Advances in the diagnosis and management of impacted canines: An updated evidence-based review

Extraction of primary canine

Interceptive extraction of the primary canine is a commonly used early intervention aimed at facilitating the eruption of palatally displaced permanent canines.^4,16,17 The rationale for removal of deciduous predecessor is it modifies eruptive guidance of permanent canine, eliminate physical obstruction, and potentially create space within the dental arch.^4,17

Several systematic reviews have reported that extraction of primary canines in minimally crowded arches increases the likelihood of spontaneous eruption of the palatally ectopic permanent canines in 50–69% of cases.^16,17 However, a Cochrane review by Benson et al. concluded that the certainty of evidence remains low due to small sample sizes, high risks of bias, and potential reporting errors across existing trials.¹ Furthermore, there is also no robust evidence demonstrating interceptive extraction significantly reduces the need for subsequent surgical intervention.¹

Despite this, there is broad consensus that the initial severity of displacement is the most critical prognostic indicator for interceptive extractions. Favourable prognostic indicators where spontaneous eruption after interceptive extraction is more likely include impacted canines located in a favourable location at sector 1-2,^1,18 exhibits a mild mesial inclination of less than 30°,^16,18 and at pre-pubertal age.¹⁸ In contrast, severely displaced canines, such as those located in sector 4-5 with alpha angles exceeding 30°, are less likely to respond to interceptive treatment.^1,6,18

An observation period of 12 months is proposed by multiple studies after interceptive extractions.^1,4 The probability of future spontaneous is low if canine is has not erupted beyond this time point.⁴

Adjunctive orthodontic interventions

These include rapid maxillary expansion (RME), transpalatal arches (TPA), or cervical-pull headgear that have been proposed to facilitate the eruption of displaced canines. Elangovan et al. reported that while some clinical trials showed increased rates of spontaneous eruption when these appliances are used either alone or in combination, many studies have small sample sizes, short follow-up periods and inconsistent randomisation. ¹⁶ Larger well-designed randomised controlled trials are required to establish the true effectiveness of these adjunctive interventions. Furthermore, interceptive treatment may prolong overall treatment duration and requires careful monitoring to determine whether additional intervention becomes necessary.

Open vs closed surgical exposure

Two main surgical techniques are routinely used to uncover palatally displaced canines. The closed technique involves raising a full mucoperiosteal flap to expose the crown, bonding an orthodontic attachment, and subsequently repositioning and suturing the flap so the tooth remains covered during initial traction. In open technique, a window of bone and soft tissue is removed from around the tooth and a dressing is placed to cover the exposed area. The tooth is either left to erupt or moved using orthodontic attachment.

Current evidence suggests that both techniques are highly effective in achieving canine eruption, with no significant differences in success rates.^19,20,21 A Cochrane review by Parkin et al. concluded, with low certainty, that there are no differences in outcomes in open versus closed surgical technique in terms of success of treatment, complications, aesthetics, periodontal outcomes, and patient-centred outcomes.³ The finding on periodontal outcomes is consistent with a subsequent systematic review specific on periodontal outcomes.⁷

Some findings by Cochrane review by Parkin et al. was inconsistent with a systematic review by Cassina et al. conducted at similar period. Cassina et al. reported that open surgical exposure is associated with shorter initial alignment duration compared to closed technique, possibly due to lack of a repositioned flap over the exposed canine.¹⁹ Cassina et al. also concluded lower odds of ankylosis in open exposure technique;¹⁹ however, this conclusion was derived from a single non-randomised prospective study,²² limiting the strength of this finding to support a definitive advantage of one surgical approach.

Subsequent to the Cochrane review, Björksved et al. conducted a randomised-controlled trials and found no significant differences in surgery time, post-operative complications, and cost.^23,24 Nevertheless, Björksved et al. reported patients in closed exposure group experienced greater pain and discomfort during active orthodontic traction phase.²⁴

Overall, the available evidence does not clearly favour either technique. Given the low certainty of existing evidence and heterogeneity across studies, the choice between open and closed exposure therefore remains guided by clinician preference, surgical experience, and case-specific anatomical considerations. ³ A summary of evidence comparing open and closed surgical exposure across eruption efficacy, periodontal outcomes, complications, and patient-centred outcomes are presented in Table II.

Modified surgical techniques and emerging approaches

Alternative surgical approaches have also been described. The tunnel technique, originally introduced by Crescini et al. is a modified closed-eruption procedure for buccal canines impacted high in the midalveolar region.²⁵ The procedure involves guiding the impacted tooth downward through the socket of the extracted deciduous canine. The primary goals of this technique are to preserve the buccal bone plate and prevent poor aesthetic outcomes, such as an elongated clinical crown or reduced labial bone support. Evidence supporting this method remains limited, case reports and clinical trials are scarce.

