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  • Dr. David Alfaro

1 tooth, 2 x-rays?

Have you ever gone to the dentist with a sore tooth and have them tell you that they need two x-rays to properly see what is wrong? What? Why two x-rays? Can’t you see what is going on from just one? Am I getting scammed?

Let me explain why we do this at our office.

There are two commonly used intraoral radiographs in dentistry: the bitewing and the peri-apical.

The Bitewing

Fillings. Tooth Pain. Caries. Dentist. Nelson, BC
Bite Wing Radiograph. Nelson Avenue Dental

For a radiograph to be an accurate image, the x-ray beams have to pass through the teeth and hit the sensor as parallel as possible to the teeth. This is best achieved with a “bitewing” radiograph, giving us a minimally distorted view of the crowns and the surrounding jawbone of both the maxilla and mandible.

Bitewings are useful for checking for dental caries that are on the surfaces between the teeth, but we cannot really see decay that is on the biting surfaces or cheek or tongue side of the teeth until it is quite extensive. They also allow us to see the position and health of the supporting bone. This is why they are routinely taken at dental checkups.

When someone has dental pain, or comes in with a broken tooth, this radiograph allows us to check for tooth decay or to assess the extent of the fracture, and to see how close the damage is to the nerve and how far under the gums (and close to the jawbone) it goes.

This x-ray, however, does not show us the roots of the teeth, so we need a second type: the "periapical".

The Periapical

Fillings. Tooth Pain. Caries. Dentist. Nelson, BC
PA x-ray, Nelson Avenue Dental

For this radiograph, the sensor is placed as far down (or up) as it can go in order to capture an image of the roots.

One of the drawbacks of this x-ray is that although we use special positioning devices, the tooth and sensor will not be perfectly parallel, so the image is often distorted, usually either taller or shorter than in reality. Because of this, even though we do see the whole tooth, including the top part where there may be tooth decay or a fracture, it does not give us the best reading of the position of the damage within the tooth.

This x-ray is used to assess the health of the root, and to look at important structures around the roots, such as sinuses and nerves. We use this to see if there is evidence of root infection, or root fractures, and to see the number and shape of the roots in case the tooth needs a root canal treatment or extraction.

If you look at the two radiographs I posted, in the bitewing, you can clearly see extensive tooth decay on the molar (big bottom tooth) that is very close to the nerve, but it is not so well defined in the periapical. If we had only taken one we would have missed out on important information. This tooth likely requires a root canal treatment, but that is not so clear on the periapical radiograph.

For those of you that are concerned that taking two x-rays for one tooth is way too much radiation, please read my article about radiation dosage. It is not as much as you think!

Thanks for reading!

Dr. Dave


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