Anchorage in orthodontics

Faculty of dentistry-Faculty of dentistry-Mansoura university - Mansoura university -

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Definition Anchorage: Resistance to Unwanted Tooth Movement.

The term anchorage, in its orthodontic application, is defined in an unusual way: the definition as "resistance to unwanted tooth movement" includes a statement of what the dentist desires. The usage, though unusual, is clearestwhen presented this way. The dentist or orthodontist always constructs an appliance to produce certain desired tooth movements. For every (desired) action there is an equal and opposite reaction. Inevitably, reaction forces canmove other teeth as well if the appliance contacts them. Anchorage, then, is the resistance to reaction forces that is provided (usually) by other teeth, or (sometimes) by the palate, head or neck (via extraoral force), or implants inbone.

An introduction to orthodontic. Laura mitchell. Second edition

CLASSIFICATION OF ANCHORAGEA. Anchorage classified according to the manner offorce application as:1. Simple2. Stationary3. Reciprocal.B. Anchorage classified according to the jawsinvolved as:1. Intramaxillary2. Intermaxillary.C. Anchorage classified according to the site wherethe anchorage units as:1. lntraoral2. Extraoral3. Muscular.

D. Anchorage classified according to the number of anchorage units as:1. Single2. Compound3. Reinforced.E. White and Gardiner classified anchorage into six categories as:1. Simple2. Stationary3. Reciprocal4. Reinforced5. Intermaxillary6. ExtraoraI.

Types of anchorage :-A- intra oral anchorage which include :-1- simple anchorage:- active movement of single tooth versus several anchor teeth.2- compound anchorage:- teeth of greater resistance to movement are utilized as anchorage for the translation of teeth which have less resistance to movement.

compound anchorageSimple anchorage

An introduction to orthodontic. Laura mitchell. Second edition

3- stationary anchorage:-this is a misnomer as it is extremely difficult to prevent movement of anchor teeth altogether.

Displacement of anchor teeth can be minimized by arranging the force system so that the anchor teeth must move bodily if they move at all, while movement teeth are allowedto tip, as in this example of retracting incisors by tipping them posteriorly. The approach is called "stationary anchorage." In this example, treatment is not complete because the roots of the lingually tipped incisors will have to be uprighted at a later stage, buttwo-stage treatment with tipping followed by uprighting can b used as a means of controlling anchorage. Distributing the forceover a larger PDL area ofthe anchor teeth reduces pressure there

CONTEMPORARY ORTHODONTICS, William . Proffit 2000

4- Reciprocal Tooth Movement. In a reciprocal situation, the forces applied to teeth and to arch segments are equal, and so is the force distribution in the PDL. A simple example is what would occur if two maxillary central incisors separated by a diastema.-crossbite elastic was used to move the upper molars buccally and lower molars liguanlly.-Maxillary expansion screw was used to move the upper molars bucally.

Textbook of Orthodontics © 2007, Gurkeerat Singh

5- Reinforced anchorage Here the anchorage units are reinforced by the use ofmore than one type of resistance units. For example,the use of headgears along with routine fixedMechanotherapy or (extraoral anchorage and intraarchcompound anchorage) or the use of a transpalatalarch in fixed mechanotherapy or simplythe banding of the second molar for the retraction ofthe permanent canine


MUSCULAR ANCHORAGEThe perioral musculature is not only very strong butalso resilient. The forces generated by the musculatureCan some times be used to bring about tooth movement.The lip bumper appliance may be used to distalize themandibular first molars (Fig. 22.8) or the transpalatalarch when kept away from the palate, may cause theintrusion of the teeth to which it is attached, themaxillary first molars.


INTERMAXillARY ANCHORAGEWhen the anchorage units situated in one jaw are usedto provide the force required to move teeth in theopposing jaw the anchorage is called intermaxillary.This type of anchorage is also termed as Baker'sanchorage. For example, when Class II elastics are usedto retract the maxillary anteriors the anchorage unitsare situated in the mandibular arch.Intermaxillary anchorage can also be furthersubdivided into three subtypes depending upon themanner of force application as:1. Simple2. Stationary3. Reciprocal.

