23.3 Ectopic and Impacted Maxillary Canines
Key Takeaways
Maxillary canines are impacted in about 1-3% of people, more often in females, and palatal impactions outnumber buccal ones in many populations.
If the permanent canine bulge cannot be palpated in the buccal sulcus by about 10-11 years, or the sides differ, radiographs should be taken to locate the canine.
With horizontal tube shift (parallax), an object that moves in the same direction as the tube is lingual (palatal) and one that moves opposite is buccal: the SLOB rule.
Extracting the primary canine at about 10-13 years can help a palatally displaced canine erupt, especially when there is no crowding, but the supporting evidence is limited.
Root resorption of the adjacent lateral incisor is the most important complication of an ectopic canine and is best assessed with CBCT.
The maxillary canine has the longest path of eruption of any tooth and develops high in the maxilla, which makes it prone to displacement. Most SDLE questions ask how to detect, locate and intercept it.
Prevalence and Causes
- Impaction of maxillary canines occurs in about 1-3% of people, about twice as often in females.
- Palatal displacement outnumbers buccal in many populations; buccal impactions are more often linked to crowding (lack of space).
- Guidance theory: the canine follows the lateral incisor root; missing or peg-shaped lateral incisors remove this guide and are associated with palatal canines.
- Genetic theory: palatal canines cluster with other dental anomalies such as hypodontia, small laterals, and infraocclusion of primary molars.
- Other causes: retained primary canine, supernumerary teeth, cysts, odontomas, trauma and clefts.
Early Detection
- The maxillary canine normally erupts at about 11-12 years.
- From about 9-10 years, a canine bulge is usually palpable in the buccal sulcus.
- Warning signs: no buccal bulge by about 10-11 years, a palatal bulge, asymmetry between sides, a distally tipped or proclined lateral incisor, a retained primary canine after about 13-14 years, or delayed eruption.
Radiographic Localization
| Method | How it works |
|---|---|
| Horizontal parallax | Two periapical radiographs (or a periapical and an occlusal) with the tube moved horizontally between exposures |
| Vertical parallax | Panoramic radiograph plus an upper standard occlusal (the tube moves vertically) |
| SLOB rule | Same Lingual, Opposite Buccal: an object that moves with the tube is palatal; one that moves opposite is buccal |
| CBCT | Gold standard for 3D position, root resorption of incisors, and surgical planning |
Panoramic prognostic features: the more the canine cusp overlaps the lateral incisor (sector position), the steeper its angle to the midline, and the higher it lies, the poorer its chance of spontaneous eruption.
Interceptive Treatment
- Extraction of the primary canine at about 10-13 years in an uncrowded arch can let a palatally displaced canine improve its path. In Ericson and Kurol's original study most canines normalized, with better results when the cusp lay distal to the midline of the lateral incisor. Systematic reviews rate the evidence as low quality, so expectations are explained to parents.
- Creating space (rapid maxillary expansion, headgear) alongside the extraction may improve outcomes in crowded cases.
- Review radiographically after about 6-12 months; if no improvement, plan active treatment.
Active Management Options
| Option | Indications and notes |
|---|---|
| Surgical exposure and orthodontic alignment | Most common; create space with fixed appliances first; then expose and bond an attachment |
| Open exposure | Palatal canines: window of tissue removed and a pack placed; canine erupts naturally before alignment |
| Closed exposure | Bracket and gold chain bonded under a replaced flap; used for deep or buccal canines high in the sulcus |
| Apically repositioned flap | Buccal canines lying coronal to the mucogingival junction, to preserve keratinized gingiva |
| Surgical removal | Severely displaced canine, ankylosis, root resorption of adjacent teeth, cystic change, or patient declines long treatment; the first premolar can substitute for the canine, or the space is restored |
| Autotransplantation | Selected cases with adequate space and bone |
| Leave in situ | Asymptomatic, deeply placed canine in an adult with good occlusion; monitor periodically for resorption or cystic change |
Treatment of impacted canines in adults is slower, with a higher risk of ankylosis.
Complications
- Root resorption of the lateral incisor (and sometimes the central incisor): the most important complication; often seen only on CBCT; can be severe and silent.
- Dentigerous cyst formation around the crown.
- Ankylosis of the canine, which prevents traction.
- Loss of attachment or gingival recession after exposure, devitalization, and relapse.
Factors Affecting Prognosis of Alignment
| Favorable | Unfavorable |
|---|---|
| Young patient with growth and an open canine apex | Adult patient, closed apex |
| Canine cusp distal to the lateral incisor, low vertical position | Cusp over the central incisor, high position near the nasal floor |
| Angle to the midline small | Near-horizontal canine |
| Space available or easily created | Severe crowding, no space |
| No ankylosis | Ankylosis (no movement under traction, metallic percussion note) |
| Good oral hygiene and cooperation | Poor cooperation with long fixed treatment |
Treatment of a palatally impacted canine with exposure and traction commonly takes longer than routine fixed appliance treatment, and patients should be told this before they consent.
Mandibular Canines
Impaction of the mandibular canine is much rarer. A mandibular canine can migrate across the midline (transmigration), when it is usually removed rather than aligned. Retained mandibular primary canines in adults may be kept while they remain functional.
Transposition
The most common transposition is between the maxillary canine and first premolar. Management may accept the transposed order rather than attempt correction, depending on root positions.
Exam Traps
- Palpate for canine bulges in every child aged 9-11; early detection allows interception.
- Do not apply traction to a canine before there is space in the arch.
- On a horizontal tube shift, a canine moving the same way as the tube is palatal.
Two periapical radiographs of the maxillary canine region are taken: the second with the tube shifted mesially. The unerupted canine appears to move mesially relative to the lateral incisor root. Where is the canine?
Buccal to the lateral incisor root
Palatal to the lateral incisor root
In the same buccolingual plane as the root
Its position cannot be found by tube shift
An 11-year-old has no palpable canine bulge on the left, a palatal swelling near tooth 22, and an uncrowded arch. A radiograph shows the canine cusp overlapping the distal half of the lateral incisor root. What is the most appropriate interceptive step?
Wait until the age of 18 years before any assessment or treatment
Start traction on the canine immediately, before any space is made
Extract tooth 22 at once to give the canine a direct path to erupt
Extract primary canine 63 and review the eruption path radiographically
Which complication of an ectopic maxillary canine is most important to detect early, and which imaging method shows it best?
Pulp calcification of the canine, best shown on a lateral cephalogram
Maxillary sinusitis, best shown on a bitewing radiograph of premolars
Resorption of the adjacent lateral incisor root, best shown on CBCT
Ankylosis of the primary molars, best shown on a hand-wrist radiograph
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