From Volume 15, Issue 1, January 2022 | Pages 19-25
A 14-year-old medically fit and well patient presented with bilaterally ectopic maxillary canines resorbing the central and lateral incisors. It is relatively rare that both maxillary ectopic canines cause resorption to the central and lateral incisors. Treatment options discussed with the patient are explored as well as case management and how potential complications were minimized. A good result was achieved at the end of the treatment, despite the complex nature of this case.
Maxillary ectopic canines have an incidence of around 1.5% in the general population.1 Around two-thirds of ectopic canines are positioned palatally and the remaining one-third are located labially.2
It is hypothesized that canines become impacted due to a combination of environmental and genetic factors. These include, missing lateral incisors, diminutive/peg lateral incisors and late developing dentitions.1 These factors can contribute to the canine being ectopic owing to a lack of guidance provided by the lateral incisor.3 The multiple genetic components that lead to ectopic canines include abnormal positioning of the tooth bud, their long eruption path and soft or hard tissue obstructions.4 Occurrence of bilaterally impacted canines, sex, familial and population differences between studied groups also suggest the patient's genetics have a role in the incidence of impacted canines.5 Overall, this phenomenon is likely to be due to a multifactorial process where both genetics and the environment play a role.
The incidence of congenitally missing canines is very low, occurring between 0.18% and 0.45% of a given population.6,7,8 Therefore, if a maxillary canine has not erupted by the age of 12, it should be considered ectopic until proven otherwise.
The case discussed demonstrates how severely palatally displaced canines causing root resorption to the upper right lateral incisor and both central incisors, are diagnosed, and carefully treatment-planned in collaboration with the patient and parents' wishes.
The patient presented at 14 years old, fit and well, taking no regular medications and had no known drug allergies. She was referred because neither of the maxillary canines had erupted. After visiting a specialist orthodontist, clinical and radiographic assessment (OPT and upper standard occlusal) suggested that both ectopic maxillary canines were present and resorbing both the upper centrals and the right lateral incisor (Figure 1). The patient was then referred for a second opinion from a consultant orthodontist. The patient's initial complaint was concern about the alignment of her upper and lower front teeth, but she was aware of the impacted maxillary canines.
The patient presented with Class I incisors on a Class I skeletal base and average Frankfort-mandibular plane angle (FMPA). Her lips were competent with a 3-mm overjet and 2-mm overbite. There was 9 mm of crowding in the upper arch and 13 mm of crowding in the lower arch. The molar relationships were one-quarter unit Class III bilaterally, and the canine relationships were Class I bilaterally. The upper centreline was coincident with the mid-face, while the lower centreline was 1-mm shifted to the left. The deciduous upper canines were Grade II mobile. The maxillary incisors were all Grade I mobile, not tender to percussion, with no crown colour changes or sinuses suggestive of apical infection.
The initial radiographs are shown in Figure 1, and suggested that the canines were palatally positioned and that root resorption appeared to be evident on the UR2, UR1 and UL1. The UL2 appeared undamaged. After discussion with the patient and mother, a cone beam computed tomography (CBCT) was ordered to determine the extent of the resorption, to gain further information and adequately describe the risks of any treatment plan formulated (Figure 2).
Figure 3 shows the 3D reconstruction of the CBCT scans and Figure 4 the pre-operative pictures.
Following review of the scans and dentition, the following treatment options were presented to the patient:
In this scenario, the patient and the patient's mother opted for treatment option 2. They understood the risk that, if further root shortening occurred (due to fixed appliances treatment, and damage already caused by the ectopic canines), the patient may require prosthetic replacement if the upper anterior teeth were lost. Informed written consent was given.
The clinician treating the case believed that option 2 would be in the patient's best interest. Option 1 did not address the patient's needs of correcting the crowded dentition. Option 2 would exert less orthodontic force on the maxillary incisors (which were already comprised) compared to aligning the canines into the central incisor position in the arch (option 3). Furthermore, the treatment time for option 2 would be shorter than option 3 and eliminated the risk of possible ankylosis of the canines if an attempt was made to introduce them into the line of the arch.
After surgical intervention as described, the patient was bonded up in the upper arch in July 2018. Initially, nickel–titanium (NiTi) wires (Neosentalloy GAC 0.016) were used for initial alignment and correction of rotations in the upper and lower arches. In this case, and in order to reduce the risk of significant root shortening of the upper central incisors, they were omitted from the bond up sequence. At the end of the first appointment, peri-apical radiographs of the maxillary incisors were taken to provide a baseline assessment of the root status for comparison later on in treatment.
After 6 weeks, an upper 0.018” stainless steel archwire was placed, with powerchain over the top of the archwire running from upper first molars to upper lateral incisors, in each quadrant (Figure 5). This had the effect of distalizing the upper laterals, thereby creating space for the maxillary centrals to begin derotation with no direct orthodontic forces being applied to the teeth.