More recently, CO₂ and diode laser technologies has been integrated into the management of palatally impacted canines have as a minimally invasive alternative to conventional approach. In addition to facilitating soft tissue removal, laser technology has been proposed to exert photobiomodulation effect, where specific wavelengths activate subcellular photoreceptors and stimulates tissue regeneration and healing.

In a randomised controlled trial, Impellizzeri et al. reported a greater tooth movement in patients treated with CO₂ or diode laser compared to conventional surgery, suggesting that the use of laser may enhance or stimulate the spontaneous eruption of impacted canine.²⁶ From a surgical perspective, the photothermal effect simultaneously coagulates small vessels during incision, resulting in minimal intraoperative bleeding and improved surgical visibility. Patients treated with CO₂ and diode lasers experience have also been reported to experience reduced post-operative pain and swelling, along with faster healing and functional recovery.²⁶ However, the study is based on studies with small sample size, restricting the strength of conclusions supporting their routine clinical use.

Mechanics and appliances

Various orthodontic mechanics have been described for the traction and alignment of impacted canines, with selection guided by canine's initial position, space availability and anchorage requirements. Orthodontic appliances and auxiliaries employed include includes nickel-titanium (NiTi) closed-coil springs for continuous light force for controlled movement, power chains and elastic threads for gradual traction forces, gold chains, Kilroy springs, Ballista springs, miniscrews, strong rigid buccal arms, and magnets.^{3,25,27,28,29}

Kilroy springs deliver constant force via a vertical loop and have been shown through finite element analyses to produce higher von Mises stress and greater displacement compared to Ballista springs and NiTi closed-coil springs, although they also tend to exert greater stress on adjacent teeth.^27,28 Piggyback wires are considered a suitable alternative for canines displaced 2–4 mm from the occlusal plane, as they produce lower reactionary forces on adjacent teeth.³⁰

Biomechanics of traction

The magnitude and direction of force application are critical determinants for successful orthodontic alignment of impacted canines.³¹ Excessive force risks root resorption, pulpal necrosis, or damage to the periodontal ligament, particularly in buccally impacted canines.^7,32 Buccally impacted canines present greater challenges in managing adverse periodontal effects and require careful consideration of surgical technique interventions, proper marginal gingival positioning with adequate attachment, inflammation control, and the application of controlled orthodontic forces.³² When positioned close to the incisor roots, buccally directed force risks root damage and may impede tooth movement; therefore, initial traction should be directed occlusally and distally before redirecting the tooth buccally into its final position.²⁵ When ankylosis is suspected, traction force should be reduced, a periapical radiograph should be obtained to assess for osteoid tissue, and referral to a periodontist if indicated.³³

Temporary anchorage devices (TADs)

The use of TADs, or miniscrews, in the management of impacted canines is growing in popularity. A systematic review and meta-analysis by Alharbi et al. reported that there is limited data on whether TADs are superior in terms of overall treatment duration, adverse effect, and number of visits; however, there is moderate-quality evidence that TADs provide a superior anchorage preservation compared to conventional methods such as TPA and headgear.³⁴

Beyond anchorage control, miniscrews have demonstrated efficacy in minimising lateral incisor root resorption during canine disimpaction. In a clinical controlled trial, Heravi et al. reported significantly less root resorption with TAD-assisted approach compared to conventional techniques.³⁵ The protocol involves inserting two bracket-head miniscrews, measuring 1.4 mm in diameter and 8 mm in length, to the mesial and distal to the maxillary second premolar, right angle to the palate and 5 mm from the embrasure.

Heravi et al. argued that the conventional technique, where initial arch alignment was done before active canine traction, carries several disadvantages. ³⁵ First, bracket placement on the lateral incisors shifts their root apices closer to the resorptive follicle of the impacted canine, particularly s torque is expressed through rectangular wires. Some clinicians mitigate this by remaining in round wires during the aligning phase; however, this represents a compromise rather than a solution. The use of rectangular archwires in conventional technique, despite able to neutralise reaction forces, carries risk of anchorage loss and extended treatment duration.³⁵ Therefore, it is crucial to move the impacted canine away from the root of the adjacent tooth prior to bracket placement.

Autotransplantation

Autotransplantation is a viable treatment option in situations where orthodontic traction is not a practical solution, for example, in high alpha angle (>30°) with high sector, a high vertical position, and dilacerated roots.^36,37 A study with mean follow-up of 21 years reported a survival rate of 67.7% for autotransplanted canines, with mean survival time of 15.8 years.³⁷ Saccomanno et al., in their systematic review, identified younger age, female sex, proper root canal treatment, and effective post-operative care as factors associated with improved outcomes. Insufficient bone support, gingival recession, interdental soft tissue defects, and deep periodontal pocketing were reported as cause of failure.^36,37 Risks include damage to the periodontal ligaments, cementum, and darkening of tooth requiring full-coverage restoration.^36,37,38 As individual outcomes remain difficult to predict, patients should be counselled for potential failure and consequences prior to proceeding with autotransplantation treatment.³⁶

