety of elastomeric ligatures in a simulated
oral environment. There was an initial force
loss of about 50-60% during the first 24-hour
interval. The force decrease continued at a
significantly slower rate for 7-10 days, and
signs of permanent deformation and alteration
of the shape of the elastomers were evident
following their recovery from the medium.







When overall diameter of the module is decreased
for a given mass of elastomer, the force delivery
increases because of the greater wall thickness; this
anticipated relationship was observed by Taloumis
et al.
Huget et al observed that water acts as a plasticizer
by weakening intermolecular forces in the
polyurethanes, leading to chemical degradation.
Chromatographic analysis has shown increased
leaching from elastomeric modules immersed in
water and subjected to 7 days of stretching.





Elastomeric ligatures may be ineffective for
the treatment applications involving large
rotational moments, where the exertion of an
substantially decreased force would fail to
completely engage the archwire in the bracket
slot for the full term of activation.
The PH and temperature variations in the oral
environment, along with accumulation of
plaque and formation of microbial colonies on
the surface of the elastomerics, may effect the
structure, surface properties, and conformation
of the polyurethanes.

Elastomeric chains:
Difference in the force decay between the ligature
and the chain are:
 Variations in the additives incorporated in the basic
polyurethane polymer to obtain the final product.
 Variations in manufacturing techniques, where die
stamping or injection moulding is used to fabricate
the modules.
 Variations in morphological or dimensional
characteristics of the chains.







Ash and Nikolai showed that the force
degradation is greater in vivo compared to in
vitro conditions.
More recently, Stevenson and Kusy employed
a Maxwell-Weichert model. The model
assumes that the force degradation arises from
two processes: a rapid mechanism that is
responsible for the large initial force loss, and
a second mechanism that accounts for the
relatively slow rate of force loss at longer
period of time.





Traditionally these modules have been used
for the retraction of the anterior teeth to close
the extraction spaces as well as for the closure
of the diastemas.
With the advent of rare-earth magnets and
superelastic NiTi coil springs that are capable
of producing constant low force over a
extended period of time, the use of
elastomerics has diminished significantly.



Several studies have also dealt with the use of
prestretching to eliminate the force loss by
elastomeric modules. Two modes of pre
stretching have been proposed; the
instantaneous prestretching technique used by
young and Sandrik and by Chang would be
much more convenient for the orthodontist
than the extended time technique of
prestretching described by Brantley et al.

Evaluation of frictional forces of different
archwires materials against preadjusted
edgewise stainless steel bracket, using two
modes of ligation: Friction has always been
one of the main factors in orthodontic
movement that has occupied the clinician’s
mind. In this study five different alloys were
used to find the least amount of friction:
Stainless steel, Nickel titanium, Chrome-cobalt,
Copper-NiTi and Beta-Titanium.









The bracket chosen for the experiment is
stainless steel preadjusted edgewise with a
0.022 x 0.025 inch slot size.
The two modes of ligation are: Elastic modules
and Stainless Steel ligature wires.
The test was done using an instrument called
“the cool flow factor controller apparatus”.
The results obtained from this study
demonstrate that the least frictional forces
generated is that of Stainless steel wires, using
elastomeric modules.



Also the most values were recorded using the
beta-titanium alloy archwire, which in addition
to high surface roughness, the form of
microwelds with the brackets in dry conditions
with process of ion implantation implemented
on TMA alloys, there is a favourable 54%
reduction of kinetic friction presenting a viable
method of reducing the amount of friction.



Conclusion: Admitting there is no such thing
as the “ideal” archwire material that can
satisfy all the criteria for an ideal treatment,
and is devoid of any disadvantages. Therefore,
the final say belongs to the clinician to use that
knowledge, strike a compromise and
improvise his objectives and treatment plan
based on the choice of the material at hand,
which in turn will differ.







So far the stainless steel has been proven to
allow the least amount of friction among the
vast number of materials available to the
clinician.
The Beta-Titanium had the highest frictional
values recorded. Therefore it is safe to say that
the material of choice for maximum anchorage
cases with least resistance in sliding of the
wire is Stainless Steel.
Also that the ligation using elastic modules
produces less amount of friction as compared
to stainless steel wire ligation.

