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.

Box 10.1 Which deciduous teeth require balancing and compensating extractions?

• It is not necessary to balance or compensate the loss of a deciduous incisor from either dental arch.

• The premature and unilateral loss of a deciduous canine is often associated with a centreline shift and a balancing extraction can help to preserve the centreline; however, compensating extractions are not required in this situation.

• First deciduous molars can also induce a centreline shift if lost unilaterally and a balancing extraction may be required to preserve the centreline, particularly in a crowded arch.

• If mandibular first deciduous molars are to be lost, some consideration can be given to compensating extractions in the maxillary arch to preserve the buccal segment relationship, particularly if these teeth have any question regarding their long-term prognosis.

• Second deciduous molars do not require balancing extractions; however, if the loss of these teeth is required bilaterally in either dental arch, and this may contribute to a significant alteration in the molar relationship, then compensating extractions may be indicated.

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:

• In an occlusion with only mild crowding where any further space loss would result in the need for more complex orthodontic treatment; and

• In an occlusion with severe crowding where any further space loss would result in more than a single tooth unit of space being required.

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.

Prolonged retention of deciduous teeth

Considerable variation can exist in the timing of deciduous tooth exfoliation and the subsequent eruption of permanent successors. The presence of marked asymmetry in the retention of deciduous teeth should be investigated radiographically.

Occasionally a permanent successor will erupt having failed to resorb the roots of the overlying deciduous tooth (Fig. 10.4). The patient should be encouraged to exfoliate these retained deciduous teeth themselves and if this is not possible, they should be extracted under local anaesthetic.

Figure 10.4 Retained deciduous incisors.

The permanent incisors have failed to resorb their deciduous predecessors and erupted palatally (upper panel) and lingually (lower panel).

Crowding, or an ectopic position affecting the permanent successor, can also lead to prolonged retention of the overlying deciduous tooth.

• Management is dictated principally by the amount of space available within the dental arch and the position of the unerupted permanent tooth. If space is at a premium, maintenance may be required following removal of the deciduous tooth, or alternatively space will need to be created.

• If space is available, extraction of the deciduous tooth alone can often lead to successful eruption if the permanent tooth is in a favourable position.

• If the position is less favourable, exposure of the permanent tooth (with or without the application of orthodontic traction) may also be required.

• Extraction of the permanent tooth may be considered if the position is poor, either in isolation or in combination with other teeth as part of an orthodontic treatment plan. The decision to extract will also be influenced by the type of tooth under consideration.

Another cause of deciduous tooth retention is congenital absence of the permanent successor. For most of these deciduous teeth, the long-term prognosis is poor and they will either be lost naturally or ultimately require extraction. However, they can often act as useful maintainers of arch space or alveolar bone in the shorter term.

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:

• Extraction to facilitate space closure;

• Extraction and prosthetic replacement; and

• Retention of the second deciduous molar.

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:

• Caries;

• Root resorption;

• Bone resorption;

• Periapical or interradicular pathology;

• Ankylosis;

• Infraocclusion; and

• Gingival recession.

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:

• Genetic predisposition;

• Failure of normal resorption by the permanent successor;

• Congenital absence of the permanent successor;

• Trauma; and

• Infection.

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.

• In the presence of a permanent successor and minimal infraocclusion, the ankylosed tooth can usually be left under observation to exfoliate naturally.

• If the infraocclusion becomes greater this can lead to displacement, tipping and overeruption of adjacent teeth. In these circumstances, consideration should be given to either restoring the vertical dimension or extracting the affected tooth.

• In the absence of a permanent successor, a decision will need to be made regarding long-term management of the hypodontia. However, the presence of ankylosis or infraocclusion in a growing patient will often make extraction more likely.

Hypodontia

The congenital absence of one or more teeth is a relatively common anomaly in human populations.

• Nonsyndromic or familial hypodontia occurs as an isolated trait; and

• Syndromic hypodontia occurs with accompanying genetic disease.

The term hypodontia is generally used to describe congenital tooth absence, but the definitions are actually quite specific (Fig. 10.7):

• Hypodontia refers to a lack of one to six teeth, excluding third molars;

• Oligodontia refers to a lack of more than six teeth, excluding third molars; and

• Anodontia refers to a complete absence of teeth in one or both dentitions.

Figure 10.7 Hypodontia and oligodontia.

In the upper case there is hypodontia with UR2, UL2, LL8, LL5, LR5 and LR8 absent. In the middle case there is more severe hypodontia, with UR8, UR5, UR4, UL4, UL5, UL8, LR8, LR5, LL5 and LL8 absent. In the lower case there is oligodontia, with UR8, UR5, UR4, UR2, UL2, UL5, UL8, LL8, LL4, LL1, LR4, LR5, and LR8 absent.

