Balancing and compensating extractions

Balancing and compensating extractions aim to preserve arch symmetry and occlusal relationships by extracting teeth opposing those requiring enforced extraction.

The decision to carry out a balancing or compensating extraction will depend upon a number of factors (Box 10.1). However, before the elective extraction of any deciduous tooth is instituted, a radiographic screen should be carried out to check for the presence, position and normal formation of the developing permanent dentition. Any other deciduous teeth of questionable prognosis should also be considered as candidates for balancing or compensating extraction, particularly if general anaesthesia is required. It can be more difficult to justify these extractions if local anaesthesia is used for the elective extraction of a single symptomatic tooth and cooperation for further extractions may be poor.

Space maintenance

A space maintainer is a removable or fixed orthodontic appliance that preserves space within the dental arches (Fig. 10.3). These appliances are most commonly used in the mixed dentition to prevent forward drift of the first permanent molars following early loss of deciduous second molar teeth, or to maintain space and serve as a prosthesis in the labial segment after traumatic loss of permanent incisors.

Figure 10.3 Lower fixed space maintainers to preserve the arch length (left panels), preservation of labial segment position with a removable retainer (upper right and middle panels) and restoration of a LLE with a stainless steel crown to prevent space loss (lower right panel) (lower right panel courtesy of Evelyn Sheehy).

A space maintainer in the posterior dentition can be useful in the following situations:

It should always be remembered that a tooth is the ideal space maintainer and every effort should be made to preserve deciduous teeth until the time of their natural exfoliation (Fig. 10.3). If a space maintainer is to be used it should be in a mouth with good oral hygiene and ideally, a low risk of further caries. Unfortunately, cases requiring elective tooth extraction due to dental caries are often the least suitable for long-term space maintenance.

Retained second deciduous molars

The second deciduous molar can often be retained due to congenital absence of the second premolar. If this is the case, several treatment options should be considered:

Treatment planning will depend primarily upon future space requirements for the correction of any underlying malocclusion and the long-term prognosis of the second deciduous molar. Clinical and radiographic examination of the crown, root and associated alveolar bone will give a useful indication of this (Fig. 10.5). Any of the following features, either alone or in combination, will demonstrate a potentially poor prognosis:

Figure 10.5 Retained deciduous molars in association with congenital absence of the second premolar.

In the upper radiograph, the LLE has a good long-term prognosis. In the lower radiograph, extensive root resorption means a poor prognosis for both the retained lower Es.

Second deciduous molars can have an excellent long-term prognosis if they are in good condition and will match the lifespan of many prostheses. Indeed, if they survive to twenty years of age, continued long-term function can be anticipated (Bjerklin & Bennett, 2000; Sletten et al, 2003).

Ankylosis and infraocclusion

A tooth becomes ankylosed when the periodontal ligament is lost and direct fusion occurs between root dentine and the surrounding alveolar bone. Ankylosis most commonly affects deciduous molars, occurring in up to 9% of children (Kurol, 1981). A number of factors are thought to contribute:

A consequence of ankylosis can be the apparent ‘submergence’ or infraocclusion of the affected tooth relative to the occlusal plane (Fig. 10.6). This occurs in the growing child because alveolar bone and occlusal height increase with development, whilst the position of the ankylosed tooth remains fixed.

Figure 10.6 Infraocclusion of the ULE in association with congenital obsence of the UL5.

Nonsyndromic hypodontia

Nonsyndromic hypodontia can either appear sporadically within a member of a family or be inherited. This form can follow autosomal dominant, autosomal recessive or autosomal sex-linked patterns of inheritance, with considerable variation in both penetrance and expressivity. This is by far the most common type of congenital tooth absence and can be further categorized based upon clinical presentation:

Within these clinical entities, certain teeth fail to develop more often than others:

Nonsyndromic hypodontia can be associated with other developmental anomalies affecting the dentition, which provides evidence of a genetic influence (Table 10.1). However, a multifactorial model has also been suggested (Brook, 1984), with the phenotypic effect being related to certain thresholds, themselves influenced by both genetic and environmental factors. Clearly, within this model, the mutation of a major gene may be a significant enough event to result in inherited tooth loss (Box 10.2).

Table 10.1 Dental anomalies associated with hypodontia

Syndromic hypodontia

Congenital tooth absence is also seen in association with other recognizable structural defects or abnormalities (Table 10.2).

Table 10.2 Syndromic conditions associated with hypodontia

Management

The management of congenital tooth absence will involve either:

Milder forms of hypodontia can usually be managed within an orthodontic treatment plan in consultation with either the general dental practitioner or restorative specialist and is usually carried out in the permanent dentition (see Chapter 11). More severe hypodontia or oligodontia requires complex multidisciplinary treatment and is usually carried out within a specialist centre.

