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.

• 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).

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.

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.

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).

Figure 11.10 Overjet re/>

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