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:

• Localized incisor–premolar hypodontia (OMIM 106600), which affects only one or a few of these teeth. This is the most common form and is seen in around 8% of Caucasians (Nieminen et al, 1995).

• Oligodontia (OMIM 604625) occurs in around 0.25% of Caucasians and can involve all classes of teeth (Sarnas & Rune, 1983).

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

• Third molars are the most commonly absent tooth;

• These are followed by mandibular second premolars and maxillary lateral incisors (around 2%) and mandibular central incisors (0.2%) in Caucasians (Neal & Bowden, 1988); and

• Congential absence of canines, first and second molars, is rare (Simons et al, 1993).

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

Box 10.2 Candidate genes for nonsyndromic human hypodontia

Targeted deletion of many genes in mutant mice can disrupt tooth formation and these have provided a reference point in the search for candidate genes in human populations. However, given the large number of potential genes available, it is somewhat surprising that only three have been positively identified in human familial hypodontia (Cobourne, 2007):

• Mutations in the human MSX1 gene have been predominantly associated with familial oligodontia (Vastardis et al, 1996). Associations between MSX1 and the more common form of incisor–premolar hypodontia are rarer.

• Mutations in the human PAX9 gene have been identified in association with variable forms of oligodontia that particularly affect the molar dentition.

• The identification of a Finnish family affected by autosomal dominant oligodontia has provided an unexpected further insight into the genetics of inherited tooth loss. Within this pedigree, those individuals affected by oligodontia were also found to carry a significant risk of developing colorectal neoplasia. AXIN2 was identified as the candidate gene for this condition because it was located in the correct chromosomal region, had a known association with colorectal carcinoma and encoded a protein that regulates the Wnt signalling pathway. Wnt proteins have a wide-ranging role during embryonic development and demonstrate expression in the tooth. Suppression of Wnt signalling in mutant mice can inhibit tooth development and crucially, all the affected family members had a mutation which produced a loss of function of the AXIN2 protein (Lammi et al, 2004).

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

Syndrome	Gene
Anhidrotic ectodermal dysplasia (OMIM 305100)	EDA
Adult (OMIM 103285)	TP73L
Ehlers Danlos (OMIM 225410)	ADAMTS2
Incontinentia pigmenti (OMIM 308300)	NEMO
Limb mammary (OMIM 603543)	TP63
Reiger (OMIM 180500)	PITX2
Witkop (OMIM 189500)	MSX1
Ellis–van Creveld (OMIM 225500)	EVC or EVC2

• One of the commonest causes of syndromic hypodontia is Down syndrome (OMIM 190685), which results from the presence of an extra copy of all or part of chromosome 21.

• Mutations in the homeobox gene MSX1 have been associated with a syndromic condition demonstrating various combinations of CLP, CP and hypodontia (van den Boogaard et al, 2000) and with Witkop syndrome (OMIM 189500), a form of ectodermal dysplasia (Jumlongras et al, 2001). Thus, MSX1 represents a candidate gene for both syndromic and nonsydromic hypodontia (see Box 10.2).

Management

The management of congenital tooth absence will involve either:

• Space closure; or

• Maintenance or opening of space, followed by prosthetic replacement of missing tooth units.

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.

Supernumerary teeth

Supernumerary teeth are teeth present in addition to the normal complement and can occur within either dentition.

• In Caucasians, supernumerary teeth are seen more commonly in the permanent dentition, affecting around 4% of the population;

• In the deciduous dentition, the range is less than 1%; and

• In the permanent dentition, supernumerary teeth are twice as common in males and five times more common in the maxilla than in the mandible.

In common with hypodontia, supernumerary teeth also occur either as an isolated trait or as a manifestation of a clinical syndrome (Table 10.3), but they are usually classified according to morphology and location:

• Conical supernumeraries are small peg-shaped teeth with normal root formation. When located in the midline of the anterior maxilla these teeth are known as mesiodens (Box 10.3); whilst in the maxillary molar region they are known as paramolars (buccal, lingual or interproximal to the second and third molars) or distomolars (distal to the third molar) (Fig. 10.8).

• Tuberculate supernumeraries are characterized by a multicusped coronal morphology and a lack of root development (Fig. 10.9). These teeth are usually found palatal to the maxillary permanent incisors, often occur in pairs and frequently prevent eruption of the permanent incisors (Fig. 10.10).

• Supplemental supernumeraries represent the duplication of a tooth within a series and can be difficult to differentiate from the normal tooth (Fig. 10.11). These teeth are usually found at the end of a series and can be seen in the incisor, premolar and molar fields. They represent the most common type of supernumerary found in the primary dentition (Fig. 10.12).