Unerupted permanent maxillary incisor

A discrepancy in eruption between contralateral maxillary incisors of greater than six months, or eruption of lateral incisors before the centrals warrants radiographic investigation. Delayed eruption of maxillary incisors is most commonly associated with the presence of supernumerary teeth (particularly tuberculate), retained deciduous incisors or dilaceration. Obstruction secondary to a supernumerary tooth is by far the commonest cause.

Figure 10.23 A conventional panoramic view (left) and cone beam CT sagittal section (right) through a severely dilacerated UR1.

Unerupted permanent maxillary canine

The permanent maxillary canine fails to erupt in approximately 2% of Caucasian children and these teeth will often require orthodontic management (Bishara, 1992; Ferguson, 1990). Deviation from the normal path of eruption is usually associated with subsequent impaction and in the vast majority of cases this occurs in a palatal direction, although the canine can also impact on the buccal side or within the line of the dental arch. A number of reasons have been suggested to explain the particular vulnerability of the maxillary canine to deviation from its normal eruptive path:

Clinical examination

At the age of 10 years, the maxillary canine should be palpable in the buccal sulcus adjacent to the lateral incisor root (Fig. 10.24). If it is not, or if there is any asymmetry in palpation, then an abnormal path of eruption should be suspected and radiographic investigation instigated (Ericson & Kurol, 1986). Other clinical features, which may alert the clinician to possible impaction include:

• A palatal bulge;

• Delayed eruption, marked distal angulation or retroclination, microdontia or absence of the permanent lateral incisor; and

• A firm deciduous canine (particularly beyond the age of 14 years) indicating a lack of resorption.

Figure 10.24 Maxillary permanent canines palpable in the buccal sulcus.

The canine position is given away by the inclination of the permanent lateral incisor crowns.

Radiographic examination

Radiographic examination is required to demonstrate the presence of the canine, its position within the maxillary arch, the condition of adjacent teeth (particularly the degree of resorption associated with the deciduous canine or presence of any resorption associated with the permanent incisors) and any other pathology. The position of the canine should be evaluated in all three planes of space:

• Buccopalatal relationship to the dental arch;

• Height relative to the occlusal plane;

• Angulation relative to the mid-sagittal plane; and

• Distance from the mid-sagittal plane.

Two films are required to definitively establish canine position and the parallax (or tube-shift) technique is commonly used to achieve this (Jacobs, 1999). Parallax is the apparent displacement of an object when observed from two different positions and, in radiological terms, relies upon taking two views with the X-ray tube in a different position for each view. Horizontal parallax uses a horizontal shift in the X-ray tube (usually with successive periapical views taken with the tube moved horizontally), whilst vertical parallax uses a vertical shift in the tube (usually achieved with a panoramic and anterior occlusal view). The advantage of the parallax technique is that it always involves an intraoral view, which gives good detail of the canine and incisors (Fig. 10.25). More recently, the use of cone beam CT has been described to precisely locate the position of ectopic canines (Walker et al, 2006) (see Box 6.5).

Figure 10.25 Vertical parallax to localize maxillary canine position.

In the upper radiographs, the coronal tip of both maxillary canines lie midway along the roots of the lateral incisors on the panoramic radiograph; whilst on the anterior occlusal radiograph they are clearly midway along the crowns of the lateral incisors. These canines have moved down as the X-ray tube has moved up and are therefore buccally positioned. In the middle radiographs, the UL3 is situated below the root apex of the UL2 on the panoramic radiograph; whilst on the anterior occlusal radiograph it is now situated above the tip. The canine has moved up as the X-ray tube has moved up and is therefore positioned palatally. In the lower radiographs the coronal tips of both maxillary canines are situated just below the apices of the lateral incisors on the panoramic radiograph; whilst on the periapical radiographs they are in a similar position. These canines have not moved significantly as the X-ray tube has moved and are therefore situated in the line of the dental arch.

Interceptive treatment

An impacted canine can be associated with a significant risk of damage to adjacent teeth, particularly the lateral and occasionally the central incisors (Fig. 10.26) and often requires surgical intervention combined with prolonged orthodontic treatment in order to accommodate it in the maxillary arch. Some evidence exists from prospective studies to suggest that early extraction of the deciduous canine can help prevent a palatally ectopic permanent canine becoming impacted (Fig. 10.27) (Ericson & Kurol, 1988; Power & Short, 1993), particularly if there is a lack of crowding or headgear is used to create space (Leonardi et al, 2004). Whilst this evidence is weak (Parkin et al, 2009), with radiographic evidence of an ectopic position and a lack of normal resorption associated with the deciduous canine, consideration should be given to elective extraction of this tooth. The best results seem to be obtained under the following conditions:

• Patient aged between 10 and 13 years and in the mixed dentition;

• Canine positioned distal to the midline of the lateral incisor root and less than 55° to the mid-sagittal plane; and

• An absence of crowding in the maxillary arch.

