This arrangement inherently causes distortion. However, when the image receptor is in this position, it is not parallel to the long axes of the teeth. In this method, the image receptor is placed as close to the teeth as possible without deforming it. An early method for aligning the x-ray beam and image receptor with the teeth and jaws was the bisecting-angle technique ( Fig. In Oral Radiology (Seventh Edition), 2014 Paralleling and Bisecting-Angle Techniquesįrom the earliest days of dental radiography, a clinical objective has been to produce accurate images of dental structures that are normally visually obscured. This problem can be solved by incorporating dyes into the base that absorb the light emitted by the screens. When intensifying screens are used, parallax distortion contributes to image unsharpness because light from one screen may cross the film base and reach the emulsion on the opposite side. Because dental film has a double coating of emulsion and the x-ray beam is divergent, the images recorded on each emulsion vary slightly in size. Parallax results from the apparent change in position or size of a subject when it is viewed from different perspectives. The presence of an image on each side of a double-emulsion film also causes a loss of image sharpness through parallax ( Fig. Diffusion of light from a screen can be minimized and image sharpness maximized by ensuring as close a contact as possible between the intensifying screen and the film. Fast intensifying screens have a relatively thick phosphor layer, which contributes to dispersion of light and loss of image sharpness. Intensifying screens with large crystals are relatively fast, but image sharpness is diminished. The spreading light causes a blurring of fine detail on the radiograph. Some degree of sharpness is lost because visible light and UV radiation emitted by the screen spread out beyond the point of origin and expose a film area larger than the phosphor crystal (see Fig. Use of intensifying screens in extraoral radiography has an adverse effect on image sharpness. In general, slow-speed films have fine grains, and faster films have larger grains. With intraoral dental x-ray film, the size and number of the silver grains in the film emulsion determines image sharpness: the finer the grain size, the finer the sharpness. In Oral Radiology (Seventh Edition), 2014 Image Receptor Blurring In the case of injuries involving body fragmentation and/or resected maxillary and mandibular structures, unusual orientations not encountered in living patients can occur. This begins with the unique orientation that often occurs in the forensic dental autopsy and the orientation of the dental structures and projection geometry relative to the beam, specimen, and image media (film/digital). There are, however, several radiographic errors that are more likely to occur in a forensic dental setting when compared to routine dental practices and services. There are numerous benefits both emotionally and often financially to all concerned in carrying this process to fruition. In addition, the forensic dentist may provide the fastest and most economical means of accurate victim identification in this process. This is at the core of the tasks demanded in forensic odontology. Weems, in Forensic Odontology, 2018 Most Common Pitfalls in Forensic Odontology Radiography Practices Spatial Orientation of the Image/Projection GeometryÄental radiography in the process of human dental identification is a cornerstone in the techniques of establishing a positive comparison and, thus, the dental identification of a deceased individual.
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