Impacted mandibular canines

Mandibular canine impaction is a rare clinical entity, with a reported prevalence ranging from 0.008% to 1.29%, while transmigration occurs in approximately 0.12% to 0.98% of the population.³⁹ Clinical management typically involves either surgical extraction for deeply impacted cases or surgical exposure for those in a favourable position for guided eruption.³⁹ Unlike the maxillary arch, where interceptive expansion is well-documented, there is a distinct lack of evidence and clinical consensus regarding interceptive protocols for mandibular canines, which are often severe by the time of detection.^39,40

In a single-centre cross-sectional study, Bolooki et al. identified that canine angulation, the horizontal position of the root apex, the vertical height of the crown, and the degree of overlap serve as the primary predictors for surgical decision-making.⁴⁰ Specifically, surgical exposure is favoured for angulations of 0°– 15°, crown heights between the CEJ and mid-root, and minimal horizontal overlap. In contrast, surgical extraction is preferred for angulations >45°, positions beneath the root apex, or transmigration across the dental midline.⁴⁰ Despite identifying these predictors, the study did not evaluate long-term success rates, and its findings highlight the need for multi-centre prospective research to standardise mandibular management protocols.

Root resorption

Root resorption of adjacent teeth is a major concern, particularly in cases of severe canine impaction.^41,42,43 Palatally impacted canines positioned in closer proximity to lateral incisors (greater mesial sector) or those with a horizontal position (higher alpha angle) are associated with increased pocket depth, gingival recession and reduced width of keratinized tissue following interceptive treatment, surgical exposure, and orthodontic traction.⁶

Delayed diagnosis and treatment lead to prolonged contact and sustained pressure on the lateral incisor roots, thereby risks root resorption and failed orthodontic alignment.^42,43 Early detection through CBCT enables accurate assessment of impaction severity and resorption risk,⁴² while judicious selection of orthodontic mechanics can further mitigate force transmission to adjacent dentition.⁴³

Periodontal outcome

Excessive force can lead to loss of periodontal attachment;⁴⁴ whereas light, continuous force induces relatively long-lasting levels of cytokines necessary for continuous periodontal remodelling.⁴⁵ Although a light force of 20–30 g is generally considered sufficient to mechanically erupt an impacted canine, clinical practice frequently involves forces that exceed this threshold, which may result in greater CEJ-to-alveolar crest distances on the mesial side of the impacted tooth and interproximal bone loss.⁴⁴

Closed surgical exposure has been favoured on theoretical grounds due to better preservation of keratinized gingiva, reduced risk of gingival recession, and a lower likelihood of plaque accumulation and inflammation. However, both Cochrane reviews and systematic reviews have concluded that available evidence is insufficient to demonstrate difference in periodontal parameters between open and closed techniques,^3,7 a finding corroborated by multiple retrospective studies examining long-term periodontal outcome.^31,46 One retrospective study proposed piezoelectric surgery as means to expose canine without damage to the periodontium; however, outcomes were compared against the contralateral spontaneously erupted canines, rather than conventional surgical bur.⁴⁷ Taken together, current evidence does not support superiority of either exposure techniques on periodontal ground alone.

Grisar et al., in their systematic review, concluded that the mesial sector and vertical position of impacted canine can influence periodontal outcomes.⁶ Buccally impacted canines are suggested to present greater risk of adverse periodontal outcomes,^6,32 yet multiple studies report no clinical significant difference in periodontal parameters between palatally and buccally impacted canines following closed management,^31,44 and neither open nor closed surgical exposure has been shown to be superior for the management of buccally impacted canines.³²

Pulp vitality

Pulpal health of orthodontically-treated impacted canines remains an under-reported outcome,⁴⁶ despite significant tooth movement involved in their traction. The extensive movement subjects the pulp to prolonged mechanical stress, risking neurovascular compromise and pulp necrosis. While some evidence suggests altered pulp testing scores post-treatment,⁴⁸ there is a paucity of data linking specific mechanical strategies to pulpal vitality.

For example, the piggyback technique warrants scrutiny in this regard. A 0.014” NiTi wire engaged during initial stage is associated with greatest tooth displacement and least predictable tooth displacement. A review of available literature identified three studies reporting the technique in sufficient detail, none of which documented pulpal outcome.^49,50,51 Singh et al. started the piggyback mechanic following crossbite correction;⁵¹ Jowett et al. commenced piggyback treatment after the archwire progression from 0.018” NiTi to 0.018” or 0.020” AJW alongside closed exposure;⁵⁰ Singh et al. described piggyback traction initiation following confirmation of adequate mesiodistal space, though this report involved a permanent central incisor rather than a canine.⁵² None of these studies specified the timing of initial piggyback archwire placement in weeks, nor did report any pulpal outcomes.