Dental Radiographic films – During the packaging process, the film is first encased in black paper, which protects it from any light that might leak into the packet. Then, a piece of lead foil is placed on one side of the film, and it is covered with a moisture-proof paper or thin flexible plastic. The lead shield is placed on the side of the film that is away from the primary beam. Its purpose is to absorb what is known as back scatter radiation.
This is radiation that has passed through the tissue and the film and gone to other areas of the mouth. Some of the radiation would scatter or bounce back toward the film and cause overexposure if the shield was not there to filter it out.
Description of Film
Dental film has a clear or blue tined polyester. It is coated on both sides with an emulsion (a light sensitive photographic mixture). A special adhesive is used to hold the emulsion to the film base. The emulsion is made up of silver halide crystals suspended in gelatin, which holds the crystals evenly distributed over the film base. Halide is composed of bromine and iodide with the chemical elements silver and potassium.
The size of the crystals determines the speed with which the emulsion reacts to the X-rays. The larger the size of the crystals, the faster the emulsion is affected by radiation and the shorter the time of exposure. This is called film speed or film sensitivity. The Radiographic films are rated according to its speed and sensitivity. A is the slowest (least sensitive) and F is the fastest. Currently, Ultra-speed (D) or Ektaspeed (E) are the fastest films used. They we reduced the amount of exposure time to fractions of seconds.
A raised dot in one corner is helpful in mounting the film for interpretation by the dentist and in film placement when taking radiographs. Most often, the dot is placed at the occlusal or incisal edge of the teeth so that it does not interfere with the apical, or tissue, areas in the radiograph. The raised dot faces the X-ray source.
CARE OF RADIOGRAPHIC FILMS
Dental X-ray film needs special handling and care because
• It is light sensitive.
• It is sensitive to secondary and scattered X-radiation,
• Like photographic film of camera, it has an expiration date referred to as “shelf life.”
• Fingerprints and fingernail scratches can ruin a film’s diagnostic value.
• It is easy to mix up patients’ films when several patients’ radiographs are developed at one time.
• They can be misplaced in other patients’ charts.
• Films are part of the legal records of the patient.
Sensitivity to Light and Other Radiation
The problem of light sensitivity is handled in two ways. First, the film is stored in a dark, cool place, and the exposed film never opened until the darkroom door is secured and the safety light is on.
Secondly, when a supply of films is kept in the room where the radiographs are exposed, it should be in a lead-lined box to protect it from scattered and secondary radiation. Only the numbers of films, needed for particular patient’s radiographic examination, are removed.
After expiration date, the chemicals in the emulsion of the film may become weak and not useful for taking a good radiograph. Film, if ordered in large quantities, may be stored in a refrigerator, which lengthens the shelf life for an undetermined length of time. Remember to remove needed film from the refrigerator before you plan to use it so it warms to room temperature.
Proper Handling and Labelling
Whenever you need to hold the film during mounting, or when you are removing it from the packet during processing, hold the film gently by the edges. This will prevent an accidental scratch by a fingernail or oily fingerprints.
For proper identification of films each film must be labelled with the patient’s name and the date the radiograph was taken.
Legally, films must be kept for at least five years for the following reasons:
1. To identify deceased persons.
2. To serve as legal protection (evidence in court).
3. To show the necessity of the procedure done and its outcome.
4. To compare conditions or progress of treatment or disease.
The radiograph is legally the property of the dentist. It should not be given to the patient. The patient may argue that he or she paid for it, but the patient paid for the dentist’s interpretation and diagnosis, not the film. A copy can be mailed to a specialist in case of referral or if the patient wants another opinion.
TYPES OF RADIOGRAPHS
Radiographs are intraoral or extraoral. The Bite- wing (BW), periapical (PA), and occiusal (0cc) radiographs are examples of intraoral films. The extraoral films are the panoramic and cephalometric (cephalogram) radiographs.
FULL MOUTH SURVEY (FMX)
The full mouth survey consists of 14 to 19 individual films, depending on the size of the film used for anterior films and if bite-wings are also taken. There are several different sizes of intraoral films, which are used for different purposes.
For FMX generally the following pattern is followed so that no area is missed or double exposed:
• Anterior. 6 Periapical films having three maxillary and three mandibular.
• Bite-wings. 4 films with two on each side.
• Posterior 8 films with two maxillary right, two mandibular right, two maxillary left and two mandibular left.
This series is only taken if the doctor feels overall conditions in the patient’s mouth need a more complete examination than is possible with a mirror and explorer.
NEW IMAGING TECHNIQUES
New technology has brought new ways to examine oral tissues and the teeth. Xeroradiography is a new method of recording Xray images on an electrically charged plate (not film). It combines X-ray exposure with the same technology used in the office copy machines to produce a photographic image rather than the transparent radiograph. No darkroom processing is needed.
This method uses a sensor placed in the mouth to project the X-ray image onto a computer screen. It can then enlarge the image or any part of it and print out a picture for patient education, record, and for diagnostic and treatment planning. The images taken so can also be stored on computer hardware. This tecimique is discussed in details in chapter 50 of this book.
Nuclear magnetic resonance (NMR) imaging (also known as MM) is used in medicine to show slices of body tissues, bones, and the brain without the use of X-radiation. It is being studied for possible application in dentistry.
Though exposure to X-radiation is being reduced in some of these new methods, the technology is very expensive.