Leader in Continuing Dental Education

ELASTICS

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


INTRODUCTION


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Important adjunct in the orthodontic
practice
combined with good patient cooperation it
provides the clinician with the ability to
connect both anteroposterior and vertical
discrepancies.
Elastics are used to effect changes in
length, depth, and breadth of the dental
arches.


Anteroposterior tooth movements including
 Anterior retraction
 Mesial molar movements
 Correction of class II or class III occlusion
 Closure of extraction space
 Correction of overbite over jet during retraction
of anteriors is due to the joint influences of the
elastics & archwire
 Changes in arch breath associated with
expansion or contraction especially in correction
of posterior cross bites, are also joint influence
of the archwires and elastics, with elastic
contributing to the preponderance of force

Historical Background
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Natural Rubber, probably used by the
ancient Incan and mayan civilization was
the first known elastomer
Limited use is because of its unfavourable
temperature behaviour and water
absorption properties
Vulcanization by Charles Good Year in
1839. Use for natural rubber greatly
increased

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In Ancient times, metal bond, and spring were
used for retraction and for other corrections
In 1846 E. BAKER described by cutting a narrow
strip from thin sheet of India rubber and
extending it to nearly it’s almost capacity without
breaking.
Henry A. Baker in 1893 introduced the use of
Intermaxillary elastics with the rubber bonds
called as “BAKER ANCHORAGE”
Later Calvin S. case claimed that he developed
the intermaxillary elastics in 1890.


From a material point of view
 the greatest problem with all types of
rubber is they absorb water and
deteriorate under intra-oral conditions.
 Gum Rubber used to make the rubber
bands commonly used in house holds and
offices Deteriorate in the mouth begins
within a couple of hours and much of its
elasticity is lost in 12 to 14 hours.


They are been largely superceded by
Latex Elastics, which have a useful
performance life 4 to 6 times or long.
 Contemporary orthodontics Latex rubber
elastics should be used.
 Presently in India, (J.P. General Agency
Calicut) are manufacturing orthodontic
elastics.
Elastics can be of two types
 Natural Rubber Elastics
 Synthetic Elastics.
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Natural Rubber Elastics-hydrocarbon
polymer of Isoprene units available from
rubber tree
Chemical structure-Cis 1,4, polyisoprene
which contains 500 isoprene units.
Bleaching of the new latex will decrease
some of the resilient properties.


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The most important limitation of natural
rubber is its enormous sensitivity to the
effects of ozone or sunlight UV light which
generating free radicals cause cracks.
Free radical breaks down unsaturated
bonds at the molecular level a water
molecule is absorbed.
This weakens later polymer chain.
The swelling and staining is due to the
filling of the voids in the matrix by fluids &
bacterial debris.

Physical properties
All rubbers are polymers.
 They possess long flexible molecules which can
be cross linked to a three dimensional network.
 Rubber develop their full potential only when
they undergo cross-linkage (uncross linked
rubber possess poor physical properties)
 Rubber manufacturer’s crosslink the rubber by
heating the raw rubber with sulphur and other
chemicals. This process is known as
“Vulcanization”

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Two properties which differentiate rubber
from other materials are
Elasticity/Stiffness
All cross linked rubber are highly elastic.
They can be stretched several folds
without breaking and will quickly return to
their original shape or releasing the force.


Chemical structure
The composition of natural rubber elastic were
classified by GEORGE NEWMAN (1963)
 1. Natural rubber
100 parts
 2. ZnO
0.05 Parts
(Activator)
 3. Stearic acid
0.05 parts
 4. Mercapto Benzothiazole 3 parts
(Accelerator)
 5. Sulphur
- 3 parts
(cross-linking elasticity)

SYNTHETIC ELASTICS
Were introduced is 1960’s and since they largely
replaced the later elastics for intra arch tooth
movement.
Used for  cuspid retraction
 Closing diastemas
 Rotational correction
 Replacement of ligature
 General space closure
 Separators
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Advantages
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Accurate continuous gentle force
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Reduce arch wire manipulation
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Easy to install (little patient cooperation)
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Highly resistant to
 breakage
 loss of elastic force
 deterioration in mouth

