Intraoral Imaging Techniques
Mastering Angulation and Placement
🎯 Learning Objectives
- Identify the 5 Basic Rules of the Paralleling Technique.
- Understand the difference between Vertical and Horizontal angulation.
- Differentiate between the Paralleling and Bisecting techniques.
- Identify the “PID” and its role in directing the central ray.
1. The Paralleling Technique
This is the Standard of Care in dental radiography. It is called “paralleling” because the sensor is placed parallel to the long axis of the tooth, and the central X-ray beam is directed perpendicular (at a 90-degree angle) to both.
The 5 Rules for Success:
- Placement: Sensor must cover the specific teeth being examined.
- Position: The sensor must be parallel to the tooth’s long axis.
- Vertical Angulation: The central ray must be perpendicular to the tooth and sensor.
- Horizontal Angulation: The central ray must be directed through the contact areas.
- Film Exposure: The X-ray beam must be centered on the sensor to avoid “Cone Cutting.”
2. Mastering Angulation
Angulation refers to the alignment of the central ray of an X-ray beam. On the exam, you must know what happens when these angles are wrong.
Horizontal Angulation
Side-to-side movement of the PID.
Error: Overlapping contacts.
Vertical Angulation
Up-and-down movement of the PID.
Error: Elongation or Foreshortening.
3. Shadow Casting Rules
To produce a sharp, accurate image, we follow the geometric principles of shadow casting:
- Small Focal Spot: Reduces blurring (penumbra).
- Long Target-Object Distance: Using a long PID (16-inch) reduces magnification.
- Short Object-Sensor Distance: The sensor should be as close to the tooth as possible (except during paralleling).
🚨 DANB EXAM ALERT: Elongation vs. Foreshortening
Foreshortening: Teeth look short and “squished.”
Cause: Too much (excessive) vertical angulation.
Elongation: Teeth look long and “stretched.”
Cause: Too little (insufficient) vertical angulation.