In the paralleling technique for maxillary canine periapical radiographs, why is the receptor kept parallel to the tooth?

In the paralleling technique for maxillary canine periapical radiographs, why is the receptor kept parallel to the tooth?

• A. To reduce contrast
• B. To decrease exposure time
• C. To avoid magnification
• D. To maintain image geometry with the central ray perpendicular to the receptor

Answer: (D)

The essential idea is preserving geometric accuracy in the image. In the paralleling technique, keeping the receptor parallel to the tooth and directing the x-ray beam so it is perpendicular to that receptor ensures the tooth is projected straight onto the receptor without angle-related distortion. When the receptor and tooth share the same alignment and the beam hits at 90 degrees to the receptor, there’s no elongation or foreshortening, so the tooth’s true size and relationships—the crowns, roots, and especially the apex—are shown accurately. If the receptor were not parallel or the beam not perpendicular, parts of the tooth would appear longer or shorter than they really are, compromising diagnostic usefulness.

The essential idea is preserving geometric accuracy in the image. In the paralleling technique, keeping the receptor parallel to the tooth and directing the x-ray beam so it is perpendicular to that receptor ensures the tooth is projected straight onto the receptor without angle-related distortion. When the receptor and tooth share the same alignment and the beam hits at 90 degrees to the receptor, there’s no elongation or foreshortening, so the tooth’s true size and relationships—the crowns, roots, and especially the apex—are shown accurately. If the receptor were not parallel or the beam not perpendicular, parts of the tooth would appear longer or shorter than they really are, compromising diagnostic usefulness.