Understanding Dental X-rays

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Dental x-rays provide a treasure trove of information to the dentist. Also called radiographs, they can show tooth decay, infection, cavities, impacted teeth, misaligned jaws, and much more. X-ray images are relatively straightforward – once you understand what you are looking at. Of course, it takes a qualified dental professional to identify problem areas. In this article we look at:

  • How does dental radiography work?
  • What are the different types of dental X-rays?
  • Reading a dental X-ray
  • Importance of dental X-rays


How does dental radiography work?

Radiography is the process of producing an image for medical examination on a sensitive film or plate using x-rays or other forms of radiation. In dental radiography, an x-ray tube is used to project beams (radiation) onto the patient’s mouth. X-rays pass through the mouth and come out the other side harmlessly (attenuation). On the other side is a receptor that captures the x-rays and creates an image. Receptors can be vinyl film packets or digital sensors.

X-rays do not pass through skin and tissue evenly. Thicker and heavier masses such as teeth will block x-rays more than other tissues such as skin.


What are the different types of dental X-rays?

There are two main types of dental x-rays. Intraoral x-rays are taken with the receptor inside the patient’s mouth. These are good for evaluating teeth and surrounding tissue. Extraoral x-rays are taken with the receptor outside the patient’s mouth. These are good for getting the big picture of the teeth and assessing the skull and the jaws.

Intraoral x-rays

  • Bitewing (shows cavities starting to develop and bone loss due to gum disease)
  • Periapical (show the root of teeth in detail)
  • Occlusal (used to look for tooth or bone fractures, tooth eruption)

Extraoral x-rays

  • Panoramic (frontal view of all teeth; “big picture” view of teeth)
  • Cephalometric (evaluate the relationship of upper and lower jaws to each other and cranial base; good for tracking growth – important in orthodontics)


Digital dental x-rays are a more recent technology. Instead of using a film that must be processed in a dark room, a digital receptor sends the image directly to the computer. It can then be viewed, shared, or printed out.

There are a few benefits of using digital dental x-rays:

  • There is lesser exposure to x-rays
  • Images are available a few seconds after being taken


Reading a dental x-ray


A dental x-ray works on the principle that harder more mineralized tissues will block more of the x-ray radiation. Due to this, hard tissues like the enamel and dentin will appear light in color. Spaces between teeth and tooth pulp appear dark because they are non-mineralized.

One easy way to understand it is the harder something is the lighter it appears. The softer something is the darker it appears.


What do cavities look like on x-rays?

Cavities appear as a dark spot in a tooth. Cavities start in the enamel, which shows as the lightest color in the x-ray. It will travel inwards into the dentin, which is softer than enamel and appears darker too. Dental x-rays also show cavities between two teeth, something that would not be visible to the naked eye.


Importance of dental x-rays

Dental radiography is an indispensable diagnostic tool for many reasons. They allow the dentist to:

  • See inside and between the teeth
  • See under the gums and locate the tooth root
  • Check for cavities
  • Assess the extent of tooth decay
  • Diagnose cysts and abscesses
  • See impacted teeth
  • Detect bone loss and periodontal disease


Do dental x-rays show infection?

Yes, x-rays can show infection and abscesses even before the person feels obvious symptoms.


What does a dark spot on a dental x-ray mean?

A dark spot in an x-ray can mean the presence of a cavity. It is a sign that bacteria have attacked the enamel and are entering the dentin. This decay must be addressed as soon as possible.


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