Malposition of single teeth
Krister Bjerklin
Key topics
- Infraocclusion of primary molars
- Ectopic eruption of maxillary first permanent molars
- Impacted maxillary canines
- Supernumerary anterior teeth – mesiodens
Learning objectives
- To know how to manage infraocclusion of primary molars
- To know how to manage ectopic eruption of maxillary first permanent molars
- To be able to diagnose and managing impacted maxillary canines at the appropriate time
- To know risks with impacted maxillary canines regarding root resorptions of adjacent teeth
Introduction
Developmental disturbances of teeth are anomalies of position or eruption path. Form, shape and number of teeth are other tooth disturbances. It has been suggested that such developmental anomalies are all micro symptoms of an inheritable developmental disturbance due to a general disturbance of the developmental tooth structures (Pfeiffer, 1974; Hoffmeister, 1977).
Eruption disturbance, such as impacted maxillary canines, is associated with ectopic eruption of maxillary first permanent molars, infraocclusion of primary molars, peg-shaped or congenitally missing maxillary lateral incisors and agenesis of mandibular second premolars (Bjerklin et al., 1992; Baccetti, 2000; Binner Bector et al., 2005; Al-Nimri and Bsoul, 2011). This means that ectopic eruption of maxillary first permanent molars, diagnosed at 6 to 7 years of age, may be a marker for the subsequent appearance of dental anomalies.
With the association between these tooth and developmental anomalies, it may be expected that in a sample of children with one of these anomalies, an increased frequency of the other associated anomalies would be found compared to the frequency found in the general population.
Infraocclusion of primary molars
The term infraocclusion describes a tooth or teeth, positioned below the occlusal plane, varying from 1 mm up to being embedded in the gingiva or in the alveolar bone. After normal eruption, some teeth start to be in infraocclusion and may show ankyloses (Figure 8.1).
Figure 8.1 At the age of 11.6 years, the mandibular second primary molars are in occlusion, and there is agenesis of the mandibular second premolars (a). Two years later, infraocclusion is evident on both primary molars (b). At the age of 16, a more pronounced infraocclusion on the second primary molars and the first premolars have started to tip distally (c).
Infraoccluded primary molars can be found in children as young as 3 to 4 years of age; however, it occurs most frequently at the age of 8 to 9 years. About 14% of children in this age group have one or more primary molars in infraocclusion. It is found twice as frequently in the mandible as in the maxilla, and the mandibular second primary molars are most affected. There is a genetic component to the anomaly, and in a group of siblings of children with infraocclusion, the prevalence of infraocclusion is higher (Kurol, 1981).
If primary molars show infraocclusion, it is very difficult or even impossible to move them into normal occlusion by orthodontic treatment. This contrasts with permanent molars, where it is sometimes possible, even in severe cases, to move the molar into occlusion again with orthodontic treatment (Figure 8.2).
Figure 8.2 Severe infraocclusion of the mandibular right first permanent molar, age 12 (a). Further tipping of the adjacent teeth (b). Space gaining and surgical exposure of the infraoccluded permanent molar (c). After orthodontic traction, the molar has erupted into occlusion (d).
Depending on the severity of the infraocclusion, there is a risk that tipping of adjacent permanent teeth will cause space loss for the permanent premolar.
In most cases with a permanent successor, the infraoccluded primary molars show progression of the infraocclusion. The exfoliation of the infraoccluded primary molars is normally delayed by about 6 months (Kurol and Thilander, 1984). However, the delay could also amount to 1 or 2 years, compared to contralateral teeth in the normal position.
An infraoccluded primary molar without a permanent successor is frequently associated with ankylosis. Percussion is a diagnostic tool for ankylosis using, for example, the handle of a metal mouth mirror. Ankylosed teeth typically have a solid sound when percussed, which is different from the sound heard when percussing a tooth suspended in a normal periodontal ligament (PDL).
