Peck S, Peck L. Classification of maxillary tooth transpositions. Am J Orthod Dentofacial Orthop. 1995; 107:505-517
Papadopoulos MA, Chatzoudi M, Kaklamanos EG. Prevalence of tooth transposition. A meta-analysis. Angle Orthod. 2010; 80:275-285
Favot P, Attia Y, Garcias D. [The transposed canine: etiology-pathogenesis]. Orthod Fr. 1986; 57:605-613
Peck L, Peck S, Attia Y. Maxillary canine-first premolar transposition, associated dental anomalies and genetic basis. Angle Orthod. 1993; 63:99-109
Ely NJ, Sherriff M, Cobourne MT. Dental transposition as a disorder of genetic origin. Eur J Orthod. 2006; 28:145-151
Shapira Y, Kuftinec MM. Maxillary tooth transpositions: characteristic features and accompanying dental anomalies. Am J Orthod Dentofacial Orthop. 2001; 119:127-134
Peck S, Peck L, Kataja M. Mandibular lateral incisor-canine transposition, concomitant dental anomalies, and genetic control. Angle Orthod. 1998; 68:455-466
Plunkett DJ, Dysart PS, Kardos TB, Herbison GP. A study of transposed canines in a sample of orthodontic patients. Br J Orthod. 1998; 25:203-208
Weeks EC, Power SM. The presentations and management of transposed teeth. Br Dent J. 1996; 181:421-424
Shapira Y, Kuftinec MM. A unique treatment approach for maxillary canine-lateral incisor transposition. Am J Orthod Dentofacial Orthop. 2001; 119:540-545
Maia FA. Orthodontic correction of a transposed maxillary canine and lateral incisor. Angle Orthod. 2000; 70:339-348
Nestel E, Walsh JS. Substitution of a transposed premolar for a congenitally absent lateral incisor. Am J Orthod Dentofacial Orthop. 1988; 93:395-399
Filho LC, Cardoso MA, An TL, Bertoz FA. Maxillary canine – first premolar transposition. Angle Orthod. 2007; 77:167-175
Shapira Y, Kuftinec MM. Tooth transpositions – a review of the literature and treatment considerations. Angle Orthod. 1989; 59:271-276
Göyenç Y, Karaman AI, Gökalp A. Unusual ectopic eruption of maxillary canines. J Clin Orthod. 1995; 29:580-582
Lewis BR, Gahan MJ, Hodge TM, Moore D. The orthodontic-restorative interface: 2. Compensating for variations in tooth number and shape. Dent Update. 2010; 37:138-148
Shapira Y, Kuftinec MM, Stom D. Maxillary canine-lateral incisor transposition – orthodontic management. Am J Orthod Dentofacial Orthop. 1989; 95:439-444
Pair J. Transposition of a maxillary canine and a lateral incisor and use of cone-beam computed tomography for treatment planning. Am J Orthod Dentofacial Orthop. 2011; 139:834-844
Geary E. Transposition of canine. Br Dent J. 1966; 121
Vuchkova J, Farah CS. Canine transmigration: comprehensive literature review and report of 4 new Australian cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010; 109:e46-e53
Peck S. On the phenomenon of intraosseous migration of nonerupting teeth. Am J Orthod Dentofacial Orthop. 1998; 13:515-517
Camilleri S, Scerri E. Transmigration of mandibular canines – a review of the literature and a report of five cases. Angle Orthod. 2003; 73:753-762
Javid BR. Transmigration of impacted mandibular cuspids. Int J Oral Surg. 1985; 14:547-549
Shapira Y, Finkelstein T, Kadry R, Schonberger S, Shpack N. Mandibular symmetrical bilateral canine-lateral incisors transposition: its early diagnosis and treatment considerations. Case Rep Dent. 2016; 2016
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This is the first article in a three-part series considering uncommon dental anomalies and treatment approaches. Dental transpositions are rare anomalies which may present to the general dental practitioner or orthodontist. The management of transpositions is dependent on several factors, including the sub-type, severity and the other salient features of the malocclusion. Transposition may either be accepted or orthodontically corrected and the adoption of either approach must be preceded by thorough assessment of the patient.
