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Introduction Classification of methods of space closure Biomechanical Concepts of Space closure Frictionless mechanics. Frictional Mechanics Extraction Space Closure with the Preadjusted Appliance. Extraction Space Closure in the Standard Edgewise Technique Retraction Mechanics with the Begg Appliance. V Bend Sliding Mechanics Extraction Space closure with headgear. The Hycon Device Implant facilitated extraction space closure Dento-alveolar distraction for canine retraction

Introduction Why do we extract teeth?? Relief of crowding. Retraction of upper anteriors for correction of overjet in Class II div 1 cases. Retraction of lower incisors to assist correction of Class III cases. Retraction of upper and lower incisors to improve facial profile in bimaxillary malocclusion cases. Help in correction of midline discrepancies.

Orthodontic space closure should be individually tailored based on the diagnosis and treatment plan. The selection of any treatment, whether a technique, stage, spring or appliance design, should be based on the desired tooth movement. Consideration of the force system produced by an orthodontic device aids in determining the utility of the device for correcting any specific problem.

Burstone’s Six Goals for Space Closure (AJO Nov 1982 The segmented arch approach to space closure) 1. Differential space closure. The capability of

anterior retraction, posterior protraction, or a combination of both should be possible. 2. Minimum patient cooperation. Headgear and interarch or intermaxillary elastics should not be a major component in controlling differential horizontal tooth movement during space closure. Their dependence on patient cooperation is reflected in a lack of precision and may limit treatment possibilities. They may have other applications treatment.

3. Axial inclination control . 4. Control of rotations and arch width. 5. Optimum biologic response. This includes rapid tooth movement with a minimum lowering of the pain threshold. In addition, tissue damage, particularly root resorption, should be at a minimum. 6. Operator convenience. The mechanism should be relatively simple to use, requiring only a few adjustments for the completion of space closure.

Classification of methods of Space closure I. Based on Wire Configuration: a. Continuous arch mechanics (Indeterminate force systems) b. Segmented arch mechanics ( Determinate force systems)

II. Based on friction: a. Friction mechanics e.g. sliding mechanics Canine retraction with coil springs, Continuous anterior retraction, Retraction with J-hook Headgear. b. Frictionless mechanics : The use of loops or specialized springs (Bull loop, T-Loop, Opus Loop, PG Universal Retraction Spring, Ricketts Retractor, etc.)

III. Based on the type of tooth movement: a. Translation (Standard Edgewise, Preadjusted Edgewise) b. Tipping / Uprighting (Begg, Tip Edge) IV.Based on the mode of retraction. a. Individual canine retraction. b. En masse retraction of anteriors.

V. Based on Anchorage Needs: Group A: Maximum Posterior Anchorage Group B. Symmetrical Space Closure Group C: Maximum Anterior Anchorage

Important Biomechanical concepts (From Raboud et al. Three-dimensional effects in retraction appliance design, AJO-DO 1997. ) To appreciate and predict the type of tooth movement that will occur from a specific force system, the effective resistance of the supporting tissue is described in terms of a center of resistance, C res. Center of resistance: is the balance point through which an applied force must pass for the tooth / dental unit to move linearly without any rotation. A single force applied at the center of resistance would cause the tooth to translate in the direction of that force.

When the force system applied is not equivalent to a single force applied at the Cres, the tooth will rotate. This movement is described by the Center of rotation, C rot, which is the axis around which the tooth rotates during the application of a specific force system. The activation of the appliance must provide both the appropriate level of force and moment-to-force (M/F) ratio if a particular movement is to occur

If the force system at the bracket is just a force (M = 0 and M/F = 0), the resulting tooth displacement is uncontrolled tipping and the center of rotation is apical to the center of resistance.

Increasing the M/F ratio can dramatically alter the C rot of the tooth or tooth segment. The center of rotation moves apically as the M/F is increased from zero until translation occurs.

With tooth translation there is no rotation and Crot is located infinitely far from Cres. Although there is some uncertainty about the specific value, it is generally accepted that an M/F ratio of approximately 8.5 mm will result in translation for a singlerooted tooth such as a canine. The M/F ratio of 8.5 mm is equal to the distance between the point of application of the force system at the bracket and C res.

Increasing the M/F ratio further now results in rotation opposite to the direction of uncontrolled tipping because C rot is now incisal to C res.

For further increases of the M/F ratio, the C rot moves toward the Cres from the incisal side. As a final limiting case when there is a very large moment, so that M/F approaches infinity (possibly caused also by a very small force), the C rot is essentially coincident with the C res.

A similar analysis can be applied in the occlusal plane. If the appliance is mounted on the buccal side then the activation forces F alone will tend to rotate the attached tooth not around the C*res (which in this plane is near the tooth axis) but around a C*rot, which is lingual to the center of resistance.

