4.4 Radiographs, CBCT, Positioning, and Safety
Key Takeaways
- Radiographic records must be ordered or prescribed according to office and dentist direction, captured with correct technique, and labeled accurately.
- CBCT creates three-dimensional information and requires careful patient positioning, artifact reduction, field selection awareness, and motion control.
- Radiation safety questions often test receptor placement, beam alignment, patient protection, exposure reduction, and avoiding unnecessary retakes.
- The RDA should recognize image-quality errors such as cone cuts, elongation, foreshortening, overlap, motion blur, and incorrect patient labeling.
Radiographic and CBCT records that the dentist can use
Dental radiographs are diagnostic records, not just pictures. A useful image shows the correct anatomy with enough clarity for the dentist to interpret. A poor image can lead to retakes, missed information, patient frustration, and unnecessary exposure. The RDA exam may test technical errors, safety steps, patient management, and documentation.
Radiographic technique depends on the image ordered. Bitewings need open contacts and correct receptor placement. Periapical images need the apex and crown with proper vertical angulation. Occlusal images show broader areas. Panoramic images require patient positioning, tongue placement, and stillness. CBCT provides three-dimensional data, but it also requires strong attention to patient position, field of view, metal artifact reduction, and motion control.
The RDA should not decide independently that an image or CBCT scan is required. The dentist or authorized protocol directs radiographic needs. The RDA's duty is to perform authorized imaging correctly, protect the patient, follow infection control, and label the image under the correct patient and tooth or area.
| Image issue | Likely cause | RDA response |
|---|---|---|
| Cone cut | Beam not centered on receptor | Reposition alignment device and follow retake policy |
| Elongation | Vertical angulation too flat | Correct angulation when retake is directed |
| Foreshortening | Vertical angulation too steep | Adjust technique according to receptor system |
| Overlapped contacts | Horizontal angulation not through contacts | Re-aim through interproximal spaces when directed |
| Motion blur | Patient or sensor movement | Re-instruct patient and stabilize equipment |
| CBCT artifact | Metal objects, motion, or positioning issue | Remove removable metal items and follow scan protocol |
Radiation safety uses the principle of minimizing unnecessary exposure while obtaining diagnostic quality. That means correct receptor placement, rectangular collimation if used by the system, appropriate exposure settings, thyroid shielding or protective procedures according to current office policy and law, and avoiding retakes through good technique. Infection control also matters because sensors, holders, and positioning devices contact the patient or contaminated surfaces.
CBCT questions may focus on preparation rather than interpretation. Ask the patient to remove removable metal objects such as jewelry, eyeglasses, removable appliances, or piercings according to office protocol. Position the patient correctly and explain that movement can ruin the scan. Confirm the correct patient and scan purpose before exposure. If the patient moves, tell the dentist or follow retake authorization procedure.
The exam may show an image-quality problem and ask what happened. Learn to associate overlapped contacts with horizontal angulation, elongation and foreshortening with vertical angulation, cone cut with beam alignment, herringbone pattern with reversed film in film-based contexts, and clear digital sensor problems with placement or equipment issues. Do not overread the image diagnostically.
Use this imaging checklist:
- Confirm patient identity and image order before exposure.
- Prepare receptors, holders, sensors, barriers, and equipment.
- Position patient and receptor for the requested view.
- Give clear instructions about staying still, biting gently, and tongue position when needed.
- Check image quality and labeling, then route the image to the dentist for interpretation.
Radiography and CBCT are high-responsibility records. The best exam answer protects diagnostic value, patient safety, and the legal record at the same time.
What image error is commonly caused by incorrect horizontal angulation on a bitewing?
Which preparation step is especially important before a CBCT scan?
What is the RDA's role after capturing a radiographic image?