In cases with agenesis of the permanent successor, a treatment plan is required already at the age of 9 to 10 years. In cases with severe infraocclusion at these ages, the infraocclusion is likely to worsen, and extraction of the primary molar is often the best solution. Later, orthodontic treatment is necessary to close the gaps and correct tipping of adjacent teeth; otherwise, a prosthetic treatment or transplantation of a maxillary third molar can be the solution.
If the primary molar is persisting at 12 to 14 years of age, without any severe infraocclusion or root resorption, there is good prognosis for long-term survival of the primary molar (Bjerklin and Bennett, 2000; Bjerklin et al., 2008).
Ectopic eruption of maxillary first permanent molar
The term ‘ectopic eruption’ describes a disturbance of the path of eruption, which causes a tooth or teeth to erupt from their normal position, usually affecting maxillary first permanent molars and maxillary canines. The diagnosis can be made from panoramic, periapical or bitewing radiographs (Figure 8.3).
Figure 8.3 Girl, 6 years of age, maxillary first permanent molars in ectopic eruption and atypical resorption on the second primary molars (a,b). Right second primary molar is lost and severe space deficiency for the second premolar due to mesial movement of the first permanent molar (c). In (d), the left permanent molar has freed itself and shows reversible ectopic eruption.
Ectopic eruption of maxillary first permanent molars occurs as a local eruption disturbance at the age of 6 to 7 years. The molar erupts in a mesial direction, resulting in a locked position, apical to the prominence on the distal surface of the second primary molar. There are two types, the reversible and the irreversible (Figure 8.3).
The reversible type is self-correcting. The permanent molar spontaneously frees itself and erupts into occlusion. The second primary molar remains in the mouth, with a variable amount of resorption of the distal aspect.
The irreversible type of ectopic eruption means that the permanent molar remains locked in its position, above and distal to the primary molar, until the primary tooth is exfoliated or some type of treatment is provided. It is generally difficult to determine whether the problem is reversible or irreversible at the age of 7 years, and it may not be clear until some years later.
No clear answer is given in the literature regarding its aetiology, although various factors alone or in combination have been mentioned. However, the hereditary factor seems to be of importance. It has been shown that the frequency of ectopic eruption of the maxillary first permanent molar is much higher in the siblings of children with the anomaly than it is for the rest of the population. One study showed that the frequency among the siblings was 20% compared to 4.3% for the rest of the population (Kurol and Bjerklin, 1982a). The ratio between the reversible and the irreversible types was equivalent to that for the general population.
Treatment recommendation
In a young child with ectopic eruption of a maxillary first permanent molar, it is recommended to wait and evaluate whether the permanent molar will self-correct spontaneously. If it becomes clear that the ectopic eruption is irreversible, and spontaneous correction does not occur, it is still recommended to postpone treatment until the second premolar is starting to erupt, because the primary molar should be retained as long as possible to hold the space. Even severely resorbed second primary molars will normally remain in situ until the normal exfoliation time (Figure 8.4) (Kurol and Bjerklin, 1982b; Bjerklin and Kurol, 1981). Most important is to advise the child and parents to keep the occlusal area of the permanent molar clean by showing correct brushing technique.
Figure 8.4 Left radiograph, girl, 7 years of age, with maxillary left permanent molar in ectopic eruption; the molar is still locked in the resorption distally on the second primary molar. Middle radiograph, 1 year later. The molar has freed itself, and the resorption is increased. Radiograph to the right shows the situation at the age of 9.5 years, with a hard tissue repair. In a follow-up study of 92 cases with resorbed second primary molar, 15 teeth showed hard tissue repair of the structure of the primary tooth, and this could be seen both on the radiographs and histologically (Kurol and Bjerklin, 1982a, 1982b).
In cases where the second primary molar is lost, the consequences are mesial movement, tipping and rotation of the permanent molar. This may result in a loss of adequate space for the succeeding premolar (Mucedero et al
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