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INDIAN DENTAL ACADEMY Leader in continuing dental education


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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 

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

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 ď Ž the greatest problem with all types of rubber is they absorb water and deteriorate under intra-oral conditions. ď Ž 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They are been largely superceded by Latex Elastics, which have a useful performance life 4 to 6 times or long.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. 

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 

Advantages  Accurate continuous gentle force  Reduce arch wire manipulation  Easy to install (little patient cooperation)  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  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,  Latex Elastics – natural rubber materials  Synthetic elastics – Polyurethane rubber contains urethane linkage According to manufacturers. 3) According to their use,  Intra oral elastics -may be light, medium to heavy  Ex: latex elastics, elastic chains, ligatures  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 ď Ž Extend within each arch (intra-arch elastics) and are primarily used as close spaces, in aid of the elastomeric chain

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

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: ď Ž 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. ď Ž 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. ď Ž

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.

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. ď Ž 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. ď Ž Check elastics can provide a potent mechanism for overbite correction.

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

The summer camp elastics: (Half-strength elastics) ď Ž 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. ď Ž 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)  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  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 non-extraction 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.

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 ď Ž Direct the patient to remove the elastic for several hours or as long as necessary, if tongue soreness develops because of elastic impingement. ď Ž 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:  The incidence of root resorption of the anterior teeth, particularly those of the upper jaw, in treatment of open bite malocclusions is rather high. 

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.

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 ď Ž ď Ž

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

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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


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     

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.


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

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. 

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.

In 1978, Ash and Nikolai compared force decay of chain extended and stored in air, water and invivo. 

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.

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: ď Ž 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 ď Ž 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; 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.

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, ď Ž Latex elastics retained significantly more force then their non-latex equivalents. ď Ž Latex elastics lost 25% of force in 24 hours. Non-latex elastics lost 50% of force over 24 hour period. ď Ž 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 ď Ž

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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 Leader in continuing dental education

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