Figure 10.26 Resorption of the UR2 (left) and the UR2, UR1 and UL2 (right) root apices in association with impacted maxillary canines.

Left panel courtesy of Jackie Silvester.

Figure 10.27 Improvement in the position of an impacted maxillary canine after extraction of its deciduous predecessor (arrowed).

If radiographic evidence of an improvement in canine position is not evident within 12 months of extraction, further treatment should be considered.

Management

The maxillary canine is a large tooth, possessing the longest root in the dentition and forming an important aesthetic and functional component of the occlusion. Every effort should be made to try and accommodate this tooth in the dental arch. However, a number of general factors should be taken into consideration when treatment planning for an impacted canine:

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• Patient attitude to treatment;

• Position of the canine;

• Presence of any associated pathology; and

• Underlying malocclusion.

The treatment of choice is generally surgical exposure followed by orthodontic alignment. However, the patient may not wish to undergo the extended orthodontic treatment that might be required to accommodate a canine following surgical exposure, or the canine may be in such a poor position that orthodontic alignment is not practical. In this case, autotransplantation of the tooth directly into the correct position is a further option. Alternatively, a decision can be made to extract the impacted canine or more rarely, leave it in situ.

Surgical exposure and orthodontic alignment

Surgical exposure aims to remove any hard or soft tissue obstruction that may be impeding eruption and can be enough to induce the canine to erupt, particularly those in more favourable positions. For those that fail to respond or are more displaced, orthodontic alignment will also be required (Fig. 10.28). When embarking upon the prescription of surgical exposure and orthodontic alignment, the following should be remembered:

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• This treatment usually involves fixed appliances and can be time-consuming; therefore patient motivation and compliance must be high.

• The canine must be in a position that makes orthodontic alignment an achievable goal. In particular, those situated as high as the apical third of the incisor roots, beyond the lateral incisor towards the midline or at an angle of greater than 55° to the mid-sagittal plane can be more difficult to align (Fig. 10.29).

• Space needs to be available in the maxillary arch for the canine. If this is lacking it will need to be generated, by either distal movement of the buccal segment or extraction. If the lateral incisor is diminutive, some consideration can be given to extracting this tooth; however, first premolars are the usual choice. It is desirable to ascertain that an impacted canine will erupt before extracting a premolar, but this is not always practical.

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Figure 10.28 Surgical open (left panels) and closed (right panels) exposure and of a palatally impacted UL3 followed by orthodontic alignment.

Figure 10.29 The prognosis for successful orthodontic alignment of a palatally impacted maxillary canine is influenced by the position of this tooth.

As the height increases, distance towards the dental midline reduces or angle to the mid-sagittal plane increases beyond 55°, the prognosis worsens.

The site of impaction will be an important determinant of the surgical technique used for exposing a maxillary canine (see Box 10.4):

• For those on the labial side, the aim is for the tooth to be erupted through attached gingiva. Therefore, if the crown is located below the mucogingival junction, an open procedure is appropriate and the crown simply uncovered. For canines above the mucogingival junction, a closed exposure and bonding with gold chain is the treatment of choice unless the canine is labial to the lateral incisor; in these cases an apically repositioned flap will provide the best chance of the tooth erupting through an attached gingiva (Kokich, 2004).

• For palatally impacted canines an open or closed technique can be used, depending on the position of the tooth. In terms of outcome there is little evidence that one technique is significantly better than the other (Parkin et al, 2008).

A variety of techniques that allow orthodontic traction to be placed on an impacted canine have been described, but all will usually involve direct bonding of an orthodontic bracket (see Box. 10.4). Either removable or fixed appliances can be used to apply traction, but for either technique space is required in the dental arch. For canines in less favourable positions, fixed appliances are essential and as this process can be quite anchorage demanding, reinforcement should be considered. Using fixed appliances, traction can be applied with flexible piggyback archwires, elastomeric chain or string, rigid buccal arms or even magnets. The choice of technique will depend largely upon canine position and preference of the orthodontic operator.

