What are dental X-rays and why are they needed?
In the list of your favorite things, getting an X-ray at the dentist's office may not rank high. Wearing that heavy apron and holding a sometimes uncomfortable device between your teeth for even a few seconds isn't much fun.
But X-rays show dental providers a lot. X-rays help them see the condition of your teeth, roots, jaw placement and facial bone composition. They also help them find and treat dental problems early in their development.
X-rays are a form of energy that can travel through or be absorbed by solid objects. This energy is absorbed by dense objects, such as teeth and bones, and show up in X-rays as light-colored areas. X-rays pass through less dense objects, such as gums and cheeks, and appear as dark areas on X-ray film.
X-rays can help find problems that cannot be seen with an oral exam. Finding and treating problems early in their development may save you money, avoid discomfort (if these problems are treated at a later time) and possibly even save your life.
What types of problems do X-rays help detect?
X-rays help your dentist diagnose problems in your teeth and jaws.
In adults, X-rays show:
- Decay, especially small areas of decay between teeth.
- Decay beneath existing fillings.
- Bone loss in the jaw.
- Changes in the bone or root canal due to infection.
- Condition and position of teeth to help prepare for tooth implants, braces, dentures or other dental procedures.
- Abscesses (an infection at the root of a tooth or between the gum and a tooth).
- Cysts and some types of tumors.
In children, X-rays determine:
- If decay is developing.
- If there is enough space in the mouth to fit all incoming teeth.
- If wisdom teeth are developing.
- If teeth are impacted (unable to emerge through the gums).
What are the different types of dental X-rays?
There are two main types of dental X-rays: intraoral (the X-ray film is inside the mouth) and extraoral (the X-ray film is outside the mouth).
Intraoral X-rays are the most common type of X-ray. There are several types of intraoral X-rays. Each shows different aspects of teeth.
- Bitewing X-rays show details of the upper and lower teeth in one area of the mouth. Each bitewing shows a tooth from its crown (the exposed surface) to the level of the supporting bone. Bitewing X-rays detect decay between teeth and changes in the thickness of bone caused by gum disease. Bitewing X-rays can also help determine the proper fit of a crown (a cap that completely encircles a tooth) or other restorations (such as bridges). It can also see any wear or breakdown of dental fillings.
- Periapical X-rays show the whole tooth — from the crown, to beyond the root where the tooth attaches into the jaw. Each periapical X-ray shows all teeth in one portion of either the upper or lower jaw. Periapical X-rays detect any unusual changes in the root and surrounding bone structures.
- Occlusal X-rays track the development and placement of an entire arch of teeth in either the upper or lower jaw.
Extraoral X-rays are used to detect dental problems in the jaw and skull. There are several types of extraoral X-rays.
- Panoramic X-rays show the entire mouth area — all the teeth in both the upper and lower jaws — on a single X-ray. This X-ray detects the position of fully emerged as well as emerging teeth, can see impacted teeth and helps diagnosis tumors.
- Tomograms show a particular layer or “slice” of the mouth and blur out other layers. This X-ray examines structures that are difficult to clearly see because other nearby structures are blocking the view.
- Cephalometric projections show an entire side of the head. This X-ray looks at the teeth in relation to the jaw and profile of the individual. Orthodontists use this X-ray to develop each patient’s specific teeth realignment approach.
- Sialogram uses a dye, which is injected into the salivary glands so they can be seen on X-ray film. (Salivary glands are soft tissue that would not be seen with an X-ray.) Dentists might order this test to look for salivary gland problems, such as blockages, or Sjogren’s syndrome (a disorder with symptoms including dry mouth and dry eyes; this disorder can play a role in tooth decay).
- Dental computed tomography (CT) is a type of imaging that looks at interior structures in 3-D (three dimensions). This type of imaging is used to find problems in the bones of the face such as cysts, tumors and fractures.
- Cone beam CT is a type of X-ray that creates 3-D images of dental structures, soft tissue, nerves and bone. It helps guide tooth implant placement and evaluates cysts and tumors in the mouth and face. It also can see problems in the gums, roots of teeth and the jaws. Cone beam CT is similar to regular dental CT in some ways. They both produce accurate and high-quality images. However, the way images are taken is different. The cone beam CT machine rotates around the patient’s head, capturing all data in one single rotation. The traditional CT scan collects “flat slices” as the machine makes several revolutions around the patient’s head. This method also exposes patients to a higher level of radiation. A unique advantage of cone beam CT is that it can be used in a dentist’s office. Dental computed CT equipment is only available in hospitals or imaging centers.
- Digital imaging is a 2-D type of dental imaging that allows images to be sent directly to a computer. The images can be viewed on-screen, stored or printed out in a matter of seconds. Digital imaging has several other advantages compared with traditional X-rays. The image taken of a tooth, for example, can be enhanced and enlarged. This makes it easier for your dentist to see the tiniest changes that can’t be seen in an oral exam. Also, if necessary, images can be sent electronically to another dentist or specialist for a second opinion or to a new dentist. Digital imaging also uses less radiation than X-rays.
- MRI imaging is an imaging method that takes a 3-D view of the oral cavity including jaw and teeth. (This is ideal for soft tissue evaluation.)
How often should teeth be X-rayed?
How often X-rays need to be taken depends on your medical and dental history and current condition. Some people may need X-rays as often as every six months. Others who don’t have recent dental or gum disease and who have ongoing scheduled visits with their dentist may only need X-rays every couple of years. New patients may have X-rays taken at their first exam. First-visit X-rays are also used to compare with X-rays taken over time to look for problems and unexpected changes.X-rays may need to be taken more often in people at high risk for dental problems. These people include:
- Children: Children generally need more X-rays than adults because their teeth and jaws are still developing and because their teeth are more likely to be affected by tooth decay than adults.
- Adults with a lot of restorative work, such as fillings: To look for decay beneath existing fillings or in new locations.
- People who drink a lot of sugary beverages: To look for tooth decay.
- People with periodontal (gum) disease: To monitor bone loss.
- People who have dry mouth: Whether due to medications (such as antidepressants, antianxiety drugs, antihistamines and others) or health conditions (such as Sjogren’s syndrome, damaged salivary glands, radiation treatment to head and neck). Dry mouth conditions cause decay.
- Smokers: To monitor bone loss that results from gum disease (smokers are at increased risk of gum disease).
Are dental X-rays safe?
The amount of radiation emitted from X-rays is extremely small. Advances in dentistry — such as X-ray machines that limit the radiation beam to a small area; high-speed X-rays; use of lead-lined, full-body aprons; and federal laws that require accuracy and safety checks for X-ray machines — are a few of the improvements that limit the amount of radiation patients receive. Despite the safety of X-rays, some questions to ask your dentist include:
- Was there something you found in your clinical exam that you feel needs to be further examined with an X-ray?
- How will these X-rays help guide the treatment plan you have in mind for me?
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