Teeth in cross-bite: the role of removable appliances Stanley G. Jacobs, BDSc, FDSRCS, DOrthRCS, FRACDS*

Key words: Case selection, cross-bite, ortho- dontics, removable appliances.

Abstract The role of removable appliances with springs for the treatment of teeth in anterior and posterior cross- bite is discussed. The indications for their use (that is, case selection), and their manipulation are examined. Cases are presented where removable appliances are the appliances of choice in the first stage of the correction of a posterior cross-bite, the final treatment being completed with fixed appliances. The ease of correcting and retaining various maxillary teeth which may be in cross-bite is discussed.

(Received for publication April 1987. Revised January 1988. Accepted April 1988.)

Introduction Patients commonly present with cross-bite which

may be anterior, posterior, or both. While the popularity of removable appliances in which the applied force is produced by a spring or a screw is diminishing, removable appliances are still preferred for the treatment of anterior cross-bite.

The role of removable appliances is more limited in the treatment of posterior cross-bite but some cases are discussed where these appliances were used to advantage in the first part of treatment. The final detailed positioning of the teeth was carried out with fixed appliances.

A. Anterior cross-bites 1. Sequelae

bite there may be: As a result of an anterior tooth being in cross-

*Orthodontist, Royal Dental Hospital of Melbourne.

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(a) Displacement of the mandible. Unless the tooth is completely excluded from the arch, in the great majority of cases an initial contact and subse- quent displacement of the mandible is present. However, temporomandibular joint problems in the patient age range of 7 years to 15 years rarely result from this contact and displacement.

(b) Attrition of the tooth in cross-bite. Usually a wear facet is present. Sometimes there may be gross wear of the incisal edge of the maxillary tooth in cross-bite.

(c) Gingival recession affecting the occluding mandibular incisor. Because the tooth may be forced labially from the crest of the alveolar ridge to a region where there is less bone, the crown of the mandibular incisor is frequently longer than its antimere.

(d) Mobility of the occluding mandibular incisor. Pressure from the maxillary incisor in cross-bite plus the loss of alveolar bone associated with the gingival recession may result in the mandibular incisor becoming mobile.

2. Case selection (a) The tooth to be moved labially should be

retroclined or upright at commencement. This is because there must be sufficient overbite at the end of treatment to hold the tooth in its corrected position.

As the tooth moves labially it shortens for two reasons:

(i) the tooth tips around a fulcrum which is approximately one-third of the root length from the apex;

(ii) the proclining force acts on the inclined lingual surface (Fig. 1).

Another way of expressing this factor in case selection is to say that if the apex of the upper tooth is labial to the lower incisor crown then the

Australian Dental Journal 1989;34(1):20-8.

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2 V Fig. 1.-Diagram showing how teeth shorten as they are proclined; forces (F) and reactions (R) produced by the spring. Fig. 2.-An unfavourable case to treat because the apex of the maxillary central incisor is lingual to the mandibular incisor

crown.

prognosis is favourable. If the apex is palatal then the tooth is more likely to relapse (Fig. 2).

A general statement which may be made is that treatment with removable appliances is best carried out when teeth are initially inclined in a direction opposite to the intended movement. This is because the teeth are moved by a tipping action.

(b) The operator should try to anticipate whether other anterior teeth will erupt into cross-bite. If this is likely, treatment is usually postponed to allow correction of additional teeth with the one appliance.

(c) Often the patients have a tendency towards Class I11 skeletal bases. The maxilla may be smaller than the mandible not only in the antero-posterior

dimension but also laterally and so a posterior cross- bite may also be present. If this is the case treatment with fixed appliances is usually indicated.

(d) There must be sufficient space into which the tooth can be moved.

(e) The position of the unerupted canine should be determined prior to proclining a lateral incisor which is in cross-bite. This is to ensure that the root of the incisor will not be forced against the crown of the canine and possibly be damaged. Fortunately canines are usually on the labial and as the incisor is moved, its apex tips away from the unerupted canine.

