Anchorage for removable orthodontic appliances

Anchorage for removable orthodontic appliances

By Prof.Dr.

Maher Fouda

Orthodontic department – Faculty of dentistry – Mansoura University

Resistance to displacement

Definition of Anchorage

the resistance to unwanted tooth

movement.

Or

Anchorage is the

The retraction of upper canines , with all the available teeth involved in the appliance. An equal and opposite force to that being generated by retracting canines will also be acting on the remaining upper arch teeth to move them anteriorly, which can comprise the anchorage unit causing unwanted tooth movement of the rest of the dentition.

Retraction of upper canine by removable appliance

Self supported buccal canine retractor with helix located distal to the long axis of the canine

Incorporating as many teeth as possible in the appliance design and covering the anterior palatal vault will increase the anchorage

Mesially inclined canine being aligned using the helical canine retractor

Helical canine retractor

A clinical scenario is the retraction of upper canines using a fixedappliance, with all the available teeth involved in the appliance.

An equal and opposite force to that being generated by retractingcanines will also be acting on the remaining upper arch teeth

to move them anteriorly, which can comprise the anchorage unitcausing unwanted tooth movement of the rest of the dentition

The effects of different force values during canine retraction. (a) The correct force produces maximum canine movement and minimum movement of the other teeth. (b) An excessive force may give reduced canine movement and will result in undesirable movement of the other teeth in the arch. An increase in overjet is a sign of this.

Assessment of anchorage during canine retraction.

(a) Initial occlusion

(b) Correct forces have been used and the appliance worn as instructed . Upper 3 has been retracted into a satisfactory class I relationship with lower 3 with little increase in overjet.

(c) Anchorage loss is demonstrated. No further retraction of upper 3 is possible as the posterior teeth have moved forwards and the overjet has increased. It will not now be possible to reduce the overjet fully

RESISTANCE TO TOOTH MOVEMENT (ANCHORAGE). Retraction of labial segment

If, following extraction of first premolars, an attempt is made to retract the entire labial segment at once, the only teeth resisting this movement are the four remaining posterior teeth. It may be expected, therefore, that the forward movement of these teeth will exceed the backward movement of the incisors and canines

When the canines alone are retracted the incisors take part in the anchorage. Only two teeth are being moved against an anchorage of eight teeth. Although these will inevitably undergo some slight forward movement, this will be small compared with the distal movement of the canines

The canines now being in the fully corrected positions, an appliance designed to retract only the four incisors can utilize all the six remaining teeth as anchorage, so producing a major movement of the incisors with little further forward movement of these teeth.

An upper removable appliance used to expand the upper arch and procline retroclined upper incisors.

Traction applied to an exposed canine using a removable appliance

Anchorage may be conserved in two main ways:

1. Keeping Forces Light

Removable appliances conserve anchorage well because they allow simple tipping movements of the teeth which require the lightest pressures. The reactionary force can be reduced by limiting the number of teeth moved.

(a) Upper lateral incisor in cross-bite. (b)Upper removable appliance used to procline the lateral incisor over the bite. (c)Corrected cross-bite

The force necessary to carry out a simple tipping move-ment on a single rooted tooth is usually said to be in the region of 30 to 50 g. There is a threshold of perhaps about 20 g below which movement does not occur.

1. Keeping Forces Light

(a) Unilateral cross-bite left side with an associated displacement of the mandible to the left. (b) Upper removable appliance with midline screw. (c) Corrected cross-bite (note correction of centre-line).

When a tooth is tipped with a removable appliance, the fulcrum of rotation is approximately 40 percent of the length of the root from the apex

Diagram showing the effect of a tipping force applied to the crown of a tooth (+ = pressure; - = tension)

Tipping movement

The intra-oral gauge is being used to measure the force applied by an activated

palatal finger spring

Examples of spring gauges. Both (a) extra-oral and (b) intra-oral versions exist. The intra-oral gauge is being used to measure the force applied by an activated palatal finger spring.

Our problem is to deliver sufficient force to move the required teeth while ensuring that the

reactionary force, when divided among the anchor teeth, is insufficient to cause movement.

1. Keeping Forces Light

magnets

The frog appliance for upper molar distalization

Only one buccal tooth per quadrant should be moved in the same direction at any one time and when an overjet is to be reduced the incisors should not be moved palatally while other teeth are being retracted.

1. Keeping Forces Light

Example of a labial bow with U-loops (a) from the front and (b) occlusally. (c) .

Removable appliance with labial bow is indicated for management of Protruded and spaced occlusion with shallow overbite and increased overjet due to thumb-sucking habit

Before Appliance for breaking tongue thrusting habit

Placed in the mouth

Tightening the labial bow across the U-loops results in the anterior section of the labial bow being moved incisally; it must therefore now be pushed gingivally (arrowed; a) so it once more rests in the middle third of the labial surface of the incisors. Before the appliance is fully inserted, the labial bow should lie more or less along the incisal edges (b); so it has to be lifted over the labial surface to sit appropriately (c;

(A–C) The ACCO appliance is used for uprighting maxillary permanent molars to regain space. To maximize anchorage, acrylic is flowed over the labial arch wire and this limits the proclination of incisors as the molars

are distalized.

• Removable appliances – Acrylic cervical occipital appliance (ACCO appliance)

T-springs drawn on the laboratory card (a) and an example of a T-spring (b; arrowed) on this appliance (which also shows an Adams’ clasp).