M* / F=0

To inhibit this longitudinal axis rotation and effect translation requires the application of a moment M*. The M*/F ratio for translation is the distance from the point of application of the appliance to the C*res (approximately 3.5 mm for a cuspid tooth if labial-lingual inclination is neglected).

M*/ F= 3.5

Increasing the M*/F ratio above this value will change the direction of tooth rotation so that C*rot is now buccal to the C*res. M* / F > 3.5

Note:The force F acting on a tooth for both the lateral and occlusal force systems is the same; however, the lateral moment M is different from the moment M* acting in the occlusal plane.

Anchorage is an important aspect of orthodontic space closure. It may be defined as the amount of movement of the posterior teeth to close the extraction space. The anchorage needs of a person could vary from absolutely no permitted mesial movement of posterior teeth (critical anchorage) to complete space closure by protraction of anteriors (Burning anchorage)

Anchorage may be classified as follows:

Space closure requiring precise anchorage control is difficult to achieve. For Group A anchorage , the mesial forces acting on the posterior teeth must be minimized or neutralized.

In order to achieve differential tooth movement, biomechanical strategies have to be incorporated into the appliance design.

Basically, in order to achieve Group A anchorage, there has to be a relative increase in the posterior moment to force ratio or a relative decrease in the anterior moment to fore ratio. This can be achieved by either altering the forces or the moments. Application of forces via extra oral appliances or elastics require patient co-operation, while the latter also have side effects.

This differential moment to force ratio in the anterior and posterior segments can be achieved by application of differential moments I.e . Increasing the posterior moment and decreasing the anterior moment. Posterior M/F ratio of about 12/1 encourages root movement, while anterior M/F ratio of about 7/1 causes a tipping type of tooth movement.

Loop Mechanics/ Frictionless mechanics Well designed closing loops allow the operator to achieve the goals of differential M/F ratio. Three important criteria in the use of closing loops are 1. Loop position. 2. Loop preactivation or gabling, and 3.Loop design.

Loop Position: Traditionally, when retracting anterior teeth, continuous closing loops are placed immediately distal to the lateral incisors or canines. The rationale behind this is that it allows repeated activation. Recent research however has shown that changing the position of the loop can augment or reduce posterior anchorage.

Off centered T loop with higher moment and extrusive force on the shorter leg, i.e. in the posterior segment.

Higher moment and extrusive force on the anterior segment due to anterior positioning of the T loop.

Loop Preactivation When a closing loop is activated, the anterior and posterior portions of the archwire deflect away from a parallel orientation. The moments acting on the archwire which is engaged in the brackets, are delivered to the teeth as the wire deactivates. Depending on the loop design, these moments encourage varying degrees of root control during space closure. Loop position has a critical role in determining the moments delivered.

However, research at the University of Connecticut has shown that moments occurring through activation are insufficient to produce an adequate force system necessary for root control. Thus, there is a need for additional preactivation bends or gable bends to increase root control, by increasing the moments delivered to the teeth. Thus the moments from the activation and from the gable bends act in concert to promote root control and anchorage.

A. Standard form and dimensions of 0.017 ´ 0.025-inch TMA T-loop described by Burstone before placement of preactivation bends. B, T-loop with preactivation bends placed, note that angulation of alpha and beta sides is produced by gradual curvature placed in wire.

Loop Design

1. 2. 3.


The final key to efficiency and space closure control is loop design. The ideal loop designs should meet the following criteria. Large activation. Low and nearly constant forces. Comfortable to the patient. Easily fabricated.

Several loop designs are available, though few meet all these criteria. In general, the more wire gingival to the bracket, the more favorable the activation moment, and therefore the better the overall M/F ratio. For example, a 10mm vertical loop has a M/F ratio of 3:1 when the activation is l mm or greater. At an activation of 0.5mm, the M/F ratio improves to 5:1, but it does not approach the 10:1 ratio needed for translation, until the activation is reduced to 0.2mm.

On the other hand, a T-loop spring with an 8mm horizontal portion and an 8mm vertical portion has an M/F ratio of 7:1 at 4mm of activation, improving to 9:1 at 2mm of activation. At 0.5mm of activation, the M/F ratio of the T-loop is 12:1, compared to 5:1 with a vertical loop. Clearly, the M/F ratio of a T-loop is better than that of a vertical loop at all levels of activation.

A vertical loop's M/F ratio can be improved by increasing its height, although there is only so much space available in the vestibule. The same is true of a T-loop, but once the horizontal section becomes equal in length to the vertical section, no improvement in the M/F ratio is gained by lengthening the horizontal section.

The addition of helices lowers the load/deflection rate without significantly affecting the M/F ratio. A loop bent from wire with a low modulus of elasticity such as TMA will have a lower Load/ deflection rate than a similar loop made from Stainless steel. Also, a closed loop has a slightly lower load deflection rate compared to an open loop, due to the small amount of wire needed to make the loop closed. A closed loop has a greater range of activation than an open loop, known as the Bauschinger effect.

