Mild crowding

If crowding is mild the removal of teeth can leave excessive space, which if closed with fixed appliances will often result in over-retraction of the labial segments. Therefore, unless this is an aim of treatment, mild crowding can usually be treated without extractions. A number of techniques that can provide space in the dental arches without the need for extraction exist.

Molar distalization

Moving the first permanent molars distally can create space. This is technically difficult in the mandibular arch and rarely attempted, but it is possible in the maxilla and appropriate for mild crowding, where the buccal segment relationship is up to half a unit class II. The most predictable technique, with the least associated anchorage loss, is extraoral traction mediated by the wearing of headgear (Fig. 11.1) (Sfondrini et al, 2002).

Figure 11.1 Molar distalization in the maxillary arch using headgear.

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• Extraoral traction is effective in average or low angle cases, using cervical or straight-pull headgear. This will also aid in bite opening through some simultaneous extrusion of the maxillary molars.

• Care should be exercised in high angle cases because molar extrusion can result in further opening of the maxillary–mandibular planes angle. In such cases, high or occipital pull headgear should be used, although distalization is generally more difficult.

• Headgear will need to be worn for 12 to 14 hours per day with a bilateral force of at least 400 g to achieve molar distalization.

• Headgear can be run directly to the first molars via headgear tubes on molar bands. This can be supplemented with a removable appliance such as the acrylic-cervical-occipital (ACCO) (see Fig. 8.18), incorporating an anterior bite plane and palatal springs mesial to the first molars to provide 24-hour force.

• Headgear can alternatively be attached directly to a removable appliance with a midline expansion screw or coffin spring (see Fig. 8.17).

• As the molars move distally along the arch the transverse dimension increases. Therefore any distalization is usually accompanied by some expansion across the maxillary molars. This can be achieved by expanding the inner bow of the facebow when running directly to molar bands or by use of an expansion screw or spring incorporated in a removable appliance.

• Even with good compliance the average distal molar movement that can be achieved is about half a unit (Atherton et al, 2002).

The biggest problems with the use of headgear are the dependence upon good compliance and favourable growth for success. In an attempt to overcome problems associated with compliance, numerous appliances have been designed to distalize the maxillary buccal segments without the need for headgear and are accordingly described as ‘non-compliance’ appliances. Most use the palate for anchorage, with a distalizing force applied directly to the maxillary first molars via either palatal springs or compressed coils. Although effective, all will tip the molars to some extent and result in anchorage loss in the form of an increase in overjet. To avoid this, implants can be used to support the anchorage further and these have been shown to be effective (Fig. 11.2) (Sandler et al, 2008).

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Figure 11.2 Distalization of the maxillary first molars using cantilever springs from an acrylic plate supported by the palate (a pendulum appliance) (left) or with compressed coil spring supported by a palatal implant (right).

Right figure courtesy of David Tinsley.

Lip bumper

A lip bumper is a mandibular fixed appliance consisting of a 1.0-mm stainless steel wire attached to bands cemented to the first permanent molars. The wire passes along the buccal and labial sulci of the dentition, so that the labial portion sits in front of the lower incisors (Fig. 11.3). The wire can be encased in acrylic to increase its dimensions and is positioned so that the pressure normally applied to the mandibular dentition from the lower lip and cheeks is now applied to the appliance. This results in:

• Uprighting and distal movement of the lower molars;

• Forward movement of the lower incisors; and

• Some transverse arch expansion.

Figure 11.3 Lip bumper.

These appliances are most effective before the lower second permanent molars erupt or if they are extracted; however, as they act to allow passive expansion of the lower arch dentition, following removal relapse is common without permanent retention.

Moderate crowding

Unless the labial segments are to be proclined significantly, a moderate space requirement usually dictates the need for extractions. The extraction choice is dependent upon the position of the crowding and the anchorage requirements to achieve the treatment aims, particularly in relation to a need for incisor retraction. If there is an increased overjet to reduce as well as crowding, the space required necessitates the removal of teeth as far forward in the arch as possible, which normally means first premolars. If incisor retraction is undesirable, second premolars should be extracted.

By timing extractions appropriately, significant alignment can result without active orthodontic treatment, especially if first premolars are being extracted to relieve labial segment crowding only. In the maxillary arch the canines often erupt buccally; if first premolars are removed as the canines erupt, they will move distally and erupt into the line of the arch. In the mandibular arch, if the canines are mesially angulated, removal of first premolars will allow some uprighting of the canines into the extraction spaces. This will relieve crowding in the labial segments and allow spontaneous alignment of labiolingually displaced teeth (Stephens, 1989). Rotated teeth are less likely to align without active treatment. All spontaneous alignment will occur in the first six months following extraction and after this, fixed appliances are often required to fully align the teeth. However, well-timed extractions can result in a shorter overall treatment duration and occasionally negate the need for further treatment.

Severe crowding

If the crowding is severe, extraction is almost always necessary and often in combination with anchorage support. This is most important in the maxillary arch where there is a greater tendency for the buccal teeth to move mesially and hence space to be lost. Various techniques for anchorage support are available and these are described in Chapter 5.

If more space is required than can be provided by the loss of premolars, not only does anchorage need to be supported but extra space will need to be created. This can be done by distalization of the buccal segments using extraoral traction or a temporary anchorage device (TAD), or occasionally by the extraction of more than one tooth per quadrant (Fig. 11.4).

Figure 11.4 A severely crowded case treated by the loss of all first premolars and upper first permanent molars.

Courtesy of Paul Scott.