CPD/Clinical Relevance: The presentation and management of transposition is variable. The general dental practitioner must be aware of the clinical features of a developing transposition as certain treatment options are only possible before the transposition is fully established. In addition, the orthodontist must be mindful of the potential for iatrogenic harm if these dental anomalies are managed injudiciously.
Article
Naeem I Adam
Uncommon occlusal problems or unusual treatment options present challenges by virtue of their rarity; they are orthodontic ‘conundrums’. In this series, transposition, finishing cases to Class III molar relationship, and the slightly unusual extraction pattern of a single lower incisor, will be covered, beginning with an update on dental transposition, its common forms and its orthodontic management illustrated through photographs from clinical cases. Transposition may be defined as the positional interchange of two adjacent teeth, or the development or eruption of a tooth into a position ordinarily occupied by a non-adjacent tooth.1 Transpositions can be complete or incomplete (also termed pseudo-transposition). In the former, both crown and root are transposed, whereas in the latter form, the crowns appear transposed with the roots being in their normal positions.1 Transposition is a form of ectopic eruption and by definition requires teeth to erupt into, or develop in, aberrant positions.2
Notation
Transpositions are commonly coded using the notation first proposed by Favot, Attia and Garcias3 and later modified in studies by other researchers.1,4 The code is composed of three elements: the jaw of occurrence, the tooth that is transposed, and the site of transposition (Table 1). For example, Mx.C.P1 would represent transposition of the maxillary canine to the first premolar position.
Jaw or Tooth
Code Meaning
Mx
Maxilla
Mn
Mandible
I1
Central incisor
I2
Lateral incisor
C
Canine
P1
First premolar
P2
Second premolar
M1
First molar
M2
Second molar
Prevalence
Although consistently found to be a rare event, prevalence figures for transposition in the literature vary significantly, depending upon the sample size and population studied. In a recent meta-analysis, the average prevalence of transposition was found to be 0.33%.2
Teeth in the maxilla are affected far more commonly than those in the mandible, accounting for 76% of all transposition cases. Transposition is also unilateral in most cases (88%).2,5 Earlier research found there to be a significant difference in the prevalence of transposition between males and females, with a female predilection being noted in many studies.2 As a result, some authors hypothesized that gender-related genes may be responsible for transposition, but in their meta-analysis Papadopoulos, Chatzoudi and Kaklamanos2 found the frequency of transposition to be no higher in females than in males. This discrepancy can potentially be explained by many of the earlier studies having samples taken from orthodontic clinics, where perhaps more females than males seek treatment.6 Similarly, earlier research found transposition to occur more frequently on the left side of the maxilla, but this finding was again not supported in the meta-analysis of the literature.2
Maxillary canine-first premolar transposition (Mx.C.P1) and maxillary canine-lateral incisor transposition (Mx.C.I2) are the most commonly encountered forms, comprising 71% and 20% of all transposition cases in the maxilla, respectively.1 Aberrant canine position appears to play a part in most maxillary transposition cases.1 In the mandible, lateral incisor-canine transposition (Mn.I2.C) is the form most frequently encountered, with a prevalence of 0.03%.7 Mx.C.M1 and Mx.C.I1 transposition are exceedingly rare, and some authors have suggested that, as they represent extreme displacements, they should be defined purely as ectopic eruptions.6 Transposition has never been reported in the primary dentition.6
Aetiology
The aetiology of transposition is not fully understood. It appears to have a genetic basis with a multifactorial inheritance pattern, as it is frequently associated with other dental anomalies, such as impaction, hypodontia and diminutive lateral incisors.1,5 An interchange in position of the developing dental lamina has been suggested as a cause, as has retention of the primary canine.5,6 Some studies focusing on specific forms of transposition have suggested local factors, such as a history of trauma to the area.6,8
Treatment
Treatment for transposition may be interceptive or definitive, with the two approaches frequently overlapping.9 Interceptive treatment is only useful before complete transposition has occurred and is typically carried out in the mixed dentition. Primary teeth in suboptimal positions can be extracted in an effort to guide the transposed tooth back to a normal position. Space may then be maintained through the use of fixed or removable appliances. This approach is most appropriate in instances of incomplete transposition (Figure 1).
