Download Application of 3D Imaging to Modern Orthodontics

SUMMARIES
ANNUAL SESSION
Application of 3D Imaging
to Modern Orthodontics
Presented by Dr. Lucia Cevidanes
Summarized by Dr. William Finnegan, Northern Region Editor
maxillary asymmetry. The final diagnosis of
hemimandibular hypertrophy was really a tissue
problem where the soft tissue on one side was
thicker than the other side.
T
he concern about radiation and the cost of Cone
Beam CT imagery has faded. A Cone Beam CT
scan uses less radiation than a full orthodontic
survey. The set-up cost of digital imaging is around
$100,000, and the cost to install a Cone Beam CT unit
will be $175,000 to $185,000.
Treatment planning with 3D imaging will evaluate more
factors than linear measurements, angles, goals of occlusion and facial esthetics. The fact that we can take a
3D image model and rotate it in any direction will help
us with root positioning, impacted teeth, future of tooth
eruption, asymmetries and craniofacial anomalies. Using
the anterior surface of the cranial base for superimpositions we can more accurately evaluate growth and
treatment response.
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A young patient (four years old) was diagnosed
with microfacial microsomia. The 3D image
revealed that the patient did not have a joint
on the right side with failure of vertical growth
of the ramus. There were then four treatment
choices: distraction osteogenisis, costochondrial
graft, functional orthopedics or post-pubertal
surgical reconstruction.
•
A 9.5-year-old patient was used to describe color
mapping and segmentation. Using the whole
structure of the cranial base or just the anterior
cranial fossa for superimposition and masking
different anatomic structures we can see changes
that occur over a period of time to the anatomic
structures that we are interested in using different
colors for before, during and after images.
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A patient was first seen at six to seven years of
age. There was some question whether one was
dealing with a case of hemifacial microsomia or
mandibular fracture. The CT scan demonstrated
that the asymmetry was probably caused by an
early fracture where the ramus on one side was
narrower and shorter than the normal side. The
Cone Beam scan taken at nine years of age, after
the use of a hybrid orthopedic appliance showed
an improvement in the ramus height.
•
A patient with restricted mouth opening with
treatment planned to have a cornoidectomy until
a CT scan showed an early case of condylar
fracture where the condyle grew around the
articular eminence. The asymmetry could be
diagnosed with a pan but the CT scan also
showed that the condyle actually articulated with
the zygomatic arch.
•
A diagnostic problem wherein a patient’s bite
started to open during orthodontic treatment. The
CT scan with a new visualization tool revealed
that this was a case of rheumatoid arthritis.
Dr. Cevidanes showed the following:
1. Failure of eruption: Cases where. . .
•
The Cone Beam CT scan showed that the failure
of eruption of lower teeth was due to the teeth
developing in the direction of the lingual cortical
bone. Today these teeth would be erupted with
implant screws.
•
Permanent lower bicuspids and cuspids were
still unerupted at age 23 because the deciduous
teeth had not exfoliated. The removal of
deciduous teeth, including an abscessed
deciduous cupsid, allowed all the permanent
teeth to erupt normally.
•
A panorex view was used to place bone anchors,
but the 3D image showed a supernumerary tooth
behind the tooth of a premolar.
•
A small odontome was found attached to an
impacted canine that was to be moved into
the arch.
2. Asymmetries: Examples included cases where. . .
•
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A patient was diagnosed as having hemimandibular hypertrophy. A 3D image discovered
that it was not a mandibular problem but a
P C S O B U L L ET I N • S P R I N G 2 0 0 7
ANNUAL SESSION
The 3D imaging can be useful in evaluating treatment
responses to functional orthopedics, orthognathic surgery
and growth of the face. The use of SNA-SNB-ANB
measurements on lateral cephalograms are not adequate
indicators of treatment response because they cannot
show growth displacements as well as 3D imaging.
The increase in the lower face height, for example, can
camouflage an increase in mandibular length. Of course
other factors affect treatment timing. The peak of growth
velocity is important, but you may have to consider compliance, which might be more important before the peak.
Functional appliances such as the Herbst and Frankel
regulator 2 were investigated. The differences between
these two appliances, of course, is that the Herbst is a tooth
bone appliance and the Frankel completely tissue borne.
In the Herbst appliance, you have to wonder how much
influence growth will have in six months so that most of
the change is tooth positioning with the lower anteriors being proclined. You also have to wonder about the statement
that the Herbst will help correct anterior disk displacement.
The results with the Frankel II regulator (completely tissue
borne) showed that the disks were positioned correctly in
the articular fossa. There was some growth in the lateral
S P R I N G 2 0 0 7 • P C S O B U L L ET I N
SUMMARIES
surface of the ramus, in the superior surface of the condyles
and in the inferior border of the mandible. These changes
were significantly different from the untreated Cl II patients
and the normal occlusion growth.
Surgical changes with records taken before surgery,
immediately post-surgery and one year post-surgery are
recorded in 3D from superimpositions at the anterior
cranial fossa. The color mapping with 3D imaging shows
changes that happened pre-surgery immediately post-surgery and then six months to a year after surgery. Not only
can you measure accurately the changes to the maxilla
and mandible and the condylar position, but you can also
see the soft tissue changes. These methods of identifying
changes should also allow studies of long-term growth
changes as well as preplanning with the surgeon where
the surgical cuts will be and where the surgical segments
can be precisely placed during surgery. This will be very
important for patients with craniofacial anomalies that
need complex surgery.
Dr. Cevidanes specified that the topics that she has presented are not from research data but are only preliminary
findings that should generate a lot of future investigation.
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