Pacific Coast Society of Orthodontists Bulletin Summer 2017 - 27

Let's Talk About That

when a child is as young as eight. Early referral is
recommended when there is no palpable buccal
canine bulge in a 10- to 12-year-old child, as this
suggests palatal impaction of canines. Unfortunately, impacted canines are usually asymptomatic, so patients are unaware of their
existence.4

The SLOB rule works thusly: when the clinician
moves the X-ray tube in a distal direction,
the tooth in question moves distally on the
radiograph, then the tooth is located on the
lingual or palatal side; if the impacted canine
is positioned buccally, the crown of the tooth
moves mesially.4

KF: How does a constricted, narrow arch relate
to an IMC?

KF: Is the path of eruption different for upper
canines than for other teeth?

JP: In a 1983 AJO-DO article, Jacoby stated that
in cases of labially impacted canines, 83% of
patients had arch-length deficiency, whereas
85% of palatally impacted canines had sufficient
space for eruption.5 I question these clinical
results because we often see palatally impacted
canine patients who show arch-length deficiencies. A more recent study by Tadinada et al.
reported that the palatally impacted canines are
also associated with significant arch perimeter
decrease and alveolar ridge reduction in all
dimensions.6

JP: Disturbances in the eruption of permanent
maxillary canines are common because they
develop deep within the maxilla and have the
longest path to travel compared to any other
tooth in the oral cavity. Canines play a vital role
in facial appearance, dental esthetics, arch development, and functional occlusion. As a result,
orthodontists have acknowledged the significance
of retaining impacted maxillary canines and have
proposed various techniques to effectively and
efficiently recover these teeth.

KF: If one does not have access to CBCT, what
other radiographic techniques would you suggest for diagnosing IMCs?

JP: Second only to third molars, maxillary canines
are the most commonly impacted teeth. IMC
is seen in approximately 2% of the population
and is twice as common in females as in males.
Canine impaction is two times more prevalent in
the maxilla than in the mandible; of all patients
with impacted maxillary canines, 8% have bilateral impactions. Approximately one-third of
impacted maxillary canines are located labially,
while two-thirds are located palatally.4

JP: Several methods can be used to radiographically evaluate IMC, including intraoral techniques
(occlusal and periapical projections) and extraoral
techniques (panoramic, posteroanterior, or lateral
cephalometric radiographs). The most practical
way to obtain an occlusal radiograph is by positioning the X-ray tube directly over the bridge of
the nose at a 60-degree angle to the occlusal
plane. This can be used to determine the buccolingual position of the impacted teeth, but the
traditional method for locating impacted teeth,
especially maxillary canines, has been to use a
two-dimensional technique with periapical radiographs (known as the buccal object rule). This
technique uses two apical radiographs with differential mesiodistal angulations and applies
the same-lingual-opposite-buccal (SLOB) rule
to determine the tooth's buccolingual position.

Summer 2017  PCSO Bulletin

KF: What is the prevalence of IMC?

KF: What is the etiology of IMC?
JP: Several etiologic factors are thought to be
behind canine impactions, e.g., localized, systemic, or genetic. Arch length discrepancy is
considered to be a primary etiologic factor for
labially impacted canines; the exact etiology of
palatally displaced maxillary canines is unknown.
There are two major theories associated with
palatally displaced maxillary canines: the guidance theory and the genetic theory. The guidance

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Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Summer 2017

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