Introduction
Occasionally, a tooth may migrate to occupy the position of another tooth within the dental arch. This condition, called dental transposition, involves the exchange of locations between two neighbouring teeth. While partial or incomplete dental transposition is relatively common, true dental transposition is characterised by the complete exchange of the crowns and roots of two adjacent teeth. Although the aberrant eruption of a tooth is frequently encountered in clinical practice, cases of true transposition remain rare.
More specifically, tooth transposition is defined as the positional interchange of two neighbouring teeth, especially of their roots, or the development or eruption of a tooth in a position normally occupied by a non-neighbouring tooth. Transposition of a tooth can be complete or incomplete and unilateral or bilateral. Unilateral transpositions are more common, and the maxillary arch is affected more often than the mandibular arch.
Complete transposition
When the body of the entire tooth, that is, the crown and the whole root of the involved teeth, exchange places in the dental arch, it is called complete transposition ( Fig. 76.1 ).
Complete canine–first premolar transposition in right and left maxillary arch.
Incomplete transposition
In a clinical condition where only the crowns of the teeth are displaced, while the root apices remain in their regular positions, this situation is referred to as incomplete transposition.
Prevalence
The transposition of teeth is rare, with an average prevalence of 0.33%. The prevalence of transposition in various ethnic groups has been reported as 0.38% in Turkey, 0.40% in India, 0.6% in Nigeria, 0.09% in Greece and 0.28% in Spain. Down syndrome patients report a prevalence of 15%, and cleft lip and palate patients report a 4% prevalence of atypical forms of tooth transposition.
Maxillary arch
The occurrence of tooth transposition in the maxilla is higher than in the mandible. The unilateral occurrence of tooth transposition is more frequent than the bilateral. The transposition of the maxillary canine with the maxillary first premolar is the most common teeth involvement in such aberrant positions. Other transpositions include maxillary canine to the lateral incisor, canine to the central incisor site, canine to the first molar site and lateral to the central incisor. The lower density of the maxillary bone may enhance the incidence of tooth transposition and a variety of types of transpositions in the maxilla.
Mandibular arch
Transposition of teeth in the mandibular arch is rare. The commonest among them transpositions in the lower arch is a canine to lateral incisor transposition, in the region where the bone is more porous than in the posterior area. The mandibular canine also tends to migrate across the midline to the other side. ,
Common dental transpositions are summarised in Table 76.1 .
TABLE 76.1
Common transpositions
| Maxillary | Mandibular |
|---|---|
| Canine and first premolar | Canine and lateral incisor |
| Canine and lateral incisor | Transmigration of canine |
| Canine to central incisor site | |
| Canine to first molar site | |
| Lateral and central incisor |
Aetiology
Apart from the genetic basis for tooth transposition, specific local factors, such as disturbances of the normal eruption path of the permanent teeth or trauma and early loss of a deciduous tooth, may create developmental disharmony in the dental arch which may lead to tooth transposition.
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1.
The maxillary canine transposition may result from inherently displaced tooth germs, early tooth loss of predecessor due to trauma or decay, or retained primary teeth. The literature has well documented its familial occurrence.
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2.
Mandibular canine transpositions are often associated with retained deciduous canines, and some show bilateral occurrence, suggesting a possible polygenic influence.
According to Howard, erupting mandibular canines with an axial inclination of more than 25 degrees to the mid-sagittal plane in the mandible were likely to be displaced. In comparison, those between 30 and 50 degrees tended to migrate across the midline, and those with a more than 50-degree inclination had a very high chance of crossing the midline.
Research indicates a direct correlation between the calcification of the sella turcica and an increased likelihood of tooth transposition. The early development stages of the pituitary gland, dental structures and skull regions are governed by common molecular signalling pathways involving bone morphogenetic proteins (BMPs), fibroblast growth factors (FGFs) and Hedgehog proteins. , Any disruption to these pathways can adversely affect the development of these structures. Calcification of the sella turcica often manifests in early childhood, presenting an opportunity for early detection of dental anomalies such as transposition and impaction. However, the superimposition of the right and left sella may mimic calcification or bridging; therefore, additional radiographs may be required to confirm the presence of calcification. , Additionally, 3D imaging could be of great help in assisting the diagnosis.
Classification of transposition
A classification comprising two major groups has been documented for improved diagnosis and treatment planning, denoting incomplete and complete transpositions. These groups are further subclassified, offering promise for improved management of dental transposition. See Table 76.2 and Fig. 76.2 .
