From Volume 15, Issue 3, July 2022 | Pages 125-130
The decision-making process in the management of a patient with a palatally displaced canine can be complex, with several clinical and patient-related variables, each requiring careful consideration, both individually and in unison. In this article, we discuss these factors, along with the available treatment options and their underlying evidence base.
Maxillary canine ectopia is a relatively common problem, affecting approximately 1–3% of those of European origin.1 Although palatally displaced maxillary canines (PDCs) were previously thought to account for around 85% of such malpositions, studies using CBCTs have demonstrated that this is closer to 60%.2
The aetiology of the PDC is multifactorial in nature, occurring due to an interaction between an individual's genetic coding and various environmental factors, such as an absent or diminutive lateral incisor. While the relative importance of the genetic and guidance theories remains the subject of debate,3,4 the familial tendency, higher female prevalence and association with other dental anomalies all suggest that the genetic component may be of greater importance (Figure 1).
The Royal College of Surgeons of England (RCS Eng) guidelines on PDCs broadly categorize management into five treatment options5. Unfortunately, the evidence base underpinning several of these options is fairly weak.
Patients should be informed of the potential risks of this option, including root resorption, cystic change, and the potential for later eruption. Although regular clinical and radiographic monitoring is advised, there is a lack of evidence regarding the optimal time interval for doing so (Figure 2). The risk of resorption is affected by age, decreasing after 14 years,6 possibly a consequence of the diminished eruptive potential of PDCs. If left in situ during treatment, a PDC can potentially impede tooth movement.7
Extraction of primary canines in children between 10 and 13 years of age has become widely accepted as a way of normalizing, or improving, the eruptive pathway of a PDC. Alternative forms of interceptive treatment involve space creation using fixed appliances (FAs),8 rapid maxillary expansion or headgear, with or without extraction of the primary canine (Figure 3). Some studies have also investigated the effect of double extractions of primary teeth on the eruption of PDCs.9,10
Historically, support for interceptive extractions was largely based on the findings of a study with no control group, in which 78% of participants who had extraction of a primary canine had subsequent eruption of the PDC.11 However, the current best evidence stems from a randomized controlled trial (RCT) which reported that interceptive extraction of the primary canine results in an increased chance of PDC eruption compared to no treatment.12
Although this study represents the best available RCT in this field, it has several methodological inadequacies. These include using teeth (rather than patients) as the units of analysis, and not stratifying the randomization process for severity of displacement. There is also an issue regarding the age at which a diagnosis of ectopia was made, which was between 10 and 11 years old. This is relevant because prior to maturity of the adjacent lateral incisor root, a permanent canine in sector 2 represents normal development and this may occur later than 11.13 Furthermore, primary canines in the control group that were not mobile after 12 months were extracted. If this group were observed for a longer period then more PDCs may have erupted, thereby reducing the effect of the intervention. These issues led to a recently updated Cochrane review concluding that there are still high levels of uncertainty associated with the success of this intervention.14
The research group from the aforementioned RCT15 later reported that the severity of medial displacement was an important factor in determining the likelihood of spontaneous eruption, recommending that if the cusp tip is between 7 and 10 mm from the mid-sagittal plane (MSP) on a CBCT, extraction is worthwhile. This finding mirrors existing recommendations, based on the more frequently taken OPT, to only consider interceptive extraction if the PDC is in sector 2 or 3 (Figure 4). Importantly, if there is no positional improvement after 12 months then alternative options should be considered.5
If the permanent canine fails to erupt following removal of the primary canine, then the resultant gap may effectively commit a patient to exposure and alignment. In some patients, particularly those with poor oral hygiene and a high caries risk, this is not ideal. These patients may be better off retaining a primary canine of good prognosis, especially in cases of severe displacement of the PDC.17
Successful exposure will remove any obstruction impeding eruption of the canine. If the tooth is in a favourable position, this may be enough to allow the tooth to erupt; if not, then orthodontic traction will be required. Although the success of alignment is generally high, failure can still occur due to either true or pseudo-ankylosis, where the direction of orthodontic traction results in the PDC impacting on surrounding teeth or the buccal cortical plate.17 Other potential risks associated with alignment include poor future periodontal health of the canine and resorption of adjacent teeth.
This can be undertaken as the treatment of choice or if an attempt at alignment has failed. If the latter occurs, it can result in a significant bony detect in an anterior location as traction may have moved the PDC into a more superficial position (Figure 5). This complicates space closure and restorative replacement with a bridge or an implant,17 particularly for patients with a high smile line. As well as the common surgical risks, the risk of iatrogenic damage to adjacent teeth and their neurovascular supply should be highlighted to patients.
This is rarely the option of choice and is only appropriate when there is sufficient space to accommodate the PDC. To minimize the risk of ankylosis, the canine must be removed atraumatically, which is harder the more ectopic it is. Following implantation, a period of non-rigid fixation is required. If the root is immature, the pulp may revascularize; if not, it will usually require root canal therapy within a week.
Potential sequelae include vitality loss, ankylosis and resorption. A recent systematic review and meta-analysis has demonstrated that there is a positive outcome in 88% of cases up to 5 years after treatment.18 However, the inclusion of retrospective studies, coupled with the high levels of heterogeneity in the follow-up periods and definitions of success, means that this finding must be viewed with caution.
Treatment planning for these patients is multifactorial in nature, with several patient-related and clinical factors requiring consideration.
Adolescents with a PDC may present with only minor dental concerns, particularly if there is a retained primary canine with a good appearance. The fact that these patients often present with a Class I occlusion (Figure 6) goes some way to explaining why PDCs are occasionally referred late. In addition, as these patients will often have received minimal prior dental treatment, the prospect of 2–3 years wearing FAs can feel like a life-sentence for some.
