Pacific Coast Society of Orthodontists Bulletin Summer 2020 - 65

Presentation Summary

Presentation Summary

Root Resorption and Class II
Correctors: Updates for the Clinician
Dr. Bruce P. Hawley
PCSO Bulletin Contributor
Dr. Glenn T. Sameshima
University of Southern California,
Los Angeles

Presented by Dr. Glenn T. Sameshima at the Washington State Society of Orthodontists Meeting, Feb.
14, 2020
Is Root Resorption a Problem?
Statistically, root resorption is involved in 17% of
the claims made to the American Association of
Orthodontists Insurance Company. According to
Andreasen, there are three types of root resorption: (1) surface resorption, which occurs on the
side of the tooth and is both self-limiting and
reversable; (2) replacement resorption, in which
the dental hard tissue is replaced by bone, with
fusion occurring as in dental trauma; and (3)
inflammatory resorption. Clinically, internal root
resorption occurs inside the pulp, while external root resorption can occur either cervically or
apically.
External apical root resorption (EARR) is unique to
orthodontics. Tooth movement is a process of resorption and apposition, but it is reversible unless
it takes place at the apex of the root (rather than
on the side of the root or tooth). External root
resorption is the irreversible shortening at the
apex of the root. Movement at the root end can
involve intrusive, extrusive, bodily, or rotational
movement and may occur at the point where
maximal orthodontic force is applied. The root
apex does not have a smooth topography, and
the cementum hardness decreases closer to the
apex. There is also a probable relationship to the
root apex as it is at the end of the pulp canal, and
there can be multiple foramina. The theory of
EARR as a defense mechanism that protects the
neurovascular bundle from damage as the apex is
moved orthodontically really does make sense.
Severity of EARR
The most commonly resorbed teeth in descending rank order are the maxillary lateral incisors,
maxillary central incisors, maxillary canines, and
the six mandibular anterior teeth. For the maxillary anterior teeth, there is an average of 1.5 mm
of resorption after orthodontic treatment. This
can be considered a "normal" outcome, which is

Summer 2020    PCSO Bulletin	

often barely visible on a panoramic x-ray but can
be seen more clearly on periapical x-rays. There
is an average of less than 1 mm of resorption for
the mandibular incisors and canines. No general
consensus exists on what constitutes severe
resorption, but for a root with a normal length,
less than 2 mm might be considered mild, 2 to 4
mm moderate, and greater than 4 mm severe.
About 5% of treated cases have greater than 4
mm of resorption for the maxillary incisors and
canines.
Why are the maxillary lateral incisors the most
commonly resorbed teeth?
Possibilities include that these teeth are often
disproportionately small or narrow, have narrow
roots, are frequently dilacerated or peg/barrel
shaped, and have a more distally located tip, so
they may require more movement in three planes
of space. Three-dimensional (3D) studies tend
to support the canine guidance theory, which
says that the maxillary canines are guided by the
roots of the maxillary lateral incisors in erupting.
Small and peg laterals tend to be associated with
canine impactions, with chunks resorbed by the
canine crowns. Although it does not show on a
two-dimensional (2D) x-ray, this resorption can
take place on the palatal aspect of the lateral
roots. There tends to be a lot of resorption in
cases where the canine tip is closer to the midline
of the dental arch. Extraction of the maxillary
primary canines for mesially oriented maxillary
permanent canine crowns is supported by three
Cochrane systematic reviews. Sometimes there
is a question as to whether the resorption can be
attributed to a dental follicle or a cyst around the
crown of the maxillary canine. A true follicular or
dentigerous cyst will often displace the adjacent
teeth rather than resorbing them. Typically,
a dental follicle is responsible in cases where
the canine has a "cystic" appearance. In these
instances, it is appropriate to obtain a 3D image
to assess the damage, and then to remove the
primary canine and expose the permanent canine
crown, which eliminates the dental follicle in the
process.

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Pacific Coast Society of Orthodontists Bulletin Summer 2020

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