Answer to Question #1193 Submitted to "Ask the Experts"

Q

What is the dose of a dental panorama x ray compared with a normal bitewing x ray for wisdom teeth examination?

A

Wisdom teeth (third molars) are generally evaluated by dental panoramic radiographs because of the broad coverage of the area that allows the relationship between the wisdom teeth and adjacent structures to be determined. Bitewing radiographs are not useful for wisdom teeth because they do not show the entire tooth. It is possible to take a single periapical intraoral radiograph of each wisdom tooth (four required) but this is not always satisfactory because of distortions and superimposition of structures, especially if the teeth are impacted. The most convenient way to talk about radiation doses from dental radiographs (and others also) is to use the effective dose (E) which estimates the uniform whole-body exposure carrying the same probability of radiation effect as a partial body exposure. This makes possible comparison of radiographs of different types and sizes in different parts of the body. It also allows comparison with exposure from natural background radiation. For a dental panoramic radiograph, the effective dose is 26 microSv (microsevert), which is the equivalent of about 3.3 days of natural background radiation. A series of four intraoral radiographs is 38 microSv, which is the equivalent of 4.8 days of background radiation. To put this in perspective, the effective dose from a chest radiograph is 80 microSv (10 days) and from a lower gastrointestinal (GI) series 4,060 microSv (507 days). (Reference: White SC, Pharoah MJ. Oral radiology: Principles and interpretation. St. Louis, Mosby, 2000, p 49.) Sharon L. Brooks, DDS, MS