First, decay never goes away. Once it has reached half way through the tooths enamel, it must be treated. Tooth decay between teeth oftentimes cannot be seen without a dental X-ray leading patients to wait until they feel pain and require more complex dental work. Standard of care is to take bitewing radiographs, or X-rays every year.
Sometimes, we have patients who have a very low caries, or decay, rates and they may wait 18 or even 24 months between radiographs, on the doctors recommendation. Some patients, may need a particular area viewed more often than once per year, if decay or caries is suspected. Normally, a dentist will order four bitewing, or biting X-rays of the back teeth, where most dental disease is present. Sometimes, the dentist may ask for an anterior film, looking between the front teeth, as some small cavities begin there as well.
Once every 5 years your dentist should take a full mouth series of X-rays to look at everything in your mouth. This set of films can show roots, bones, abscesses and many other normal and abnormal things in your mouth. For children, this may be in the form of a panoramic film, which looks at the development of the arch and any teeth that are forming or will form. It can show missing teeth, extra teeth, or malpositioned teeth. The panoramic film is often also used by an orthodontist to determine if a child needs to wear braces, or for an oral surgeon in accessing wisdom teeth or third molars. This radiograph is also done for those wearing or wanting dentures.
Some people worry about the radiation in dental radiographs. First, a safe amount of radiation exposure per year is 620mrem. For example, a mammogram of one side uses 42mrem and smoking a pack of cigarettes exposes you to 36mrem of radiation. A standard dental X-ray uses just 0.5mrem of radiation and a digital X-ray which is used by most dental offices is just 0.1mrem of exposure. When you weigh the cost to benefit ratio of letting decay progress to a stage where it can cause infection and pain, the exposure is minimal.