Orthodontic adhesive systems


The basis for the adhesion of brackets to
enamel has been enamel etching with
phosphoric acid, as first proposed by
Buonocore in 1955.



Bonding of brackets to enamel has been the
crucial issue in orthodontics research.
The introduction of an acid-etching technique
in the 1950s to bond dental restorations to
tooth structure was the breakthrough point in
the history of orthodontic bonding.






The chemically activated orthodontic adhesives
employ benzoyl peroxide as an initiator, which is
activated by a tertiary aromatic amine such as
dimethyl-p-toluidine or dihydroxyethyl-p- toluidine.



Two-phase products were the first to be tried by
orthodontist in the early days of bonding.
The manipulative process is problematic, relatively
time consuming, and these materials are gradually
being eliminated from orthodontic practice.






Mixing of the two components causes surface
porosities and air voids in bulk of the material,
owing to the prolonged exposure to air and
the inevitable entrapment of air bubbles.



Studies have shown that photo-cured
composites, intentionally mixed as if they
were chemically cured materials, also
demonstrated severely porous surfaces and air
voids in the bulk materials.





One phase adhesive system: The principle of
inhomogeneous polymerization was
introduced in orthodontics with the
development of the no-mix bonding resins,
which were intended to minimize the mixinginduced defects of the material.
Recent evidence suggest that the degree of
cure for these adhesives is comparable to that
of the two-phase systems for surfaces in
contrast with the enamel.



This might be attributed to the surface-tovolume ratio of the adhesive layer, which can
depend on several factors. A study found that
the thickness of adhesive layers prepared
under simulated clinical conditions ranged
from 120-250 µm, depending on the
morphology and design of the bracket base.


D.N Kapoor, V.P Sharma, Pradeep Tandon,
Kamlesh Pandey: Comparative evaluation of
Tannic acid, Citric acid and phosphoric acid as
etching agents for direct bonding (JIOS 2002)
Concluded that:
1.Application of 37% phosphoric acid for
15 seconds produced comparable etching
topography when 50% tannic acid was applied
for 90 seconds.
2. Electrothermal debracketing technique
produced bond failure at adhesive bracket
interface with no iatrogenic damage to enamel.



3.Assessment of penetration depth revealed that
37% phosphoric acid dissolves more enamel than
tannic acid or citric acid.
5. 50% Tannic acid when applied on enamel for
90 sec provided the tensile bond strength closer to
37% phosphoric acid.
So 50% Tannic acid could be an alternative to
phosphoric acid for etching as it dissolves lesser
amount of enamel and at the same time provides
similar tensile bond strength.

Ashima Valiathan, Ashil A.M. African Journal of
Oral Health Sciences 2006 _ Invitro study (In press)


Found out the efficacy of Transbond Moisture
insensitive primer , in the dry state and in the
presence of saliva and compared it with
conventional Transbond XT.



It was found that in the presence of salivary
contamination, brackets bonded using Transbond
MIP showed significantly higher bond strength
(14.53 Mpa) as compared to brackets bonded with
conventional primer (9.36 Mpa)



Francesca, Cacciafesta, Andrea, Brinkmann AJO
April 2006

assessed the effect of light tip distance on the shear bond
strength and failure site of the bracket cured with 3 light
curing units (halogen, LED, Plasma arc)
At a light
tip distance from bracket base of 0 mm they showed no
significantly different shear bond strength,
At light tip distance of 3mm no significant differences
were found between the halogen and plasma arc lights
but they showed higher bond strengths than the LED.
At 6mm plasma arc cure showed significantly higher
shear bond strengths than the other two.


Conclusion: In hard to reach areas plasma arc cure
light is suggested for optimal efficiency

Moisture-resistant adhesive:
Transbond MIP(3M).,Assure (Reliance)





It is available in a primer formulation (MIP) that
replaces the conventional bonding agents applied to
the enamel surface and is based on the hydrophilic
attraction of its constituents.



The main reactive component of this product is a
methacrylate-functionalized polyalkenoic acid
copolymer originally used in the dentin bonding
system marketed by the same manufacturer.






Moisture-active adhesives:
They require rather than tolerate the presence of
moisture for proper polymerization.
They require no bonding agent.
However, the surface must be intentionally
wetted prior to application.