Figure 1. (a) A developing Mn.I2.C transposition managed through extraction of LRB (seen on the OPT) and fixed appliances. (b–f) The result achieved upon completion of treatment.
Definitive treatment must consider the nature of the malocclusion in its entirety, including the extent of crowding, aesthetics, position of root apices, potential resorptive damage to teeth and patient motivation. Treatment of transposition usually takes one of three approaches:
One of the transposed teeth is extracted and the teeth aligned;
The transposed positions are accepted, and teeth aligned;
Teeth are orthodontically moved to their correct positions.
The last of these approaches can be difficult, unpredictable and can significantly prolong treatment time with variable success rates. The width of the alveolus, particularly in the mandible, can limit the movement of teeth, and injudicious attempts may result in significant root resorption, or gingival recession.9,10
Mx.C.P1
Background and presentation
This is the most common form of transposition and the most reported form in the literature.1,5 In these cases, the transposed maxillary canine is most often excluded from the arch and positioned buccal to the first and second premolars (Figures 2 and 3). The canine is also often rotated mesiobuccally, and the first premolar rotated mesiopalatally and tipped distally. Transient crowding is a common finding as the primary canine is frequently retained (Figures 1 and 2).1
Figure 2. (a–e) Right-sided Mx.C.P1 transposition showing a typical presentation.Figure 3. OPT showing complete Mx.C.P1 on the right.
Unlike other types of maxillary transposition, local factors, such as a history of dental trauma, appear to play less of a role in Mx.C.P1 transpositions.1,10,11
Treatment
In cases of Mx.C.P1 transposition, interceptive extraction of a retained primary canine may allow spontaneous correction, particularly if the roots of the first premolar are distally angulated.9 Although retention of primary teeth may result in transient crowding, the simultaneous presence of true crowding and transposition is uncommon as transposition is usually associated with microdontia and hypodontia (Figure 4).5 The presence of crowding or the need to correct an increased overjet, however, may allow for the correction of transposition through extraction of the first premolars.
Figure 4. Left-sided Mx.C.P1 transposition and severe crowding.
Individuals with maxillary transpositions are more likely to exhibit dental abnormalities, both in general and on the same side (Figure 5).5,6
Figure 5. (a–d) Mx.C.P1 transposition and a diminutive lateral incisor are seen on the left, with maxillary lateral incisor agenesis on the right. The transposition was accepted and the right lateral incisor space closed.
Where Mx.C.P1 transposition is accompanied with absent lateral incisors, there are two possible approaches, depending on the space available in the arch. In a spaced arch, the transposition may be accepted with a view to redistribute spaces and plan for long-term prosthetic replacement in the lateral incisor position. Attempting closure of the space requires mesializing the premolar into the lateral incisor space. This potentially risks placing the buccal root of the maxillary first premolar outside of the envelope of bone and may result in an alveolar dehiscence. In addition, the first premolar provides a poor aesthetic substitute for a lateral incisor, owing to its bulbosity and emergence profile. Given these issues, extraction of the premolar and opening of the lateral incisor space for a prosthesis may be a more suitable approach.12
In cases of Mx.C.P1 transposition, where extraction is not indicated, the transposed positions may be accepted. Figure 6 illustrates the end result of treatment of the case in Figure 2 where transposition was not corrected. In such scenarios, the appearance can be improved with careful grinding of teeth or the addition of composite material. The upper first premolar makes an acceptable substitute for the canine when considering a canine guidance, with mesiopalatal rotation of the premolar and reduction of its palatal cusp facilitating smooth guidance on lateral excursion.9
Figure 6. (a–e) Alignment of a right Mx.C.P1 transposition in the transposed positions.
Compared to accepting Mx.C.P1 transposition, full correction can require complex mechanics. Some authors advocate initial palatal movement of the displaced premolar, to facilitate correction of the canine from its ectopic starting point to a normal position.13 (Figures 7 and 8).