• Odontomes are developmental malformations that contain both enamel and dentine (Fig. 10.13), and can be compound (containing many small separate tooth-like structures usually situated in the anterior jaw) or complex (a large mass of disorganized enamel and dentine usually situated in the posterior jaw).

Table 10.3 Syndromic conditions associated with supernumerary teeth

Syndrome	Gene
Cleft lip and palate
Cleidocranial dysostosis (OMIM 119600)	RUNX2
Gardner (OMIM 175100)	APC
Ellis–van Creveld (OMIM 225500)	EVC; EVC2
Incontinentia pigmenti (OMIM 308300)	NEMO

Box 10.3 Managing the mesiodens

The mesiodens is one of the commonest forms of supernumerary tooth and is often detected in the anterior maxilla as a chance radiographic finding. Whilst removal is indicated if they interfere with the eruption, position or proposed orthodontic movement of adjacent teeth, quite often they are asymptomatic and in these circumstances, they should be left alone (Kurol, 2006). The potential risks associated with leaving these teeth in situ, such as follicular enlargement, cystic formation and resorption of maxillary incisor roots, would appear to be small (Tyrologou et al, 2005). In addition, if the mesiodens subsequently erupts, it can be removed with a relatively simple extraction under local anaesthesia.

Figure 10.8 Conical supernumeraries.

Mesiodens positioned in the anterior maxilla, either vertically (left and middle) or horizontally (middle). Distomolar erupting behind the UL8 (right).

Figure 10.9 Extracted tuberculate supernumeraries and the effect of these teeth on the developing dentition.

Figure 10.10 Erupted tuberculate supernumerary.

The URA has been exfoliated and the UR1 is unlikely to erupt whilst the supernumerary is in situ.

Figure 10.11 Supplemental UR2’s.

Figure 10.12 Supplemental URB.

Courtesy of Thantrira Porntaveetus.

Figure 10.13 Complex odontome in the anterior maxilla.

The Scanora view on the right reveals the full extent of the odontome overlying the UR1.

Supernumerary teeth occur individually or in groups and can be unilateral or bilateral. These teeth are found most frequently in the anterior maxilla, but are also seen in the premolar and molar regions. In the permanent dentition, the majority fail to erupt and are asymptomatic, only being discovered during routine radiographic screening. However, they can also cause dental problems, which include:

• Failure of tooth eruption—the presence of a supernumerary can prevent the eruption of a permanent tooth (Fig. 10.14). In these circumstances, the supernumerary should be removed and provided space is available and the tooth is in a good position, there is a high chance the impacted tooth may well erupt unaided. However, exposure of the tooth is often undertaken at the same time, particularly in older children so orthodontic traction can be applied to the tooth to mechanically erupt it into the dental arch if it does not erupt spontaneously (see Fig. 10.22).

• Crowding—supernumerary teeth can contribute to dental crowding, either directly as a result of eruption (particularly for supplemental teeth) or indirectly by causing displacements or rotations of adjacent erupted teeth (Fig. 10.15). These supernumerary teeth will usually require extraction as part of a definitive orthodontic treatment plan. When extracting these teeth, care must be taken to ensure the most poorly formed is removed.

• Spacing—supernumeraries can also produce spacing between erupted teeth, particularly a mesiodens producing a maxillary diastema between the central incisors. If orthodontic space closure is planned, these supernumeraries will require extraction.

• Cystic formation—as with any unerupted tooth, cystic formation can occur. Any evidence of follicular enlargement or cystic formation and these teeth should be removed.

Figure 10.14 Supernumerary preventing eruption of the UR1.

Figure 10.22 The impacted UL1 has been exposed, bonded with a gold chain and traction applied using a removable appliance.

Fixed appliances were subsequently used to detail the permanent dentition.

Figure 10.15 Supplemental UL2 causing crowding of the UL1 and UL2.

Asymptomatic supernumerary teeth not affecting the occlusal relationships of the erupted dentition can be left in situ. These teeth should be kept under periodic radiographic review to ensure they are not damaging any adjacent structures or undergoing cystic change.

Abnormalities of tooth size

Teeth either larger or smaller than the normal population range for dimensions are usually referred to as megadont or microdont, respectively. These variations in tooth size can affect either the crown or root in isolation, or the whole tooth. Little is known about the aetiology of tooth size variation but it is almost certainly genetic.

• Megadontia most frequently affects the maxillary permanent incisors (Fig. 10.16) or mandibular second premolars and is often symmetrical. These teeth can be differentiated from double teeth by the absence of coronal notching and presence of normal pulpal morphology. Extraction of megadont teeth is often indicated, particularly with maxillary central incisors, because the aesthetics can be poor. Depending upon the space requirements, either the lateral incisors can be approximated and adjusted restoratively to look like central incisors or space maintained for prosthetic replacement.