A recent product based on a cyanoacrylate formulation
(Smartbond, Gestenco International AB,Sweden)
has demonstrated superior properties, excellent in
vitro performance and easy clinical application
without the need for etching and liquid resin
coating.






Srivastava A; Gorantla S; Valiathan A.
(TIBAO 2002) compared the bond strength of
two indigenously developed cyanoacrylates
(N-Butyl cyanoacrylate and Isoamyl-2cyanoacrylate) with a conventional self-cured
composite (Right On).
Results :
N-Butyl cyanoacrylate had higher bond
strength than the control composite, but it
deteriorated when stored in physiologic saline
for 48 hours.



Isoamyl-2-cyanoacrylate had significantly
lower bond strength when compared to the
other samples in all the three groups under
study.



So this study showed the need for further
work to be done with cyanoacrylates to
decrease their bio-degradability, so that they
can be clinically useful in orthodontics.











James Sunny P, Valiathan A. A comparative invitro
study with new generation ethyl
cyanoacrylate(smartbond) and a composite bonding
agent (TIBAO 2003)
Cyanoacrylate (Smart Bond) was compared with a conventional
composite (Right-On)
Shear bond strength was measured at 1 hour (dry), 24 hrs and
48 hrs (in artificial saliva).
Results: Composite showed higher bond strength than
cyanoacrylate at all time intervals.
Smartbond achieved a maximum bond strength of 5.07 Mpa at 24
hours, which declined at 48 hours to 5.01Mpa.
It was concluded that Smartbond might not be a better option
for bonding compared to conventional composite.



Ashima Valiathan, Gikku Philip, Sunil
Sachdeva: Clinical evaluation of Chitra
Composite - A comparative study



In 1992 The first and only BIS_GMA based, 2 component
chemically cured composite was developed by Valiathan et
al at the Sree Chitra Thirunal Institute of Medical Sciences
and Technology (Trivandrum)



Aim: To evaluate clinically Chitra composite in
comparison with Right-On ( commercially available
imported composite).



Subjects and Methods: 50 patients that reported to the
orthodontic department were selected.12-35 years.

Teeth on Left side bonded with Chitra composite (Test)
1 batch,25 patients with smaller filler size particle.
2 batch,25 patients with larger filler size particle.
Right side with Right-On composite (Control)
42 cases were bonded with standard edgewise brackets, 7 Beggs
and 1 straight wire.
The duration of evaluation was 6months to 15 months. Results:
The Overall Bond Failure for Chitra composite was on an average
17%
1st batch – 20% failure
2nd batch – 14% failure
For Right- On group it was 14.3%

In 24 hours failure:
For Chitra composite, it was 7.6%
For Right- On group it was 4.7%
The difference of 1.07 was statistically insignificant among
the test and control groups
Conclusion:
1.The bond failure of Chitra composite is
comparable to Right-On group.
2. Chitra composite with larger filler size had
greater bond strength at both 24 hrs and overall breakage.
3. There were no incidence of white spot
decalcification.





Upendra Kumar Gurjar, D.N. Kapoor, Amita Jain,
V.P. Sharma and Pradeep: (JIOS 1998) A
comparative evaluation of growth of
microorganisms on the surface of various
orthodontic bonding materials.
This study was conducted to evaluate and compare
the adherence and growth of alpha-haemolytic
streptococci on the surface of commonly used nomix orthodontic bonding materials and further to
scan the surfaces of these materials to find out a
correlation between their surface roughness and
adherence and growth of alpha-haemolytic
streptococci.





Microscope and alpha-hemolytic streptococci were
grown on their surfaces. Weight gain due to microbial
adhesion and growth was measured on the basis of
measured weight of dried sample after microbial
adhesion and growth of microorganisms minus weight of
sample before adhesion and growth.
It was found that the different no-mix orthodontic
bonding materials have different surface roughness even
when they were optimally prepared to be as smooth as
possible, the adherence and growth of alpha-haemolytic
streptococci on the surface of bonding materials was
significantly different from each other and there was a
definite correlation between the surface roughness and
adherence and growth of alpha-haemolytic streptococci
on the surface of bonding materials.

References
1.

2.

3.

William R. Proffit, Henry W. Fields,Jr., and
James L. Ackerman: Contemporary
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R.J. Dobrin, I.L. Kamel, and D.R. Musich:
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4.


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7.