EXTRAORALANCHORAGEAs the name implies, here the anchorage units aresituated outside the oral cavity or extraorally. Theextraoral structures most frequently used at the cervical region (as with the use of the cervical pull headgear,the occiput (as with the occipital pullheadgear , the forehead and the chin (e.g.,the face mask with the use of extraoral anchorage the anchorage units are situated far away from the actual site where the movement is taking place hence there is hardly any chance of any changestaking place in the anchorage units. The biggestdisadvantage of extraoral anchorage is the apparent lack of patient cooperation. The anchorage assembly is bulky and externally visible making patients.

.A , High-pulhl eadgear (headcap)to the first molar.T o produceb odilymovementof the molar (no tipping), the line of force (blackarrow) musl passt hrough the centero f resistanceof the molar tooth. This will produce both backward andupward movement of the molar.

B , Cervical headgear( neck strap) to the first molar. Again, bodily movement is produced by an outer bow length and position that places the line of force through the center of resistance of the molar; but with a lower direction of pull, the tooth is extruded as well as moved backward.

CONTEMPORARY ORTHODONTICS, FOURTH EDITION William . Proffit 2007

CLASSIFYING ANCHORAGE REQUIREMENTSBegg, the inventor of the light wire differential forcetechnique or the Begg technique, as it is frequentlyreferred to estimated that one-third the extractionspace is lost as anchor loss if no additional means are used to conserve anchorage. Based on this premise he classified cases depending upon the space requirements of the particular case as maximum anchorage, moderate anchorage and minimum anchorage.


1-MAXIMUM ANCHORAGEThese include cases where the anchorage demand iscritical Or in other words maximum space should beused to correct the malocclusion proper and anchorloss should be minimum. In such cases no more thanone-fourth the extraction space can be lost to theforward movement of the anchor teeth, i.e. anchor loss.All care should be taken to preserve anchorage andthe use of additional methods to augment anchorageshould be planned in the treatment plan.


MODERATE ANCHORAGEThese are cases where the anchor teeth can be allowedto move forward into the extraction space for one fourthto half the total extraction space. Reinforcingthe anchorage might not be required.


MINIMUM ANCHORAGEThese include cases where a very less amount (lessthan half) of the extraction space is required for theactual resolution of the malocclusion. The rest of thespace, Le. more than half the extraction space needsto be closed by bringing the anchor teeth forward orto anchor loss.


Sources of anchorage:- Anchorage can be obtained from intra-oral and extra-oral sources and we should not forget the possibility of favourable growth and the question of our ability to enhance it. It is sensible to firstly summarise the possibilities for maximising intraoral anchorage.Sources of intra-oral anchorage• root surface area, this is a fundamental source of anchorage• bony cortexIn spite of widespread hope that this may prove source of anchorage, there seems little evidence that this is indeed the case. It is clearly not difficult to move teeth labially right through the cortex. Rebellato et al (1997) found that lingual arches did not prevent mesial migration of molars even when no intra-arch traction was applied. A study by Ellen, Schneider and Sellke (1998) found no enhancement of vertical or horizontal anchorage when using utility arches to set up cortical anchorage. These papers would also suggest that palatal arches would not be expected to add to posterior anchorage.

Excellence in Orthodontics 2005Lecture Course Manual

• mucosa and underlying boneThis is the source of anchorage which is sought with Nance buttons, removable appliances and lingual flanges on functional appliances. It is hard to measure, but appliances which cover a larger area of mucosa would be expected to provide additional anchorage.• occlusal interferencesSome extraction patterns e.g. upper first and lower second premolars can create usefulinterlocking of the dentition and increase the root surface area resisting a loss of upper arch posterior anchorage. Conversely upper canines stuck mesial to lower canines can lose upper arch anchorage as can attempted reduction of an overjet in the presence of a complete overbite.• implants/onplantsThese are a powerful source of intra-oral anchorage and are discussed more fully in aseparate section later in this presentation.