TABLE 76.2
Classification of transposition
Source: Modified from Rai A, Sachan A, Verma VK. Transposition revisited: new classification and notation system. J Indian Orthod Soc. 2016;50:228–33.
| (1) Incomplete transposition | (A) Coronal | (B) Radicular | (C) Overlapping |
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|
|
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| (2) Complete transposition | (A) Reciprocal adjacent | (B) Reciprocal non-adjacent | (C) Non-reciprocal/non-adjacent |
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Features and types of incomplete transposition.
The crown of the transposed tooth changes its position, while the root lies in its normal position. The affected tooth is angulated. (A) Coronal transposition: The maxillary right canine crown is transposed over the lateral incisor. (B) Radicular or root transposition: The root of the affected tooth changes its position, while the crown lies in its normal position. (C) The affected tooth as a whole (the crown and the root) has changed its normal position. Transposed teeth overlap each other in a buccolingual position. Such a situation is seen when the deciduous maxillary canine is retained, and the maxillary canine erupts buccal to the maxillary lateral incisor.
Features and types of complete transposition along with the crown and the root.
Complete transposition can occur with a combination of reciprocal or non-reciprocal teeth, and adjacent or non-adjacent teeth. (A) Complete reciprocal adjacent (RA) transposition. For example, the maxillary canine is completely transposed with the first premolar. In such a situation, maintenance of transposition is considered a viable option. (B) Transposition can occur between non-adjacent teeth; for example, this figure shows a complete transposition of the maxillary canine, which has substituted the central incisor, is seen. (C) Transposition of non-adjacent teeth/non-reciprocal teeth. This figure shows the transposition of a canine with a central incisor. (D) The canine lies next to the first molar, and the canine transposed with the second premolar.
Source: Modified and adapted based on the concept and drawing by Rai A, Sachan A, Verma VK. Transposition revisited: new classification and notation system. J Indian Orthod Soc. 2016;50: 228–33.
Transposition notation system
A transposition notation system can describe the condition better and improve communication. ‘T’ is used to denote a transposed tooth. The buccolingual location of the tooth can be denoted as ‘F’ (facial) or ‘P’ (palatal). The eruption levels can be denoted as ‘I’ (transposed and impacted) or ‘E’ (erupting/partially erupted).
The tooth is identified by numbers 1 to 8, representing the central incisor to third molar. The upward-facing arrow ↑︎ denotes the maxillary arch, and the downward-facing arrow ↓︎ denotes the mandibular arch.
In cases of unilateral transposition, the position of the letter T denotes the side involved, and in cases of bilateral transposition, the letter T is written in between.
For example, ↑︎ 3 P –4 F T denotes the transposition of the canine positioned palatally and the first premolar positioned facially in the maxillary arch on the right side.
A bilateral transposition in the maxilla or maxillary arch will be denoted as ↑︎ 3 F –4 P, I T ↑︎3 P, E –4 F . The canine is positioned facially on the left side, first premolar palatally, and impacted. On the right side, the canine is positioned palatally and erupting, and the first premolar is facial.
Treatment considerations
A thorough and diligent diagnosis and thoughtful treatment planning are critical to managing transposed teeth ( Table 76.3 ). If the child reports erupted transposed teeth, the treatment options may be limited. However, critical decisions may be required when a patient reports an age when the teeth are still in their formative stages, and the transposition of teeth seems a definite possibility. In such situations, assessing the benefits and risks of early intervention is essential compared to late intervention.
TABLE 76.3
Summary of management considerations for transposed tooth
Source: Adapted from Ngan DC, Kharbanda OP, Darendeliler MA. Considerations in the management of transposed teeth. Aust Orthod J . 2004;20(1):41–50.
| TYPE OF TRANSPOSITION TREATMENT | |||
|---|---|---|---|
| Management considerations | Extraction | Correction | Maintaining |
| Treatment simplicity | Simple | Difficult | Moderate to simple |
| Treatment duration | Least | Prolonged | Decreased |
| Risk of root resorption | Least or no risk | Very high | Minimal |
| Risk to alveolar bone | Least or no risk | High | Low or little |
| Risk of gingival recession | No or minimal | High | Low |
| Patient motivation required | Low | High | High to low |
| Occlusal relationship(s) | Compromised | Normal | Compromised |
| Functional relationships | Compromised | Optimal | Compromised |
| Aesthetics | Compromised | Normal | Compromised |
| Adjunctive dental treatment | Yes | No | Yes |
| Cost | Dependent on treatment time and adjunctive dental work required | ||
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