Pacific Coast Society of Orthodontists Bulletin Summer 2017 - 28
Let's Talk About That
Figure 2. Panoramic radiograph
showing the maxillary canine
(arrow) without eruption guidance
due to a missing lateral incisor.
theory suggests that the canine is guided along
the root of the lateral incisor as it erupts, so if the
root of the lateral incisor is absent or malformed,
the canine does not erupt (Figure 2). The genetic
theory identifies genetic factors as the primary
cause of palatally displaced maxillary canines. It
includes other possibly related dental anomalies,
such as missing or small lateral incisors.4
KF: How frequently do we see root resorption
of adjacent teeth associated with IMC?
JP: Unerupted canines may increase a patient's
risk of developing a cystic lesion and infection,
causing root resorption of the nearby lateral
incisors and jeopardizing the longevity of lateral
incisors. For example, lateral incisors adjacent to
ectopically erupted canines have an incisor root
resorption incidence of approximately 0.7%, but
even with continued root development, an abnormally erupting canine can harm the adjacent lateral incisor.4 Ericson and Kurol reported that the
middle one-third of the root was the most likely
area to be attacked by resorption (82%) associated with ectopic eruption of maxillary canines,
followed by the apical one-third (13%) and the
cervical one-third (5%) of the root.7
KF: Is interceptive orthodontic treatment effective in the treatment of IMC?
JP: Prevention of maxillary canine impaction is
the best form of treatment and comes with the
best long-term results. The success of early interceptive treatment for impacted maxillary canines
is influenced by the amount of impaction and
patient age at treatment. Using panoramic
techniques, Ericson and Kurol found that early
extraction of primary maxillary canines may
result in normal eruption of ectopically displaced
permanent maxillary canines. They suggest that
extracting the primary canine before a patient is
11 normalizes the erupting position of the permanent canine in 91% of the cases if the crowns are
distal to the midline of the later incisor root, but
the success rate drops to 64% when the permanent canine crown is mesial to the midline of the
lateral incisor root.8
28
KF: How does the axial inclination of the unerupted canine relate to the tooth becoming
impacted?
JP: Another factor that can influence prognosis of
the IMC is canine angulation. The probability of
successful eruption of an impacted canine after
extraction of the primary canine decreases as the
horizontal angulation increases. Power and Short
stated that when the vertical angulation exceeds
31%, the chance of normal eruption after extraction significantly decreases.9 Prognosis, however,
is influenced more by the degree of canine overlap with the lateral incisor than by its angulation.
Ericson and Kurol mentioned that lateral incisor
root resorption increases when the canine cusp
tip is positioned more mesially on the lateral
root.8
KF: What are the effects on the periodontium
when an IMC is brought into proper position in
the arch?
JP: Study results have differed on the subject of
the periodontium, including gingival attachment
and bone level of recovered impacted maxillary
canines. To prevent undesirable periodontal
responses, clinicians should consider impaction
depth, anatomy of the edentulous site, and speed
and direction of the orthodontic force. Several
studies have shown that surgical exposure
and orthodontic eruption of palatally impacted
maxillary canines have only a minor impact
on the periodontium. Schmidt and Kokich discovered that open surgical exposure of impacted
maxillary canines had minimal effects on the
periodontium, and that the overall effects on
the impacted canine appeared to be better than
those from the closed exposure and early traction techniques.10 Zasciurinskiene et al. found
that surgical exposure and orthodontic extrusion
of palatally impacted maxillary canines resulted
in clinically acceptable periodontal conditions,
but these results depended on the initial vertical
and horizontal position of the impacted canine.11
PCSO Bulletin Summer 2017
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