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Intraoral Radiography: Principles, Techniques and Error Correction

Gail F. Williamson, RDH, MS

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Prior to presenting technique errors and the means to correct them, a clear understanding of technique must be established. Although the bisecting angle technique is still utilized by some practitioners, the paralleling technique is the method of choice for intraoral radiography because it follows the majority of the shadow-casting principles.

Paralleling Technique

The paralleling technique is the most accurate intraoral radiographic technique, meeting four of the five shadow-casting principles. The paralleling technique does not allow for a short as possible object-to-receptor distance (Principle Three). This technique produces truer images that are preferred for diagnostic quality. Due to the use of film-holding devices, the paralleling technique is also easy to standardize and execute.

The paralleling technique is accomplished by placing the receptor parallel to the long axis of the tooth. After this parallel relationship has been established, the central ray must be directed perpendicular to both the tooth and receptor. Because the receptor cannot always be placed as close as possible to the tooth due to the film-holding device, image magnification may occur. However, this can be compensated for by using an increased source-object distance, which decreases magnification and unsharpness. The paralleling technique, when performed correctly, is superior to the bisecting angle technique by producing an image with both linear and dimensional accuracy.

Bisecting Angle Technique

The bisecting angle technique is accomplished by placing the receptor as close to the tooth as possible. The central ray of the x-ray beam should be directed perpendicular to an imaginary line that bisects the angle formed by the long axis of the tooth and the plane of the receptor. Principle Three of shadow casting is met by using this technique.

Images produced by the bisecting angle method are in true linear relationship. However, this technique does not follow several of the shadow-casting principles and also requires extensive visualization of the bisected angle in order to accomplish it properly. Bisecting angle images are not anatomically accurate and are prone to shape distortion. However, bisecting angle provides an alternative technique when parallel placement cannot be achieved.

Bitewing Technique

The bitewing radiograph is used to examine the interproximal areas of the teeth and is particularly useful for the detection of dental caries and alveolar bone levels. The receptor is placed into the mouth parallel to the crowns of the maxillary and mandibular posterior teeth. The patient stabilizes the receptor by biting on a tab or bitewing holder. The horizontal angle of the x-ray beam is then directed through the contacts of the posterior teeth and at a +5º to +10º vertical angle.

Film-holding devices or bitewing tabs may be used to stabilize the receptor in the mouth. Receptors may be positioned in the horizontal or vertical dimension with this technique, depending upon the area to be examined. Bitewings may be taken in the anterior segments of the dentition as well. Some dentists, particularly periodontists, may prescribe a 7 image bitewing survey consisting of 4 vertical bitewings in the posterior with size 2 receptors and 3 vertical bitewings in the anterior using size 1 receptors. This permits evaluation for both the bone levels and caries detection.

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