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).
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 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.Continue Reading