Maximising root surface areaAlthough far from proven, there seems strong indirect evidence that the differential force theory has substance. I.e. that within limits, the rate of tooth movement is related to the applied force per unit root surface area. For example, the study by Saelens and De Smit (1998) showed a greater mesial movementof molars and a lesser amount of anterior crowding resolved when second premolars rather than first premolars were extracted. Other studies supporting this theory are discussed in the chapter on Diagnosis and Treatment Planning in the section on planning extractions. Maximising root area in the anchorage unit.

is therefore sensible when anchorage is at a premium. In addition to choosing more anterior extractions,root surface area in the anchorage unit can be increased by:• including second molars• separate retraction of canines• correcting centrelines one tooth at a time.• semi-transverse forces eg. pushing rather than pulling canines distally.Practical considerations may lessen the applicability and effectiveness of any of these in a given situation,but they are all useful sources of anchorage.


Retracting six teeth at onceIn extraction cases where anchorage is not at a premium, clinicians traditionally retract the canines until there is sufficient space to align the incisors and then the complete labial segment of six teeth is retracted as a unit as opposed to fully retracting the canines to a class 1 relationship and then retracting the incisors.On theoretical grounds, retracting all six teeth simultaneously would be expected to increase anchorage demands and although this increase is not necessarily apparent clinically, there must be good reasons for choosing this theoretically more anchorage demanding plan. These reasons fall into two categories,namely, simplicity and not re-tracing steps of tooth movement.

Sliding all six teeth as a unit along a stiff wire involves very simple archwire fabrication and activation when compared with three sectional archwires and closing loops. Also, the chances of trauma to the lips, cheeks and gingivae are very small and the obstacles to oral hygiene are minimised. This method also makes it easy to keep all teeth under control and at the end of space closure, there is no need to align the teeth for a second time before finishing. These advantages must be weighed against the possible increase in anchorage required.


Straight-Wire Appliance and anchorageJohnston et al (1998) reported that use of the Straight-Wire Appliance - probably involving the retraction of the six front teeth simultaneously - cost 0.8 mm more anchorage (measured by his pitchfork analysis) in the maxilla when compared to treatment with plain edgewise appliances. It must also be remembered in thiscontext that a fully programmed appliance makes it harder for the clinician to finish a case with inadequate palatal root torque of the upper incisors and the slight extra anchorage requirement may be partly explained by the achievement of more anchorage - demanding occlusal goals.


Self-ligating brackets and anchorageThe chapter Self-ligating brackets – theory and practice discuss in detail the potential benefits of using self ligating brackets such as SPEED, Opal, In-Ovation or Damon 2 and 3. One such benefit is the ability to slide a tooth along a wire with very low friction and with no loss of control. This previously unusual combination reduces the potential disadvantages of separate retraction of canines. We would therefore expect anchorage preservation to be enhanced if these mechanics are used with self-ligating brackets. It has certainly been reported in a very interesting study by Rajcich and Sadowsky (1997), that retraction of canines with sliding mechanics when the molar is prevented from tipping or sliding mesially incursimpressively low anchorage loss. There are simpler ways of controlling molar tip and slide than the one they suggest which uses an auxiliary arch. A crimped stop or hook is one of them. This combination of a self-ligating bracket, a stopped archwire and separate canine retraction is worth close consideration foranchorage enhancement.


MECHANICAL ASPECTSOF ANCHORAGE CONTROL

When teeth slide along an arch wire, force is needed fortwo purposes: to overcome frictional resistance, and to createthe bone remodeling needed for tooth movement. Aswe have pointed out in Chapter 9, controlling the positionof anchor teeth is accomplished best by minimizing the reactionforce that reaches them. Use of unnecessarily heavyforce to move teeth creates problems in controlling anchorage.Unfortunately, anchor teeth usually feel the reactionto both frictional resistance and tooth movementforces, so controlling and minimizing friction is an importantaspect of anchorage control.

