III. Dental Radiographic Installations
III-l. Introduction
Many items discussed in the Medical Radiographic
Installation Section, Section I, are applicable to dental
x-ray units.
Pages 45-47 contain a checklist of the
physical parameters which
evaluation and the
information important to the
require
radiation protection survey
of dental radiographic installations. While this
section's checklist is
complete,
only information and
parameters unique to dental installations are discussed
here.
Dental radiographic equipment can be divided into
three major categories:
intraoral, cephalometric, and
panoramic systems. The panoramic
x-ray
system is a
tomographic unit unique to dentistry.
It usually has a
fixed SID in the range of 18" to 22" (45-56 cm) and an
exposure time of 15 to 25 seconds. The radiation beam is
usually collimated with two slit collimators,
one at the
end of a short
cone attached to the x-ray tube and the
other in front of the image receptor.
The intraoral system uses small image receptors which
are held in place by the patient's teeth during the
exposure.
Therefore, this unit has no attached image
receptor holder.
Normally,
the x-ray beam is collimated
by a cylindrical cone.
The cephalometric unit
may be dedicated or may
consist of an intraoral x-ray tube assembly attached to a
mechanical device which supports the image receptor. The
image receptor normally is 8"
x 10"
(18 cm x 24 cm) in
size; the SID is from 60" to 65" (152 to 165 cm).
III-2. Beam-On Controls and Indicators
With the exception of the comment
on cut film
changers,
all the statements of
dental radiographic installations.
Section I-3 apply to
In
addition to
surveying the unit, the physicist should verify that the
operators are using
cord properly.
the exposure time and the exposure
Manually terminating
the
releasing the
deadman
exposure switch or not
exposure by
far away from
standing as
possible error.
the x-ray source as possible are two
III-3. Minimum Source Skin Distance: Intraoral Unit
The minimum x-ray source to skin distance (SSD) of a
dental unit used with intraoral image receptors shall be
18 cm (7") if the unit is operable above 50
kVp
(Reference
#1). If the unit operates at or below 50 kVp, the minimum
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