Disadvantages
 They stain permanently shortly after being
placed in mouth
 Variability in force delivery is greater compared
to the later elastics.
 % deformation of original length of synthetic
elastomers in greater than that of latex elastics.
 They decompose moist heat / and also cause
swelling and slow hydrolysis (fluids and bacterial
debris)
 -Autocatalytic process-degradation
 Prevented by the addition of anti-oxidants like
phenyl α and β napthalamines

STAINING
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Elastomeric materials do stain from certain
food such as mustard. The attempt to solve this
problem by masking with metallic colour
inclusion reduces the strength and elasticity.
Study in 1990 by Kenneth K. khew
 No staining
with coca-cola /colourless
food stuffs
 Gradual staining chocolate drinks, Tomato
ketchup
 Rapid staining Tea/coffee

Classification of Elastics
According to material,
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Latex Elastics
–
natural rubber materials
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Synthetic elastics – Polyurethane rubber contains
urethane linkage
According to manufacturers.
3) According to their use,
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Intra oral elastics -may be light, medium to heavy
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Ex: latex elastics, elastic chains, ligatures
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Extra oral – Elastic modules plastic chains and heavy
elastics


Different trade names, further classified by the internal diameter, force
loads, on their colour coding eg. T. P. Orthodontics.


Anteroposterior Elastics : 1/4 inch,
3.502 (light) 1/4 inch, 602 (heavy)
Class 1 Elastic
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Extend within each arch (intra-arch
elastics) and are primarily used as close
spaces, in aid of the elastomeric chain


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Class II elastics
Extend from the lower molar teeth to the
upper cuspids (inter arch elastics)
They are primarily used to cause anteroposterior
tooth changes e.g. aid in obtaining class I cuspid
relationship from a class II relationship.
If the lower second molars are banded and
included in the treatment mechanotherapy, it is
best to extend the elastic from the 1st molar to
the cuspid tooth to avoid extrusion of the second
molar and the creation of an open bite anteriorly.


Side effects of elastics
 extrusion of the lower posterior teeth
 labial tipping of the lower anterior teeth
 lowering of the anterior occlusal plane
 creation of a gummy smile
 If any TMJ discomfort, elastics should be
discontinued

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Class III Elastics
Exact opposite of the class II, they extend from
the upper molar to the lower cuspids and are
used in the treatment of class III malocclusion.
They promote extrusion of the upper posterior
teeth and flaring of the upper anteriors, along
with lingual tipping of the lower anteriors.
In over treated class II it is occasionally
necessary to use class III elastics towards the
end of 3rd stage in order to eliminate an edge to
edge of anteriors

Vertical elastics: 1/8 inch, 3.5 oz,3/16
inch, 6 oz (heavy)
Triangle elastics:
 Aid in the improvement of class I cupid
inter cuspation and increasing the overbite
relationship anteriorly by closing open
bites in the range of 0.5 to 1.5mm.
 They extend from the upper cuspid to the
lower cuspid and first bicuspid teeth.

Box elastics
Box elastics are worn during the final
stages of the treatment. Most box elastics
are 3/16 inch, 6 ounce
3 Types of boxes are, the anterior, lateral
and buccal.
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Box shape configuration and can be used
in a variety of situation to promote tooth
extrusion and improve inter cuspation.

Anterior elastics
 →Are used to improve the overbite
relationship of the incisor teeth
 → Open bites upto 2mm may be corrected
with these elastics
 → They may extend from the lower lateral
incisors, to the upper laterals (or) central
incisor teeth or from the lower cuspids to
the upper laterals.

Asymmetrical Elastics:
 → Class II on one ride / class III on the
other
 → Used to correct dental asymmetries
 → If a significant dental midline derivation
is present (2mm or more) on anterior
elastic from the upper lateral to the lower
central lateral incisor should also be used.