Autotransplantation

Autotransplantation involves the surgical removal of an impacted canine and subsequent implantation into its normal position within the maxillary alveolus. Space will need to be available to accept the transplant and a short period of orthodontic treatment may be needed to generate this, particularly if a deciduous canine has been retained; but this process will generally be less time-consuming than aligning a canine with orthodontic traction (Fig. 10.30). If the position of the ectopic canine prevents any initial orthodontic treatment, the canine can initially be removed and ‘parked’ under the buccal mucosa whilst the necessary orthodontics is undertaken. Once space has been created for the tooth, a secondary surgical procedure can be undertaken to autotransplant the tooth.

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Figure 10.30 Autotransplantation of an impacted UL3 in an adult patient. Fixed appliances were used to create some space for this tooth prior to transplantation (upper panels).

A retained URC with a poor long-term prognosis and aesthetics in a 43-year old woman who previously had the impacted UR3 extracted as a teenager (even though the UR2 was congenitally absent) (middle panels). Implant restoration to replace a previously extracted UL3 after orthodontic treatment to create space (Lower panels). Transplant and implant placement carried out by Jerry Kwok.

A disadvantage of autotransplantation is that these teeth can be susceptible to subsequent ankylosis or external root resorption and generally have a reduced long-term prognosis in comparison to canines aligned orthodontically. In addition, the success of this technique is highly dependent upon the skill of the surgical operator.

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• Surgical removal of the canine should be as atraumatic as possible (which can be difficult because these are often the very canines that are in the worst position) to avoid subsequent ankylosis;

• The canine should be kept out of occlusion and semi-rigidly splinted for a maximum of three weeks following the transplant;

• Once the splint is removed, the canine should be root canal treated to reduce the risk of subsequent external resorption; and

• Orthodontic movement of transplanted canines is possible but often limited in scope.

Extracting the canine or leaving it in situ

If a decision is made not to accommodate the impacted canine, then it can be extracted or left in situ. In either case, if the deciduous canine remains, the patient should be aware of the long-term prognosis and the likely need for eventual replacement of this tooth (see Fig. 10.30, middle panels). Alternatively, if the deciduous canine is not retained, a good contact between the lateral incisor and first premolar should be established (see Fig. 7.14). This may already be present if there is no spacing in the arch and orthodontic treatment may be avoided. However, if there is any residual spacing, either space closure or prosthetic replacement will be necessary and in both cases, some orthodontic treatment may be required (particularly if there is also an underlying malocclusion). A number of factors should be remembered when extracting a permanent canine:

• If it is in a poor position, this will almost certainly involve a general anaesthetic.

• If the extraction is prescribed because the patient has declined orthodontic treatment, any options to accommodate the canine in the future will be lost.

• If the extraction is part of an orthodontic treatment plan, either unilaterally or in combination with other teeth, space distribution will need to be considered within the context of the whole malocclusion. Ideally, space should be closed and a contact between the lateral incisor and first premolar established (Box 10.5). However, this may not be possible in the absence of crowding or an increased overjet.

• If space is not to be closed, prosthetic replacement of the canine with a single unit bridge or implant will be required.

• In the presence of severe resorption and a poor long-term prognosis associated with any incisor teeth (see Fig. 10.26), canine extraction should be avoided and ideally, this tooth accommodated in the dental arch (Fig. 10.31).

Box 10.5 Putting a first premolar in the canine position

The morphology of the maxillary first premolar differs from that of the canine in several respects:

• The root is smaller and often bifid, lacking the characteristic wide and prominent labial surface seen in the canine.

• The crown is also smaller from the buccal aspect and there is an additional palatal cusp.

However, from the buccal aspect the premolar crown does resemble that of the canine and this tooth can make an excellent substitute, which can be enhanced by a few modifications:

• The premolar root should be placed more buccally in the maxilla to create a canine eminence.

• The crown can also be rotated mesiopalatally which increases the mesiodistal width, helps to hide the palatal cusp and improves the occlusal relation with the mandibular canine.

• The palatal cusp can also be ground to reduce its prominence.

• Group function in lateral excursion is preferable to guidance, which avoids heavy loading of the less robust premolar root.

Figure 10.31 Marked resorption of the UR1 in association with an impacted canine. The UR1 was extracted, the canine brought down into the arch and then modified with composite to resemble the central incisor.

The option to leave a maxillary canine in situ is usually made on the basis that the patient is happy with their dental appearance and does not wish to have any form of treatment.

• Ideally, the canine should not be closely associated with the erupted dentition;

• There should be no evidence of any pathological change or root resorption affecting the adjacent teeth;

• Regular radiographic review is recommended in the growing patient because incisor roots can be vulnerable to resorption; and

• Longer term pathological change, such as follicular enlargement and cyst formation, should also be monitored radiographically.