With open loop, activation unbends loop. B. With closed loop, activation in direction of last bend increases range of activation. (Bauschinger effect)

Opus Loop (Siatkowski, AJODO 1997)

The PG Spring (Poul Gjessing, 1985)

Ricketts maxillary canine retractor (1974)

The Mushroom Loop (University of Connecticut)

Nickel Titanium Canine Retraction Spring( Watanabe, Miyamoto 2002)

Friction Mechanics This involves either moving the brackets along the archwire or sliding the archwire through the brackets and tubes. Friction plays a major role in sliding space closure, hence the term frictional mechanics. For translation to occur, a force system must be placed on the crown of the tooth at the bracket in such a manner as to create a moment which is equivalent in magnitude and opposite to that resulting from the force acting on the bracket.

In sliding mechanics such a balancing moment is not necessary

The force applied for sliding retraction should be of sufficient magnitude to overcome friction and also lie within the optimum range of force necessary for tooth movement. A mathematical equation can be derived to describe the overall resistance to sliding of an appliance. RS = FR + BI + NO

FR is caused by contact between the archwire and the bracket slot floor and/or a slot wall as the bracket slides along the archwire. When the archwire just contacts both edges of the slot walls as the bracket is angulated relative to the archwire, the BI component begins to contribute to RS. The angle at which the archwire first contacts the edges of the slot walls is called the critical contact angle for binding At still greater values, the bracket may physically deform the archwire, thus adding the NO component to the BI and FR component of RS

The variables affecting frictional resistance A) PHYSICAL VARIABLES: 1. Archwire: a. Material b. Cross sectional shape/ size. c. Surface texture. d. Stiffness. 2. Ligation of archwire to bracket: a. Ligature wires. b. Elastomerics c.Method of ligation/Self ligating brackets

3. Bracket: a. Material b. Manufacturing process. c. Slot width and depth. d. Design of bracket: single/twin. e. First order bend (in-out) f. Second order bend (angulation). g. Third order bend (torque).

4. Orthodontic appliance: a. Inter bracket distance. b. Level of bracket slots between adjacent teeth. c.Forces applied for retraction. B. BIOLOGICAL VARIABLES: 1. Saliva 2. Plaque 3. Acquired pellicle. 4. Corrosion.

a.     Wire material: Most studies have found stainless steel wires to be associated with the least amount of friction. This is further backed up by specular reflectance studies which show that stainless steel wires have the smoothest surface, followed by Co-Cr, β-Ti, and NiTi in order of increasing surface roughness. Kusy & Whitney (1990) found Stainless steel to have least coefficient of friction & the smoothest surface. However B titanium showed greater friction compared to Ni Ti

B. Wire Size: Several studies have found an increase in wire size to be associated with increased bracket-wire friction. In general, at non-binding angulations, rectangular wires produce more friction than round wires. However, at binding angulations, the bracket slot can bite into the wire at one point, causing an indentation in the wire.

C. Wire stiffness: Drescher et al (AJO-DO 1989) stated that friction depends primarily on the vertical dimension of the wire. An 016” stainless steel round wire and an 016 x 022” stainless steel rectangular wire showed virtually the same amount of friction. This was however lower than that for 018 X 025” wires. The authors stated however, that for mesiodistal tooth movement, rectangular wire is preferred because of its additional feature of buccolingual root control.

2. Ligation method Various methods of ligation are available: stainless steel ligatures, elastomeric modules, polymeric coated modules and finally the self ligating brackets, which may be having a spring clip (Hanson SPEED and Adenta Time) which pushes the wire into place, or it may have a passive clip which does not press on the wire (Activa and Danson II brackets.) Elastomeric ligatures are adversely affected by the oral environment, and demonstrate stress relaxation with time and great individual variation in properties. Stainless steel ligatures can be tied too tight or too loose depending on the clinicians technique.

Self ligating brackets with a passive clip have been shown to generate negligible friction. Henao & Kusy (Angle Orthod. 2004) compared the frictional resistance of conventional & self ligating brackets using various archwire sizes. They reported that self ligating brackets exhibited superior performance when coupled with smaller wires used in early stages of orthodontic treatment. However when larger 016 x 022� and 019 x 025� AW were tested, the differences between self-ligating & conventional brackets were not so evident.

3. Bracket a. Bracket Material: For most wire sizes, sintered stainless steel brackets produce significantly lower friction than cast SS brackets. (upto 38-44% less friction.) This difference in frictional forces could be attributed to smoother surface texture of sintered SS material. Ceramic brackets, in spite of their superior esthetics, have frictional properties far inferior to stainless steel. Highly magnified views have revealed numerous generalized small indentations in the ceramic bracket slot, while SS brackets appear relatively smooth

Since ceramic brackets on anterior teeth are often used in combination with stainless steel brackets and tubes on premolar and molar teeth, retracting canines along an archwire may result in greater loss of anchorage because of higher frictional force associated with ceramic than steel brackets. Greater caution in preserving anchorage must be exerted in such situation.

