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EDITORIAL
THE PUSH/PULL SURROUNDING
CONE BEAM COMPUTED
TOMOGRAPHY (CBCT)
By Dr. Gerald Nelson, Editor in Chief, PCSO Bulletin
W
ith CBCT, orthodontists are faced with
a rapidly developing technology that
stimulates interesting discussion
among colleagues and the general
public. Do you feel that you are being pressured
into ordering 3D radiograms for your patients? The
following are comments heard on the street:
•
UCSF takes a 3D scan three times on every patient.
•
A recent New York Times article criticizes orthodontists who take a CBCT on every patient.
•
In our 2D Berkeley practice, several patient families have mentioned the article in worried tones.
•
Recent studies have shown that diagnosis and
treatment planning of impactions is enhanced
with use of 3D images.
•
A paper in the American Journal of Orthodontics
and Dentofacial Orthopedics (AJO-DO) exhibits
“Four Curious Cases” in which 2D x-rays were
inadequate to screen for important findings.
•
A PCSO Southern Region presentation by
Dr. Mah and Dr. Hatcher showed many cases
in which the use of CBCT was critical to the
treatment planning.
Most readers were not in the field at the time of
the revolutionary introduction of the cephalometer
to orthodontics. The controversy in the specialty
around the routine use of lateral headfilms was no
less confusing or passionate than what we are currently witnessing for CBCT. The radiation dose for
headfilms and the number taken in the early years is
surprising today. According to orthodontic historian
Norman Wahl, T. Wingate Todd (the originator of the
SPRING
2011 • PCSO Bulletin
Image from Kodak 9500
cephalometer) and his assistant, B. Holly Broadbent Sr.,
exposed more than 4,500 children annually, “thus establishing standards of normal development at any period
of childhood.” Dr. Broadbent introduced the technique
to the specialty in 1931. The article, “A New X-Ray Technique and Its Application to Orthodontics,” is available
as a free download at the Online Angle Orthodontists,
www.angle.org. (Volume 1, Issue 2). It took many years
before the specialty accepted the routine use of lateral
headfilms in orthodontic diagnosis.
CBCT AND DIAGNOSIS
A
study done at UCSF by Dr. Erik Haney (Fairfax, CA)
in 2009 involved orthodontists and oral surgeons
reviewing stations with 2D and 3D images of canine
impactions. Twenty-five impacted teeth had had both
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EDITORIAL
types of x-rays, which were distributed around the
room randomly. Of the treatment plans for extraction of the impacted tooth using the 2D images, 53%
were changed to recovery when viewed in 3D. The
recommended vector of force application also differed
between the two image techniques. Since then, other
studies have confirmed the value of 3D scans for
impacted teeth.
Another study at UCSF confirmed the value of 3D
scans to evaluate root positions achieved with orthodontic appliances. We know that a 2D panogram has
serious distortions when evaluating root positions.
The patient benefit of using CBCT is established. The
question is, when should you employ the technique?
One suggestion is to first take a 2D pano and ceph and
then use these films to make a decision to take the
3D scan. This approach has some merit, and there are
a couple of machines available that can do both the
2D and 3D image. However, the “Four Curious Cases”
presented in the April 2010 AJO-DO are a bit unnerving, as the 2D image missed some problems.
LIABILITY
R
isk is an issue. A primary risk is that you will
miss something important in your diagnosis with
2D. When a disgruntled patient goes to an attorney
to take action against an orthodontist, the typical first action is to order a CBCT scan to see if any
pathology was missed. The second risk is a less than
ideal treatment plan, since we know that treatment
plans change with the benefit of 3D images. The third
liability is the responsibility to detect pathology in
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the entire 3D volume (not to diagnose every aberration,
but to notice and refer when appropriate). We handle
this at UCSF by ordering radiologist reports. These
reports are very instructive, and after reviewing a few
dozen of them, one becomes quite comfortable evaluating the image on one’s own. Of course, we have similar
responsibilities with 2D images. A lateral headfilm
and panogram can reveal obscure pathologies that we
should be ready to notice. The concern of one’s responsibility for the 3D images will fade as we become more
comfortable with reviewing the images. As Dr. Hatcher
says, the key is the software. Current programs are easy
to use, and getting better every year.
RADIATION DOSE
R
adiation is a concern, and the public is alerted to
this issue. For the orthodontist in private practice,
this means educating the patient family when a 3D
x-ray is proposed. In fact, the radiation dose from 3D
scans is not out of line, taking into account the benefits.
Doses these days are under 200 microsieverts, which is
comparable to an orthodontic 2D series that includes a
full-mouth series of x-rays.
FINAL THOUGHTS
O
rthodontists must recognize that this technology
offers important benefits to the patient, and we
need to move toward utilizing CBCT on all our patients—
and developing our diagnostic skills appropriately. The
technology offers an excellent tool to improve our treatment plans and avoid missing important pathology in
our patients.
S
PCSO Bulletin • SPRING
2011