Why does some magnification occur with paralleling technique?

• A. Long PID Reduces Magnification
• B. Receptor Not Right Behind Tooth
• C. Receptor Behind Tooth
• D. Tooth Tilted

Answer: (B)

Magnification in radiography mainly comes from geometry: the farther the tooth is from the receptor, the larger the image becomes. In paralleling technique, the receptor should sit as close to the tooth as possible and directly behind it, with the X-ray beam perpendicular to both. If the receptor is not directly behind the tooth, the distance from tooth to receptor increases, causing the image to magnify. That’s why some magnification occurs. The other points describe ways to reduce magnification or relate to distortion, but the key reason at play here is the receptor not being right behind the tooth.