Dimple-down technique The dental professional should position film using the “dimple- down” technique so that the dimple is on the mandibular side of the film for bite wing x-rays and closer to the incisal or occlusal surface for periapical films. Dimples should be facing the beam, and the tab opening for the film packet should be facing away from the beam. If the film packet faces the wrong way during exposure, the film will show a waffle-weave or herringbone effect. (This is not to be confused with grid overlays. Some periodontal offices may use the overlay on the front of the film packet to show the grid pattern on their developed film, which Paralleling techniques Different types of film positioning devices are available, making x-rays easier to take and more exact. These include bite wing adhesive tabs or loops, bite blocks, and film positioning kits. Some kits are color-coded and offer shorter positioning arms for a number of different intraoral projections, including a positioner for endodontic x-rays. With the advent of film positioning devices, most offices use the paralleling technique. This reduces distortion from possible Focal lengths The focal point of the radiation beam is emitted from the end of the tube that is farther from the patient. Tube head lengths vary from 8 to 16 in. (short-head and long-head tubes, respectively). The term long -head tube is more appropriate than long cone because cones have been discontinued. Most heads are no longer than 16 in. because film clarity is not improved with increased length and tubes longer than 16 in. are more cumbersome to maneuver. There must be a balance between the proper focal point-to-film distance and the proper object-to-film distance. A greater focal point-to-film distance, which can be achieved with a longer tube head, provides a clearer picture because there is less scatter radiation and more of the primary beam is focused on the target. Therefore, the patient is exposed to less radiation. Shorter heads (8-in. tubes) produce less-focused beams and more scatter radiation. Most tubes are at least 8 in. long because shorter lengths not only produce more radiation exposure of poor quality but also increase the likelihood that the object will be magnified on the resulting film. Magnification does not allow the entire object to be captured on the film. Changing the object-to-film distance also has an effect on magnification. The film should be as close as possible to the object in order to decrease the chance of magnification. However, the placement of rigid digital sensors is usually closer Collimation Studies have shown that rectangular collimation exposes the patient to less radiation than does circular collimation. The decreased cross-sectional surface area of a rectangular collimator is less than that of a circular collimator thus a decreased area of the patient’s tissue are being exposed to radiation (Steinberg, 2018). A 40%-50% reduction in radiation exposure has been reported when rectangular collimation is used for dental x-rays (Shetty, et al., 2019). Safelights and white-light leakage According to the American Dental Association digital intraoral radiography is used by approximately 90% of dentists in the United States (Monnin, 2021). However, this section will review the use of darkroom film processing and the use of automatic developers given their historical and continued use. Therefore, knowledge of darkroom and processing techniques continues to be important. Safelights are typically 7- to 15-W frosted bulbs. The safelight installed in the dental office must be compatible with the film
then serves as a built-in measuring device for bone height and pocket depth.) In addition to using the dimple-down technique, the practitioner should follow a consistent order when taking a full-mouth set of x-rays. This may include doing bite wing x-rays first, followed by the maxillary right side, the mandibular left side, the maxillary left side, the mandibular right side, and the anterior exposures. A consistent scheme prevents erroneous exposure and helps the practitioner remember which teeth have already been x-rayed. foreshortening and elongation, which commonly occur with the bisecting angle technique which is less precise than the paralleling technique (Lintag, et al., 2019). The paralleling technique should cause fewer errors as it is still considered the gold standard for the acquisition of periapical images (Lintag, et al., 2019; Bhatti, et. al., 2020). There may be some slight magnification of the image if the film is placed too far away from the object being radiographed. to the midline while the flexibility of conventional films allows them to be much closer to the tooth / teeth which are being radiographed (Ostrander, 2018). recommend an ideal object-to- film distance of 1.5 to 1.8 m (or about 5 to 6 feet). The farther away the film is from the object, the greater the magnification of the image. The distance from the tube to the patient’s face should also be considered. The tube should be placed as close to the face as possible. This prevents scatter to other areas of the body and results in a clearer image. Placing the tube opening against the face or the positioning ring also decreases the chance of the tube drifting. The clinician should never hold the x-ray tube, the sensor or any type of holder for conventional films during exposure of the radiograph (Vavrosky, 2020). In summation, there are three major points to remember: 1. The distance from the focal point to the end of the tube should be as long as possible (16-in. tubes are preferable to 8-in. tubes). 2. The object-to-film distance should be as short as possible to prevent magnification, with the ideal distance being 5 to 6 ft. 3. The distance from the tube to the patient’s face should be as short as possible to prevent additional scatter radiation and provide a clear film. Rectangular collimation restricts radiation to approximately the size and shape of the film or digital receptor, notably reducing the amount of radiation a patient receives. There is increased parallelism and decreased backscatter radiation when rectangular collimation is used (Steinberg, 2018). However, rectangular collimation requires precise positioning and alignment to avoid cone-cuts (unexposed portions of the film or receptor), which may require retaking the x-ray and effectively doubling the patient’s radiation exposure (Shetty, et al.,).
DARKROOM AND PROCESSING TECHNIQUES
being used. Some safelights are ruby red; some are amber (i.e., orangish yellow). Ruby red safelights are safe for use with all types of x-rays film, whereas amber safelights are not. If slower-speed intraoral film is used exclusively, an amber safelight may be sufficient. Amber light provides more visibility in the darkroom than a red safelight does. An amber safelight is usually placed about 4 ft. from the workstation where film is being developed. Amber light is not recommended for dental practices using extraoral film or high-speed intraoral film, nor is
Page 148
EliteLearning.com/Dental
Powered by FlippingBook