Titanium brackets are comparable to SS brackets in the active configuration & are a suitable substitute for SS in sliding mechanics.

b. Bracket slot width: Bracket slot width refers to the bracket dimension in the mesial distal direction. The effect of bracket width on friction has been controversial. Some studies have found bracket width to have no effect on friction. Others have found frictional resistance to increased with bracket width. Yet others have reported a decrease in friction with an increase in bracket width. Frank & Nikolai (AJO 1980) related greater friction with a wider bracket to the fact that binding occurs frequently at smaller degrees of angulation with wider brackets than with narrow brackets.

Kapila et al (AJO-DO 1990) reported that 018� slot sized medium twin brackets were associated with 1.5 times more friction than narrow single brackets, while wide twin brackets produced twice as much friction. Medium twin & wide twin 022� brackets also produced more friction than narrow single 022� brackets. They suggested that with a wider bracket the elastomeric ligature was stretched more than with a narrow bracket, producing almost twice as much friction, due to greater normal force exerted on the wire.

Drescher et al (AJO-DO 1989), Beduar et al (AJO-DO 91) & Omana et al (JCO 1992) suggested that with a narrow bracket, the tooth could tip considerably before binding occurred & once binding occurred it was of a severe nature, which resisted further sliding of the archwire. Bracket width is closely related to interbracket distance. The narrower the bracket, the greater the interbracket wire, and the greater the flexibility of the wire. This may result in greater chance of binding with the more flexible wire. Also, narrow brackets have the disadvantage of less rotational & tipping control due to smaller section of archwire engaged within the slot.

Frank & Nikolai (1980) found that frictional resistance increased in a NON LINEAR manner with increased bracket angulation. Ogata et al (AJO DO 1994) also noted that as second order deflection increased, frictional resistance was found to increase for every bracket-wire combination evaluated by them. Clinical Significance: For patients requiring maximum anchorage protection, complete leveling of the arch prior to using sliding mechanics is imperative. This will reduce the force required for retraction of the teeth because the frictional resistance will be decreased.

C. The role of third order torque: When torque is applied to the wire, its projected size is larger than the actual size of the wire. This further decreases the clearance between the archwire & the bracket and contributes to frictional resistance to sliding.

Extraction Space closure with the Preadjusted Appliance In the early days of the preadjusted appliance, in an attempt to prevent anterior teeth from tipping forward during the initial stages, elastic forces such as chains, modules, and inter- or intra-arch elastics were often applied prematurely between the anterior and posterior teeth. Thus, the anterior crowns were not merely held in position, but actually tipped distally.

In extraction cases, the premature application of elastic tension caused the cuspids to tip distally, which in turn opened the bite in the premolar area and deepened the bite anteriorly

This situation could normally be corrected, but it did result in a longer leveling stage and usually an extended total treatment.

McLaughlin and Bennett (JCO 1989) recommended placing figure-8 .010'' ligature wires (called "lacebacks") from the most distally banded molar to the cuspid in each quadrant. They are most advantageous in extraction cases, in which they can provide surprisingly efficient distal cuspid movement .

The figure-8 ligatures, when lightly and passively secured, initially cause a slight tipping of the cuspids with compression of the periodontal ligament in the area of the alveolar crest. However, because there is no elastic tension on the teeth, the cuspid roots have more than enough "rebound time" to upright into correct position as the main archwire takes effect

This technique provides 6-7mm of space opening in the anterior segments over six months, while leveling proceeds from light, multistranded wires into .020" round wires. If this space is more than desired, the lacebacks are discontinued before leveling is completed. If the case has more than 6-7mm of crowding, the most crowded teeth are not bracketed, and light push-coil springs are inserted to provide additional space. These springs are normally not used until .016" or . 018" round archwires are in place;

Push-coil springs used in especially crowded case. Headgear, Class III elastics, lacebacks, and bent-back archwires are used for anchorage control.

For comprehensive space closure with sliding mechanics, Mc Laughlin and Bennett (JCO 1990) recommended the use of 019"´.025" working archwire in an .022 "-slot system. Larger wires, although more rigid, restricted free sliding. Round wires and smaller rectangular wires provided less precise control of torque, curve of Spee, and overbite.

Hooks of .024 " stainless steel or .028 " brass are soldered to the upper and lower archwires. The average distances between hooks— 38mm in the upper arch and 26mm in the lower arch were found to cover most cases., Additional sizes of 35mm and 41mm (upper) and 24mm and 28mm (lower) cover most of the remaining cases.

The force required for space closure is delivered by elastic "tiebacks" An elastic module stretched by 2-3mm (to twice its normal length) usually delivers .51.5mm of space closure per month.