CHAPTER 10 Mechanical Principles in Orthodontic Force Control contemporary orthodontic 2000 proffit

Frictional Effects on Anchorage

When one moving object contacts another, friction at theirinterface produces resistance to the direction of movement.The frictional force is proportional to the force with whichthe contacting surfaces are pressed together and is affectedby the nature of the surface at the interface (rough orsmooth, chemically reactive or passive, modified by lubricants,etc.). Interestingly, friction is independent of the apparentarea of contact. This is because all surfaces, no matterhow smooth, have irregularities that are large on amolecular scale, and real contact occurs only at a limitednumber of small spots at the peaks of the surface irregularities. These

spots, called asperities, carry all the load between the two surfaces. Even under light loads, local pressure at the asperities may cause appreciable plastic deformation of those small areas.

Because of this, the true contact area is to a considerable extent determined by the applied load and is directly proportional to it.

When two solid surfaces are pressed togetheror one slides over the other, real contact occurs only at a

limited number of small spots, called asperities, that represent the peaks of surface irregularities. Even under light loads, as when an orthodontic arch wire is tied into a bracket, local pressure at the asperities is likely to form junctions between the two surfaces. These junctions shear as sliding occurs. If two materials of differenthardness slide past each other (for instance, a metal wire in a ceramic bracket), the coefficient of friction is mainly determined bythe shear strength and yield pressure of the softer material.

Surfaces of Wires and Brackets.

The concept that surface qualities are an important variable in determining friction has been emphasized by experiences in the late1980s with both titanium wires and ceramic or plastic brackets. Stainless steel brackets slide reasonably well on steel wires, but the situation is not so fortunate with some other possible combinations.

Surface Qualities of Wires.When NiTi wires were first introduced, manufacturers claimed

that they had an inherently slick surface compared with stainless steel, so that all other factors being equal, there would be less interlocking of asperities and thereby less frictional resistance to sliding a tooth along a NiTi wire than a stainless steel one.

This is erroneous-the surface of NiTi is rougher (becauseof surface defects, not the quality of polishing) than that ofbeta-Ti, which in turn is rougher than steel. More importantly,however, there is little or no correlation for orthodontic wires

between the coefficients of friction and surfaceroughness' 8 (i.e., interlocking and plowing are not significantcomponents of the total frictional resistance). AlthoughNiTi has greater surface roughness, beta-Ti hasgreater frictional resistance.

Surface Qualities of Brackets.Bracket surfaces also are important in friction. Most modern

orthodontic brackets are either cast or milled from stainless steel, and if properly polished have relatively smooth surfaces comparable with steel wires. Titanium brackets now are coming into use, primarily because of their better biocompatibility- some patients have an allergic response to the nickel in stainless steel and do not tolerate steel appliances. Ceramic brackets became quite popular in the 1980s because of their improved esthetics, but problems related to frictional resistance to sliding have limited their use. The ones made from polycrystalline ceramics have considerably rougher surfaces than steel brackets.

Force of Contact. The amount of force between the wire and the bracket strongly influences

the amount of friction.This is determined by two things. First, if a tooth is pulled along an arch wire, it will tip until the corners of the bracket contact the wire and a moment is generated that prevents further tipping. If the initial tipping is to be prevented and true bodily movement produced, any wire that is smaller than the bracket initially

must cross the bracket at an angle. The greater the angle, the greater the initial moment and the greater the force between the wire and the bracket. As, friction goes up rapidly as the angle between the bracket and the wire increases. Because of this, the elastic properties of the wire influence friction, especially as bracket angulation increases. A more flexible wire bends and reduces the angle between wire and bracket. As noted earlier, when teeth slide along an arch wire, it is easier to generate the moments needed to control root position with a wide bracket because the wider the bracket, the smaller the force needed at its edges to generate any necessary moment. The smaller force also should reduce the frictional force proportionally.

A second force, however, is the one that largely determinesfriction: the force that pulls the wire into the bracket,which would be produced by the ligature holding the wirein place. 25 Perhaps this explains why laboratory data indicatethat bracket width has surprisingly little effect on friction.More importantly, it illustrates why sliding alongarch wires works much better when the system that holdsthe arch wire in the bracket does not hold the wire tightlythe bracket.