Tooth size–arch length discrepancy

One of the commonest manifestations of a tooth size–arch length discrepancy is a midline diastema in the maxilla, often associated with diminutive lateral incisors. A small midline diastema is often seen during normal dental development prior to eruption of the maxillary canines, but this will usually close on eruption of these teeth. However, a larger diastema can persist into the permanent dentition and can be a cause of concern to the patient. Fixed appliances are usually required to close the space, possibly with some buildup of the adjacent teeth if they are small.

The labial frenum has been considered to be a primary aetiological factor in the persistent midline diastema, due to the insertion of fibrous tissue into alveolar bone between the central incisors, and frenectomy suggested if the diastema is going to be closed (Edwards, 1977). However, this does not result in greater closure or a reduced potential for the diastema to reopen in the longer term following active treatment. Commonly, a frenum will remodel superiorly on closure of the space, and therefore if a frenectomy is performed, it can be carried out after the diastema is closed (Bergstrom et al, 1973; Shashua & Artun, 1999). For those cases where the frenum does not remodel and is unsightly or is causing problems, frenectomy is indicated. The closure of any diastema, irrespective of adjunctive surgical procedures, will be very prone to open up again after treatment and will require permanent retention.

Hypodontia

With the exception of third molars, hypodontia most commonly affects the maxillary lateral incisor and mandibular second premolar teeth in most populations. Localized hypodontia, when only one or two of these teeth are missing, is often encountered and commonly associated with spacing in the dental arches. Generally there are two treatment options:

Maxillary lateral incisors

Whether the space is opened or closed for congenitally absent maxillary lateral incisors depends primarily upon the underlying malocclusion and whether space requirements in the lower arch justify the need for extraction. The size, shape and colour of the adjacent canine is also important, although this can be modified. General guidelines for management of congenitally absent maxillary incisors include:

• In class I cases if the lower arch is crowded consider extraction of premolars in the lower arch and space closure in the upper arch, substituting the upper lateral incisors with the permanent canines;

• In class II cases space from the missing teeth can be used to reduce the overjet and correct the incisor relationship; and

• In class III cases space closure will tend to retract the upper labial segment and worsen the incisor relationship. Therefore it is generally better to open space.

Space closure

When planning the substitution of a maxillary lateral incisor with a canine, this tooth may need to be adjusted to optimize the aesthetic result (Fig. 11.5) and there are several ways this can be achieved (Table 11.1). The first premolar distal to the canine should also be slightly rotated in a mesiopalatal direction to hide the palatal cusp and increase the amount of labial surface on show anteriorly to more accurately mimic a canine.

Figure 11.5 Maxillary canines substituting for the lateral incisors.

On the left, there has been no modification of the canines. On the right, the crown tips have been built up with composite.

Table 11.1 Optimizing dental aesthetics when a maxillary canine is substituting for a lateral incisor

• Localized vital bleaching or veneering; • Extrusion of tooth to lower the gingival margin; • Reshaping the tip by grinding or composite buildup; • Reducing the buccal and palatal bulge; and • Reducing the width.

Space creation

Creating space for a missing maxillary lateral incisor will mean that the patient is reliant upon a prosthesis for the rest of their life and it is important that they understand the implications of this. Generally, the choice of prosthesis will be between an adhesive bridge or implant (Fig. 11.6). In the younger patient a simple denture or retainer incorporating the tooth can provide a useful temporary prosthesis. In patients where implant replacement is being considered, careful planning is required to ensure adequate bone and space are available (Table 11.2). Unless sufficient space already exists in the arch, space will actively need to be created. This usually involves fixed appliances and the use of compressed coil springs.

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Figure 11.6 Replacement of the maxillary lateral incisors with adhesive bridges (left panels). Replacement of the UR1 and UR2 with implant restorations (right panels).

Table 11.2 Considerations when creating space for the implant replacement of missing teeth

Care must be taken that adequate space is created between the roots of adjacent teeth. This invariably requires bodily movement and fixed appliances. In addition, enough bone must be present buccolingually. • Implants cannot be placed until around 18 years of age when vertical alveolar bone growth has ceased; otherwise, the implant and supragingival restoration will appear to submerge. • If space for the prosthetic tooth is created too early and retained, there will be a reduction in width in the alveolus especially on the labial side, potentially compromising the position of the implant (Beyer et al, 2007).

Generalized hypodontia

Where there is more than one missing tooth in each quadrant, treatment becomes more complex and will involve space redistribution with fixed appliances and prosthetic replacement of missing teeth. This treatment needs to be planned and executed within a multidisciplinary specialist team. Depending on how many teeth are missing and their position, anchorage management can be a problem, although recent advances in the use of temporary anchorage devices can help overcome this (Fig. 11.7). There is also an association between hypodontia and microdontia, meaning that existing teeth may require buildup to achieve the aesthetic and occlusal aims of treatment.

Figure 11.7 Temporary anchorage device to facilitate space closure in the lower arch.

Courtesy of Paul Scott.

Increased overjet

An increased overjet is associated with a class II malocclusion and there are essentially two options for its reduction:

Which option is chosen will depend on a number of factors, which relate primarily to the skeletal and soft tissue pattern, and patient age:

Mechanotherapy for reducing an overjet

The options for reducing an increased overjet range from simple incisor tipping mediated by a removable appliance, functional appliances that attempt alteration of dental and skeletal relationships, fixed appliances to tip and move teeth bodily or orthognathic surgery to reposition the jaws.