Group movement and sliding mechanics are combined for gentle, controlled space closure, so that about .5mm of incisor retraction and .5mm of mesial molar movement can be seen each month. The tiebacks are replaced every four to six weeks. Alternative force delivery systems were tested by the authors but found to have disadvantages: An elastic modular chain gave variable force, was difficult to keep clean, and sometimes fell off. Elastic bands, changed daily by the patient, relied on sometimes inconsistent cooperation. Pletcher-type wire coils delivered excessive force that caused tipping and binding, and they also proved unhygienic.

Considerations in Sliding Mechanics Proper alignment of bracket slots is essential to eliminate frictional resistance to sliding mechanics. Mc Laughlin and Bennett recommend tying the rectangular wires passively for at least the first month, until leveling and aligning is complete and the archwires are passively engaged in all brackets and tubes.

Leveling and aligning continues for at least a month after insertion of the rectangular wires, and space closure cannot proceed during that period.

Conventional elastic tiebacks are then placed In some cases, this phase takes three months.

There are three primary sources of friction during space closure First-order or rotational resistance at the mesiobuccal and distolingual aspects of the posterior bracket slots is produced by rotational forces on the buccal aspects of the posterior teeth. Second-order or tipping resistance at the mesio-occlusal and distogingival aspects of the posterior bracket slots is caused by excessive and overactivated tieback forces, which lead to tipping of the posterior teeth, inadequate rebound time to upright these teeth, and a resultant binding of the system.

The importance of light forces (50-150g) and minimal activation length (to provide time for uprighting) cannot be overemphasized. Third-order or torsional resistance occurs at any of the four areas of the bracket slot where the edges of the archwire make contact. Like tipping resistance, this is produced mainly by excessive and overactivated tieback forces, which cause the upper posterior lingual cusps to drop down and the lower posterior teeth to roll in lingually

Sources of friction during space closure. A. First-order or rotational resistance. B. Second-order or tipping resistance. C. Thirdorder or torsional resistance.

Problems during space closure 1.Since forces are directed from the first molars to anterior hooks on the archwire, small spaces occasionally open between the first and second molars. This can be managed in one of three ways: The first and second molars can be tied together before beginning space closure The tieback can be extended t o the archwire hook from the second molar instead of the first molar A "K-2" elastic can be extended from the second molar to the archwire hook, in addition to the elastic or wire tieback to the first molar

2. A damaged lower premolar or first molar bracket, can hinder space closure. Local thinning of the archwire can allow space closure to resume, but it is better to replace the bracket. Bracket damage is seen less than once a month with a typical case load.

3. Interference from opposing teeth sometimes restricts lower arch space closure, particularly if bracket placement was incorrect or a fullunit Class II molar relationship existed. Correcting the band or bracket position usually solves the problem.

4. As spaces close, the distal ends of the archwires will protrude more and more, and these protruding wires will tend to become bent gingivally by chewing forces. The archwires should be shortened whenever they extend more than 2mm from the molar tubes, both for patient comfort and for ease of archwire removal. Anything such as a ligature wire or an erupting molar that could restrict the steady distal emergence of the archwire should be eliminated.

Certain tissue factors can hinder full space closure with any kind of mechanics. Soft-tissue build-up can result from poor plaque control or overly rapid space closure. The alveolar cortical plate, mesial to the lower first molars, tends to narrow after extraction of the second premolars, especially in lowerangle situations. Retained roots, ankylosed teeth, and bone sclerosis are other possible factors to be considered.

Anchorage Control During Extraction Space closure In the maxilla, extracting the first premolars instead of the second premolars provides more anchorage gain. The effect is less pronounced in the mandible, because of a tendency for the cortical bone to form an hourglass shape, especially in lower-angle cases, which restricts mesial movement of the first molars The usual choice in balancing anchorage control is to extract upper 5s and lower 4s in Class III cases and upper 4s and lower 5s in Class II, division 1 cases.

Intermaxillary elastics are a convenient and effective method of anchorage control. They can be used routinely at force levels of l00g in average or low-angle cases. Much more care is needed in high-angle patterns, where muscular forces are less able to resist the extrusive component of intermaxillary force. In such cases, elastics can be used selectively for short periods, sometimes only at night, with force levels reduced to 50-70g. Rigid, soldered palatal and lingual arches can support anchorage during the leveling and aligning phase and during resolution of crowding, but were not found helpful during space

The facebow of conventional combination headgear, worn at night, can be used to control upper molars. In cases requiring intrusive force on the incisors, a J-hook headgear can be applied directly to upper archwire hooks. Reverse headgears (or facial masks) have been well accepted by some patients and have been effective in "losing" anchorage. The elastics are applied either directly to molar hooks or to archwire hooks after modification. A reverse headgear can deliver an asymmetrical force in cases of unilateral problems or midline shifts.