The increased time period in FAs, with all their inherent risks, requires high levels of commitment for a successful outcome. Committing patients who are unable to attain, or maintain, suitable levels of oral hygiene is unlikely to be the most appropriate option.
With increasing age, the risk of resorption associated with leaving a PDC in situ decreases, while the risk of ankylosis increases. The latter is particularly relevant for patients presenting after the third decade of life.19 Alignment should, therefore, be performed with caution in older individuals, who should be informed of this increased risk.
The presence of carious teeth of poor prognosis elsewhere in the arch may influence orthodontic extraction choice and therefore, the decision about whether to align or extract the canine. In the absence of crowding, alignment of the PDC may be required to maximize the number of available tooth units. Embarking on orthodontic treatment would, of course, be dependent on an improved caries risk status.
Owing to a combination of difficult surgical access, prolonged operating time and the age group generally involved, general anaesthetic (GA) is often the modality under which both surgical exposure and extraction are undertaken. An obvious prerequisite is for these patients to possess no medical contraindications for GA.20 In the presence of a true contraindication, then either the use of local anaesthetic or leaving the PDC in situ are more appropriate options.
This is the most important clinical factor when considering the feasibility of alignment. PDCs can be localized bucco-palatally using either conventional radiographs or the parallax technique,21 with magnification of the canine relative to adjacent teeth on an OPT indicating palatal displacement.22 Importantly, the accuracy of both methods is reduced if the canine is particularly high. Due to the increased dosage, CBCTs should only be undertaken when clarity is required regarding either canine position, or the presence and extent of root resorption.
This can influence both the difficulty of alignment and the timespan involved.23 It is often classified according to sectors (Figure 7),11 with a PDC located in sector 5 the least amenable to successful alignment relative to the others. When assessing this using an OPT, consideration should be given to the slight underestimation of the PDC's medial displacement.
The greater the distance above the occlusal plane, the worse the prognosis for alignment (Figure 8).24 The potential for resorption during treatment is also more of a concern if the PDC lies directly above the apices of the surrounding teeth.
The more horizontal the crown–root axis of the PDC, the lower the prognosis for successful alignment (Figure 9). An alpha angle greater than 45 degrees to the MSP is often considered the threshold for a reduced prognosis in this plane.24 Angulation may be overestimated on an OPT.23
Finally, the closer the root of a PDC is to the MSP, the poorer the prognosis for alignment.24 A severely palatally displaced root will also have the effect of increasing the time taken to achieve an adequate amount of buccal root torque (BRT).
Some degree of resorption in conjunction with PDCs occurs in approximately 38% of lateral incisors and 9% of central incisors (Figure 10).6 Those at highest risk are patients aged between 10 and 11 years, females, and those with severely medially displaced PDCs with an enlarged follicle.25 While up to 60% of lateral incisors can have severe resorption with pulpal involvement,6 these teeth can still have a reasonable long-term prognosis.26 In some instances, however, extensive resorption of adjacent incisors may mean that the PDC ideally needs to be aligned and modified to resemble the extracted incisor.
If resorption of adjacent teeth is detected early, then surgical extraction of the PDC could be considered. Although rare clinically, pathological changes associated with the PDC itself, including the formation of dentigerous cysts and internal resorption, are further indications for its removal.7
The mid-to long-term prognosis of this tooth is also influential (Figure 11). For example, if the primary canine crown is particularly worn or displays excessive mobility, then alignment becomes a more suitable option. If primary canine retention is planned, its lifespan and the likelihood of future restorative treatment to fill the gap should be discussed. The long-term prognosis of the primary canine is unpredictable, but can be excellent, particularly in the presence of severely displaced PDCs where minimal root resorption has occurred.
The overall space requirement of the malocclusion is another decisive factor. Owing to the retention of the smaller, primary canine and drifting of the adjacent teeth, some form of space creation or redistribution is often required to accommodate the PDC. In the presence of upper arch spacing (eg due to hypodontia or previous extractions), or other teeth of poor prognosis, the ideal solution would be to align the canine. However, if there is insufficient space, then distalization, expansion or extractions will be required. In the presence of severe crowding, or even contact between the lateral incisor and first premolar, extraction of the PDC is often the best option.
If a PDC is extracted, then the first premolar is often camouflaged to mimic its appearance. If the aesthetics of the first premolar are acceptable, and there is a good contact with the lateral incisor, then no further treatment may be required. If this is not the case, or if space closure/additional orthodontic treatment is required, then several potential modifications can be made (Table 1). The amount of gingival show and the patient's attitude towards additional restorative treatment are likely to determine any vertical micro-management in such situations. When changing the vertical position of a bracket, the effect on torque should always be considered.
| Morphological differences ( |
Camouflage considerations for |
|---|---|
| Palatal cusp | Bond bracket distally to hide cusp |
| Incremental reduction of palatal cusp | |
| Gingival margin zenith | Intrude/extrude 4 depending on smile line |
| Composite build up/veneer or gingival surgery | |
| Reduced mesio-distal width | Bonding bracket distally will increase apparent width |
| Reduced buccal root prominence with smaller bifid root | Consider bracket with increased buccal root torque, third-order bends or torqueing auxillaries |
Where feasible, interceptive treatment should always be considered as a means of avoiding the need for exposure and alignment. When this is not possible, exposure and alignment is generally the preferred treatment option for mild to moderate displacement in the presence of minimal crowding. For severely ectopic PDCs, and for those patients who are either unsuitable, or unwilling, to have orthodontic treatment, either surgical removal or leaving the PDC in situ are likely to be more suitable options.
Patients should be presented with the various options available to them, the likelihood of success and the relative benefits and risks of each. They should of course be guided by their orthodontist; however, ultimately, the decision is theirs and the discussion should therefore be tailored to their individual needs.
