Common Errors in Dental Radiology

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Operator errors

Operator errors in film or sensor placement and angulation of the tube head often result in non diagnostic x-rays. X-rays that are non diagnostic are useless to the dentist and must be retaken. Every effort should be taken to minimize the following errors, because each retake exposes the patient to more radiation.

Film or Sensor Placement

• Correct film or sensor placement is critical for success with x-rays. If the correct technique is followed every time, positioning errors will be minimized.
• In all premolar views, the distal of the cuspid is visible.
•  All molar views should contain the third molar region even if the tooth is not present in the mouth.
• When focusing on a specific tooth, it should be centered on the film or sensor.
• The film must be placed high enough in the palate or low enough in the floor of the mouth to clearly show the apex of the tooth in question and 3 to 4 mm of bone.
• Films should not be bent if possible, but if the patient is uncomfortable with the edge, try gently reshaping the edge and repositioning the film in the mouth. This is obviously impossible with sensors, but in either case, asking the patient to "gently" close often decreases the discomfort especially in the floor of the mouth.
• Before placing an x-ray film in a patient's mouth, check to make sure that it is not backwards. The lead foil will leave an artifact on the exposed x-ray and it will be confusing to mount.
• Make sure that exposed films are not mixed up with unexposed ones.

Angulation Of The Tubehead

Errors of angulation of the tube head are common. When using an instrument such as the Rinn, make sure that the tube head is aligned correctly, parallel with the indicator rod and aligned with the ring. If not using a Rinn, the beam should be parallel with the bitewing tab, or at an angle that splits the difference between the angulation of the film and the angulation of the tooth.  Film positioning devices are helpful and, when used correctly, they generally produce acceptable results.  When the patient's anatomy alters the usefulness of the instrument, it is best to revert to the the bisecting angle technique. For example, if the patient has a shallow palate, and the instrument will not allow the film to be parallel with the long axis of the tooth, this is an ideal time to compensate using a split angle technique to avoid foreshortening.

Overlapping is another common error of angulation. If the cone is not perpendicular to the film, the contacts will be overlapped. Some offices routinely use a size 3 film for a bitewing view that contains all the teeth from premolar to molar. Due to the curve of the arch, some area is bound to be overlapped. It is better to position two size 2 films in a premolar view and then a molar view so all contacts will be opened. 

Cone cutting is another common error.  It happens mostly because of positioning the cone too far to the distal (mesial cone cuts are the most frequent kind). The final radiograph will be cone cut when the tube head is not covering the whole area of the film. The best way to avoid this is by looking at the film or sensor in the patient's mouth and aiming the cone head directly toward it instead of guessing from extraoral landmarks. Ask the patient to "grin wide" like the joker in the batman series so you can see down the buccal corridor (the area between the buccal surfaces of the teeth and the buccal mucosa).  This makes it much easier to aim the cone.

If the patient moves, the film will be affected. Watch the patient as you expose the film to make sure they don't move. The patient should be instructed to hold very still and not swallow until he or she is told it is OK.

Incorrect film processing

Correct film processing procedures were previously discussed in the section on film processing, but the following table summarizes common film processing errors, the results, and possible solutions.

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