Lower utility arches for incisor intrusion and molar uprighting. This type of mechanics also provides additional lower anchorage. Archwire thinning is effective, but has been discarded because of reduced tooth control in the thinned areas. Selective torque application is more effective (especially in the incisor regions.) Flat wires can be adjusted quickly and easily at chairside to carry a customized 10-15째 of incisor torque. Molar torque can be selectively applied to resist mesial movement of the molars and create a basis for sound functional movements.

Selective application of torque in rectangular archwires can affect anchorage balance in both anterior and posterior regions.

Comparison of different force delivery systems in sliding mechanics. Samuels et al (AJO DO 1998) in a study of en masse anterior retraction, found that Sentalloy NITi closed coil springs produce more consistent space closure than an elastic module. There was no difference in the rate of space closure with 150g and 200g springs, but both were higher than that with a 100g spring or elastomeric module.

Dixon et al (JO 2002) compared the rates of orthodontic space closure using active igatures, polyurethane power chains and NiTi springs. Mean rates of space closure were 0.35 mm with active ligatures, 0.58 mm with powerchains and 0.81 mm with Ni Ti springs. The difference between the rate of closure between NiTi spring and active ligatures was significant. The authors concluded that NiTi springs are the most rapid, and are the treatment of choice, but power chains offer a cheaper option.

A later clinical study by Nightingale and Jones (JO 2003) comparing NiTi coil springs and elastomeric chains concluded that NiTi springs can exert very heavy forces when stretched between two hooks, which result in high force decay. Elastomeric chains retained a greater percentage of their initial force and achieved a rate of space closure similar to that of NiTi springs.

Jacob, Karanth and Shetty (JIOS 2002) studied the force characteristics of open and closed coil NiTi springs in a simulated oral environment. They reported that for a spring, as the size of the lumen increased there was a decrease in force delivered. With increase in diameter of wire used, the force increased. They found that greater length of open coil springs with large lumen showed good super elastic property, as compared to shorter closed coil springs.

Extraction space closure in the Standard Edgewise technique (Tweed) Charles Tweed, in the treatment of Class I bimaxillary protrusions with extractions, recommended anchorage preparation with tip back bends, followed by individual canine retraction and then incisor retraction.

Mandibular canine retraction 020 x .026 inch archwire. Tip back bends sufficient to maintain anchorage. Sections of open coil,length 1.5 times the distance between brackets of lateral & cuspid teeth. Tie back ‘T’ are soldered 1mm mesial to molar tubes. Intermaxillary hooks soldered in arch wire between between central & lateral. Maxillary headgear 14hours per day + Class III intermaxillary elastics.

Complete retraction of mandibular incisors .020 x .026 inch archwire is made. Vertical loops are bent 1mm distal to cuspid bracket. Posterior leg of 5mm and anterior leg of 4mm,elevate the occlusal plane in buccal segments thus preventing elongation of incisors as they are moved lingually. Type & amount of torque is governed by what lateral cephalogram indicates.

Maxillary canine retraction O20 x 026� arch wire with second order bends in the buccal segment. Use of open coil springs tied back to T stops for retraction of canine, similar to that in the mandibular arch. Intermaxillary hooks for elastic or headgear use. Headgear 14 hours per day. Use of Class II elastics when not wearing headgear.

Complete upper incisor retraction 020 x 026� archwire with distinct curve of Spee and second order bends placed 0.5 mm distal to the brackets on 2nd premolar and 1st molar. Sections of open coil spring are threaded on each leg and lay-on stops soldered 2.5 mm mesial to each second premolar bracket. The open coil springs are tied back to the second premolar bracket which in turn is tied to the molars.

Use of high pull headgear attached to hooks located between central and lateral incisor brackets. Use of intermaxillary Class II elastics continuously. Lingual root torque in incisal segment of arch wire for bodily movement.

Alternatively, Bull loops in a continuous archwire, incorporating tip backs and torque, could be used for upper anterior retraction. Again Headgear and Class II elastics are used for anchorage control.

Retraction mechanics with the Begg Technique Extraction space closure with the Begg technique is carried out in the second stage of treatment, following leveling and alignment. Some degree of space closure occurs during the first stage of treatment. Extraction spaces are closed by means of horizontal elastics or intramaxillary elastics(one on each side). In addition, Class II elastics (2 on each side) may be worn to maintain molar relations almost in Class III.

At the end of the second stage, the extraction spaces are closed by tipping backwards to a marked degree, known as “dishing in.�

A third stage of treatment accomplishes the uprighting of these teeth using special auxiliaries.

Staggers and Germane (JCO 1991) Because Begg brackets permit only a point contact between bracket and archwire, no moment is produced by wire bracket interaction. As a result, only uncontrolled tipping of the anterior teeth (center of rotation between the apex and the center of resistance) occurs during the stage of retraction. The third stage involves lingual torquing of the anterior roots, usually by means of a torquing auxiliary. A moment-to-force ratio of about 12:1 is required for such movement, and such a high ratio is technically difficult to achieve. For this reason, two-stage retraction with initially uncontrolled tipping is not the most efficient retraction method.