Figure 7. (a–e) Left-sided Mx.C.P1 transposition before commencement of orthodontic correction.Figure 8. (a–c) The combination of a modified transpalatal arch along with elastic traction, and a fixed appliance, along with controlled push/pull mechanics, is utilized to correct a Mx.C.P1 transposition.
Once the canine is repositioned, the premolar may then be brought into alignment. Orthodontic correction can prolong overall treatment time, but the potential for an optimal aesthetic and functional outcome may be greater.13,14 In the case presented, there has been some compromise in the gingival health, although this gives rise to little appreciable aesthetic concern as the patient does not have a high smile line (Figure 9).
Figure 9. (a–f) The combination of a modified transpalatal arch along with elastic traction, and a fixed appliance, along with controlled push/pull mechanics, is utilized to correct a Mx.C.P1 transposition.
Mx.C.I2
Background and presentation
This is the second most common form of transposition, comprising 20% of the total number of maxillary transpositions.1 Incomplete transposition is more common than complete transposition in these cases, and the characteristic features of Mx.C.I2 transposition are as follows:6
The primary canines are retained;
Labially displaced and frequently rotated canine and lateral incisor;
Diminutive lateral incisors and missing second premolars;
Impaction of the canine or central incisor on the side with the transposition.
Local factors, such as a history of dental trauma, appear to play more of a role in Mx.C.I2 than in other maxillary transpositions. These cases frequently demonstrate the sequelae of early dental trauma, such as dilacerated or shortened roots.1,10,11
Treatment
Treatment should consider the prognosis of the affected teeth and the nature of the malocclusion as a whole. If the central incisor has significant root resorption, from previous trauma or the eruptive path of the ectopic canine, it may be extracted and the canine moved into the central incisor position.15 This approach would obviously necessitate restorative camouflage of the canine to deliver acceptable aesthetics.
Where the central incisor is unaffected, the principle problems in Mx.C.I2 transposition arise from the ability of the lateral incisor to function as a canine, and the capacity for the canine and lateral incisor to be camouflaged as one another9
The relatively small root of the lateral incisor makes it a poor substitute for a canine in canine-guided occlusion. In such instances, to aim for group function may be wise. Should the appearance of the canine be unsuitable for camouflage, or if the lateral incisor demonstrates significant root resorption, consideration can be given to extraction of the lateral incisor and movement of the canine into its normal position, creating space for prosthetic replacement of the lateral incisor.
Where the transposition is accepted and the canine is camouflaged in the lateral incisor position, enameloplasty and the addition of composite can be used to optimize the aesthetic result.16
As with Mx.C.P1 transposition, orthodontic correction and full resolution of the transposition often results in prolonged treatment, with the additional increased risk of root resorption should root interferences arise.11,17 Attempts at orthodontic correction have the potential to move the root of the canine out of alveolar bone, as it is distalized labial to the lateral incisor, resulting in the appearance of a long clinical crown.18
Mx.C.M1
Background and presentation
This is an extremely rare condition with very few cases being reported in the literature.1 In these instances, the maxillary canine occupies the position of the maxillary first permanent molar, after the molar's earlier loss. The literature on Mx.C.M1 transposition is scant, and a search found no reported cases in the last 50 years. As this form of transposition appears to require premature loss of first permanent molars, it may be reasonable to conclude that a global reduction in caries experience, through effective fluoride exposure, has led to a reduction in incidence of Mx.C.M1 transpositions.1
Treatment
It would seem prudent to accept the transposition in such cases as moving the canine to its normal position would likely be extremely difficult and fraught with risk. The one case report concerning the treatment of Mx.C.M1 described extraction of the transposed canine.19
Mx.l2.l1
Background and presentation
This form of transposition is unique in that it is the only type, reported on multiple occasions, where there is no canine involvement. These cases are typically preceded by dento-alveolar trauma, resulting in changes to tooth form or orientation, such as dilacerations or rotations.1
Treatment
The lower and narrower gingival contour of the lateral incisor presents the main challenge when managing this type of transposition. The transposed positions may be accepted and aesthetics improved with restorative treatment, but an interdental ‘black triangle’ may persist at the gingival aspect. An alternative approach would be to extract the lateral incisor, move the transposed central incisor into its correct position and provide prosthetic replacement of the lateral incisor.9
Mx.C.I1
Background and presentation
This is another rare form of transposition. In a similar manner to Mx.C.M1 transposition, it appears to be the result of aberrant canine migration following early loss of the central incisor. There has been little reported on the treatment of this variant.1
Canine transmigration (intraosseous migration)
Background and presentation
In rare instances, an unerupted mandibular canine may migrate intra-osseously and cross the symphyseal midline (Figure 10). This phenomenon appears to be unique to the mandible.20 Authors disagree on what constitutes transmigration, with some accepting it to have occurred when only the cusp tip has crossed the midline, and others requiring the canine to have crossed over by at least half its length.20,21,22,23
Figure 10. (a, b) OPT and cone-beam CT demonstrating intra-osseous migration of the right mandibular canine to the midline.