Unerupted permanent mandibular canine

The permanent mandibular canine fails to erupt less commonly than the maxillary and when this does occur, it is usually a consequence of crowding. These teeth are often vertically orientated, labially placed and will erupt spontaneously once space is available in the arch. If surgical exposure is required, care should be taken to ensure these teeth erupt through attached gingiva. Occasionally an impacted mandibular canine can fail to erupt and migrate within the mandible, particularly if it is orientated horizontally (Fig. 10.32) (Peck, 1998). These teeth are not generally amenable to orthodontic traction and the options are then extraction or autotransplantation.

Figure 10.32 Retained LLC and horizontally displaced LL3.

Courtesy of Jackie Silvester.

Impacted maxillary first permanent molar

Impaction of a maxillary first permanent molar against the second deciduous molar (Fig. 10.33) occurs in around 4% of the population and is usually indicative of crowding in the posterior maxilla (Kurol & Bjerklin, 1982).

Figure 10.33 Impaction of the UR6 against the URE.

Occasionally these teeth will spontaneously erupt but if this does not occur within 6–12 months, some intervention is indicated:

Primary failure of eruption

Primary failure of eruption (PFE) is an isolated condition associated with a localized failure of tooth eruption:

Diagnosis of PFE is usually made when there is an absence of any clear genetic, pathological or environmental factor responsible for preventing the eruption of an affected tooth (Fig. 10.34).

Figure 10.34 Primary failure of eruption affecting the LR6.

Transposition

Dental transposition is the complete positional interchange of two adjacent teeth, or the development, or eruption of a tooth in a position normally occupied by a non-adjacent tooth.

Figure 10.35 Correction of bilateral Mx.C.P1 transpositions using a fixed appliance.

Table 10.6 Classification of dental transposition^a

a Peck et al, 1993, 1998.

Several mechanisms to account for the phenomenon of dental transposition have been proposed:

However, many types of transposition are often associated with factors that have a genetic basis:

On this basis it has been suggested that the primary aetiological basis of transposition is genetic, within a model of multifactorial inheritance (Peck et al, 1993, 1998).

Early loss of first permanent molars

The decennial National Children’s Dental Health Survey has clearly shown a progressive reduction in dentinal caries experience in the permanent dentition of children aged between 8 and 15 years over the past thirty years (Pitts et al, 2006). However, in those children who do experience dental caries, first permanent molars can be susceptible to progressive and rapid decay (Fig. 10.36). In addition, combined first molar–incisor hypomineralization (MIH) is a recognized condition of unknown aetiology seen in around 15% of Caucasian children, which can significantly affect the long-term prognosis of first permanent molars in more severe cases (Koch et al, 1987). The increased use of fixed orthodontic appliances has meant that a good occlusal result can be obtained following the enforced loss of these teeth in a wider range of cases (Sandler et al, 2000). However, those children who require first molar extraction are often the least suitable for subsequent fixed appliance treatment because of high caries susceptibility and low potential compliance.

Figure 10.36 Carious mandibular first permanent molars.

Ideally, premature loss of first molars should be followed by successful eruption of the second molars to replace them, ultimately followed by third molars to complete the molar dentition (Fig. 10.37). If any space is required within the arches to correct an underlying malocclusion, the first molar extraction sites should provide this. However, extraction of these teeth often results in a large amount of space being created at some distance from those sites where it is required to relieve incisor crowding or reduce an overjet. In these circumstances, fixed appliances will be required to control this.

Figure 10.37 Good occlusal results following extraction of the lower first permanent molars (upper panels) and all four first permanent molars (middle and lower panels). The second molars are at a good angulation with minimal spacing and there is evidence of third molar development.

First permanent molars are never the ideal choice of teeth to extract because significant occlusal complications can result, particularly if they are removed before the age of 8 years:

Delayed extraction, during the later stages of second molar eruption, can also result in occlusal problems (Fig. 10.38):

Figure 10.38 A poor occlusal result following extraction of the lower first permanent molars.

The second permanent molars are spaced and mesially angulated after late extraction of the first molars.

However, in many cases the poor prognosis associated with carious, hypoplastic or heavily restored first molars will dictate that extraction is required. Indeed, radiographic evidence of caries into dentine affecting first permanent molars should elicit consideration of their elective extraction. The best spontaneous occlusal results are obtained in the following circumstances:

In most circumstances, not all of the first permanent molars will have a poor prognosis and the need for balancing or compensating extractions will have to be evaluated. Generally, extraction of a mandibular first molar may require compensatory extraction of the opposing maxillary molar to prevent overeruption of this tooth. This decision is more difficult if space is required in the maxillary arch to correct a malocclusion (Box 10.6):

Balancing first molar extractions are rarely required to preserve a centreline. However, these extraction decisions will need to be made as part of the overall treatment plan for the whole occlusion.