V-Bend Sliding Mechanics Originally developed by Mulligan, this approach is particularly efficacious for closing space by moving individual teeth (I.e. canine retraction or premolar protraction) along a round wire such as 018 or 020 SS. It is based on the principle that an off center bend applies a greater moment on the bracket adjacent to the shorter arm. Thus during canine retraction, an off center bend placed closer to the posterior teeth ie. adjacent to premolar bracket, (or molar bracket if premolar is not banded) would produce differential moments anteriorly and posteriorly, leading to differential M/F ratios.

Special considerations in adults:

Adults are likely to have two conditions that have an impact on mechanics of space closure: apical root resorption and inflammatory periodontal disease with concomitant bone loss. In both cases, the result is a shift of the center of resistance of the tooth and a consequent need to alter the moment to force ratio.

For every 1 mm of apical root loss, the required M/F ratio decreases by 0.21 mm (21%). For every 1 mm of marginal bone loss, the required M/F increases by 0.65 mm (65%)

General guidelines for adult space closure Bring periodontal disease under control and institute maintenanc measures. 2. Avoid mechanics with extrusive side effects. 3. Reduce force magnitudes. 4. Increase M/F ratio for translatory movement. 5. Avoid uncontrolled tipping mechanics (reduced PDL area results in higher localized stresses, with increased risk of tissue damage. 1.

Use of headgear for extraction space closure Farrant (BJO 1977) first described the use of a high pull head gear with J hooks for maxillary canine retraction, combined with straight pull headgear for mandibular canine retraction. Hickham (JCO 1974) in his Directional Edgewise Orthodontic Approach advocated canine retraction with J hook headgear, with the vector of force 15 degrees above the occlusal plane.

Variable pull headgear used in the directional edgewise orthodontic approach.

Perez et al, AJO Nov 1980 used a three-

dimensional photoelastic model reproduced from a human skull to permit an analysis of the effects of the forces transmitted to the alveolus and surrounding structures complex by the use of headgear with J hooks for maxillary canine retraction. Three different vectors of force, representing high-, medium-, and low-pull headgear, were applied. It was deduced from the photoelastic analysis that the high-pull headgear has a slight intrusion tendency which was lessened by the application of mediumpull traction. Tipping effect was observed when the low-pull force was applied. This effect was reduced with the medium-pull force component and was lessened to a greater extent with the application of high-pull traction. Therefore, it was concluded that the high-pull headgear produced the least tipping during maxillary canine retraction.

Enis G端ray and Metin Orhan (AJO DO 1997) introduced a technique for the "en masse" retraction of maxillary anterior teeth after first premolar extraction by the application of extraoral traction on canines, with consolidation of maxillary anterior teeth, to form them as a mass. Total force of 128 grams was applied for retraction of anterior seqment.

Modified inner bow of Kloehn type facebow.

Hickham type variable pull headgear.

Advantages Anterior headgear may have the advantage of retracting anterior teeth with minimum strain on posterior anchorage. The adjustability of the outer bow in relation to the premaxilla's center of resistance, provides effective desired movements. Intrusion and torque control are achieved in the course of anterior segment retraction.

Disadvantages: In this technique, like in all classical edgewise techniques, headgear cooperation is required for good treatment. In case of lack of cooperation with anterior headgear, loss of posterior anchorage will become unavoidable, or may cause interruption of the treatment. Consequently, the success of the "anterior headgear treatment" depends on the patient cooperation that is vital for this technique.

The Hycon Device The Hycon Device for extraction space closure was developed in Germany in the 1980s. This system uses a screw mechanism that is attached posteriorly to the molar tube and anteriorly to the anterior segment to be retracted. The nut and bolt assembly can be turned by the patient for space closure. It is compatible with all common fixed appliances.

Use of implants to facilitate retraction mechanics In recent years, with the introduction of miniscrews, palatal implants and miniplates, absolute anchorage or skeletal anchorage has become a reality. In case of direct anchorage, a miniscrew or miniplate is inserted near the upper first molar during retraction of anterior segment. Nickel titanium coil springs or elastics are used to connect this bone anchor with the anterior segment. In many cases, incisors and canines can be distalized simultaneously with slidin mechanics.

Indirect skeletal anchorage (Miniscrew assisted TPA; Park, JCO 2006)

Dento-alveolar distraction for canine retraction Distraction osteogenesis was used as early as 1905 by Codivilla and was later popularized by the clinical and research studies of Ilizarov in Russia. Distraction osteogenesis was performed in the human mandible by Guerrero in 1990 and McCarthy et al in 1992. Since then, it has been applied to various bones of the craniofacial skeleton. With conventional orthodontic treatment techniques, biologic tooth movement can be achieved, but the canine retraction phase in extraction cases usually lasts 6 to 8 months.