Magnitude of Friction.Perhaps the most important information to be gained from a

consideration of friction isan appreciation of its magnitude, even under the best of circumstances. if a 19 x 25 steel

wire is placed in a 22-slot bracket and tied with a (presumablytypical) wire ligature, the minimum frictional resistanceto sliding a single bracket is about 100 gm. In otherwords, if a canine tooth is to slide along an arch wire as partof the closure of an extraction space, and a 100 gm net force

is needed for tooth movement, approximately another 100gm will be needed to overcome friction (Figure below ).The total force needed to slide the tooth therefore is twiceas great as might have been expected. The frictional resistancecan be reduced, but not eliminated, by replacing theligature tie with a bracket cap so that the wire is held inplace loosely.


In terms of the effect on orthodontic anchorage, theproblem created by friction is not so much its presence asthe difficulty of knowing its magnitude. To slide a toothor teeth along an arch wire, the clinician must applyenough force to overcome the friction and produce the biologicresponse. It is difficult to avoid the temptation toestimate friction generously and add enough force to becertain that tooth movement will occur. The effect of anyforce beyond what was really needed to overcome frictionis to bring the anchor teeth . Then either unnecessary movement of the anchor teeth occurs, or additionalsteps to maintain anchorage are necessary (e.g.,headgear).


Methods to Control AnchorageNearly all the possible approaches are actually used in clinical orthodontics, andeach method is affected by whether friction will be encountered. Considering them in more detail :-Reinforcement. The extent to which anchorage should be reinforced depends on the tooth movement that is desired. In practice, this means that anchorage requirements must be established individually in each clinical situation.

Reinforcement of anchorage can be produced by adding additional teeth within the same arch to the anchor unit, or by using elastics from the opposite arch to help produce desired tooth movement, as with the interarch elastic shown here. Additional reinforcement can be obtained with extraoral force, as with addition of a facebow to the upper molar to resist the forward pull of the elastic.



Once it has been determined that reinforcement is desirable,however, this typically involves including as many teeth as possible in the anchorage unit. For significant differential tooth movement, the ratio of PDL area in the anchorage unit to PDL area in the tooth movement unit should be at least 2 to 1 without friction, 4 to 1 with it. Anything less produces something close to reciprocal movement. Obviously, larger ratios are desirable if they can be obtained.

This anchorage could be reinforced even further by having the patient wear an extraoral appliance (headgear) placing backward force against the upper arch. The reaction force from the headgear is dissipated against the bones of the cranial vault, thus adding the resistance of these structures to the anchorage unit.

The only problem with reinforcement outside the dental arch is that springs within an arch provide constant forces, whereas elastics from one archto the other tend to be intermittent, and extra-oral force is likely to be even more intermittent. Although this time factor can significantly decrease the value of cross-arch and extra oral reinforcement, both can be quite useful clinically.


Subdivision of Desired Movement. A commonway to improve anchorage control is to pit the resistance of a group of teeth against the movement of a single tooth, rather than dividing the arch into more or less equal segments. In our same extraction site example, it would be perfectly possible to reduce the strain on posterior anchorage by retracting the canine individually, pitting its distal movement against mesial movement of all other teeth within the arch. After the canine tooth hadbeen retracted, one could then add it to the posterior anchorage unit and retract the incisors. This approach would have the advantage that the reaction force would always be dissipated over a large PDL area in the anchor unit. Its disadvantage is that closing the space in two steps rather than one would take nearly twice as long.

one at a time without friction, of course, will put less strainon anchorage than sliding them one at a time.

Retraction of the canine by itself, as the first step in a two-stage space closure, often is used to conserve anchorage, particularly when sliding teeth along an arch wire.


Tipping/Uprighting. Another possible strategy for anchorage control is to tip the teeth and then upright them,rather than moving them bodily. In our familiar extractionsite example, this would again require two steps in treatment. First, the anterior teeth would be tipped distally by being pitted against mesial bodily movement of the posterior segment. As a second step, the tipped teeth would be uprighted, moving the canine roots distally and torquing the incisor roots lingually, again with stationaryanchorage in the posterior segments. It would be extremely important to keep forces as light as possible during both steps, so that the teeth in the posterior segment werealways below the optimum force range while the anterior teeth received optimum force.