• Removable appliances—if the upper labial segment is proclined and spaced, particularly when the lower lip rests behind it, an increased overjet can be reduced by simply tipping the upper incisors back. A removable appliance with an activated labial bow is an effective way of doing this (see Fig. 8.13).

• Functional appliances—in a growing patient, growth can be utilized to reduce an overjet and an effective way of doing this is the use of a functional appliance. Although there is little evidence that this will result in significantly increased mandibular growth beyond what might be expected naturally, this approach can utilize growth early on in treatment. These appliances are most effective during the pubertal growth spurt and, if successful, will result in effective overjet correction and reduced anchorage demand later on in treatment because there is no longer an overjet to reduce. However, this must be offset by the greater compliance required and the overall extension of treatment time (see Chapter 8).

• Fixed appliances—if bodily retraction of the upper labial segment is required, it necessitates the use of fixed appliances. Space will need to be created by either distal movement of the buccal segments or mid-arch extractions. Once space is available, the labial segment can be retracted to reduce the overjet. Treatment aims can be facilitated by the following:

• If extractions are required in both arches to relieve crowding, extract further forward in the upper arch than the lower arch (Fig. 11.8).

• If the lower arch is well aligned or treatment is planned without extraction, consider loss of upper premolars and treat to a class II molar relationship (Fig. 11.9).

• Use class II intermaxillary elastics to support anchorage.

Figure 11.8 Class II division 1 malocclusion with an increased overjet treated by extraction of upper first premolars, lower second premolars and fixed appliances.

Courtesy of Saba Quereshi.

Figure 11.9 Class II division 1 malocclusion treated by extraction of upper first premolars only, treating to a class II buccal segment relationship.

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When using an edgewise bracket system the incisors are moved backwards bodily on a heavy rectangular wire. This can be done using space closing loops, although when using a preadjusted system, sliding mechanics are generally used. A stretched elastomeric module or nickel titanium coil spring is connected between the terminal molar and hooks situated on the archwire in the labial segment (Fig. 11.10). This will result in the archwire shortening as it slides through the brackets in the buccal segment and is often facilitated by the use of class II elastics. If anchorage has been correctly planned, bodily retraction of the incisors and a reduction in the overjet will take place. When using the Begg or Tip-Edge appliance the overjet is reduced early in treatment by tipping the teeth with light class II elastics (Fig. 11.10). The teeth are later uprighted using auxiliary springs.

• Orthognathic surgery—once growth has ceased the only way to reduce an overjet is by orthodontic tooth movement. If there is a significant skeletal discrepancy tooth movement alone may result in an unacceptable compromise to the patient’s soft tissue profile. Therefore a combined orthodontic–orthognathic solution may have to be considered. Considering that mandibular retrognathia is a common aetiological factor in many significant class II malocclusions and that surgical setback of the maxilla to any great extent is difficult to achieve, this usually consists of mandibular advancement (see Chapter 12).

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Figure 11.10 Overjet reduction using a preadjusted edgewise appliance and intra-arch traction provided by nickel titanium coil springs (upper) or a Tip-Edge appliance and class II intermaxillary elastic traction (lower).

Reduced or reverse overjet

A reduced or reverse overjet is associated with a class III malocclusion and the options for correction include:

Anatomical limitations mean that there is less scope for the retraction of lower incisors and advancement of the uppers using orthodontic mechanics. Therefore, the more severe class III cases are more reliant on surgical intervention. Whether a class III case can be treated by orthodontic tooth movement alone will depend significantly on the degree of existing incisor compensation for the skeletal pattern (Table 11.3). The upper incisors are often already proclined and the lowers retroclined and for orthodontic treatment to be successful it is important that this is minimal; otherwise, it limits the potential for further movement of these teeth aimed at correcting the class III incisor relationship.

Table 11.3 Features of a class III malocclusion that would indicate it is suitable for orthodontic camouflage treatment

The stability of incisor correction will depend in part on whether a positive overbite can be achieved at the end of treatment. Stability will also depend on future adolescent growth because any increase in mandibular prognathism will tend to worsen the class III incisor relationship. If there is any doubt, it is better to monitor growth in patients with a class III malocclusion before final treatment decisions are made, which can be done using serial cephalometric lateral skull radiographs taken a year apart (Table 11.4).

Table 11.4 Skeletal factors contributing to the development of a class III malocclusion^a

a  Guyer et al (1986).

Mechanotherapy for correcting a class III incisor relationship

Correcting a reduced or reverse overjet with simple upper incisor tipping can be mediated by a removable appliance, whilst bodily tooth movement or lower incisor retraction will require fixed appliances. In more severe cases, orthognathic surgery to reposition the jaws will be required in combination with orthodontic treatment. The adverse nature of facial growth and difficulty in addressing the reduced maxillary or increased mandibular growth seen in many class III cases means the use of growth modification is more problematic in these patients. Functional appliances and protraction headgear, if used, are usually commenced in the mixed dentition. Options in the permanent dentition include:

• Removable appliances—a removable appliance can be used to push one or two maxillary incisors over the bite to correct an anterior crossbite if they are retroclined and a positive overbite can be achieved at the end of treatment to hold the corrected position (see Fig. 8.15).

• Fixed appliances—comprehensive treatment usually involves bodily movement of the incisors in both arches and therefore fixed appliances are more appropriate. The aim is to create a positive overjet and overbite at the end of treatment and this can be facilitated by the following:

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• If extractions are required in both arches to relieve crowding, extract further forward in the lower than in the upper arch (Fig. 11.11).