Finishing elastics: 3/4 inch, 2oz
 Are used at the end of treatment for final
posterior settling.
 In class II cases, the elastic begins on the
maxillary cuspid and continues to the
mandibular first bicuspid and in the same
“up –and-down fashion it finishes at the
ball hook of the mandibular first molar
band.

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In an open bite or class III case, the elastic
begins at the lower cuspid, continues to the
maxillary cuspid and finishes at the maxillary
molar.
The elastics are attached to ball hooks on the
brackets or to the K- hooks (heavy ligature wires
with an extension).
They should preferably be worn full time for
maximum effect, although 12hr a day wear may
be indicated to minimize the side effects.
They should be changed once or twice a day
because elastics fatigue (but e-chains can last
three to five weeks)

Lingual elastics
 This can be used as a supplement or a counter
balancing agent to buccal elastic force, thereby
increasing the efficiency of force distribution.
For example
 Lingual elastic forces can be used to correct
molar rotation. During space closure the
horizontal elastic on the buccal surface causes
molar to rotate slightly. This undesired rotation
can occur because of the tipping (or) rotational
freedom of the 0.016 inch archwire in the 0.036
inch buccal tube.
 Approximately, 10 degrees of toe – in bend is
required to nullify this rotational freedom.
 Lingual elastics can be placed on the lingual
hooks (or) cleats. This will prevent undesirable
rotation.

Check elastics by Hoecever .
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One end of the elastic is hooked over the
cinched distal end of the upper arch wire; both
strands are hooked under the cinched distal end
of the lower arch wire and the other end of the
elastic hook mesial to the upper canine. By this
way vertical anchorage can be increased.
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Check elastics can provide a potent
mechanism for overbite correction.

Elastic in removable appliance
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Elastics in conjunction with the removal
appliance are used for the movement of
single and groups of teeth and for
intermaxillary traction.
 It can be used to more impacted canine to
proper place along with the Hawleys
appliance.


The summer camp elastics: (Half-strength
elastics)
 when a second stage patient will be away from
the office for a long period of time, such as an
entire summer camp season and when it is
anticipated that the remaining extraction spaces
will close before he returns, he should be
directed to wear half-strength horizontal elastics
on both the buccal and lingual surfaces.
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Forces will be exerted on both the surfaces,
so that after the space closure there will be no
tendency for the anchor molar to rotate, which
happens when buccal horizontal elastics are
kept after all teeth have come into proximal
contact

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Diagonal elastics
Although midline shift are often selfcorrecting, diagonal elastic may be used
to supplement other mechanics in
correction of these asymmetries.


Zig – zag Elastics (Full strength elastics )
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When a second stage patient is to have a
bicuspid rotated this can be combined with
extraction space closure through use of zig-zag
elastics
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These are full strength elastics which do not
stretch all the way from cuspid to molar but
extend only from cuspid to bicuspid or from
bicuspid to molar as required. When viewed
from the occlusal surface, this gives zigzag
appearance hence the name.

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Since the anteroposterior pulling forces of the
two elastics combine to rotate the bicuspid and
simultaneously close the extraction space, these
elastics should not be used after the teeth in the
buccal segments are in contact, because this
can cause undesirable molar movements
including contraction, expansion and rotation.
So, zigzag elastics are not used in nonextraction case unless spaces are present in the
buccal segments

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Cross-bite elastics
These are worn bilaterally in the case of
double posterior cross bites and are worn on the
abnormal side in unilateral cross bite.
are also used to expand and upright lower
molar which are tipped somewhat lingually and
when the arch width of the lower has become
narrower than desired.
The correction of a posterior cross bite is
largely due to elastic force.
A 0.016 inch plain archwire of average size and
width extends between ¼ and ½ ounce of
expansive force while heavy rubber elastics can
exert 5,6 or 7oz.
So, the preponderant force in cross bite
correction in derived mainly from the elastics.