Displacement of anchor teeth can be minimized by arranging the force system so that the anchor teeth must move bodily if they move at all, while movement teeth are allowed to tip, as in this example of retracting incisors by tipping them posteriorly. The approach is called "stationary anchorage." In this example, treatment is not complete because the roots of the linguallytipped incisors will have to be uprighted at a later stage, but two-stage treatment with tipping followed by uprighting can beused as a means of controlling anchorage.


Friction and Anchorage Control Strategies. Anchorage control is particularly important when protruding incisors are to be retracted. The goal is to end up with the teeth in the correct position, not necessarily to retract them as much as possible. The desired amount of incisor retraction for any patient should be carefully planned, and the mechanotherapy should be selected to produce the desired outcome.


At this point, however, it is interesting to consider arelatively typical extraction situation, in which it is desiredto close the extraction space 60% by retraction of the anterior teeth and 40% by forward movement of the posterior segments. This outcome would be expected from any of three possible approaches: (1) one-step space closure with a frictionless appliance; (2) a two-step closure sliding the canine along the arch wire, then retracting the incisors (as in the original Tweed technique); or (3) two step space closure, tipping the anterior segment with some friction, then uprighting the tipped teeth (as in the Beggtechnique).


Factors affecting the anchorage

TeethTeeth by themselves resist movement. Forces can beexerted from one set of teeth to move certain otherteeth. The anchorage potential of teeth depends upona number of factors including-the root form, the sizeof roots, the number of roots, the position of the teeth,the axial inclination of the teeth, their intercuspation,etc.Root form The root form, to a large extent is responsiblefor the degree of anchorage provided by a tooth.The root in cross section can be either round, flat(mesiodistally) or triangular . The distributionof the periodontal fibers on the root surface aidin anchorage.

The more the fib ers the better the anchorage potential. The direction of attachment of the fibers also effects the anchorage offered by a tooth.Round roots have only half their periodontal fibers stressed in any given direction. Hence, offer the least anchorage. Mesiodistally flat roots are able to resist mesiodistal movement better as compared to labiolingual movement, as more number of fibers are activated on the flatter surfaces as compared to the relatively narrower labial or lingual surfaces.Triangular roots, like those of the canines are able toprovide greater anchorage. Their flatness adds to resistance.

The tripod arrangement of roots , likethat seen on maxiUary molars also aids in increasingthe anchorage. The round palatal root resists extrusionand the two flat buccal roots resist intrusion and themesiodistal stresses. Under clinical situations wherethe buccal tube is bonded/welded on the buccal aspectof these teeth they show a tendency to 'roll' mesially,the crown rotating mesiopalatally under a mesiallydirected force .

Size of roots The larger or longer the roots the more is their anchorage potential. The maxillary canines, because of their long roots can, at times, be the most difficult teeth to move in certain clinical circumstances

Number of roots The greater the surface area the greater the periodontal support and hence, greater the anchorage potential. Multirooted teeth provide greateranchorage as com pa red to single rooted teeth wi th similar root length.Position of tooth Sometimes the position of the teeth in the individual arches also helps in increasing their anchorage potential. As in the case of mandibular second prernolars, which are placed between two ridges-the mylohyoid and the external oblique, they provide an increased resistance to mesial movement.Axial inclination of the tooth When the tooth is inclined in the opposite direction to that of the forceapplied, it provides greater resistance or anchorage.

Root formation Teeth with incomplete root formationa re easier to move and are able to provide lesseranchorage.Contact points Teeth with intact contacts and/ orbroad contact provide greater anchorage.Intercuspation Good intercuspation leads to greateranchorage potential . This is mainly becausethe teeth in one jaw are prevented from movingbecause of the contact with those of the opposing jaw,this is especially true for teeth in the posterior segmentwhich also show the presence of attrition facets.

