Hybrid Mechanics for Efficacious Management of a Palatally Impacted Canine: a Case Report

Abstract

Maxillary impacted canines are commonly encountered in orthodontics; their frequency is well reported in the general population. Approximately 2.5% of maxillary canines become impacted. Various traction modalities have been employed in orthodontic literature with both vestibular and lingual appliance systems for both labially and palatally impacted canines. This case report is amongst the first to describe hybrid mechanics, staging, and clinical protocols with aligner therapy for successful management of a palatally impacted canine.

Key Words

Aligners, Hybrid Mechanics, Invisalign, Palatally Impacted Canines

Introduction

Palatally displaced canines or PDCs, commonly known as 'eye' teeth, are often displaced in the roof of the mouth. This can leave unsightly gaps, cause damage to the surrounding roots (which can be so severe that neighboring teeth are lost or have to be removed) and, occasionally, result in the development of cysts. PDCs are a frequent dental anomaly, present in 2% to 3% of young people. Female patients are more prone to palatally impacted cuspids, compared to a male cohort.

Management of this problem is both time consuming and expensive. It involves surgical exposure (uncovering) followed by fixed braces (either vestibular or lingual) for two to three years to bring the canine into alignment within the dental arch. The challenge is further compounded when patients refuse fixed appliances and indicate a preference for aligner therapeutics. The reason for this challenge is because forced eruption of impacted teeth warrants “pull mechanics”, while as aligner therapy primarily employs “push” mechanics for orthodontic tooth movement.

Scholarly literature has indicated that aligners have become more predictable in treating malocclusions. This can be attributed to a variety of factors including material and technological developments, and the orthodontists’ better understanding of mechanics and therapeutic limitations with the system. Currently none of the studies have reported a sizeable cohort of impacted teeth treated with aligners, and case reports are scarce too.

This case report showcases a 16-year-old with a palatal impacted canine, that was successfully treated using aligner therapy integrated with hybrid mechanics in a phased manner. The three-phase protocol with rationale employed is described and can serve to be a learning resource for clinicians.

Diagnosis

A 16-year-old female patient presented with an asymmetric Class II malocclusion, mild overbite, and missing upper left cuspid with the presence of the preceding deciduous tooth was observed.

The upper and lower incisors were slightly protrusive. The patient's smile was not esthetic due to a midline diastema, Narrowness of the upper jaw and negative buccal corridors were observed. The maxillary midline was shifted to the right.

Panoramic Radiograph demonstrated the impacted cuspid crown tip mesial to the central incisor, indicating a Sector IV location of the impacted tooth. The Cephalogram and two Peri-apical Radiographs (using the SLOB rule) confirmed the palatal position of the impacted tooth.

Fig. 1: Pre-Treatment Composite Images

Fig. 2: Pre-Treatment Lateral Cephalogram and OPG

Treatment objectives

Treatment objectives in the case were to:

1. Correct Buccal Occlusion
2. Level and Align Both Arches with ideal inter and intra arch parameters
3. Gain Space in Upper Arch for Impacted Cuspid
4. Facilitate Forced Eruption of Impacted Cuspid
5. Improve Facial and Smile Micro and Mini Aesthetics

Treatment alternatives

Scholarly literature has demonstrated various adjuncts including temporary anchorage devices along with fixed appliances and hybrid mechanics for uncovering and traction of palatally impacted cuspids. The patient was not willing to undertake therapy with either a fixed appliance, or a palatal TAD supported adjunct. Hence, traction with hybrid mechanics and aligners was the only viable alternative. The possible limitations and risks were explained to the patient and guardians.

Treatment plan

The orthodontic treatment with aligners would include III (three) phases, each with well-defined objectives:

• Phase I: Arch Development and Sagittal Correction
  This was carried out with the Invisalign appliance. A slight expansion of the arches, correction of incisor inclinations, correction of the CLII (with accelerated distalization protocol and Class II elastics 6Oz full time), midline correction and space gain for the impacted cuspid were planned in this phase. A total of 40 aligners were planned (5-day change protocol).