Early loss of the maxillary central incisor

Traumatic loss of a maxillary central incisor is seen in around of 3% of children and usually occurs unilaterally, in the mixed dentition and in a child with an increased overjet (Jarvinen, 1978). Reimplantation should always be attempted if possible, because regardless of the long-term prognosis, these teeth will serve as a useful maintainer of both arch space and alveolar bone. If they are subsequently lost, longer term space maintenance can be achieved with a simple upper partial denture. If these teeth are not reimplanted, a decision will need to be made regarding space management. Long-term space maintenance can be achieved with a partial denture; however, this can be associated with a loss of alveolar bone height, which can make subsequent prosthetic replacement more difficult. Alternatively, the space can be allowed to close and reopened in the permanent dentition prior to prosthetic replacement. This allows preservation of alveolar bone, but will require fixed appliance treatment and often space creation in the upper arch.

Management

Unilateral loss of a maxillary central incisor will usually require prosthetic replacement, with either a resin-retained bridge or implant, because a lateral incisor rarely makes a good unilateral substitute for the central incisor. If space is required elsewhere in the maxillary arch, this is usually dealt with on its own merit. Occasionally, if premolar extractions are planned to correct any underlying malocclusion, autotransplantation and subsequent coronal modification of one of these teeth can provide a further option for replacing the maxillary incisor (Fig. 10.39).

Figure 10.39 Premolar transplanted into the central incisor position and built up with composite

Courtesy of Joanna Johnson.

In cases of bilateral loss, if space is required to reduce an overjet or relieve crowding and the lateral incisors are of a reasonable size and form, consideration can be given to moving them into the position vacated by the centrals (Fig. 10.40), although it can be difficult to obtain good aesthetics without modifying their coronal morphology restoratively.

Figure 10.40 Lateral incisor teeth as the centrals following traumatic loss.

Maxillary midline diastema

A maxillary midline diastema can be a normal feature of dental development and will often improve following eruption of the permanent canine teeth. However, a number of other causes also exist (Fig. 10.41):

Figure 10.41 Maxillary diastema.

Digit sucking

A prolonged digit sucking habit can give rise to a number of characteristic features as part of a malocclusion and these often manifest in the late deciduous or early mixed dentitions (see Fig. 1.10):

These features are associated directly with the habitual placement of the digit and indirectly with the reduced tongue position and negative intraoral pressure generated with the habit. The underlying pattern of facial growth will also influence the malocclusion, any tendency toward vertical excess and a posterior mandibular growth rotation will potentially worsen the effects of any habit, or even make a more significant contribution than the habit itself.

Digit sucking occurs quite commonly in children below the age of 10 years and will often cease spontaneously. In most of these cases, the anterior open bite will resolve, although correction of the crossbite may require some maxillary arch expansion. However, in a minority of cases the habit can persist into the teenage years and can be the main contributing factor in the aetiology of a significant malocclusion. These children should be encouraged to stop the habit, ideally without intervention, although a variety of commercial aids are also available. If these fail occasionally a simple removable or fixed orthodontic appliance may be required to finally break the habit.

Crowding

As the permanent incisors are larger than their deciduous predecessors, space must be made available in the dental arches if they are to erupt without crowding. Spacing between the deciduous incisors can provide some of this (see Box 4.5 and Fig. 4.15); but the permanent incisors commonly erupt into crowded positions, particularly in the lower arch. A small improvement in this crowding can sometimes occur prior to eruption of the permanent canines, due largely to incisor proclination during eruption and some transverse expansion into the canine regions (Lundy & Richardson, 1995). However, once the permanent canines have erupted, there will almost certainly be no further improvement in incisor alignment and often an increase in crowding.

A variety of interceptive measures for alleviating incisor crowding during the mixed dentition, including arch expansion, extraction of the deciduous canines and serial extraction, have been described. Expansion across the intercanine width is largely unstable, particularly in the lower arch and is not recommended. Extraction of the deciduous canines will result in some short-term improvement in lower incisor alignment; however, whilst this can be effective for labiolingual displacements, it is less so for rotations. In addition, the incisors may tip lingually, which can reduce arch length and result in greater crowding in the long-term. Despite these limitations the extraction of deciduous canines can be a useful strategy in the following circumstances:

Posterior crossbite

A posterior crossbite in the mixed dentition can be an early manifestation of a skeletal discrepancy, or be related to a persistent digit-sucking habit and can occur unilaterally or bilaterally. There is a weak association between posterior crossbite with displacement and the later development of temporomandibular dysfunction (Mohlin & Thilander, 1984); whilst asymmetric muscular activity associated with an established mandibular displacement can be perpetuated from the primary and mixed into the permanent dentition. For these reasons, it is considered appropriate to correct a posterior crossbite and eliminate the displacement as early as possible (Harrison & Ashby, 2001) and a number of relatively simple methods are available to do this.