• If the upper arch is well-aligned but space is required to align and retrocline the lower incisors, extraction of a single lower incisor can be an option (see Fig. 7.12).

• Closing space on a round wire in the lower arch will facilitate retroclination of the lower incisors.

• Use of class III intermaxillary elastics will help procline the upper incisors and retrocline the lowers.

Figure 11.11 Class III malocclusion treated by extraction of lower first premolars, upper second premolars and fixed appliances.

Orthognathic surgery and class III malocclusion

If there is a moderate or severe skeletal III skeletal base relationship, especially if the lower face height is increased and there is a reduced overbite, correction will almost certainly require a combination of orthodontics and surgery. A class III malocclusion is usually not due to a single factor, but a combination of morphological traits; therefore one surgical procedure does not fit all, and the surgical plan will need to be tailored to each individual case (see Table 11.4). There is also the tendency for a class III malocclusion to worsen with age, as mandibular growth persists. Surgery should be delayed until all adolescent growth has ceased, which will be the late teens. This does not mean that a crowded maxillary arch cannot be treated in the interim if this is a concern to the patient or teeth are ectopic (Fig. 11.12), even if it involves extractions. If the upper labial segment is left in the correct position in relation to the dental base it will not compromise any further surgical treatment although the patient will not have an ideal incisor relationship until definitive treatment is carried out. In the mandibular arch, extractions are best avoided in growing patients who look like they may need orthognathic surgery. Any retroclination of the lower labial segment will need to be undone as part of the presurgical orthodontic preparation and this is difficult following mid-arch extractions without reopening the extraction sites.

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Figure 11.12 A 14 year-old class III case with impacted maxillary canines (left panel). The canines were aligned with a fixed appliance following the extraction of upper first premolars (right panel). No attempt was made to camouflage the underlying malocclusion and a reverse overjet was created. Once facial growth is complete, fixed appliances will be used to achieve full decompensation and orthognathic surgery carried out to definitively correct the malocclusion

(Courtesy of Poh Then).

Bimaxillary proclination

Bimaxillary proclination or protrusion occurs when both the maxillary and mandibular incisor dentitions are perceived to be forwards in relation to their dental bases and the cranial base. It can occur in relation to an underlying skeletal discrepancy, with an associated increase or reduction in the overjet. If the skeletal base relationship is class I, the overjet is often within a normal range despite the labial segment proclination. As the incisors are proclined there will be a tendency to a reduced overbite and in extreme cases an anterior open bite.

Bimaxillary protrusion is a common finding in patients of African-Caribbean and Chinese descent and should therefore be considered part of the normal clinical spectrum of variation in these patients. However, in extreme cases it can cause unacceptable protrusion and incompetence of the lips, for which treatment is sought. This will usually involve retraction of the anterior teeth, necessitating mid-arch extractions and the use of fixed appliances. Using round wires and allowing the teeth to tip means that even very proclined teeth can be uprighted, which will improve lip competence and profile. However, as the teeth occupy a position of balance between the pressures from the tongue on one side and the lips and cheek on the other, any significant change in the position of the incisors will be unstable. Therefore permanent retention is usually required.

Increased overbite

An increased overbite occurs when the incisors have erupted past each other and is often, although not always, associated with reduced vertical facial proportions. An increased overbite is a common feature of class II division 2 malocclusion and its reduction will be necessary to establish a class I incisor relationship.

It is much easier to correct an increased overbite in a growing patient because growth of the mandibular condyles can help compensate for any posterior dental extrusion that may be used to facilitate overbite reduction. In addition, correction of the inter-incisal angle is important for the stability of overbite reduction, as the establishment of an occlusal stop is essential to prevent the incisors from erupting past each other and the overbite increasing again following treatment. This is especially relevant for class II division 1 cases associated with proclined upper incisors because unless maxillary incisor inclination is corrected, an occlusal stop will not be established and the overbite will relapse (Houston, 1989) (Fig. 11.13). Management of deep overbite in cases with a low maxillary–mandibular planes angle is also made easier with a non-extraction approach. If teeth are extracted as space is closed towards the end of the treatment, overbite control becomes difficult as the incisors will tend to upright, which can lead to the overbite deepening again.

Figure 11.13 Creating the correct interincisal relationship to avoid relapse of overbite reduction following treatment.

Simple tipping of the upper incisors to reduce an increased overjet in the presence of an increased overbite is not appropriate treatment because no occlusal stop is created. The upper incisors can retrocline and the lower incisors over-erupt, resulting in a worsening of the overbite (upper panel). The key to stable overbite reduction is moving the upper incisor root into the correct position behind the plane of the lower incisor edge (lower panel).

Mechanotherapy for correcting an increased overbite

There are essentially four ways to reduce a deep overbite associated with an increased curve of Spee in the lower arch using conventional orthodontic mechanics: buccal segment extrusion (relative incisor intrusion in a growing patient), incisor intrusion or incisor proclination (Fig. 11.14).

Figure 11.14 Levelling the curve of Spee in the mandible.

(1) Relative incisor intrusion. (2) Buccal segment extrusion. (3) Incisor intrusion. (4) Incisor proclination.

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• Buccal segment extrusion—extrusion of the lower buccal segments whilst maintaining lower incisor eruptive position, is a very effective way of reducing an increased overbite. This is particularly true in a growing patient, where these tooth movements will produce relative incisor intrusion because vertical growth at the condyle helps compensate for any increase in the vertical dimension induced by the molar extrusion (Fig. 11.14 (1)). In an adult, there is little or no growth potential at the condyle and buccal segment extrusion will simply result in a downward and backward rotation of the mandible, steepening of the occlusal plane and an increase in the lower face height (Fig. 11.14 (2)). This will reduce the overbite but tends to worsen any underlying skeletal class II relationship and is prone to relapse following treatment. For these reasons, overbite reduction can be more difficult in adult patients.

