It has become increasingly common to use 3D X-rays, known as CBCT, to assess the position of the wisdom tooth in the lower jaw. But lowering the dose of radiation for such X-rays, or using panoramic radiographs, provide at least as good a basis for treatment, shows new research.

When a patient has problems with wisdom teeth, a common treatment is to remove all or part of the tooth. In the lower jaw, a nerve runs close to the tooth roots and during surgery there is a risk of damaging the nerve, which can lead to a loss of sensation. Therefore, an X-ray examination should be performed to assess the positioning and relationship of the problematic tooth and the nerve.

Even with the low dose, the nerve and root anatomy could be seen clearly, making it a useful method in the vast majority of cases.

Josefine Cederhag

A panoramic radiograph, where all the teeth are seen in one image, are common method in this instance, however, CBCT scans, which provide three-dimensional images of the tooth and surrounding tissue, have also become increasingly common.

“It has an advantage because it gives more accurate depictions of the position of the tooth and nerve, which can create greater certainty before a surgical removal. But CBCT, which gives a much higher radiation dose than other methods, is also used in cases where it is not needed,” says Josefine Cederhag, a doctoral student at the Faculty of Odontology.

Her thesis consists of four sub-studies: in the first, the researchers reviewed panoramic images of more than 400 people to see how useful the method is for assessing how the wisdom tooth is located in relation to the nerve.

“In over half of the cases, we could clearly see how the roots of the wisdom tooth were located above the nerve canal. This means that a panoramic image is sufficient to use as a basis from this perspective.”

In the second study, oral surgeons, residents in oral surgery, and general dentists responded to a survey. Of the more than 170 respondents to the survey, most said that they most often used panoramic images rather than CBCT or intraoral images, where only part of the mouth is seen.

“The respondents stated that panoramic images and CBCT provided more information than intraoral images, and a majority felt that CBCT also reduced the risk of complications after tooth removal. But no matter which method was used, the decision to remove the tooth was not affected.”

The last two studies in the thesis focus on the radiation dose in CBCT examinations. Partly by comparing different methods for measuring radiation and partly by testing whether it was possible to reduce the radiation dose without impairing the image quality. A clinical study included 48 people with a total of 62 wisdom teeth. They underwent scans with the usual CBCT settings and with a lower dose. The image quality was then evaluated between the two scans.

“Even with the low dose, the nerve and root anatomy could be seen clearly, making it a useful method in the vast majority of cases. What was less clearly visible was the very small ligament space between the tooth and the bone, so sometimes the usual radiation dose is still needed," says Cederhag.

“My hope is that the thesis can contribute to more people reflecting on the different methods and how they are best used,” she adds.

Text: Anna Dahlbeck & Adrian Grist

Find out more

Read the thesis, 'Radiographic Imaging in Relation to the Mandibular Third Molar'