X-RAY FILM AND DIGITAL RECEPTORS
The use of high-speed film, rare-earth intensifying screens, digital radiography, rectangular collimation, and long tubes has advanced the field of dental radiology. In addition, these and Intraoral film Most intraoral film comes in waterproof packets. Inside the packet, the film is wrapped in black paper to further protect it from light. The wrapper has a lead foil sheet behind it to decrease the chance of film fog from secondary radiation. This foil also decreases secondary radiation to areas behind the film target (e.g., the tongue). Intraoral film comes in single- and dual-film packs. Different film sizes are listed in Table 1. Table 1: Intraoral Film Sizes (in inches) Size 0 Pedodontic 7/8 × 1 3/8 Size 1 Narrow anterior periapical 1 5/16 × 1 9/16 Size 2 Standard periapical or bite wing 1 1/4 × 1 5/8 Size 3 Bite wing 2 1/8 × 1 1/16 Size 4 Occlusal 2 1/4 × 3 Extraoral film and projections In addition to intraoral film, there are a variety of extraoral film projections. Extraoral film is typically placed in hard or soft cassettes for exposure. For some extraoral film projections, a metallic grid may be placed between the object being x-rayed and the film cassette to reduce secondary radiation and provide a clearer image. Panoral, panoramic, and tomographic films are typically 5 in. × 12 in. and should be marked to identify the right or left side of the patient’s face before exposure. Cephalometric film is typically 8 in. × 10 in. Cephalometric radiographs are used for a variety of extraoral x-ray projections. The lateral cephalometric projection is common for orthodontic evaluations and is taken with the patient’s left ear near the film cassette. The patient’s ala-tragus line (i.e., the ala of the nose to the tragus of the ear) should be parallel to the floor. The posteroanterior (PA) projection has the patient facing the film, with the patient’s nose touching the film and the x-ray beam traveling from the posterior to the anterior – hence, the name posteroanterior. The patient directly faces the film so that his or her ala-tragus line (or occlusal plane) is parallel to the floor. The Waters’ projection is similar to the PA projection except that the patient’s chin is tilted upward so that it, rather than the nose, touches the film cassette. The Waters’ projection shows the zygoma, the maxillary and frontal sinuses, and the nasal septum. The reverse-Towne projection is also similar to the PA projection except that the patient’s chin is tilted downward so that the forehead, rather than the nose, touches the film. The reverse- Towne projection shows the structures of the inner ear; if the patient’s mouth is open wide during the exposure, the condyles and neck of the condyles can also be inspected for fracture or displacement (Chopra, et.al., 2020). Digital receptors Compared with conventional dental film, digital imaging can reduce a patient’s radiation exposure by up to 90% compared to E-speed films (Monnin, 2021). There are three kinds of digital sensors: charge-coupled devices (CCDs), complementary metal- oxide-semiconductor (CMOS) receptors, and photostimulable phosphor (PSP) receptors. Two of these, CCDs and CMOS sensors, are solid-state detectors that, upon being irradiated, send image data directly to a computer, with the resulting image appearing on the computer screen. These are called direct receptors. When PSP receptors are irradiated, a latent invisible image is created in the receptor, which is then scanned by a
other technologies and techniques have cut radiation exposure dramatically.
The three standard film speeds for dental radiography are D-speed, E-speed, and F-speed, with D-speed being the slowest and F-speed the fastest. In its guidelines for patient selection and limiting radiation exposure, the American Dental Association (ADA) Council on Scientific Affairs included the following statement: According to the U.S. Food and Drug Administration, switching from D to E speed can produce a 30 to 40 percent reduction in radiation exposure (United States Food and Drug Administration, 2017).The use of F-speed film can reduce exposure 20 to 25 percent compared to use of E-speed film, without compromising diagnostic quality (Issrani, 2017). Many film types have a shelf life of about two years and should be stored away from excessive heat and radiation sources, including sunlight. The submentovertex projection is the reverse of the Waters’ projection. The patient is facing the x-ray beam with the film facing the back of the patient’s head. The patient’s chin is lifted so that the top of the head touches the film cassette. Unlike the preceding projections, which direct the beam perpendicular to the film cassette, the submentovertex projection directs the x-ray beam upward from an angle below the mandible. The submentovertex projection shows the zygomatic arches (especially if fractured), the condyles, and the sphenoid sinuses (Saha, 2016; Murphy 2021). Another common extraoral projection is the lateral oblique projection. Orthopanoramic and posteroanterior radiographic surveys of the mandible are usually utilized to determine the presence of a mandibular fracture. However, lateral oblique radiographs can still be of diagnostic utility in determining the presence of a mandibular fracture when the other radiographic surveys are inconclusive (Hong, 2016). The use of the lateral oblique projection is often used to examine the ramus or the body of the mandible when an image with greater resolution is required (Yildirim, et. al., 2017).The patient’s head is tilted toward the side being examined. The patient holds the film cassette against the cheek on the side being examined. The beam is angled from the opposite side of the face below the border of the mandible and pointing upward. Angling in this way prevents both sides of the mandible from being superimposed on the film. If the beam is angled midway on the opposing mandible, the body of the mandible will appear with the molar- premolar region on the film. If the beam is positioned more anteriorly to the midpoint of the mandible, the more distal part of the mandible, including the wisdom teeth, ramus, and condyles, should be visible on the film. laser to produce a digital radiograph. PSP receptors are called indirect. Digital receptors have a wider dynamic range (the ability to record information over a wider range of x-ray exposure values) than do film-based receptors. Digital radiographs can be digitally processed to correct exposure problems, resulting in fewer retakes. It is possible to manipulate contrast and density, as well as adjust image noise and artifacts (Huff, 2107). Digital radiography offers other advantages such as eliminating the need for a darkroom, associated chemicals, and other consumables, including film.
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