To address this problem, a technique of rapid canine retraction in which the concepts of distraction osteogenesis are used has been developed: dentoalveolar distraction (DAD). In this technique, which has been described and used by Iseri et aland Kisnisci et al, osteotomies surrounding the canines are made to achieve rapid movement of the canines in the dentoalveolar segment, in compliance with the principles of distraction osteogenesis.

With the DAD technique, anchorage teeth can withstand the retraction forces with no anchorage loss and without clinical or radiographic evidence of complications, such as root fracture, root resorption, ankylosis, periodontal problems, and soft tissue dehiscence. The DAD technique reduces orthodontic treatment duration by 6 to 9 months in patients who need extraction, with no need for an extraoral or intraoral anchorage devices and with not unfavorable short-term effects in the periodontal tissues and surrounding structures

Kontham, Bhagtani and Wadkar (JIOS 1999) reported a case of an adult patient with bimaxillary protrusion in whom rapid canine retraction using DAD was achieved in a period of 2 weeks without any complications.

References: Burstone C.J. The segmented arch approach to space closure. AJO 1982; 82: 361-378. Raboud D.W, Faulkner M, Lipset A, Halberstock D. Three dimensional effects in retraction appliance design. AJODO 1997; 112: 378-92. Staggers J, Germane N. Clinical considerations in the use of retraction mechanics. JCO 1991; 25; 365-9. Kuhlberg A, Burstone CJ. T loop position and anchorage control. AJODO 1997; 112: 12-8.

Siatkowski R. Optimal orthodontic space closure in adult patients. DCNA 1996; 40: 837-873. Gjessing P. Biomechanical design and clinical evaluation of a new canineretraction spring . AJODO 1985; 87: 353362. Nanada R. Dr. Ravindra Nanda on his treatment philosophy Part II. JIOS 2005; 38: 120-128. Frank C, Nikolai R. A comparative study of frictional resistances between orthodontic bracket & arch wire. AJO 1980; 79: 593-609

Drescher D, Bourel C., Schumacher H. Frictional forces between bracket & archwire. AJO-DO 1989: 96 : 397-404. Angolkar P, Kapila S, Duncanson M, Jr., and Nanda R.S . Evaluation of friction between ceramic brackets and wires. AJODO 1990; 98:499 - 506 Henao S, Kusy.R. Evaluation of frictional resistance of conventional & self ligating bracket designs using standardized archwires & Dental typodonts. Angle Orthod. 2004; 74: 202-211

Nightingale C, Jones S.P. A clinical investigation of force delivery systems for orthodontic space closure. Journal of Orthod 2003; 30: 229-236. Dixon V, Read M. A randomized clinical trial to compare three methods of orthodontic space closure. Journal of Orthod 2002; 29: 31-6. Samuels R, Rudge S, Mair L. A clinical study of space closure with nickel titanium coil springs and an elastic module. Perez C, Alba J. Canine retraction with J hook headgear. AJO 1980; 78: 539-47.

Guray E, Orhan M. En masse retraction of maxillary anterior teeth with anterior headgear. AJODO 1997; 112: 473-9. Jacob J, Karanth H, Shetty S. Force characteristics of Nickel Titanium Open and closed coil springs in a simulated oral environment. JIOS 2002; 35: 76-88. Bennett J, Mc Laughlin R. Controlled space closure with a Preadjusted Appliance System. JCO 1990; 24: 251-260. Watanabe Y, Miyamoto K. A Nickel Titanium Canine Retraction Spring. JCO 2002; 36:384-8.

Park H. A miniscrew assisted transpalatal arch for use in lingual orthodontics. JCO 2006; 40: 12-16. Cornelis M, Clerck H. Biomechanics of skeletal anchorage Part1. JCO 2006: 40:261-269. McLaughlin R, Kalha A, Schuetz . An alternative method of space closure: The Hycon Device. JCO 2005; 39: 474-84. Iseri H, Kisnici R, Bzizi N. Rapid canine retraction and orthodontic treatment with dentoalveolar distraction osteogenesis. AJODO 2005; 127: 533-41.

Kontham, Bhagtani TM, Wadkar PV. Rapid canine retraction through distraction of the periodontal ligament: A case report. JIOS 1999; 32: 142-145. Tweed C.H. Clinical Orthodontics.Vol 1. Saint Louis, C.V. Mosby Co. 1966: 214-218. McLaughlin R.P, Bennett J.C, Trevisi HJ. Systemized orthodontic treatment mechanics. London, Mosby, 2001: 249-77 Ravindra Nanda. (Ed): Biomechanical and Esthetic Strategies in Clinical Orthodontics. Philadelphia, W.B. Saunders and Co.2005: 194-209.

Begg P.T., Kesling P.C. Begg orthodontic theory and technique. Philadelphia: W.B. Saunders 1977: 217-214 Mulligan .F. Common Sense Mechanics in everyday orthodontics. Phoenix, CSM Publishing, 1998: 260281.

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