What is an X-ray?

What is an X-ray?

X-rays (or radiographs) are an essential part of dentistry. Your teeth are embedded in your jaws, so without them we can only ever see half the story.

An image is formed by passing X-rays through an object (e.g. your tooth) onto a film.

They are used to help diagnose problems and are needed before and during certain treatments to ensure a good outcome.

What are the Different Types of X-rays and What do they Show?

In dentistry, X-rays can be divided into two categories; Intra-oral X-rays and Extra-oral X-rays.

Most of you will have had these taken at some stage or other; if you have had a lot of dental work, then you probably have had them taken many times.

  • Intra- oral X-rays

These, as the name suggests, are X-rays where the film is placed inside (‘intra’) your mouth to take pictures of the teeth and supporting structures. These X-rays are the most common type of dental X-ray and show small areas in great detail. They help the dentist look for signs of decay and gum disease, check the teeth and any fillings or work you have already had done to ensure they are all OK.

The main types of intra-oral X-ray are listed below; each is a different view and provides different information:

(i) Bite wings (BWs)
Here a patient bites down on a holder or a tab attached to the X-ray. It can sometimes be a little uncomfortable (depending on the size of your mouth) but is only for a few seconds. The X-ray shows us the crowns and the top part of the supporting bone for the back teeth. It shows the top and the bottom of one side only. This view is the routine screening X-ray that allows us to diagnose decay in-between the teeth; decay around existing fillings, see calculus; overhanging margins of fillings; the quality of the fit of crowns and bone loss from periodontal disease that is under 4mm.

(ii) Periapicals (PAs)
This view shows the whole tooth in question and one tooth either side including the crowns, roots and surrounding tissues. It is useful in diagnosing problems which involve the nerve of the tooth, peri-apical abscesses (tooth abscesses), more severe periodontitis (bone loss) and they are needed during a root canal procedure, or for the assessment prior to extraction.

(iii) Occlusals
These are rarely taken, but can be useful for helping to locate impacted teeth or in trauma cases. They are larger X-rays that show most of the arch of the teeth, in either the upper or lower jaw.

  • Extra-oral X-rays.

These, as you would probably now guess, are X-rays where the film is placed outside your mouth to show images of the skull, face and jaws. They show us a good general view of all the teeth too, however they do not provide the accuracy and detail of the intra-oral X-rays for detecting decay and problems with individual teeth.

They are useful for monitoring the growth and development of the teeth and jaws, assessing bone levels, looking at wisdom teeth (and other impacted teeth) and problems with the TMJ. Also in the assessment of dental implants. There are numerous different extra-oral views that can be taken in maxillofacial surgery, but in dentistry, by far the most common views taken are:

(i) Dental panoramic tomograph (OPG) |
This is the standard screening view that shows us your entire top and bottom jaw.

It shows us clearly the location of the inferior dental nerve, which supplies sensation to all the lower teeth and the lower lip. This is important when assessing wisdom teeth for extraction, since the roots can lie very close to this nerve and there can be a risk of damaging it.

Since it shows us the bone support for all the teeth, the OPG is useful in assessing the severity of gum disease throughout the whole mouth. The spine is superimposed across the front teeth so the image is often quite blurry and difficult to interpret. It is considered a good alternative to the full mouth X-ray series which can be taken for periodontitis patients to allow close monitoring of their bone levels.

We can also see the sinuses and if they are full of fluid (sometimes sinusitis is mistaken for tooth ache) and how much bone is available for placement of implants, though supplementary scans are often needed.

(ii) Lateral cephalometric view (lat ceph)
This is used almost exclusively for orthodontic treatment and shows the face, jaws and teeth in side profile. There are standard features and angles that apply to the teeth and jaws and the assessment of these. Also comparison to the normal ranges is useful in diagnosis, planning and monitoring treatment. It uses a cephalostat to ensure that the image can be reproduced exactly for comparative purposes, therefore changes in teeth position can be monitored.