Buccal segment extrusion can be achieved using a removable appliance with a flat anterior bite plane. The appliance opens up the bite and allows eruption of the buccal segments, levelling the curve of Spee and reducing the overbite (Fig. 11.15). Many functional appliances have a similar bite-plane effect if the acrylic of the appliance is removed over the lower premolars and molars to allow eruption of these teeth.

Figure 11.15 Overbite reduction can be achieved with a removable appliance by incorporating a flat anterior bite plane (upper left panel). Fixed appliances can reduce an increased overbite by placing a reverse curve of Spee in the lower archwire (upper right, lower left and lower right panels showing progressive overbite reduction; and see Fig. 9.30).

Using an edgewise-fixed appliance with a continuous archwire can also achieve buccal segment extrusion, although this will also be accompanied by some incisor intrusion. These changes can be accentuated by using a rectangular stainless steel archwire with a reverse curve of Spee (Fig. 11.15). The lower second molars are generally included to increase vertical anchorage and aid these movements. Care must be taken, as there will also be a tendency for the lower incisors to procline, which will assist bite opening, but may not desirable or stable. Therefore it is often necessary to place lingual crown torque in the labial section of the archwire to counter this. The judicial use of class II inter-maxillary elastics will also assist in overbite reduction as the vertical component of force will tend to extrude the mandibular molars. Class II inter-maxillary elastics are integral in the Begg and Tip-Edge appliances which aim to reduce an increased overbite early on in treatment by the use of rigid round steel arches that bypass the premolar teeth to create a long range of action and light forces. An intrusive force is applied to the labial segments from the archwire by tip-back or anchor bends placed into the molar tubes and an extrusive force applied to the molars by the use of light class II elastics. Together this is very effective at reducing an increased overbite (see Fig. 9.29).

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• True intrusion of the incisors—in cases with a high maxillary–mandibular planes angle and a class II malocclusion, molar extrusion can result in an undesirable downward and backward rotation of the mandible, especially in non-growing patients. A deep overbite in these cases, although not common, should be reduced by intrusion of the incisor teeth (Fig. 11.13 (3)). Absolute intrusion of the incisors is mechanically difficult to achieve and requires fixed appliances. The general principle is to establish an anchorage unit in the buccal segments and intrude the incisors with a utility or bypass arch pitched against the buccal teeth (see Fig. 9.31). The utility archwire when passive will lie above the incisors in the gingival sulcus. By tying this archwire into or above the incisor brackets an intrusive force will be applied, which can achieve around 1 to 2-mm of incisor intrusion (Ng et al, 2005). Direct high-pull headgear applied to the upper incisors will also result in intrusion but unless the forces are kept light, this can increase the risk of root resorption. More recently, the use of micro-implants has been described to intrude anterior teeth, whilst intrusion can also be achieved using segmental surgery.

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• Proclination of the incisors—a deep overbite can also be reduced by incisor proclination and an associated reduction in the inter-incisal angle (Fig. 11.13 (4)). As a general rule, lower incisor proclination is unstable and there will be a tendency for these teeth to return to their pre-treatment position, with a potential return of the increased overbite. However, where the lower labial segment is markedly retroclined, such as a class II division 2 malocclusion, some proclination of the lower incisors may be necessary to establish a class I incisor relationship with an acceptable inter-incisal angle (Fig. 11.16). This can effectively be achieved with fixed appliances, especially in the presence of crowding. By engaging the initial aligning archwire fully, the teeth will align by proclination and this can be supplemented further by placing a rectangular stainless steel wire in the lower arch once the teeth are aligned with a reverse curve of Spee. Any significant proclination will invariably require long-term or permanent retention following appliance removal to prevent relapse of the overbite.

Figure 11.16 Proclination of the labial segments to reduce an increased overbite in a class II division 2 malocclusion.

Anterior open bite

An anterior open bite is associated with a lack of vertical incisor overlap. It may be localized, affecting only a few teeth; or it may be caused by a divergence of the skeletal planes. Treatment is often required because the patient has trouble incising food due to the lack of an anterior occlusion. Speech may also be a concern, as an anterior open bite can be associated with lisping. While treatment can improve both the occlusion and function, there is no guarantee that speech will improve as speech patterns are established early in life, long before establishment of the permanent dentition.

When planning treatment it is important to establish the aetiology (Table 11.5). In the presence of an anterior open bite, the tongue will come forwards between the incisors to fill the gap and create an anterior seal during swallowing. For many years it was thought that this tongue activity or ‘tongue thrust’ was the primary aetiological factor in the development of anterior open bite. It is now recognized that in the vast majority of cases this is an adaptive behaviour. If the main aetiological factor is a digit-sucking habit, as long as this ceases at an appropriate time, there can be complete and stable resolution of the anterior open bite. The main problems arise with anterior open bites that are skeletal in origin.

Table 11.5 Aetiology of anterior open bite

Mechanotherapy to correct an anterior open bite

There are essentially three ways that a skeletal open bite can be treated:

• Extrusion of the labial segments—an anterior open bite occurs when the labial dentition is at the limits of its eruptive potential. Therefore any further mechanical eruption or extrusion will be inherently unstable and is not advised unless it is related to a digit-sucking habit which has prevented eruption of the incisors. Occasionally, towards the end of fixed appliance therapy, a small anterior open bite can be resolved and occlusal settling achieved by the short-term use of anterior elastics (Fig. 11.17).

