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CHAPTER 1
DENTAL RADIOLOGY
INTRODUCTION
The purpose of dental radiography is to record
images of a patient's oral structures on film by using
X-rays. When the X-ray films are processed, the
resulting radiographs provide the dental officer with a
valuable diagnostic aid. In the case of death,
radiographs can be used to aid in identification as
discussed in chapter 10, "Forensic Dentistry."
The first section of this chapter covers the basic
fundamentals of dental radiography. Included are the
physics and biology of radiography.
Since X-radiation can be harmful, you must
observe certain safety precautions when using an
X-ray machine or working in an area where one is
being used. These precautions are covered in the
second part of this chapter.
The major portion of this chapter is devoted to
explaining how to operate a dental X-ray machine,
expose intraoral radiographs (radiographs taken inside
the patient’s mouth), process the X-ray films, and
mount the finished radiographs.
The last part of this chapter covers the panoramic
X-ray machine, which you will use to make extraoral
radiographs (radiographs made outside the patient’s
mouth).
FUNDAMENTALS OF DENTAL
RADIOLOGY
Oral radiography is the art of recording images of a
patient’s oral structures on film by using X-rays
(roentgen rays). The rays were recognition of
Wilhelm Konrad Roentgen, a scientist, who first
discovered X-rays in 1895. While experimenting with
a device called a Crookes tube, which generated
cathode rays, he noted that a photographic plate
completely wrapped in black paper and lying near the
tube was fogged when developed. He realized that
some form of invisible ray, able to pass through the
black paper, must be coming from the tube. Later,
while in his darkened laboratory, he noticed that a
fluorescent screen located six feet away was glowing.
He knew that the cathode rays could travel only short
distances outside the cathode tube and realized he was
1-1
observing a new, unknown ray, which he called an
X-ray because the symbol "X" is used for the
unknown in mathematics.
The first dental radiograph was taken the same
year by Dr. Otto Walkoff. Within 10 years,
radiographs were being used for diagnosis of medical
and dental conditions, for X-ray therapy, and- for
scientific studies. Although technology over the years
has made tremendous improvements in X-ray
equipment, the basic concepts are the same.
Like visible light rays, X-rays are electromagnetic
rays that travel in a wave motion. The measurement of
this wave motion is called a wavelength. The basic
difference between X-rays and other electromagnetic
rays is in their wavelength. X-rays have an extremely
short wavelength, which enables them to penetrate
matter that usually absorbs or reflects light or other
electromagnetic rays with longer wave-lengths.
Although X-rays share the properties of other
electromagnetic rays, their action is considerably
different. Some of the characteristics and properties of
X-rays are:
They travel in straight lines at the speed of light.
They affect photographic film by producing a
hidden image made visible by processing.
They cause certain substances to fluoresce
(glow).
They cause irritation of living cells and, in large
amounts, can cause necrosis (death) of the cells,
a fact that necessitates caution in using X-rays.
X-rays are produced when a metal (tungsten)
target is bombarded by a stream of electrons. The
X-rays are emitted in the tubehead and directed by the
tubehead cone through the subject, producing an
image on the film.
The density of the X-ray image is controlled by
four factors: kilovoltage (kVp), exposure time,
milliamperage (mA), and target-film distance (TFD).
All of these factors are interrelated and may be varied
by the operator. The procedures for setting these
factors will be discussed later.
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