19.1
The paralleling technique is also known as the E=extension cone paralleling technique, the right-angle technique, or the long-cone technique. The paralleling technique is one method that can be used to expose periapical and bite-wing image receptors.
An understanding of these basic terms is necessary before learning the paralleling technique.
Term |
Definition |
| Parallel | Moving or lying in the same plane; always separated by the same distance and not intersecting. |
| Intersecting | Cutting across or through. |
| Perpendicular | Intersecting at or forming right angles. |
| Right angle | Measures 90 degrees and is formed by two perpendicular lines |
| Long axis of the tooth | An imaginary line that divides the tooth longitudinally into two equal halves |
| Central ray | The central portion of the primary beam of x-radiation, abbreviated CR. |
Principles of Paralleling Technique
The receptor is placed in the mouth parallel to the long axis of the tooth being radiographed.
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| A tooth with a highlighted root and a dashed blue line indicating the long axis of the tooth. | A molar tooth with a highlighted root within the gum, and a dashed blue line indicating the long axis of the tooth. |
The central ray of the x-ray beam is directed perpendicular to the film and the long axis of the tooth. Below is a diagram of a dental x ray setup, showing the alignment of the long axis of a tooth, a receptor holder with the receptor, and the Position Indicating Device (PID). It highlights the central ray (CR) and the target-receptor distance for optimal imaging.
A beam alignment device must be used to keep the receptor parallel with the long axis of the tooth. The image below is a collection of various colored dental beam alignment devices, each consisting of a film holder and aiming ring, used to position and align dental x-ray films accurately.
Rules must be followed to obtain accurate images. Object-receptor distance must be increased to keep the receptor parallel with the long axis of the tooth, and target-receptor distance must be increased to ensure that only the most parallel rays are directed at the tooth.
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| A dental x-ray setup with a tooth diagram indicating the long axis of the tooth, a receptor, and a receptor holder. A red line labeled “CR” (Central Ray) illustrates the alignment of the X-ray beam. | A dental x-ray setup with a tooth diagram indicating the long axis of a tooth, a receptor in its holder, and a line labeled “CR” indicating the central ray of the x-ray beam. |
Media Attributions
- Iannuci: Dental Radiography, 6th Edition, Chapter 19, CC BY-NC-ND
