Some Information about Conventional Periapical Radiographs
Periapical radiographs are not always accurate in assessing the spatial relationship between the root and their surrounding anatomical structures such as periradicular lesions, and the location, nature and shape of structures within the root ( for e.g. root resorption).In cases of surgical planning, the accurate establishment of the diagnostic information in the missing “third dimension” is of particular importance .Periapical radiographs from more than one direction should be taken to ensure that at least some 3D information is obtained .
Obtaining additional exposures with 10-15 degree changes in horizontal angulation is a recommended method to achieve this. To avoid multiple radiation exposures to patients ; two images from different angulations are always recorded. The most important limitation of periapical radiographs is that they do not always accurately reflect the anatomy being assessed because of the complexity of the maxillofacial skeleton . In endodontic practice, radiographs are recorded using the paralleling technique / long-cone or right-angle technique, instead of the bisecting angle technique, as it produces more geometrically accurate images.
For accurate reproduction of anatomy in the paralleling technique, the radiographic film or RVG sensor should be placed parallel to the long axis of the tooth, and the x-ray beam should be directed perpendicular both to the image receptor and the tooth being assessed. The lack of long-axis orientation results in geometric distortion of the radiographic image. Over-angulated or underangulated radiographs decrease or increase the radiographic root length , and increase or decrease the size – or even result in the disappearance – of periradicular lesions.
Under ideal conditions, approximately 3% – 5% of magnification in the radiograph should be anticipated as recording the radiograph using the parallelling technique, the tooth and the image receptor are slightly separated and the x-ray beam is slightly divergent . The use of a long focus-to-skin distance may limit, but will not eliminate this magnification.
Additional radiographs may once again be exposed in an attempt to overcome anatomical noise and to visualize endodontic lesions more clearly .The temporal perspective of the periapical radiographs is another limitation. To assess the outcome of endodontic treatment, radiographs exposed over a time period should be compared .
Pre-treatment, post-treatment and follow-up radiographs should be standardized to the utmost in respect to their radiation geometry, density and contrast in order to allow reliable interpretation of any changes in the periapical tissues that may have occurred as a result of treatment .Poorly standardized radiographs may lead to under- or over-estimation of the degree of healing or failure.
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