3. Appliances The following are some of the appliances that can

be used. (a) Removable appliances with either cantilever

springs (helical coil springs, finger springs); Z springs; or screws.

(b) Inclined planes. (c) Tongue spatulas. (d) Chin cups. (e) Stainless steel crowns. ( f ) Bands or bonds with elastics crossing the

occlusion andlor arch wires. Whilst any appliance may occasionally be

successful, the removable appliance with a cantilever spring is the one recommended for use on the grounds of efficiency and comfort. The cantilever spring appliance consists of three parts:

(1) Clasps. (2) Bite planes (as part of the acrylic framework). (3) Springs.

1. Clasps (a) Adams clasps are placed on 16 and 26.

Sometimes Adams clasps are also used on the deciduous first molars.

(b) Circumferential clasps are placed on the deciduous canines or first molars or on a permanent incisor for it is important that there is retention near the spring. Because the spring is applied to an inclined plane the reaction tends to dislodge the appliance (Fig. 1):

(1) downwards, and therefore the appliance must be clasped anteriorly, and

(2) backwards. (This backwards reaction is usually helpful as it tends to increase arch length which may relieve slight crowding.)

As Muir and Reed’ stated ‘neglect of this principle of retention is one of the commonest causes of failure’.

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2. Posterior bite planes The purpose of the posterior bite planes is to free

the occlusion so the teeth in cross-bite can easily be pushed labially. They should cover the permanent first molar and the two teeth in front of the molar bilaterally.

The bite planes are made in the shape of wedges to correspond to the form of the interocclusal clearance and thus should be low in the molar region and higher anteriorly. They are frequently made of even thickness and as a result the patient occludes only on the permanent first molars. The bite planes then require a considerable amount of adjustment at the chairside.

The bite planes only need to cover the lingual cusps of the posterior teeth in order that (1) the operator can gain easy access to the Adams clasps to adjust them; and (2) the Adams clasps will be more flexible and so be less susceptible to breakage.

The bite planes are made 0.5 mm to 1.0 mm higher than required for the tooth in cross-bite to clear the occlusion. This is because acrylic is soft and often wears and chips.

However, a contrasting view is held by Muir and Reed2 who stated that simple incisor teeth cross- bites can usually be treated without opening the bite despite the presence of a positive overbite.

3. Cantilever springs The spring should be made from 0.5 mm stainless

steel wire and should be: (1) as long as practicable so contact will not be lost with the tooth towards the end of movement and to ensure that the force will be low thus avoiding displacement of the appliance; and (2) fabricated so it can act at right angles to the intended path of tooth movement.

The coil of the spring should have two turns and be positioned where the tag of the spring emerges from the acrylic. If the coil is positioned in such a way that the spring unwinds in function, that is the coil is placed on the side opposite to the intended direction of movement of the tooth, this will induce less stress in the coil which will then be less susceptible to fracture.

The spring should be cranked so that it does not hit adjacent teeth as the tooth in cross-bite is moved.

The spring should contact the tooth gingivally, not half-way down the crown, otherwise the spring can slip off the tooth as it proclines. Therefore, the spring should be activated not only forward but also upward at 30 degrees and should be activated 3-4 mm. Adams3 stated that a cantilever spring of 18 mm length, 0.5 mm diameter and with one coil of internal diameter 2.5 mm, if deflected a

distance of 3 mm produced a force of 20 g (0.2 N).

The spring may be open or boxed-in. If the spring is open it is covered by a guard-wire made from 0.7 mm diameter stainless steel wire on the tongue surface which protects the spring from damage during eating. In addition the guard-wire acts as a guide to the spring and helps prevent the spring from slipping off the tooth. Instead of using a guard- wire the spring may be boxed-in by acrylic. Boxed- in springs cannot be positioned or cleaned as easily by the patient as can open springs.

