Approximation and contact of the maxillary central incisor roots with the incisive canal after maximum retraction with temporary anchorage devices_ Report of 2 patients

500 Chung, Choi, and Kim
Fig 8. Posttreatment intraoral photographs, radiographs, and cephalometric superimposition.
preventing potential complications, especially in
patients requiring maximum retraction.
The application of skeletal anchorage has enabled orthodontists
to effectively achieve 3D control of the anterior
teeth without the risk of losing anchorage. Thus, a
modified “envelope of discrepancy” was recently proposed,
indicating the broadened range of orthodontic
tooth movement with skeletal anchorage compared
with the original inner envelope. 2 The application of skeletal
anchorage allowed us to retract the maxillary incisors
by more than 8 mm in both patients, thus exceeding the
conventional guidelines according to the esthetic needs.
However, the basic biologic structure and the response to
tooth movement may vary among patients, and evidence
is still lacking with regard to the changes or adaptations
of the anatomic structures after the application of
advanced biomechanical techniques. When temporary
anchorage devices are applied as absolute anchorage
during en-masse retraction, greater amounts of retraction
along with anterior root movement and spontaneous
intrusion can be achieved relatively effectively
and easily compared with conventional mechanics. 21,22
Thus, the application of temporary anchorage devices
may provide biomechanical advantages in terms of
increased amounts of retraction along with torque and
vertical control of the incisors, but this may have also
aggravated the severity of the root resorption and
raised the possibilities of root approximation to the
incisive canal.
Orthodontic movement of the mandibular molars
sometimes induces temporary paresthesia when the
molars are in close contact with the mandibular canal,
9,10,23 and excessive amounts of mandibular molar
intrusion also resulted in approximation or touching of
the molar root to the inferior alveolar nerve in dogs. 11
In general, neurovascular bundles in the incisive canal
are covered by cortical bone. Similar to the structures
of the incisive canal, the mandibular canal surrounds
the inferior alveolar neurovascular bundle. But in the
mandibular molar region, cortical bone surrounding
the mandibular canal is deficient in some patients,
possibly causing temporary paresthesia in response to
mandibular molar movement. 9,24,25 Interestingly,
repositioning of the inferior alveolar neurovascular
bundles and remodeling of the canal after tooth
movement were suggested in histologic sections. 11
However, based on our 3D superimpositions, it is
apparent that the remodeling of the incisive canal was
not clinically detected after tooth movement (patient
2) and during retention (patient 1).
September 2015 Vol 148 Issue 3
American Journal of Orthodontics and Dentofacial Orthopedics