Anterior crossbites

An anterior crossbite can cause gingival recession associated with the lower incisors if there is a displacement on closing, particularly if these teeth are displaced labially (Fig. 10.42). This is an indication for treatment in the mixed dentition and correction can be achieved with removable or fixed appliances. In the presence of a positive overbite, a corrected anterior crossbite will usually be self-retaining.

Figure 10.42 Gingival recession affecting the LL1 in two cases of anterior crossbite.

Fixed appliances

If space or bodily tooth movement are required to correct an anterior crossbite, removable appliances are inappropriate. In these circumstances, a fixed appliance with four brackets placed on the upper incisors and bands on the first molars (2 × 4 appliance) (Fig. 10.43) can be very effective. The bite can be opened with glass ionomer cement placed on the occlusal surface of the first molars. Simple fixed appliances offer a number of advantages over removable appliances:

• Bodily tooth movement;

• Less dependent on patient compliance;

• Rapid correction of an anterior crossbite;

• Multiple tooth movement;

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• Space possibly created for tooth movement if necessary; and

• Possible tooth extrusion for creating a positive overbite.

Figure 10.43 Correction of an anterior crossbite with a 2 × 4 fixed appliance.

Class II malocclusion

Class II malocclusions are amenable to early treatment using functional appliances; however, the timing of treatment should be carefully considered. Several large randomized controlled trials have shown little difference in outcome, in terms of both overall growth and the final occlusal result, between patients who underwent an early phase of treatment to reduce an overjet in the mixed dentition and those who received comprehensive treatment in the late mixed and early permanent dentition (see Chapter 8). Whilst overjet correction can be rapid in the mixed dentition, a significant problem is the length of time this correction must be retained whilst waiting for a patient to enter the permanent dentition, prior to a final stage of fixed appliance orthodontic treatment to detail the occlusion. The only significant difference would appear to be the overall treatment time; patients who undergo early correction ultimately spend longer in treatment. As a general rule, the most effective time for undertaking correction of a class II malocclusion is during the adolescent growth spurt, as this will optimize mandibular growth whilst limiting the overall treatment time. However, several exceptions do exist (Box 10.7) and these relate primarily to reducing the risk of trauma and improving self-esteem.

Class III malocclusions

A reduced or reverse overjet in the mixed dentition is usually a sign of an underlying class III skeletal relationship and this will tend to worsen with age. Treatment decisions are often delayed at this stage to monitor further growth and to better determine the extent of the skeletal problem; however, early treatment may be considered in patients with the following features:

A class III malocclusion on a skeletal I base with a significant forward mandibular displacement is sometimes referred to as a ‘pseudo class III malocclusion’, because the incisor relationship does not reflect the underlying skeletal relationship (see Fig. 6.17). This type of class III malocclusion is very amenable to early orthodontic treatment, but creating a positive overbite as well as overjet is crucial for stability following correction. When the overbite is reduced or there is an anterior openbite, it is more sensible to monitor growth into adolescence before final treatment decisions are made.

Functional appliances

Functional appliances are most commonly used to correct class II malocclusion; however, numerous appliances have also been described for the treatment of class III cases. These are only really able to treat the milder class III cases described above. This is largely because their effects are restricted to inducing the following tooth movements:

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• Upper incisor proclination;

• Lower incisor retroclination; and

• Backward and downward rotation of the mandible.

A class III version of the Fränkel Functional Regulator (FR III) is most commonly used, but this appliance is bulky, prone to breakage and difficult to wear. More recently, a class III twin block, with the blocks reversed in comparison to the class II version, has been described (Fig. 10.44).

Figure 10.44 Reverse twin block for class III malocclusion.

Protraction headgear

Extraoral force can be utilized in an attempt to move the maxilla forwards in class III cases, applied by attaching heavy elastics from either a removable or fixed appliance to a facemask, which rests on the patient’s forehead and chin for anchorage (Fig. 10.45). If worn for 12 to 14 hours each day, a significant anterior skeletal displacement of the maxilla is possible, making this approach the most appropriate for patients with maxillary hypoplasia (Fig. 10.46). This technique is theoretically more effective when combined with rapid maxillary expansion, because the expansion will disrupt the maxillary sutures and allows greater anterior displacement of the maxilla by the headgear. Greater skeletal change is seen in pre-adolescent patients, which essentially means those in the early mixed dentition. However, long-term results are dependent on further growth and patients with a vertical growth pattern or mandibular prognathism will often tend to outgrow any early positive effects of treatment. In addition, these appliances are some of the most demanding to wear in terms of patient compliance.

