If kVp is lowered, the mean energy of the
beam decreases. This results in:
(1) an image with greater contrast
(assuming that exposure time is
(2) a beam with more low-energy photons
that carry the potential for risk but are
not useful in making an image
(3) reduced beam intensity requiring
increased exposure time, thus
increasing the risk of the patient
moving and blurring the image.
Although image diagnosis may be improved
slightly with increased image contrast (low
kVp) images, the patient dose is somewhat
reduced with higher kVp exposures. The
best balance is to use 60 to 80 kVp.
The availability of constant-potential (fully
rectiﬁed), high-frequency or direct current
(DC) dental x-ray units has made possible
the production of radiographs with lower
kilovoltage and at reduced levels of
radiation. The surface exposure required to
produce a comparable radiographic density
using a constant-potential unit is
approximately 25% less than that of a
conventional self-rectiﬁed unit operating at
the same kilovoltage. Currently several
manufacturers produce DC units.
FIG. 5-15 Radiographs of a
step wedge made at 40 to
100 kVp. As the kVp
increases, the mA is
reduced to maintain the
density. Note the long gray
scale (low contrast) with
high kVp. (Courtesy
Carestream Health, Inc.,
exclusive manufacturer of
GRANULAR CELL TUMOR: A submucosal mass
consisting of diffuse sheets of large cells of either
nerve or muscle origin, with a cytoplasm of densely
packed eosinophilic granules (lysosomal bodies) and
commonly found on the dorsal surface of the
The OKC exhibits a recurrence rate of 25%
to 60%, similar to that of an ameloblastoma.
Also known as the nasoalveolar cyst and the Klestadt
cyst, this rare condition occurs entirely in the soft
tissues of the anterior maxillary vestibule, below the
ala of the nose and deep in the nasolabial crease .
Most of these cysts occur in the fourth and ﬁfth
decades of life and have a female predilection of
approximately 3 to 1.
NASOPALATINE DUCT CYST (INCISIVECANAL CYST)
The nasopalatine duct cyst is the most common non-
odontogenic cyst of the oral cavity. occurring in about I% of
MEDIAN PALATAL (PALATINE) CYST
The media n palatal cyst is a rare fissural cyst that
theoretically develops from epithelium entrapped
along the embryonic line of fusion of the lat eral
palatal shelves ofthe maxilla . This cyst may be
difficult to distinguish from a nasopalatine duct cyst.
In fact . most "median palatal cysts" may represent
posteriorly positioned nasopalatine duct cysts.
Because the nasopalatine ducts courseposteriorl y
and superiorly as they extend from the inci-
The radiosensitivity of a tissue or organ is measured by its response to irradiation. Loss
of moderate numbers of cells does not affect the function of most organs. However, with
the loss of large numbers of cells, all affected organisms display an observable result. The
severity of this change depends on the dose and thus the amount of cell loss.
The following discussion pertains to the effect of irradiation of tissues and organs when
the exposure is restricted to a small area. Moderate
The response of cells, tissues, and organs to irradiation depends on exposure conditions
and the cell environment
Three methods exist for minimizing this
loss of image clarity and improving the
quality of radiographs:
1. Use as small an effective focal spot as
2. Increase the distance between the
focal spot and the object by using a
long, open-ended cylinder.
3. Minimize the distance between the
object and the ﬁlm.
The purpose of ﬁltration is to remove the low-energy x-ray photons
selectively from the x-ray beam. This results in decreased patient
exposure with no loss of radiographic information.
When an x-ray beam is ﬁltered with 3 mm of aluminum, the surface
exposure is reduced to about 20% of that with no ﬁltration. In light of
this and other information, the federal government has designated the
speciﬁc amount of ﬁltration, expressed as minimum half-value layer,
required for dental x-ray machines operating at various kilovoltages.
Practically, these requirements can be met by having 1.5 mm Al total
ﬁltration when operation from 50 to 70 kVp and with 2.5 mm Al total
ﬁltration when operating above 70 kVp
Occasionally it is desirable to obtain radiographs of a woman who is pregnant.
The x-ray beam is conﬁned to the head and neck region in dental x-ray
examinations; thus, fetal exposure is only about 1 microgray (μGy) for a full mouth
examination. This exposure is quite small compared with that received normally
from natural background sources. However, concerns have been raised about a
possible relationship between maternal radiation dose to the thyroid gland from
dental radiographs and low birth-weight babies, prompting the ADA to recommend
the use of protective thyroid collars and aprons during dental radiography,
especially of children, women of childbearing age, and pregnant women. Because
the use of radiographs in all patients is predicated on there being a diagnostic need
for them, the guidelines apply to patients who are pregnant as well as those who