In paralleling technique, where should the central ray be aimed?

In paralleling technique, where should the central ray be aimed?

• A. Angled mesially toward the crown.
• B. Perpendicular to the occlusal plane.
• C. Parallel to the receptor and the tooth's long axis.
• D. Perpendicular to the receptor and the tooth's long axis.

Answer: (D)

In paralleling technique, you place the receptor parallel to the tooth’s long axis and direct the x-ray beam so it is perpendicular to the receptor. Because the receptor is aligned with the tooth, this also makes the central ray perpendicular to the tooth’s long axis. This perpendicular alignment prevents distortion, yielding a true-size image. If you angle the beam toward the crown or along the occlusal plane, distortion occurs. So the central ray should be aimed perpendicular to the receptor (and, by placement, to the tooth’s long axis).

In paralleling technique, you place the receptor parallel to the tooth’s long axis and direct the x-ray beam so it is perpendicular to the receptor. Because the receptor is aligned with the tooth, this also makes the central ray perpendicular to the tooth’s long axis. This perpendicular alignment prevents distortion, yielding a true-size image. If you angle the beam toward the crown or along the occlusal plane, distortion occurs. So the central ray should be aimed perpendicular to the receptor (and, by placement, to the tooth’s long axis).