4. Retention If the post-treatment overbite is 3 mm or more,

then retention is unnecessary. If the post-treatment overbite is less than 3 mm then retention is advisable. The spring can be deactivated and used as a retaining mechanism. However, because the spring is flexible it is liable to distortion.

Acrylic, being rigid, is superior for the long term retention of proclined teeth.

The spring and guide wire should be cut off and an impression taken with the plate in situ. After the model is poured and has set, acrylic is added behind the moved tooth. It should be of minimal thickness and not cover the cingulum. Its purpose is to prevent palatal relapse of the moved tooth but it should not impede the tooth’s eruption. The posterior bite planes should also be removed at this time.

If only one tooth has been proclined the spring may be cut off and the guide wire adapted to hold the corrected tooth labially.

Figure 3 shows the casts of a patient whose four incisors were in cross-bite and were corrected in 14 weeks. Figure 4 illustrates the appliances used. Its components have been described above. The cantilever springs cross over and each contacts two incisors.

ad am^,^ and Houston and Tulley5 illustrated cases treated with doubled back cantilever springs. The doubled back spring can move two to four incisors simultaneously.

Alternatives to the cantilever spring A few comments about Z springs and screws

which are occasionally used instead of cantilever springs on removable appliances.

1. Z springs McDonaldt indicated that he frequently used Z

tMcDonald J. Dennis. Lecture, Melbourne, October 1986.

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Fig. 3.-Cross-bite of the four maxillary incisors was corrected in 14 weeks. Fig. 4.-Appliance used to treat the case illustrated in Fig. 3.

springs to procline individual teeth. He stated that the spring is not as popular as the cantilever because it is usually constructed too rigidly and displaces the appliance downwards. He said that it is better to make the spring flexible and the best way to do this is to increase the number of arms from the usual three to four or five, but without coils.

The significant advantage of the Z spring is that it can be used to move the tooth first in one direction and later in a second direction. Other advantages listed by McDonald were that this spring does not have to be positioned by the patient, fractures less often, can be used on as many teeth as necessary without fouling adjacent springs or their tags and is very simple to design and construct. The Z spring is made of 0.5 mm stainless steel wire.

2. Screws These apply intermittent large forces which

decrease as the tooth moves. The activation at any one time is usually small (< 0.2 mm).

The appliance is usually bulky in the region of the screw. The one time that a screw may be the

moving mechanism of choice is when there are no teeth for clasping close to the teeth to be moved. If a screw is used then the teeth to be moved can be clasped as well.

B. Posterior cross-bites Various appliances have been employed to correct

posterior cross-bites. These include: (1) Removable appliances with a mid-line screw. (2) Various lingual arch type appliances with

(3) Rapid maxillary expansion appliances. (4) Bonds or bands with elastics and/or arch

wires. The use of removable appliances with a mid-line

screw is becoming less popular. However, in the following two cases, removable

appliances with 0.5 mm cantilever springs were used for correction of the cross-bites and final detailing was carried out with fixed appliances.

bands cemented on 16 and 26.

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Fig. 5.-a, Posterior cross-bite treated with a removable appliance. b, After the removal ofthe fixed appliances which were fitted for final alignment. c, The alignment of the maxillary right buccal segment was not disturbed by the

use of the removable appliance or d, By the use of the fixed appliances.

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Fig. 6.-Removable appliance which achieved the result shown in the bottom models of Fig. 5a.

Removable appliances were used in both cases because it was decided that unilateral expansion of the maxilla was necessary. Utilizing the palate as well as the non-moving teeth, is an excellent means of reinforcing the anchorage, that is, resisting the reaction to the forces which are used to move the teeth which are in posterior cross-bite. Without this reinforcement the reaction sometimes places the non-moving teeth in undesired positions.

The patient whose casts are shown in Fig. 5a had a cleft lip and palate, and 23, 63, 25 and 26 were in cross-bite. An upper removable appliance was inserted to correct the cross-bite and this stage was completed in 13 weeks. Final alignment, which primarily involved correcting the position of 23 and the rotation of 21, was carried out with maxillary bands in a further eight months (Fig. 5b).