Fig. 3:  Phase I Clin Check: Arch Development & Sagittal Correction (Pre and End of Phase 1: 40 aligners)

• Phase II: Hybrid Mechanics & Forced Eruption Phase (Figure 4a, 4b, 4c)Within six months of starting Phase I,a) surgical exposure of the impacted canines (closed technique-i.e., involves uncovering the canine, attaching an eyelet and traction hooks, and then suturing the palatal mucosa back over the tooth. The tooth is then moved into position covered by the palatal mucosa.) Fig 4a
  b) strategic employment of the deciduous canine for anchorage Fig 4b, and a
  c) segmental hybrid arch overlayed with passive aligners (40) for traction of the impacted tooth towards the arch was employed in this phase. Lower Incisor MBT brackets (022’’slot) with a 16x22 SS arch wire was used in the quadrant with the impacted canine as additional anchorage on the lingual surface as a partial hybrid appliance.

Fig. 4a: Closed technique for occlusal and distal guidance of the impacted canine

Fig. 4b: The deciduous canine strategically employed for anchorage of the impacted tooth

Fig. 4c: Segmental Hybrid Mechanics (Lingual Brackets) to de-rotate the impacted cuspid (40 passive aligners). Appliance: Lower Incisor MBT brackets (022 slot), Arch wire: 16x22 SS.

• Phase III: Finishing and Settling Phase (Figure 5)
  The third and penultimate phase was aimed at finishing occlusion and intercuspation, by using 48 aligners. Appropriate attachment geometry (conventional attachments on upper cuspids and lower arch and optimized on premolars) and final tooth positions with overcorrections built in were carried out using 3D controls.Total number of aligners planned were 128 (including 40 passive aligners in Phase II). Total treatment time: 30 Months

Fig. 5: Phase III Clin Check: Finishing and Settling Phase (48 aligners)

Treatment results

Final clinical records show good esthetics and functional positioning of upper right impacted canine in the arch. The patient's smile considerably improved, and the treatment was completed within 30 months. Periodontal evaluation at the end of treatment showed healthy marginal tissues with pale pink and firm gingivae. (Figure 6 and 7) The gingival smile line was improved, with the gingival parabolas of the canines at the same height of the central incisors, contributing to the pleasant smile esthetics. The patient does desire some micro esthetic gingivoplasty, which will be carried out six months later.

Occlusal results evidenced a proper bilateral Class I relationship and a correct overbite. A mutually protected occlusion with canine guidance during excursive movements was achieved. Proper interdigitation of the upper functional lingual cusps into the fossae of the lower teeth was achieved. Moreover, upper and lower midlines were facially centered. A critical appraisal of our results would probably indicate the need for more precise root alignment in the upper right quadrant.

Retention strategy for the patient involves upper and lower Vivera retainers.

Fig. 6: Post Treatment Images

Fig. 7: Post Lateral Ceph and OPG

Fig. 8: Pre Ceph Values

Fig. 8: Post Ceph Values

Discussion

This case successfully illustrates how an impacted canine can be incorporated in the arch, by using clear aligner therapy effectively. Hybrid appliances even when employed were phased into an aligner overlay, making additional anchorage requirements redundant. Though this case report cannot be representative of all permutations of impacted cuspids that may present themselves, it does demonstrate an encouraging trend in contemporary protocols where forced eruption can be carried with an appliance system that –

• is Aesthetic and patient friendly.
• allows simultaneous alignment and traction.
• controls reactionary forces.
• minimizes emergencies and gingival abuse during the traction phase.

Conclusions

Current orthodontics increasingly calls for patient centric therapeutics that incorporates quality of life during therapy as well. Mechanics have to be carefully crafted with efficacy and efficiency both being accounted for. Aligners are an esthetic and minimally invasive solution for most malocclusions, and current reports in scholarly literature do indicate promising trends.

Forced eruption of impacted teeth by means of dental extrusion can be a challenging movement to achieve using aligners alone. Inter disciplinary orthodontics with aligners warrants careful staging and phase-based planning as demonstrated. The combined use of buttons, lingual segmental appliances, labial sectional arches, elastics and aligners allows effective solutions that can be customized in a phase-based manner as demonstrated.

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