Answer to Question #12483 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Dental

The following question was answered by an expert in the appropriate field:

Q

My son had four bitewing x rays and a panoramic x ray when he was eight. Recently, the orthodontist took another panoramic x ray and cephalometric x ray. They did not put a thyroid collar on him because they said it may give a bad image. Please help me with the following questions (1) will this total amount of dental x rays within a time span of 16 months increase his risk of developing cancers, (2) is there increased harm in not wearing a thyroid collar during panoramic and cephalometric x rays, and (3) what is the radiation dose for panoramic and cephalometric x rays? This is a pediatric dental office. They use digital x-ray equipment.

A

The general answer to your question is that these doses are so small that the risk of developing cancer is negligible.

You ask about increased risk of not using a thyroid shield on children when radiographs are taken. Unfortunately, the thyroid shield interferes with panoramic imaging, casting a white shadow over the front teeth as the x-ray beam does a partial circle around the patient's head. With cephalometric x rays, the issue is different. The orthodontists use the stage of development of the vertebrae in the neck to judge where the child is in terms of growth stage so that orthodontic treatment can be timed correctly to work with the child's natural growth spurts. Thus, they don't want to cover the neck because then they can't get this information. The risk to your child of not using the shield for these images is minimal.

I will give you some detail on my thinking below.

The main purpose for taking x rays on a child is to evaluate the child for tooth decay and proper arrangement of the teeth (dentition). Decay can occur anywhere on the tooth, but is most common on the sides or on the chewing surface. Unfortunately, it is generally not possible to detect decay on the sides of the teeth just with a clinical examination unless the teeth are very far apart (unlikely) or the cavity is very large. For that reason dentists use bitewing x rays to examine the teeth for decay. The term "bitewing" refers to the method of taking the x ray, where the film or digital sensor has a tab or "wing" attached to it that the patient bites on to secure the film or sensor in place. The x-ray beam is angled in such a way to provide a clear picture of the sides of the teeth so they can be checked for decay. The American Dental Association recommends bitewings on children every 6–18 months. This frequency depends on the child's risk for decay (fluoride in the drinking water, amount of sugar consumed, etc.).

Another concern with children is how their permanent dentition is developing: Are all the permanent teeth forming, are there any extra teeth forming, are there any abnormalities in size, shape or location of the teeth, are there any other problems occurring in the jaws? For these questions, the panoramic radiograph is a very good technique because it can show both jaws, including the jaw joints, on one image at a very low radiation dose.

If a child is suspected of having some type of problem, such as crowded teeth or the upper and lower jaw not seeming to fit well together, he may be referred to an orthodontist for evaluation and treatment. The orthodontist typically wants to see a recent panoramic x ray and a cephalometric x ray. The cephalometric x ray is a side view of the head that shows the relationships between the upper and lower jaws, and the jaws to the rest of the skull. The orthodontist will make many measurements that will help determine the best kind of treatment for the child’s condition.

The radiation dose for panoramic and cephalometric x rays is variable because there are going to be minor variations depending on the specific x-ray machine and type of film or digital sensor used. The numbers I am going to present are taken from probably the most widely used textbook of dental radiology in dentistry by White and Pharoah (2014).

For panoramic x rays, the effective radiation dose is 9–24 microsievert (µSv) or equivalent to about 1–3 d of a person's natural background radiation exposure. Cephalometric x rays have an even smaller dose, 2–6 µSv or about 0.5 d of background radiation.

For your peace of mind in the future, it is perfectly appropriate to ask the dentist why they are recommending x rays for your child (and yourself!) at any specific time. The dentist should have no difficulty in answering this question for you. And, please remember that the benefits of the diagnostic information gained from dental x rays far outweigh the negligible risk.

Sharon L. Brooks, DDS, MS
Professor Emerita
Diplomat, American Board of Oral and Maxillofacial Radiology

Reference

White SC, Pharoah MJ. Oral radiology: principles and interpretation. 7th ed. St. Louis, MO: Elsevier; 2014.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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