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Cross – palate elastics
This may be used to correct undesired
expansion of the upper molars during the third
stage.
The elastic extends from the lingual hook
placed on the upper molar of one side to the
other side.
Upper molar expansion during the third stage
in usually bilateral – the cross palate elastic is
appropriate because the force it exerts in pulling
one molar lingually is equal and opposite to the
force it exerts in pulling the other lingually.

Precaution – before wearing the elastics
 Direct the patient to remove the elastic for
several hours or as long as necessary, if tongue
soreness develops because of elastic
impingement.
 Caution the patient about the appearance of a
shallow furrow in the tongue, due to contact with
the elastic which disappear completely within a
week or two after the elastic is discontinued.


Open –bite elastics
These are used for the correction of
open bite and should be continued until
the anteriors are in an overcorrected
relationship of several millimeters.
Precaution:
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The incidence of root resorption of the
anterior teeth, particularly those of the
upper jaw, in treatment of open bite
malocclusions is rather high.
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This should be checked periodically with Xray and if root resorption is noted, discretion
should be exercised before attempting
correction of the anterior open bite since the rate
of relapse of these corrections in very high
Vertical elastic are contraindicated in open
bite case until the mesial cusps of the upper
first molar occlude on the mesial of the lower
second bicuspid.
The use of vertical elastics – for correction of
open bite, should be deferred until such time as
all spaces are closed and the occlusion are
normal.

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It is preferable to use a box or rectangular
elastic stretched around all four intermaxillay
hooks.
When the elastic is worn in this fashion, the
vertical portions of the elastic will stretch as the
patient opens his mouth, but will also pull some
of the elastic around the intermaxillary hook and
there by stretch the horizontal portion as well.
This reduces the increase in force created by
opening the mouth, such as occurs when short
vertical elastics are placed on the intermaxillary
tooth of each side.

Elastic Separators
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William E. Hoffman AJO 1972-73 July
Angle discussed the need for separation
in 1907. He explained the use of a brass
wire ligature passed under the contact,
and then carried on over the contact, after
which the ends were rightly tinsted
together. If it is worn for of few hours, the
ample space will be available for the
accommodation of the band

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Dalton in 1914 secured space between
teeth by means of a thin separating rubber
strip
1921- Calvin Case advocated the use of a
separating tape, which was a waxed tape
wrapped around the contact. If should be left on
for only 24hrs and then changed if separation
was not sufficient


Space gained after one day of wearing
 Latex elastics - 0.009 to 0.016”
 Plastic elastics – 0.006 to 0.014”
 Brass wire – 0.005 to 0.012”
 Plastic and latex separator give a rapid initial
opening and then continue separating until they
are removed. The latex are infrequently lost,
sometimes disappear sublingually below the
contact point and it is most painful
 Provide adequate early separation /and
continued to separate.
 Rarely sensitive and remain clean and in
position

ELASTOMERIC CHAINS
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Elastomer is a general term that encompasses
materials that after substantial deformation,
rapidly return to their original dimensions
Amorphous polymers made from poly urethane
materials
Were introduced in orthodontics in 1960s &
since then they largely replaced latex for intra
arch tooth movement

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Polyurethanes are not direct polymers of
urethane, but derived through a process of
reactions with either- polyethers with di (or)
polysiocyanates to produce a complex structure
of urethane linkage.
The basic respecting structure of this polymer
leads to enormous varieties in physical
properties they excel in strength and resistance
to abrasion when compared with natural rubber.

ADVANTAGES
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They are inexpensive
easily applied
relatively hygienic
require little or on cooperation compared to the
rest.
Coil springs are difficult to keep clean, retraction
springs and closing loop arch wires can impinge
the patient’s gingival and irritate mucosa.
Magnets are bulky, expensive and also difficult
to keep free of food debris.


