A tooth is transposed if it improperly occupies the position of another tooth in the dental arch. The most commonly transposed tooth is the permanent canine.1 In the maxilla, where transposition is more often encountered, the canine is most frequently transposed with the first premolar (Figure 1) followed by the lateral incisor.2 Interestingly, in the mandible, only canine-lateral incisor transpositions occur, with a majority being unilateral.3 There is a high incidence of congenitally absent teeth, peg-shaped lateral incisors, and/or supernumerary teeth associated with transposition, suggesting a genetic influence.1,3,4
Transposed lateral incisors erupt distal to and/or underneath the deciduous cuspids and, if left untreated, are unable to be brought into their natural position5 (Figure 2). Therefore, treatment of transposed mandibular lateral incisor teeth should be managed as soon as the diagnosis is made. The diagnosis of a transposed lateral incisor is most likely to be made by the alert general practitioner as these teeth erupt in the 7-9 year old age group well before the need for comprehensive fixed-banded orthodontic treatment and often before the first visit to the orthodontist. A pretreatment panoramic radiograph is invaluable in recognizing of the transposition. Diagnostically, the deciduous cuspid may have been lost, but occasionally the tooth erupts totally distal to the deciduous cuspid. Successful management of transposed lower lateral incisors is to a great extent dependent on moving the lateral incisor to approximate the central incisor prior to the eruption of the cuspid with which it is transposed. Delaying treatment will cause the lateral incisors to continue to erupt further distal to normal and allow the permanent cuspid to erupt into a position mesial to the lateral incisor. The longer treatment is delayed, the more difficult or impossible the treatment becomes. Once the transposition is complete (i.e. the cuspid is mesial to the root and crown of the lateral), then successful movement of the mandibular lateral incisor is not usually possible. The treatment of choice is removal of the lateral incisor and regaining of space for the subsequent replacement of the lateral incisor.
The treatment of transposed lateral incisors falls within the capabilities of those practitioners who understand the diagnosis and are familiar with placement of “2×4” fixed-banded appliances. This includes bands or bonds on the permanent lower first molars and incisors. Frequently the transposed lateral incisor erupts rotated and a band with a labial bracket and lingual cleat may allow for easier rotation and bodily movement of the incisor than with a bonded bracket, especially if there is minimal crown length available or the tooth is severely rotated. Treament usually involves the removal of the deciduous cuspid on the transposed side as soon as the transposition is recognized.
CASE REPORT 1
An 8-year-old male presented for evaluation of unerupted mandibular lateral incisors (Figure 3). As can be seen from the pretreatment panorex (Figure 4), the permanent lateral incisors are unerupted and the crowns are positioned abnormally distal to the central incisors. The crowns of the lateral incisors are resorbing the deciduous first primary molars. However, the roots of the laterals are in a favorable position next to the central incisor roots, where they must be for a favorable prognosis. Adequate space is not available for either lateral incisor.
The treatment plan was as follows:
(1) Extract 73, 74, 83, 84 to allow for eruption and movement of 32 and 42.
(2) Fit bands on 36, 46, 32, 31, 41 and 42 with edgewise slots .018* x .025* (usually incisors are bonded except as noted above).
(3) Level, align and approximate 42, 41, 31 and 32 with round wire progression (i.e. .016* round nitinol, .014*, .016*, .018* round stainless steel wire progression and elastomeric chains).
(4) Deband all teeth. Figure 5 shows a .016* nitinol arch wire with ligature ties placed only on the mesial tie wings. Distal tie wings were free to move lingually. Once approximated 31 and 41 were gangtied (i.e. 31 and 41 were laced together with a ligature tie to prevent movement); Figure 6 shows an .016* stainless steel arch wire with 31 and 41 gangtied and elastomeric chains placed from 31 to 32 and 41 to 42 to approximate the lateral incisors.
Figure 7 shows the approximated mandibular incisors. The panoramic radiograph (Figure 8) shows that both cuspids are now properly positioned to erupt when space is made available in the future. An “invisible” retainer was placed.
CASE REPORT 2
A 9-year-old female presented for evaluation of a distally erupted 42 (Figure 9). In contrast to Case 1, both lateral incisors are present and there is no evidence of crowding. The lower right primary canine (i.e. 83) has been resorbed by the ectopically erupted 42. Radiographically the lateral incisor roots were in a favorable position.
The treatment plan was as follows:
(1) Band 36, 46 and 42. Place lingual holding arch. Bond 41, 31 and 32.
(2) Level, align and approximate 42, 41, 31 and 32 with round wire progression and elastomeric chains.
(3) Deband and retention. Figure 10 shows a lingual holding arch and a .016* nitinol round archwire. Figures 11 and 12 show the use of elastomeric chains to move the mandibular midline to the left. When 41, 31 and 32 were approximated these teeth were gangtied and an elastomeric chain was placed to 42. Figure 13 shows all incisors gangtied prior to debanding and retention.
These cases illustrate a number of points:
1. Transposed lateral incisors erupt ectopically and may be associated with crowding. In Case 1, a lingual holding arch (LHA) was not used because, in the future, this case will need permanent extractions and preserving inadequate space is unnecessary. In Case 2, however, a LHA was utilized because there was adequate space and the LHA assisted in providing anchorage (resistance to movement) of, in particular, the 36 with the use of elastomeric chains in midline correction. In this case maintaining space and preventing lingual collapse of the lower incisors is critical to allow for the eruption of permanent teeth in the future.
2. Adequate radiographs must be taken. In Case 1, for example, it was established that the lateral incisors were present but in an abnormal position due to transposition and complicated by anterior crowding.
3. A critical factor in the success of treatment of transposed incisors is the position of the roots of the lateral incisors. In both cases, the root apices were in close approximation to the roots of the central incisors and mesial to the erupting mandibular cuspids.
4. It is of the utmost importance to approximate the lower incisors before the cuspid starts to erupt. Otherwise the cuspid erupts into the lateral incisor position.
5. Figure 2 shows the result of delayed diagnosis. Treatment options now would include the extraction of the transposed lateral incisor and making space for the lateral incisor with subsequent fixed prosthodontic replacement, or alternatively aligning the lateral incisor distal to the cuspid, a poor alternative.6
The purpose of presenting these case reports and discussion is to assist the general practitioner in recognizing when and how to treat transposed mandibular lateral incisors. Examples of treatment plans, involving fixed appliances to approximate the lateral incisors, were discussed to aid the practitioner in understanding the management of these cases. Due to the need for early recognition and treatment, and the failure of cases where cuspids start to erupt before the necessary mechanotherapy has been instituted, early diagnosis and treatment of this situation will improve success rates.
r. Peter Konchak is Professor and Head, Division of Orthodontics, Department of Community and Pediatric Dentistry, University of Saskatchewan.
Dr. Michael Lypka is a student in the Oral and Maxillofacial Surgery Externship Program at Los Angeles County, University of Southern California Medical Centre, Los A
Oral Health welcomes this original article.
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