Z-springs drawn on the laboratory card (a) and an example of Z-springs (b; arrowed) on this appliance (which also shows C-clasps and Adams’ clasps)

Nevertheless it is unwise to assume that anchorage loss will be completely

avoided merely by the use of light forces

1. Keeping Forces Light

2. Increasing the Resistance of the Anchor TeethThe Base Plate The resistance offered by the fit of the base plate against the teeth and mucosa contributes to the good anchorage offered by removable appliances. This may be maximized by keeping the acrylic fitted around as many teeth as possible.

Correction of an anterior crossbite with an upper removable appliance

2. Increasing the Resistance of the Anchor TeethA-The Base Plate

Caspal Interlock

It seems likely that good cuspal interlock with the teeth of the opposing arch will offer added resistance to any anchorage loss. A problem, however, is that extractions in the opposing arch may allow the interlocked teeth to move mesially together..

Tongue thrusting: (a and b)

Removable platewith palatal crib which were bent

posteriorly to avoid lower

interference.

The helpful effects of cuspal interlock may be eliminated by lower extractions or the use of bite planes.

Further, when bite planes of any sort are used, cuspal interlock ceases to be effective

Caspal Interlock

Anterior bite-planeCaspal Interlock

Management of 100% anterior overlap (impinging deep bite) in a 10-year-old boy

A. When the mandible is brought into centric occlusion, the lower incisor is slided over the guide plane to bring the mandible forward. This may be act as mandibular repositioning splint; B. Upper anterior inclined plane

ANTERIOR INCLINED BITE PLANE Instead of being flat, the bite plane is inclined it faces downwards and forwards at an angle of 60°to the occlusal plane and engages the lower incisors and canines when the jaws are approximated guiding the mandible forward. The inclined bite plane reinforces the anchorage and proclinesthe lower anterior teeth in addition to the correction of anterior deep bite

Anterior bite plane with capped maxillary incisor to give an additional anchorage to the maxillary plate

A clearance of 1.5 to 2 mm should exist between the upper and lower posterior teeth

Self supporting canine retractor

The traditional textbook view claims that the significant vertical separation between the palatal acrylic and the labial wire increases the anchorage value of the incisor teeth by establishing a rotational force couple.

The sagittal section of a model demonstrates the minimal vertical separation of wire and acrylic

Long labial bow is a modification of short labial bow where in the bow extends from left first premolar to right first premolar . Thus, greater length of the wire used allows greater anterior retractoin as compared to short

Fitted labial bow A short fitted labial bow on upper central incisors (0.7 mm wire). This design permits some drifting of the lateral incisors as the canines are retracted.

A removable appliance with a finger spring can be used to regain space by tipping a permanent first molardistally. A, The applianceincorporates multiple Adams'clasps and a helical spring that isactivated 1 to 2 mm per month. B,Premature loss of the primarysecond molar has led to mesialdrift and rotation of thepermanent first molar. C, Thisremovable appliance can be usedto regain up to 3mm of space. D,After space regaining, the spaceshould be maintained with a bandand loop or lingual arch if thepermanent incisors have erupted

tipping the permanent first molardistally

Palatal finger springs to distalize maxillary first molars to recreate space following early loss of primary molars

A removable appliance can be used in the mixed dentition to retract spaced and protruding anterior teeth. A, The labial bow is activated 1.5 to 2 mm and will achieve approximately 1 mm of retraction per month as the maxillary anterior teeth tip lingually. At each appointment, the labial bow should be adjusted and lingual acrylic removed to provide space for the tooth movement. B, A near normal occlusion in the late mixed dentition

Methods to reinforce anchorage of removable

appliance

The removable retainer incorporates headgearTubes

attached to the Adam‘s clasps on the upper

molars to facilitate insertion of the facebow

Retraction headgear fitted to a removable appliance. Locking facebow (a) closed (b) attached to

clasp of upper removable appliance

Children with a long face pattern generally have a maxilla rotated down posteriorly with short mandibular ramus. The ideal treatment in these patients will be to control all posterior vertical growth. This can be accomplished by high pull headgear attached to molars or maxillary splint

Max. splint with headgear

Orthodontic headgear consisting ofthe facebow and black nylon strapsthat fit around the patients head tokeep the device in place

a) Mixed dentition patient with maxillary midline diastema. (b, c) A removable appliance with finger springs was used to close the median diastema. (d) Note the close proximity of the erupting right maxillary canine with the root of the lateral incisor. Because of the risk of root resorption, mesial tipping of the lateral incisor was avoided

Forward movement of the buccal teeth produces prominence of the second premolars unless the arch width is reduced.

CONCLUSIONS

Anchorage planning is about resisting unwanted tooth movement. Whenever teeth are moved there is always an equal and opposite reaction. This means that when teeth are moved there is often a side-eff ect of unwanted tooth movement of other teeth in the arch. When planning a case it is therefore important to decide how to limit the movement of teeth that do not need to move. It is vital that anchorage is planned correctly for a treatment plan to work .

References1- An Introduction to orthodontics- Laura Mitchel2-Tooth Movement with Removable Appliances - Muir And Reed 19793-The design, construction and use of removable Orthodontic Appliances – Adams4-Removable Orthodontic Appliances - Vijayalakshmi – 20105-Orthodontic Retainers and Removable Appliances – 20136-Orthodontic Removable Appliances - Talmale