Safe time between repeat x-ray procedures

There is no specific time period recommended between
radiographs. A panoramic x-ray is a very low dose dental radiograph. Published
radiation doses in terms of effective dose range from about 9 µSv to about 26
µSv (White and Pharoah 2009). To put this in perspective, the average
background radiation dose in the United States is about 8 µSv per day.
Background radiation includes things like cosmic radiation, radon, naturally
occurring radioactive materials in soil, building materials, etc. The typical
panoramic radiograph has a radiation risk equivalent to approximately one to
three days of natural background radiation. There is no reason to delay having
the repeat radiograph taken if it is needed for planning the orthodontic
treatment.

It is very reasonable, however, to ask the person taking the
radiograph what went wrong the first time and what steps are being taken to
correct the problem. Sometimes the issue is with something the patient did, for
example, moving while the scan was taking place or not holding the tongue
against the roof of the mouth. Not holding the tongue up can cause a dark air
shadow to cross the roots of the teeth, making them hard to interpret. Probably
the most common cause for a retake is incorrect positioning of the patient in
the machine. Even though the machine looks pretty simple, the procedure is very
dependent on correct patient positioning. Most machines have lights that shine
on the patient’s face, which can guide the operator. With film-based panoramic
radiographs, another source of error was problems in the developing of the
film. That is not an issue with modern digital equipment.

Sharon L. Brooks, DDS, MS

Reference
White SC, Pharoah MJ. Oral radiology principles and
interpretation, 6^th ed. St. Louis: Mosby; 2009.