• Distal tipping of the molar dentition—it has been noted that the buccal dentition, especially the molars, is more upright or mesially angulated in the presence of an anterior open bite. A technique whereby the molars are tipped distally using multilooped wires with divergent curves of Spee built into them has been described (Kim, 1987). Heavy anterior elastics are used to stop the anterior open bite getting worse and bring the incisors together as the molars tip distally. This is further facilitated by removal of the terminal molars. As the mandible works on a hinge the removal of terminal molars, which are closer to the hinge access, should help close down an anterior open bite by removing the posterior occlusal contact.

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• Vertical control or intrusion of buccal segments—this is difficult to achieve with orthodontic tooth movement. The aim is to reduce posterior dental heights, which will result in a forward rotation of the mandible and closing down of the anterior open bite. Because the molars are closer to the condylar hinge, even a small amount of intrusion should result in a greater closure anteriorly. Numerous techniques that attempt to achieve this have been described (Table 11.6). Similarly, any extrusion of the molars will worsen the anterior open bite. It is important to avoid the use of class II and class III elastics in such cases. If intermaxillary traction is required, the elastics should be short and not run to the molars.

Figure 11.17 Anterior elastic to close an anterior open bite during the final stages of treatment with a fixed appliance.

Table 11.6 Treatment modalities to correct an anterior open bite

• High-pull headgear; • Posterior bite blocks; • Repelling magnets; • Implants; and • Surgical impaction of the maxilla.

In a growing child, the use of high-pull headgear, especially when there is a skeletal class II base relationship, will control posterior vertical growth of the maxilla. This will theoretically redirect mandibular growth in a more anterior than vertical direction. The headgear can be run directly either to bands on the upper first molars or to a removable appliance with posterior capping (an intrusion splint) (Fig. 11.18). Headgear can also be used in combination with a functional appliance to try and correct an increased overjet when there is a reduced overbite and a vertical growth pattern. The main problem with this approach is that vertical growth continues throughout adolescence and therefore to be truly effective, headgear will have to be worn until adolescent growth has stopped.

Figure 11.18 Anterior open bite treated with high-pull headgear attached to a buccal intrusion splint.

In adults growth will have essentially ceased. Therefore, treatment of an anterior open bite will necessitate intrusion of the buccal segments. Although implants and microscrews potentially provide an exciting new way of achieving this, at present the most predictable and stable way of correcting an anterior open bite in an adult is by surgical impaction of the maxilla (see Fig. 12.27). This will reduce the posterior dental height, allowing the mandible to auto-rotate and close the anterior open bite.

Buccal posterior crossbite

Posterior crossbite can be unilateral or bilateral, depending upon whether one or two sides of the dental arch are affected.

The greater the skeletal contribution to a crossbite, the more difficult it is to correct. A skeletal crossbite with no associated displacement of the mandible on closing is often best accepted, especially if it is bilateral. Attempting orthodontic correction in these cases may result in the creation of a unilateral crossbite with a displacement, which is occlusally less acceptable. As it is very difficult to constrict the mandibular arch, any treatment will usually involve expansion of the maxillary arch. Various techniques can be used to achieve this, but all will produce considerable tipping of the maxillary buccal teeth, with the exception of surgical expansion. On expansion, there will be a relative extrusion of these palatal cusps as the teeth are tipped. This can be a problem in patients with a reduced overbite, as this will worsen due to displacement of the mandible downwards and backwards (Fig. 11.19). Therefore caution should be exercised when expanding patients with an increased vertical pattern of growth and the use of techniques to control this, such as high-pull headgear in combination with expansion, should be considered.

Figure 11.19 Increase in the vertical dimension and reduction in overbite following expansion of the maxillary dental arch.

Mechanotherapy to correct a posterior crossbite

The following techniques can be used to produce maxillary expansion:

• Removable appliances are effective for expansion particularly in the mixed dentition using a midline expansion screw which the patient activates.

• Fixed palatal expanders such as the quadhelix can be used for dental expansion; whilst rapid maxillary expansion (RME) can produce a significant component of skeletal expansion in growing patients.

• The quadhelix appliance (see Fig. 9.20) is cemented to bands on the first molars and activated by expanding approximately a molar width. This will produce slow dental expansion, mostly by tipping the teeth buccally. It is therefore contraindicated when skeletal expansion is needed or when the maxillary molars are already tipped buccally. As active arch expansion has a high potential for relapse, the maxillary arch should be overexpanded so expansion is continued until the palatal cusps of the maxillary molars occlude on the lingual inclines of the buccal cusps of the mandibular molars. If no further treatment is planned, the quadhelix should be left in place for a further three months as a retainer.

• RME is undertaken over a period of 2 to 4 weeks with the patient activating the appliance between one and four times a day, producing up to 1-mm of expansion a day (Fig. 11.20 and see Fig. 9.21). This generates large forces that in a child or adolescent will split the maxillary suture, resulting in initially mostly skeletal expansion. A transient midline diastema usually develops, but the maxillary arch should be overexpanded as relapse is inevitable. The appliance is then left in place following the active phase of treatment to maintain the expansion for at least three months. Despite this there is considerable relapse, with much of the skeletal expansion being lost. Even so, up to 10-mm of expansion is possible using this technique. In an adult the interdigitation of the maxillary suture makes it harder to achieve skeletal expansion without surgery.