Once space had been created distal to each upper central incisor, the maxillary centrals were bonded and a continuous 0.016” NiTi was used to complete the correction of the derotations. It was felt that this wire would allow transition to a rectangular NiTi wire at the next visit, rather than using a lighter wire and potentially extending the treatment time (Figure 6).
At each visit, the patient was questioned about whether any unusual symptoms had been experienced in regard to the maxillary incisors. Upon archwire removal, the mobility of the upper incisors was reviewed. Any colour change was assessed by comparing the teeth at that visit with the previous intra-oral photo taken at 6–8-weekly intervals.
Once progressed into working archwires (19/25 stainless steel), NiTi closing coils in all quadrants were employed on posted 19/25 stainless steel wires to close the residual space (Figure 7).
Since both the upper central incisors differed in crown and root morphology, it was difficult to perfectly align the maxillary central incisor crowns from a labio-palatal perspective. It was discussed with the patient and parents that one option could be the use of torqueing auxiliaries or individualized wire bends to attempt to correct this. However, due to the root damage and unusual root shape it was felt these mechanics might have produced unpredictable results while potentially shortening the roots further. Torque mechanics can transmit high forces to the roots and result in further root resorption. Instead, soft flex discs were used to smooth the incisal edges of both upper centrals to create an even aesthetic result. The maxillary 1st premolars served as a good substitute to the maxillary permanent canines and it was decided no further restorative work was required after orthodontic treatment.
In summary, the emphasis of the treatment plan was to ensure that the minimal amount possible of orthodontic force was applied to the already resorbed incisors, and to keep the treatment duration as short as possible. The total treatment time was 16 months (Figure 8).
In terms of difference in root length, the UR2 root was measured at 9.4 mm at the end of treatment (2 mm root length loss). The UR1 root length was measured at 8.4 mm (2 mm root length loss). For the UL1 tooth, the root length at its maximum was measured at 7.4 mm (1.4 mm root length loss) and minimum point 4.1 mm (2 mm root length loss). The UL2 root length was measured at 11.1 mm post-operatively (1.7 mm root length loss). It must be noted that the lack of standardization in intra-oral radiographs means there may be some error in these measurements.
In the case discussed, the patient had a moderate amount of root resorption of the upper central incisors at the time of initial presentation. The combination of both central and lateral incisor root resorption is a relatively rare occurrence. Using CT scans, Eriscon and Kurol found that seven out of 156 ectopic canines caused resorption to both the central and lateral incisors.3 In another study carried out at University of Athens, three canines out of 61 patients being treated for ectopic canines demonstrated resorption of the central and lateral incisors.9 Cernochova et al concluded that three out of 334 (0.009%) ectopic canines caused resorption to both the central and lateral incisors.10
Owing to the complex nature of the case, it was important to discuss the treatment options in detail with the patient and parents, and enable sufficient time for them to make an informed decision. For the treatment option that was selected, the patient and parents understood the long-term questionable/unpredictable prognosis of the maxillary incisors. In the future, if the incisors were compromised, replacement options could include a denture, bridges or implants. The ideal long-term replacement option would be implants once jaw growth was completed. Maintaining the incisors until then would be ideal to maintain the alveolar bone for as long as possible and reduce the chances of requiring a bone graft.
There was no pathological mobility in all four upper incisors at initial presentation and this was maintained until the end of treatment as well (Grade I mobility). Considering the degree of root resorption at initial presentation, this was acceptable. It is important to remember that roots are conical in shape and that the amount of periodontal attachment is greater coronally than apically. Accordingly, and in work presented by Kwalkorf et al, up to 7 mm of apical root loss can occur in a single rooted maxillary incisor tooth and still leave the tooth with up to 57.3% of its periodontal attachment retained.11 In a conventional 2-year fixed appliance case, it is expected to have 1 mm of root loss occurring, which is not clinically significant to the periodontal attachment of the tooth overall.12 While the upper incisors in this case may have received slightly more than 1 mm of root resorption, this did not affect their periodontal attachment clinically.
Although this case was rescued, GDPs should be mindful of the Royal College of Surgeons guidelines that focus on timely detection of ectopic maxillary canines to reduce the chances of complications of this nature occurring. If canines cannot be palpated in the buccal sulcus between the ages of 10 and 11, it should be assumed that the canines are ectopic.1
Overall, an excellent aesthetic and functional result was achieved given the very complex nature of this case. The upper premolars were good substitutes for the missing upper canines and using the soft flex discs to smooth the incisal edges of the central incisors produced a great aesthetic result. The patient and mother were happy with the overall results and the treatment delivered met their expectations.
This case highlights how careful diagnosis and orthodontic management of bilaterally impacted maxillary canines, associated with maxillary incisor root resorption, can be safely treated using efficient and effective modern orthodontic mechanics.
