During a dental visit, a visual examination alone may not tell the dentist everything they need to know. Should you have any symptoms or abnormalities in your teeth, a radiograph (also known as an X-ray image) is necessary in order to establish the correct diagnosis and subsequently the correct treatment to be rendered. Even in a routine check-up where the patient has had no complaints, X-rays can help to detect any developing decay or pathology that would have been missed visually, and early intervention can be performed before the problem worsens.
Types of Dental Radiographs and Their Uses
BITEWINGS
- Normally taken as a pair (right and left) at a patient’s first visit, and best repeated every 1 to 2 years.
- Very useful in detecting interdental caries (decay in between teeth) in posterior teeth as these can be missed during a visual examination.
- Also great for checking the status of existing fillings and other restorations such as crowns and bridges.
This decay was not visible during a visual examination, and was only detected when bitewings were taken. Patient did not have any symptoms, but if this had been left untreated, it would have soon become sensitive and possibly painful.
This crown has a gap in one of its margins, which means it needs to be replaced to prevent the decay from spreading deeper into the tooth. The white patches marked “F” are metal fillings.
PERIAPICALS
- Captures the tooth and the full length of its roots.
- Taken for a specific symptomatic tooth to aid diagnosis.
- Is a necessary step prior to starting root canal treatments, extractions, crowns and bridges.
This shows a molar with severe infection surrounding its entire roots; the tooth will need to be extracted.
This X-ray image shows a premolar with severe bone loss. The red line shows where a normal bone level should be.
The circled tooth is a retained milk tooth which never exfoliated due to the absence of a permanent premolar. The shorter roots means this tooth will not last as long as the other permanent teeth.
ORTHOPANTOMOGRAM (OPG) / DENTAL PANORAMIC TOMOGRAPHY
- Also known as the Panoramic X-ray, it captures the whole mouth as well as neighbouring structures such as the nasal cavity, sinuses and temporomandibular joints.
- Very useful in providing the dentist with an overview of the oral and surrounding structures.
- Good for investigating the presence and angulation of wisdom teeth, extra teeth (supernumerary) and even absence of teeth, as well as certain pathologies of the jaw such as cysts.
The panoramic radiograph above shows a large cyst (an expanding fluid-filled pathology which erodes into the neighbouring bone and teeth) over the left jaw (red arrow). One of the molars also has evidence of an infected pulp (green arrow) which requires a root canal treatment.
LATERAL CEPHALOGRAM
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- A radiograph of the side view which shows the skeletal profile, and is routinely taken for patients requiring orthodontics (braces).
- Lateral cephalogram helps with the analysis of the skeletal profile, the protrusiveness of the front teeth, the soft tissue profile of the face, to aid orthodontic treatment planning.
- Also useful to assess the airway space at the nose and throat area.
CONE BEAM COMPUTED TOMOGRAPHY (3D)
So far all the radiographs we have described are two-dimensional (2D) images with limitations in what they can show the dentist. The Cone Beam Computed Tomography (CBCT) is the latest trend in dentistry, where a digital 3-dimensional image of a specified region in the mouth is generated on the computer, and allows the dentist to visualise bone thickness for implant dentistry, exact position of pathologies or unerupted teeth, and the root anatomy that conventional 2D radiography cannot show. However, because the amount of radiation needed for a CBCT is significantly higher than normal radiographs, they are only indicated when necessary.
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Concerns about Radiation
Today, with the advent of digital radiography where the photographic film is now replaced with an electronic sensor, the amount of radiation exposure necessary to produce an image is significantly lower. Additionally, dental X-rays are normally a lot smaller than medical X-rays (e.g. the chest X-ray) and therefore use lower amounts of radiation.
Fears about radiation are largely unfounded as we are all exposed to low doses of background radiation daily, and an occasional increase in radiation exposure, be it during long distance flights, medical imaging or even dental radiography rarely results in any pathological effects. And since dental radiographs are indicated with the specific intention of aiding diagnosis and early detection of disease, the benefit of having them definitely far outweighs the risk of mild additional radiation exposure.
Even so, precautions are still taken, for example, by using a lead apron when taking the X-ray, to reduce the amount of radiation to the patient’s body. However, if you are pregnant or suspect that you are pregnant, please let the dentist know.
How Often are X-rays Necessary?
Baseline X-rays are usually taken at your first visit to the dentist. If you had X-rays taken at your previous dentist within the last year, you should request a copy of the X-ray images and bring them with you when you visit your new dentist.
Once you have established a routine 6-monthly or yearly check up with your regular dentist, do not be surprised if your dentist requests for new X-rays to be taken after some time. For most patients, an interval of 1-2 years is recommended. For patients who are considered “high risk“, yearly radiographs are recommended. Patients who have good oral hygiene and appear to be decay-free (“low risk”) should still have new X-rays taken every 2-3 years. This is to ensure nothing is missed out despite the regular visits, as some tooth decay and bone loss are very hard to spot without the aid of the radiographs, as illustrated in the two real-life examples below:
This patient has been seen by the dentist regularly, and advised to take a bitewing radiograph after 2 years. A superficial decay had progressed into the dentine, and therefore needed a filling. Without this X-ray image, it would have been very hard to spot such a small cavity in between the teeth.
Within a span of 4 years, the bone loss at the lower left first molar had worsened, as traced out with the red line. Patient did not have any pain or discomfort and was unaware he had gum disease. The X-ray helped to pick this up, and the patient could then receive the necessary treatment to slow down the progression of his gum disease.