DISADVANTAGES
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When exposed to an oral environment, they
absorb water and saliva, permanently stain, and
suffer breakdown of internal bonds leading to
permanent deformation.
They also experience rapid loss of force due to
stress relaxation, resulting in gradual loss of
effectiveness.
Also, they are unable to deliver a continuous
tooth moving force over an extended period of
time

Modules are manufactured by- injection
moulding process
Stamped modules
 Chain elastic
 Morelli chain elastic
 Ormco power chain
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Injection moulded
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Energy chain (Rocky mountain)
Elast - o - chain and alastiks

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Are polymers which may be stretched on a
manner similar to rubber and which will
relax to their original dimension when
unscratched.
Non-crystalline at room temperature, but
crystalline under tensile stress.
Another requisite is that the chains be
cross-liked , if cross linking is complete,
a network configuration prevails and the
resin become rigid.

Force Delivery / force degradation of
elastomeric chains
 one characteristic feature of elastomeric
chain is the inability to deliver a continuous
force level over an extended period of time.
 The fact that the orthodontic elastic lose their
elasticity thus leading to a reduction of force
has been well documented.


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In 1931, Betran suggested that elastics
lose over 30% of their elasticity and that
they should be replaced every day. It can
be termed a “reactivation cycle”.
During the course of a day of opening and
closing the month, about 1/3 of the
elasticity was lost.


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In 1970 Andresen and Bishara compared
latex elastics and unitek C-1 alastik
modules they found that after 24 hrs of
load Alastik suffered a 74% less of force
delivery latex elastics – 42%
They concluded that rubber elastics
maintain relatively constant force when
compared with plastic alastiks

Am.J. Orthodontics – Sept 1977.
 Force extension characteristics of orthodontic
elastics by Thomas R. Bales, Spiro J. Chaconas.
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The purpose of the study was to test the index
as given by the manufactures.
For example, the standard index employed by
suppliers indicates, at three times the lumen
size, the elastic will exert the force stated on the
package.
For example, a ¼ inch 3 1/2 ounce elastic
stretched to ¾ inch should yield a forced of 3 1/2
ounces.

The study was conducted in two different testing
environments
 A simulated oral environment
 Dry state.
 Unitek elastics / Ormco series were taken for
study.
 Instron test machine. (simulated oral
environment). No significant difference was
found between elastic tested in the dry and wet
environment.
They concluded their study by
 Selection of elastics based on 3 x lumen size will
probably result in more force being generated
than was previously reported.

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In 1978, Ash and Nikolai compared force
decay of chain extended and stored in air,
water and invivo.
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More force decay invivo than those kept in air.
No difference was noted between the chains
maintained in water and those invivo until 1
week.
They postulated that the effects of
mastication, oral hygiene, salivary enzymes
and temperature variation within the mouth
influenced the degradation rates of invivo
chains.

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In 1985 De Genova investigated force
degradation of 3 chains (Ormco power chains,
Rocky mountain energy chain, TP Elasto-ochain)
Chains were maintained at constant length and
stored in artificial saliva. One set of specimens
were maintained at 37°C and another was
thermal cycled between 15°C and 45°C.
They reported that the thermal cycled chain
displayed significantly less force loss after 3
weeks.
Short filament chains – higher initial force level
and retained a higher percentage of the
remaining force than the long filament chains.

A study in Bapuji dental college by Dr. Balajee
katta under the guidance of Dr. Sadasiva shetty
in 1993 showed continuous force decay
throughout. An initial decay and most of the
drop occurred during the 1st day.
 For Alastiks- 53%
 Elasto-o-chain- 48%
 e- links- 43.3%
 greatest percent of force decay per unit time
occurred during the first hour for
 alastiks – 57.7%
 elasto-o-chain- 40.6%
 e-links- 33.1%

Pre-stretching of elastics:

Attempts to alleviate the large initial force
degradation and improve the constancy of force
delivery have led several investigators to look at
the effects of pre stretching the e -chains before
placement
 In 1976 Allew k.wong recommended that the
elastomeric materials should be pre stretched
1/3rd of the original length to pre stress the
molecular polymer chains. The procedure will
increase the strength of the material. so for no
studies to substantiate his claim