10. Rodney K. Rhodes, Manville G. Duncunson, Jr.,

11.

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Ram S. Nanda, and Frans Currier: Fracture
strengths of ceramic brackets subjected to
mesial-distal archwire tipping forces: Angle
Orthodontist 1992; vol62: Page 67-75.
Sunil Kapila, Padmaraj V. Angolkar, Manville
G. Ducanson, Jr., and Ram S. Nanda:
Evaluation of friction between edgewise stainless
steel brackets and orthodontic wire of four
alloys: AJODO August 1990: vol 98: Page 117126.
Daniel A. Flores, Joseph M. Caruso, Garland E.
Scott, and M. Toufic Jeiroudi: The fracture
strength of ceramic brackets: a comparative
study: Angle Orthodontist May 1989; vol 60:
Page 269-276.

13. Mark H. Holt, Ram. S. Nanda, and Manville G.

Duncanson: Fracture resistance of ceramic
brackets during archwire torsion: AJODO April
1991; vol 99: Page 287-293.
14. Garland E. Scott, Jr.: Fracture toughness and
surface cracks – The key to understand ceramic
brackets: Angle Orthodiontist January 1988:
Page 5-8.
15. Theodore Eliades, George Eliades, and William
A. Brantley: Microbial attachment on
orthodontic appliances: Wettability and early
pellicle formation on bracket materials: AJODO
1995; vol 108: Page 351-60.

16. Sandra Gunn, John M. Powers: Strength of
ceramic brackets in shear and torsion tests: JCO
1991; vol 25: Page 355-358.
17. Thomas R. Katona: A comparison of the stress
developed in tension, shear peel, and torsion
strength testing of direct bonded orthodontic
brackets: AJODO 1997; vol 112: Page 244-51:
18. Thomas R. Katona: Engineering and
experimental analyses of the tensile loads
applied during strength testing of direct bonded
orthodontic brackets: AJODO August 1994; vol
106: Page 167-174.

19. Upender Kumar Gurjar, D N Kapoor, Amita
Jain, V P Sharma, and Pradeep Tandon: A
comparative evaluation of growth of
microorganisms on the surface of various
orthodontic bonding materials: JIOS 1998; vol
31: Page 47-52.
20. Ashima Valiathan, Ashil A.M. Efficacy of
moisture insensitive primer- An in vitro study.
African Journal of Oral Health Sciences 2006 (In
press)
21. K. Vijayalakshmi, M.S Rani: Comparison of
shear bond strength Of GIC with composite
resins- An Invitro Study JIOS 1995 Vol26 Num4
Page 144- 147
22. Denny J.Payyappilly, Ashima Valiathan, and
Surendra Shetty: Wires in orthodontics: JIOS
April 1993; vol 24: Page 60-65.

23. Reddy BR, Vijayalakshmi K: Estimation of
lactic acid around the brackets bonded with GIC
and no mix adhesive. JIOS 1998 Vol 31 Num1
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24. D.N Kapoor,V.P Sharma, Pradeep Tandon,
Kamleash Pandey: Comparative evaluation of
Tannic acid, Citric acid and phosphoric acid as
etching agent for direct bonding. JIOS 2002
Vol35 Num 2 page 54-62.
25. Amit Srivastava, Suresh Gorantla and Ashima
Valiathan. In Vitro evaluation of indigenously
developed cyanoacrylates as bonding agents in
comparison to a conventional bonding agent
Trends Biomater. Artif. Organs 2002: 16:25-27.

26. James Sunny and Ashima Valiathan “A comparative

In vitro study with newer generation Ethyl
Cyanoacrylate (Smartbond) and a Composite-bonding
agent” Trends Biomater.Artif.Organs. 2003;16(2):
page 83-89
27. Koyal Sarin and Ashima Valiathan. Comparison of
bond failure of Fuji Ortho LC Transbond XT – A
clinical study. Journal of Pierre Fauchard Academy
2003; 17:17-25
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Kumar Varshney: Bond strength as related to
different guaze mesh size: JIOS 2001; vol 34: Page 2-7.
29. Nitin D. Gulve, T. M. Bhagtani: A comparison of
shear bond strength and mean survival time treated
and untreated mesh backed stainless steel brackets, an
in-vitro assessment: JIOS 2002; vol 35: Page 124-128.

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