Figure 10.45 Facemask therapy to induce protraction of the maxillary dentition.

Figure 10.46 Considerable improvement can be achieved in a class III malocclusion treated with reverse headgear and palatal expansion.

However, long-term stability is less predictable.

Enamel defects

The enamel of deciduous teeth begins to calcify at around 4 months in utero and is complete by the end of the first year of life. In the permanent dentition, this process occurs between 4 months and around 8 years of age (excluding third molars). A range of local and systemic factors can disturb enamel formation, which can lead to chronological hypoplasia and hypocalcification of the tooth crown (Table 10.7).

Table 10.7 Anomalies of enamel and dentine

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Amelogenesis imperfecta (OMIM 104510)

Amelogenesis imperfecta (AI) is a collective term for a group of inherited conditions characterized primarily by abnormal enamel formation in either dentition (Fig. 10.47). AI can be inherited as an autosomal dominant, autosomal recessive or sex-linked trait and has a prevalence that can range from 1 : 1,000 to 1 : 14,000, depending upon the population. The predominant enamel phenotype is either:

• Hypoplastic (normally mineralized but the matrix is deficient, resulting in thin enamel); or

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• Hypomineralized (either hypomature or hypocalcified, or a combination of the two).

Figure 10.47 Amelogenesis imperfecta.

Left panel courtesy of Joanna Johnson.

The classification of AI is complex, being based historically upon phenotype (Table 10.8). However, as knowledge of the genetic basis underlying this condition has improved, the classification has been adapted (Wright, 2006).

Table 10.8 Classification of amelogenesis imperfecta^a

Type I hypoplastic

• IA hypoplastic, pitted, autosomal dominant • IB hypoplastic, local, autosomal dominant • IC hypoplastic, local, autosomal recessive • ID hypoplastic, smooth, autosomal dominant • IE hypoplastic, smooth, X-linked dominant • IF hypoplastic, rough, autosomal dominant • IG enamel agenesis, autosomal recessive

Type II hypomaturation

• IIA hypomaturation, pigmented, autosomal recessive • IIB hypomaturation • IIC snow-capped teeth, X-linked • IID autosomal dominant

Type III hypocalcified

• IIIA autosomal dominant • IIIB autosomal recessive

Type IV hypomaturation–hypoplastic with taurodontism

• IVA hypomaturation–hypoplastic with taurodontism, autosomal dominant • IVB hypoplastic–hypomaturation with taurodontism, autosomal dominant

a Witkop (1988).

Dentine defects

In addition to systemic factors, localized environmental factors such as infection and trauma can interfere with dentinogenesis (Table 10.7).

Inherited conditions affecting dentine

A number of genetic conditions exist that can affect the dentine within teeth, either in isolation or in addition to other structures within the body (MacDougall et al, 2006) (Table 10.9). All of these conditions exhibit an autosomal dominant pattern of inheritance and can be classified as:

• Dentine dysplasia; or

• Dentinogenesis imperfecta.

Table 10.9 Genetic defects affecting dentine

• Dentine dysplasia type I (OMIM 125400) (rootless teeth) • Dentine dysplasia type II (OMIM 125420) • Dentinogenesis imperfecta • Type I (osteogenesis imperfecta) • Type II (OMIM 125490) (hereditary opalescent dentine) • Type III (OMIM 125500) (Brandywine staining)

Dentinogenesis imperfecta (DGI) represents the most common group of inherited dentine disorders (Fig. 10.48) and there are three essential subgroups, types I–III:

• Type I is associated with osteogenesis imperfecta or brittle bone disease and is caused by mutation in the COLA1 or COLA2 gene, both of which are essential for type I collagen formation in bones and dentine. The deciduous and permanent teeth are affected by discolouration, attrition and pulp canal obliteration.

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• Type II (OMIM 125490) is seen in around 1 : 7,000 Caucasians and also affects teeth in both dentitions, causing translucent, amber and bluish grey discolouration, enamel chipping and marked attrition. The crowns are bulbous and the pulp canals also become obliterated.

• Type III (OMIM 125500) affects certain subpopulations of people, including Native American Indians and European Caucasians. Both dentitions can be affected by so-called ‘shell teeth’, which lose enamel and have poorly mineralized dentine, leading to multiple pulp exposures.

Figure 10.48 Dentinogenesis imperfecta in the deciduous and permanent dentitions.

Courtesy of Evelyn Sheehy.