The right side of the models, before and after the removable appliance therapy, can be seen in Fig. 5c, and before and after the fixed appliance treatment in Fig. 5d. The models demonstrate that the position of the teeth in the maxillary right buccal segment was not disturbed during treatment.

Details of the removable appliance used can be seen in Fig. 6. In order to be able to see the details of the springs the appliance has not been seated home firmly.

The patient whose models are to be seen in Fig. 7a also had a posterior cross-bite. She had a mandibular asymmetry, 13, 14, 15 in cross-bite, missing 12 and 22, while 36 was non-vital. A

removable appliance was inserted and after six months produced the arrangement seen in the bottom models in Fig. 7a. Maxillary bands were in place for five months to achieve final alignment (Fig. 7b, lower models). Again it can be seen (Fig. 7c) that the arrangement of the teeth on the opposite side has not altered during the expansion with the removable appliance or after the final alignment with the fixed appliances (Fig. 7d). Details of the removable appliance used can be seen in Fig. 8.

Ease of proclination and permanence of the treated result: a ranking

The upper central incisors are the easiest to procline and to maintain in their corrected position; next follow the first and second premolars and permanent first molars, and finally the lateral incisors and canines.

A maxillary lateral incisor is more troublesome to procline and retain than a central incisor because:

(1) It is near the corner of the arch and so it is more difficult to have a spring working in the correct direction.

(2) It is a smaller tooth and therefore has less overbite. (3) The deciduous mandibular canine may

exfoliate and then the overbite is lost. (4) The apex is more palatal. (5 ) The canine may be labial to the lateral incisor

and obstruct the incisor’s path of movement.

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Fig. 7 . - a, b, Another posterior cross-bite treated with a removable appliance followed by maxillary bands. c, d, Again the non-cross-bite side has not been disturbed.

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Fig. %-Removable appliance which achieved the result seen in the bottom models in Fig. 7a.

Fig. 9.-a, The palatal 23 has been proclined and as a result it has shortened. b, Relapse of 23 due to insufficient overbite.

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Canines are difficult teeth to procline for they have a very sloping palatal surface, and are large teeth often incompletely erupted. Frequently their apices are quite displaced and this combined with their pointed incisal edges mean that canines are prone to relapse. It is particularly important that sufficient overbite exists after correction to maintain their new position. There should not be an open contact between the opposing lower canine and premolar through which the maxillary canine crown can move palatally. As well, canines are often rotated. The difficulties associated with palatal canines are such that removable appliances are rarely suitable to treat them.

The patient whose models are shown in Fig. 9a had a palatal 23 moved labially with a removable appliance. It can be seen in the bottom models that the tooth has shortened considerably during treatment (note, in particular, the height of the gingival margin of 23 compared with that of 22), and a minimal overbite. The tooth was proclined for three months and retained for 18 months. However, it relapsed as can be seen in the bottom models in Fig. 9b.

Summary Some principles in the design and manipulation

of removable appliances which utilize cantilever springs have been discussed. Treated cases of teeth in cross-bite have been illustrated. Two of the cases had a posterior cross-bite.

The central incisor is the tooth in the maxillary arch which is the easiest to procline and retain in its corrected position.

References 1. Muir JD, Reed RT. Tooth movement with removable

2. Ibid.:17,144. 3. Adam CP. The design, construction and use of removable

orthodontic appliances. 5th edn. Bristol: Wright, 1984:17. 4 . Ibid.:36-8. 5. Houston WJB, Tulley WJ. A textbook ofonhodontics. Bristol:

appliances. Tunbridge Wells: Pitman Medical, 1979: 145.

Wright, 1986:207-9.

Address for correspondencelreprints: Orthodontic Department,

Royal Dental Hospital of Melbourne, 71 1 Elizabeth Street,

Melbourne, Victoria, 3000.

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