In 1979 Brantley et.al; using elastomerics from two
companies pre stretching 4 sets of chains 100%
of their original length .
 Two sets were immersed in water at 37 degree
for 24hrs and three 3 weeks.
 Two sets were kept in air at room temperature
for the same time.
 After the pre stretching the chains were
extended 100% of their initial length and the
force decay rates were compared with
unstretched controls, they concluded that the
pre stretched chain in water provided nearly
constant forces if used immediately after
removal from the fluid media
 However chain pre stretched in air had
essentially the same force decay properties as
un stretched chains

In 1996 J.J.G.M.Pilon tested the time
dependent behaviour of orthodontic
elastics in different media invitro. six types
of elastics were tested under 4 different
conditions
 artificial saliva in the dark
 distal water in the dark
 in air in natural daylight
 in air in the dark

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elastics kept in artificial saliva and water
produced almost constant forces for 3 weeks.
Because a large variations was in intial forces
between elastics of same type ,they should
always be measured if forces are critical.
when elastics are kept in natural daylight ,the
force decay is significantly larger than when they
are kept in the dark.


A recent study – Angle orthodontist 2003.
 A comparison of dynamic and static testing of
latex and non-latex orthodontic elastics.
 The purpose of this study was to determine the
effects of repeated stretching (cyclic testing) and
static testing on the force decay properties of
two different types of orthodontic elastics.
 Samples – American orthodontics 0.25 inch 4.5
ounce latex and non-latex.

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Static testing – stretching the elastics to
three times marketed internal diameter
measuring force levels at intervals of 24
hours.
Cyclic testing – Used the same initial
extension but cycled the elastics an
additional 24.7 mm to simulate extension
with maximal opening in the mouth.

They concluded their study as follows,

Latex elastics retained significantly more
force then their non-latex equivalents.

Latex elastics lost 25% of force in 24 hours.
Non-latex elastics lost 50% of force over 24 hour
period.

Because of higher rates of force loss that
continued throughout testing, it is more
important that non latex elastics be changed at
regular intervals not exceeding 6 hours.

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Coil springs Vs Elastics
To overcome the drawbacks of
elastomeric material Andrew.L. Sonis in
1994 conducted a study to compare
niticoil springs and elastics.
He wanted to overcome the initial force
decay of elastics and to use a material
which provides optimal tooth moving force
and minimal operator manipulation.

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He found out that NiTi coil spring produced nearly
twice rapid a rate of tooth movement as
conventional elastics and NiTi coil springs
produced constant force over varying length with
no decay.
The super elastic sentalloyNiTi coil spring has
a desirable springback so tooth movement can
occur more quickly, efficiently, comfortably. The
coil maintained constant force whether it is
activated 5 or 15 mm.


Elastomeric versus steel ligatures
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Elastomeric ligatures are used in initial
positioning when immediate full bracket
engagement is not crucial, otherwise steel
ligatures are recommended.
Elastomers carry with them the problems of
fatigue and discoloration. The steel ligature puts
more definite force on the tooth, so that instant
arch wire placement in the slot is obtained.
Elastomers are also good traps which discolor
over a period of time. They should be replaced
at each appointment.

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Steel ligatures are generally used to tie
rotations, or when a rectangular arch wire is
placed.
Elastomeric ligatures are not used as often is the
mandibular arch. Usually the first wire is
rectangular and multistranded, since mandibular
incised torque control is so important. Thus,
ligature wires are used beginning with the first
appointment. However, where serious rotations
exists, elastomers are used usually in
conjunction with a round wire.
When using rectangular wires following the initial
archwire steel ligatures are always preferred.

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Fluoride release from orthodontic elastic chain
( 1993 JCO ) study done by Joseph , Grobler
and Russouw.
Orthodontic patients have been shown to run an
increased risk of developing plaque induced
dental and periodontal disease
Stannous flouride- inhibits plaque formation
The study was designed to determine the rate
and amount of stannous fluoride release from a
fluoride impregnated elastic power chain
The fluoride release was initially high and
dropped to a very low level after a week


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