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• Fixed appliances incorporating expanded heavy stainless steel archwires will result in expansion of the dental arch. Rectangular wires should be used to prevent buccal tipping of the molars and maintain torque control in the buccal segments. Alternatively, an auxiliary buccal arch constructed from 0.9-mm steel can be placed in the molar headgear tubes and expanded (Fig. 11.20). Cross-elastics can also be run from the palatal aspect of the maxillary teeth and buccal aspect of mandibular teeth to correct crossbites (Fig. 11.21). As well as a transverse force component, these will also produce a vertical force and as such, is contraindicated in patients where extrusion of teeth in the buccal segments should be avoided. If an archwire with a larger arch form is chosen from the outset of treatment and twinned with a low friction bracket system, significant expansion and change in arch form is possible. However, there is no evidence that this is any more stable than any other method of expansion.

Figure 11.20 Maxillary expansion using RME (upper panel) and a buccal expansion arch (lower panel).

Figure 11.21 Cross elastics.

Irrespective of what type of expansion is undertaken, relapse potential is high. This can be reduced by establishing good intercuspation of the buccal dentition at the end of treatment, but a long period of retention will usually be required. Vacuum-formed retainers, if used, should be reinforced with a wire placed in the palate.

Lingual posterior crossbites

Localized lingual posterior crossbites can also occur, particularly when crowding causes a maxillary premolar to be displaced buccally. Complete lingual posterior crossbites are less common and usually associated with an underlying skeletal class II discrepancy. In a child, a functional appliance can be used to correct this relationship, and by doing so this may help correct the lingual crossbite. In an adult, fixed appliances can be used with cross-elastics and an expanded mandibular archwire. However, orthodontic expansion of the mandibular arch to any significant extent is problematic. If there is a skeletal class II base relationship, mandibular advancement surgery may help correct the lingual crossbite. Surgical techniques using distraction osteogenesis for widening the mandibular arch have also been described.

Periodontal and gingival tissues

Following orthodontic tooth movement, the tissues of the periodontal ligament and gingivae remodel to the new position of the tooth. Whilst collagen fibres in the periodontal ligament take between three to four months to remodel, those in the gingival tissues take slightly longer, at around six months. The slowest turnaround occurs in the elastic supracrestal fibres, which take up to one year. This has important implications for teeth that were rotated, as this slow remodelling is implicated in the very high relapse rate for rotational correction. The retention regime for these teeth can be supplemented by supracrestal fibrotomy (or pericision), a surgical procedure involving sectioning of the supracrestal fibres. This is carried out under local anaesthetic, once the rotation has been orthodontically corrected. A surgical blade is inserted into the gingival sulcus, severing the supracrestal and transeptal fibres. It has been shown to reduce rotational relapse in the maxillary incisor region with no loss of periodontal attachment (Edwards, 1988). However, this procedure should not be done on the mid-labial portion of any tooth with a narrow zone of attached gingivae or thin plate of alveolar bone, particularly the lower incisors. An alternative technique is simply to divide the interdental papilla. Overcorrection of rotated teeth early in treatment and maintaining them in their new position for a significant period before appliances are removed is also recommended which will allow for some relapse.

Soft tissues

To a large extent the soft tissues define the limitations of orthodontic tooth movement. Any change in the position of the teeth can move them out of the zone of soft tissue balance and increase the chance of relapse. For this reason the arch form, particularly of the lower arch, is not amenable to any significant change. If expanded during treatment, especially across the intercanine width, this will be very prone to relapse. Similarly, labiolingual movement of the lower incisors to any great degree is notoriously prone to relapse.

Vertically, the lower lip position is very important in the stability of overjet reduction. If the lips are competent following treatment and the lower lip rests labially to the upper incisors, there is greater stability. This is in part dependent on growth of the soft tissues, which grow vertically more than the underlying skeletal bases during the preadolescent period. This results in an increase in lip competence, especially in boys whose lips grow later and to a greater extent than girls (Nanda, 1990).

An endogenous tongue thrust is primarily neurological in origin, resulting in anterior position of the tongue and excessive force exerted on swallowing. Although this phenomenon is real, it is very rare and most abnormal tongue activity is adaptive. To create an anterior seal on swallowing with an anterior open bite, the tongue will invariably come forwards to fill the gap. If the anterior open bite is corrected, the tongue activity is normalized and the result will be stable. However, if a true tongue thrust is present, no amount of treatment will guarantee stability, as the primary aetiological factor will remain (Fig. 11.22).

Figure 11.22 Large anterior open bite due to an endogenous tongue thrust.

Occlusion

Teeth retained by the occlusion are often stable. Correction of an anterior crossbite with a positive overbite following treatment requires no retention. It is also a widely held belief that a well-interdigitated class I occlusion aids stability at the end of treatment and there is some evidence for this (Kahl-Nieke et al, 1995). This is certainly true for overbite reduction and buccal segment correction but there is little evidence that it will prevent relapse or reappearance of incisor crowding. Occlusal forces themselves act in an anterior direction, and have been postulated to be causative in the development of lower incisor crowding (Southard et al, 1990); however, the short duration of these forces makes this unlikely.

Growth

Facial growth continues throughout life, generally in the same direction as that occurring during adolescence, but to a much smaller degree (Behrents, 1985). Facial growth is not linear but rotational, especially mandibular growth. This can lead to forces being placed on the teeth from either soft tissues or the occlusion as the dentition compensates to maintain the occlusal position. This can manifest most notably as late lower incisor crowding, as the lower labial segment uprights to compensate for mandibular growth. This is thought to be a major factor in late lower incisor crowding seen in both orthodontically treated and untreated individuals.

