Case report
Canine-lateral incisor transposition: Controlling root resorption with a bone-anchored T-loop retraction

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Highlights

  • Segmented mechanics are optimal for individualized movement of target teeth.

  • Continuous archwires to correct a transposition invite root resorption.

  • Skeletal anchorage was used to retract the canine and correct the Class II relationship.

  • T-loop springs anchored with a bone screw were effective for this patient.

A 12-year-old girl presented with a Class II Division 1 malocclusion, complicated by a complete transposition of the maxillary left canine into the position normally occupied by the left lateral incisor. Dental and medical histories were noncontributory. Brackets were bonded on all maxillary teeth, from first molar to first molar, except for the left lateral incisor. Because the lateral incisor was not engaged on the archwire, the tooth was free to physiologically move out of the path of canine root movement. To prepare the site for canine retraction, a coil spring was used to open space between the left central incisor and the first premolar. A 2 × 12-mm stainless steel miniscrew was placed in the infrazygomatic crest, labial to the mesiodistal cusp of the maxillary left first molar. A 0.019 × 0.025-in titanium-molybdenum alloy T-loop, anchored by the miniscrew, was used to retract the canine root over the labial surface of the root of the distally positioned lateral incisor. In 24 months, this difficult malocclusion, with a Discrepancy Index score of 18, was treated to a Cast-Radiograph Evaluation score of 26.

Section snippets

Diagnosis and etiology

The clinical examination of this 12-year-old girl in the permanent dentition showed an Angle Class II molar malocclusion with a complete transposition of the maxillary left canine and lateral incisor (Fig 1, Fig 2). The ectopic eruption of the maxillary left canine positioned it high in the vestibular fold between the central and lateral incisors (Fig 3, Fig 4).

From the patient's perspective, the anomaly was camouflaged by normal midlines and a functional deciduous canine, so the chief

Treatment objectives

The treatment objectives were to (1) establish functional Class I molar and canine relationships, (2) correct the transposition and restore natural tooth order, (3) create ideal overbite and overjet, (4) correct incisor inclinations and root angulations, and (5) improve facial esthetics.

Treatment alternatives

Compared with the mandibular arch, there are more therapeutic options for the maxillary dentition because the supporting bone is less dense. Esthetically and functionally, it is generally preferable to move transposed teeth to their normal positions in the arch.1

Consistent with the treatment objectives, the most conservative treatment plan was nonextraction alignment of the malposed teeth. Bilateral infrazygomatic crest (IZC) bone-screw anchorage was indicated to retract the transposed canine

Treatment progress

Treatment was started in the maxillary arch, with a 0.022-in passive self-ligation system (Damon 3mx; Ormco, Glendora, Calif); low-torque brackets were placed on the incisors. An open-coil spring was placed between the left central incisor and the first premolar to create space. One week later, the deciduous canine was extracted, and 2 OrthoBoneScrews (2 × 12 mm) with 0.022 × 0.028-in rectangular openings (Newton's A, Hsinchu, Taiwan) were inserted bilaterally in the IZCs, buccal to the

Treatment results

The transposed canine was successfully retracted to the ideal position in 5 months. The keratinized gingival tissue on the canine was normal; there was no gingival recession or dehiscence. The nasolabial angle was maintained, and a pleasant facial profile was achieved after 24 months of orthodontic treatment. The canine and molar relationships were corrected to Class I, and the upper, lower, and facial midlines were coincident (Fig 17). A functional occlusion was established with stable

Discussion

A successful orthodontic result is often predicated on the design of the force system.18 The IZC is a convenient placement site in the maxilla for orthodontic miniscrews or miniplates.19 It has been used successfully to provide skeletal anchorage for retraction of canines and incisors, both individually and en masse, as well as intrusion of the maxillary posterior teeth.20, 21, 22, 23, 24, 25 For our patient, an OrthoBoneScrews in each IZC was used to retract the entire maxillary arch to

Conclusions

A complete maxillary canine transposition is a complex anomaly that presents a significant orthodontic challenge. Conservative correction of the problem entails risks that require carefully controlled appliances. Segmented mechanics are optimal for individualized movement of target teeth. On the contrary, the use of continuous archwires for correction of a transposition invites adverse effects, particularly root resorption. For our patient, skeletal anchorage provided an independent force

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    • The relationship between local alveolar bone housing and size of canine in maxillary canine-lateral incisor transposition: A retrospective cone-beam computed tomography–based study

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      His young age was the greatest advantage. When individualized and controlled movements of teeth are required, fixed appliances such as customized fabricated loops9-12 or cantilever15,19 are widely applied. In the current case, with the combination of 0.012-in NiTi archwire and 0.019 × 0.025-in SS archwire, a continuous archwire technique was employed to bypass the lateral incisor palatally.

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      Although alignment of teeth in their transposed positions is more predictable, some patients may not be satisfied with accepting transpositions, due to the compromises in esthetics and/or function. There are some case reports in the literature describing orthodontic correction of transpositions.9,15–24 Most of these cases end up with long treatment times, less than ideal root parallelism, and gingival recession.9

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