• Microdontia is commonly associated with hypodontia and can affect the whole dentition or individual teeth. The maxillary permanent lateral incisor is one of the commonest teeth to be affected, often having a characteristic peg-shaped crown morphology (Fig. 10.17) and this has a causal association with palatal impaction of the maxillary canines. Whether a microdont maxillary lateral incisor is retained or extracted depends not only on the underlying malocclusion and the need for extractions, but also on the shape and form of the lateral incisor and whether it can ultimately be an aesthetic and functionally viable tooth. If this tooth is to be retained, the crown will require restorative buildup to improve the aesthetics and symmetry if it is unilateral. Space will often need to be created to allow this, which usually necessitates fixed appliances. If the lateral incisor is extracted, space will also need to be created if prosthetic replacement is planned, as these teeth are usually smaller than the space required for suitable pontics.

Figure 10.16 Megadont UL1.

Figure 10.17 Microdont UL2’s.

Abnormalities of tooth form

A number of anomalies associated with tooth form have been described. These conditions are generally rare, occurring with prevalence well below 5% of Caucasians, and with the exception of double teeth, they generally affect the permanent dentition more commonly than the deciduous.

• Double teeth can range from a slightly enlarged tooth with minor coronal notching to almost complete separation of two normally formed teeth. They are most commonly seen in the labial region of the mandibular deciduous dentition (Fig. 10.18), but can also affect permanent teeth. In the deciduous dentition, it is important to establish whether a double tooth is associated with hypodontia because this can indicate possible tooth absence affecting the permanent teeth. Conversely, if the double tooth is part of a normal complement, supernumerary teeth may be seen in the permanent dentition. Localized crowding or spacing can be seen in association with double teeth in both dentitions but in the deciduous, extraction is rarely indicated. Permanent double teeth can be managed restoratively if the coronal portion is not too large; however, those with more deviant anatomy may require extraction followed by space closure or prosthetic replacement.

• Accessory cusps are quite a common finding in both the deciduous and permanent dentition. Talon cusp, which can affect the maxillary permanent incisors, occasionally causes occlusal problems and tooth displacement. Treatment usually involves cusp removal, either with selective grinding or in combination with pulpotomy (Fig. 10.19).

• Invaginated teeth are characterized by the presence of an enamel-lined cavity, normally situated within the coronal portion of the tooth. These cavities can range from a simple pit in an otherwise normal tooth, to a deep fissure associated with marked distortion of tooth form. Treatment depends upon severity of the invagination; pulpal infection will require endodontics, whilst more severely distorted teeth will often require extraction.

• Evaginated teeth have an external enamel-covered projection on the surface of the tooth. The size of these evaginations and the degree of pulpal involvement can vary greatly. Treatment choices are comparable with those for accessory cusps.

• Dilaceration is an abnormal angulation between the crown and root of a tooth, usually affects maxillary incisors, and can occur as a consequence of intrusive trauma to their deciduous predecessors, although in the majority of cases there is no history of trauma (Stewart, 1978) (Fig. 10.20 and see Fig. 10.23). The most common scenario is a failure of the affected incisor to erupt and unless the dilaceration is mild, these teeth usually require extraction.

• Taurodont (OMIM 272700) or bull-like teeth have a pulp chamber enlarged at the expense of the roots (Fig. 10.21). This condition is seen in around 2.5–5% of adult Caucasians and can occur in isolation, or in association with amelogenesis imperfecta.

Figure 10.18 Double incisor teeth in the deciduous dentition with minor (left) and marked (right) coronal notching.

Right panel courtesy of Rudi Keane.

Figure 10.19 Talon cusp.

Courtesy of Evelyn Sheehy.

Figure 10.20 The UR1 is dilacerated as a result of previous trauma to the URA and has failed to erupt.

Figure 10.21 Taurodont first permanent molars (LR6 is also carious).

Abnormalities of eruption

A number of systemic conditions are associated with delayed eruption and these can affect both dentitions (Table 10.4). In the permanent dentition, great individual variation can exist in the timing of tooth eruption, with symmetrical deviation of anything up to two years from the mean not necessarily being a cause for concern. In the majority of children, local factors will be the main cause of any eruption disturbances that do occur (Table 10.5).

Table 10.4 Systemic conditions associated with delayed tooth eruption

• Down syndrome

• Cleidocranial dysostosis

• Turner syndrome

• Hereditary gingival hyperplasia

• Cleft lip and palate

Table 10.5 Local factors causing disturbances of tooth eruption

• Crowding

• Trauma

• Ectopic position of the tooth germ

• Supernumerary teeth

• Retained deciduous teeth