In class III malocclusion, mandibular growth can result in the reappearance of a reverse overbite following early correction. This is one of the main reasons for monitoring growth in class III cases during adolescence before final treatment decisions are made.

Original malocclusion

If the original malocclusion was severe, a small amount of relapse following treatment may be acceptable, as the overall aesthetic improvement will remain good. However, if the patient only presented with a mild malocclusion, any relapse may be unacceptable. This is especially true when mild labial segment crowding is treated. Numerous strategies for improving the stability of lower incisors following alignment have been devised. One of these is interproximal enamel reduction. Removing a small amount of enamel creates broader, flatter contact points between these teeth and theoretically reduces the chance of them slipping past each other and becoming crowded (Boese, 1980a, b). Despite these added precautions, all patients need to be made aware of the relapse potential prior to beginning treatment and the necessity for long-term or even permanent retention.

Growth pattern

Following treatment the original growth pattern will re-impose itself and continue to a greater or lesser degree throughout life. This is true for both sagittal and vertical growth. Thus, a corrected class III incisor relationship will relapse if there is unfavourable mandibular growth and an anterior open bite, which will reappear with continued vertical growth. Retention should therefore be involved in maintaining the skeletal correction. If a functional appliance or headgear was used to control growth during the active treatment phase it should ideally be continued during the retention phase, at least until adolescent growth is complete. This of course is very much compliance-based and provides a good argument against starting treatment too early where there is a skeletal discrepancy.

Type of retainers

Retainers are appliances designed to maintain the position of the teeth following orthodontic treatment. Retainers can be either removable or fixed.

Removable retainers

Removable retainers can be taken out of the mouth by the patient and therefore rely on good compliance. They are generally easy to maintain and do not compromise oral hygiene although like all removable appliances, they can affect speech. Although many different types of retainer have been described, the main types include the following:

• Hawley retainers are simple, robust and retentive; consisting of Adams cribs on the first molars and a labial bow around the incisors. The labial bow can be fitted (contoured around the incisors) or acrylated (with an acrylic facing) to improve retention and rotational control of the incisors (Fig. 11.23). Hawley retainers will allow some occlusal settling and in first premolar extraction cases, the labial bow can be soldered directly to the first molar cribs, which avoids the wire crossing the extraction spaces and allowing them to reopen. A bite plane can also be incorporated to maintain overbite reduction.

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• Begg retainers have the labial bow extending around the distal aspect of the terminal molar (Fig. 11.23). They allow occlusal settling, as no wire work crosses the occlusion. These retainers are less retentive than Hawley retainers and the labial bow is more prone to distortion.

• Spring or Barrer retainers carry acrylated bows both labially and lingually (Fig. 11.23). The original appliance extended only to the canines; however, due to the risk of swallowing or aspiration, a modification which includes cribs on the first molars has been described. These retainers can be used to realign minor lower incisor relapse if the teeth are realigned on the working model by the technician.

• Vacuum-formed retainers are clear thermoplastic retainers (Fig. 11.23). They are easy to construct by heating a sheet of clear plastic, which is then sucked down onto a dental cast by a vacuum. They provide good aesthetics and better control of incisor alignment than Hawley type retainers (Rowland et al, 2007), but they are not as robust. They can be extended just from canine to canine or back to the second molars, in which case they will not allow any occlusal settling after treatment. A palatal wire should be incorporated if used in cases where there has been significant maxillary expansion. Vacuum-form retainers can also be used for active tooth movement. The teeth can be aligned on a working model from which the vacuum-formed retainer is constructed. Once fitted, if there is space for the teeth to move minor irregularities can be corrected with this type of appliance. Vacuum retainers should not be worn for eating or drinking, as they can act as a reservoir for fluids, increasing the risk of decalcification in the presence of a cariogenic diet.

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Figure 11.23 Hawley retainers with acrylated labial bows and a prosthetic tooth replacing the UL2 (upper-left); Begg retainer with acrylated labial bow (upper-right); Barrer spring-loaded retainer (lower-left); Essix-type vacuum-formed retainer (lower-right).

Fixed retainers

Fixed retainers usually consist of a wire cemented or bonded to the teeth, which the patient cannot remove. These retainers are used when long-term or permanent retention is required, particularly for the lower incisors, and the wire usually extends from canine to canine. They can also be used for the upper incisors to prevent reopening of a midline diastema, but a higher failure rate can occur in this region, especially with an increased overbite. Early designs were made from plain wires with steel pads at each end bonded to the canines. This design was very good at maintaining the lower intercanine width but less effective at preventing rotational relapse of incisors not bonded to it. Later fixed retainers consisted of flexible multistrand stainless steel wires bonded to the lingual surfaces of the teeth with composite (Zachrisson, 1977) (Fig. 11.24). These are well tolerated, allow some physiological movement of the teeth, do not compromise on aesthetics and can provide excellent retention. They do not interfere with speech and are less reliant upon compliance than removable retainers. Fixed retainers do not seem to produce any long-term periodontal problems, although calculus can build up around them, particularly in the lower incisor region. Their placement is time-consuming and technique-sensitive and a back-up removable retainer should also be supplied to the patient to preserve tooth position if the fixed retainer fails.

Figure 11.24 Bonded upper retainer.

Duration of retention

The duration of retention required following orthodontic treatment is variable. However, the only way to permanently guarantee stability of tooth position is to retain it indefinitely.