Basal BoneCertain areas of the basal bone like the hard palate and the Lingual surface of the mandible in the anterior region can be used to augment the anchorage. TheNance palatal button is one such appliance that makes use of the hard palate to provide resistance to the mesial movement of the maxillary molars

Cortical BoneRicketts floated the idea of using cortical bone foranchorage. The contention being that the cortical boneis denser with decreased blood supplies and boneturnover. Hence, if certain teeth were torqued to comein contact with the cortical bone they would have agreater anchorage potential. The idea as such remainscontroversial as tooth roots also show resorption insuch conditions and the risk of non-vitality of suchteeth is also more.

MusculatureUnder normal circumstances the perioral musculatureplays an important part in the growth and developmentof the dental arches. Hypotonicity of the perioralmusculature might lead to spacing and flaring of theanterior teeth. The hypertonicity of the very samemuscles has the reverse effect. Lip bumper is anappliance that makes use of the tonicity of the lipmusculature and enhances the anchorage potential of themandibularmolars preventingtheir mesialmovementmusculature and enhances the anchorage potential ofthe mandibular molars preventing their mesialMovement .

LOSS OF ANCHORAGEThis is defined as the unplanned and unexpectedmovement of the anchor teeth during orthodontictreatment.There are several causes of loss of anchorage.Some examples of these are:• Poor appliance design• Poor appliance adjustment• Poor patient wear

Poor appliance designFailure to adequately retain the appliance, orincorporate as many teeth into the anchor blockas possible are common causes of anchorageloss. If fixed appliances are used, as many anchor teeth as possible should be banded inorder to produce optimum anchorage. Removableappliances should have adequate retentionusing appropriate well-adjusted cribs or claspswith as much contact with the teeth and oralmucosa as possible.

258 BRITISH DENTAL JOURNAL VOLUME 196 NO. 5 MARCH 13 2004

Poor appliance adjustmentThe use of excessive force or trying to move toomany teeth at the same time may result inunwanted movement of the anchor teeth. Toavoid loss of anchorage, simultaneous multipleteeth movement should be avoided. If theappliance is poorly adjusted so that it doesn'tfit very well, or the force levels applied to theteeth are too high, then undesired tooth movementmay occur. High force levels produced byover activation are one of the key reasons foranchorage loss.

BRITISH DENTAL JOURNAL VOLUME 196 NO. 5 MARCH 13 2004

The optimal force for movement of a single rooted tooth is about 25–40 g for tipping and about 75 g for bodily movement. If the force is too low there will be very little movement, whereas too much force may result in loss of anchorage. Excess force does not increase therate of tooth retraction, As the force levels rise the rate of tooth tipping also increases up to about 40 g. Beyond this very little extra tooth movement occurs. Thus increasing the force levels above about 40 g willnot increase the rate of tooth tipping.


The force levels that wires from fixed or removable appliances exert on teeth usually depends on the following:• The material the wire is made from• The amount it is deflected• The length of the wire• The thickness of the wireSteel wire will exert a force that is directly proportional to the amount the wire is deflected up to its elastic limit. Figure 11 demonstrates how decreasing the wire thickness and increasing the length (sometimes by adding loops) controlsthe force produced. Modern alloys such as super elastic nickel titanium wires do not act in the same way as steel.These remarkable wires are capable of producing


a continuous level of force almost independent ofthe amount of deflection and have transformedthe use of fixed appliances in recent years. Heatactivated wire is now available that will increaseits force level as the temperature changes. Thesewires exhibit a so-called shape memory effect. Ifthe wire is cooled and tied into the teeth it deflectseasily into position. As the wire warms in themouth it gradually returns to its original shapemoving the teeth with it.


• Absolute anchorage• Mini implant anchorage is excellent for

• - adjunctive tooth movement• -En masse retraction• -molar distalization • - molar intrusion or extrusion

Complications:- - root injury from inadequate inter radicular

space.-Vessels injury and sinus injury. -soft tissue inflammation around the screw if

bad oral hygiene.-screw may break during insertion or

removal.-uncomfortable to the patient if placed in

lingual aspect of mandible.-some times can loosen and become lost.

Anchorage in orthodontics

Health & Medicine

Transcript of Anchorage in orthodontics