Treatment
Treatment options for transmigrated mandibular canines include: surgical removal, transplantation, exposure and orthodontic alignment, and observation.22 Reports in the literature find surgical removal to be the most commonly performed treatment for transmigrated canines. The teeth are often in unfavourable positions, frequently orientated horizontally, and consequently orthodontic movement is difficult, complex, and in some instances mechanically impossible.20,21,22,23
Mn.I2.C
Background and presentation
Mandibular transpositions occur less frequently, and with fewer permutations, than those in the maxilla.2,7 In Mn.I2.C transpositions, the canine usually erupts in a relatively normal position, but distal migration of the lateral incisor is principally responsible for the positional interchange.
Mn.I2.C transposition frequently presents with distal tipping, rotation and displacement of the lateral incisor as it erupts into the position normally occupied by the ipsilateral canine and premolar (Figure 11). When the mandibular canine eventually erupts, it is typically positioned mesial to the ectopic lateral incisor, resulting in a transposition.7
Figure 11. (a, b) Bilateral Mn.I2.C transposition showing the typical features of this variant.
The early mixed dentition phase, between ages of 6 to 8, is thought to be the optimal time to assess the development and path of eruption of the mandibular lateral incisors. Radiographic investigation is likely to prove useful if an aberrant eruptive pathway or ectopic eruption are suspected.24 At the early stage of this form of transposition, approximately age 9, the mandibular lateral incisor begins to tip distally, and its crown rotates mesiolingually. The canine can be seen to be developing mesial to the lateral incisor radiographically. The lateral incisor and canine crowns appear transposed, but the roots occupy their normal positions. The ectopic lateral incisor also frequently undermines the primary first molar, precipitating its premature exfoliation.7 The later stage of Mn.I2.C transposition, approximately age 12, can result in the roots of the lateral and canine fully transposed and upright, to give a mature complete transposition.7
Treatment
As before, treatment options centre on either aligning the teeth in their transposed positions, extraction or attempted orthodontic correction. The choice of which approach to take is typically based on when the anomaly is detected.25
Should the transposition be detected early, the primary canine and lateral incisor should be removed. Thereafter, fixed appliances may be used to correct the rotation of the lateral incisors, upright them and move them mesially to occupy the space adjacent to the central incisors (Figure 12). However, one should be mindful of the position of the developing canine, as attempting mesial movement of the transposed lateral when the canine lies in its path may precipitate root resorption.
Figure 12. (a–c) Mesial movement of the transposed mandibular lateral incisors to their normal position.
Once the lower incisors occupy their normal positions, space may be maintained to allow the mandibular canine and first premolar to erupt into the appropriate sequence.
Rarely is Mn.I2.C transposition a true transposition (Figure 13) but in such a case management would involve accepting the tooth sequence.
Figure 13. True transposition of left mandibular lateral incisor and canine.
Conclusion
Transpositions are rare dental abnormalities with varied presentations. Each subtype presents a unique challenge to the orthodontist, and injudicious attempts at orthodontic correction have the potential to cause significant harm to the patient through iatrogenic root resorption and deleterious effects on the gingival contour.
General dental practitioners should be aware of the signs of a developing transposition, as early detection and referral may allow for interceptive treatment and reduce overall treatment time. In addition, the negative consequences of ectopic eruption patterns on adjacent teeth, such as root resorption, may also be avoided.
