Radiography is indispensable in the field of dentistry. It allows a precise examination of the tooth structure and enables accurate diagnoses to be made. It is also useful if surgery is planned.
In recent years, with the rapid evolution of technology, 3D sectional imaging has been used more and more in dental surgery. What does this imaging technique consist of? What is its usefulness? This is the point in this article.
What is 3D sectional imaging in dental surgery?
Before any surgery on the teeth, jaw or mandible, certain examinations must be carried out by the dentist. For greater precision, these examinations must be followed by a 3D or three-dimensional X-ray. This imaging technique consists of exposing the patient’s head to a beam of X-rays in order to obtain an accurate three-dimensional representation of the patient’s oral structure. In the case of an implant placement, for example, this image helps the dentist to anticipate possible complications that may arise during the operation and therefore to act accordingly.
In dentistry, 3D X-ray acquisitions are usually obtained using a CT scanner (cross-section) or a cone-beam computed tomography (CBCT) scanner. These two devices do not operate in the same way. The CT scanner projects a flattened x-ray beam, which allows a linear section to be obtained with each revolution. Depending on the desired result, it may be necessary to make a large number of cuts for the same examination.
The volumetric tomograph, on the other hand, projects a conical X-ray beam, which allows a minimum of 4 simultaneous slices to be obtained in one revolution.
Usefulness of 3D imaging.
3D sectional imaging finds its usefulness in the shortcomings of 2D imaging. As a reminder, the latter has geometric limitations due to the conical projection principle underlying the construction of the devices used. The enlargement of the image leads to a summation and distortion of the image. Moreover, 2D imaging does not allow precise measurements to be made. Finally, the dental arch designed with this technique rarely corresponds to the patients’ morphology. On the other hand, sectional radiography makes it possible to obtain very sharp images in three dimensions (height, width and depth) with a resolution almost 10 times higher than that of a 2d rendering.
With a 3D image, the dental surgeon can have precise information about :
- The extent of a tooth fissure;
- The density of the alveolar bone;
- The configuration of the maxillary sinuses;
- The position of the inferior alveolar nerve.
As mentioned above, this is very useful for making a complete diagnosis.
The Cone Beam: the current reference in 3D sectional imaging
Cone Beam Computed Tomography is a 3D sectional imaging technique invented in the late 1990s. It uses large matrix detectors and promotes the global exploration of calcified tissue in a single rotation of the system.
How does it work?
An X-ray generator emits a conical irradiation beam in a 360° (or 180°) rotation around the patient’s head. After attenuation, the beam is picked up by a detector which starts the data acquisition process to obtain the final images. A single CBCT scan can produce hundreds of images. This makes it easier for the surgeon to plan the operation based on the results obtained.
A Cone Beam examination session is virtually no different than a conventional dental X-ray. It usually requires no special preparation. The radiologist immobilises the patient’s head and holds the jawbone apart with a plastic piece. The X-ray exposure lasts about 20 seconds. After this acquisition time, a digital 3D reconstruction of the structures explored will be carried out with the help of software. This lasts between 20 and 30 minutes.
Advantages of the technique
The Cone Beam considerably reduces the patient’s exposure time to X-rays, since its operating principle consists of scanning the volume to be explored in a single pass. Moreover, its overall radiation dosimetry is much lower than that of a conventional medical scanner. It is one of the few imaging techniques that currently meet the ALARA (As Low As Reasonably Achievable) optimisation principle relating to protection against ionising radiation. It is also the least irradiating sectional technique according to worldwide dosimetric studies.
The CBCT also makes it possible to circumscribe to a certain extent the beam of irradiation to the only area that one wishes to explore. For example, when examining a group of teeth for an operation, the other parts of the patient’s skull will receive very little radiation.
Finally, the cost of a CBCT examination is much more affordable than that of a conventional dental scan. Average fees vary between 80 and 200 euros depending on the regions to be explored.
How to prescribe a Cone Beam exam? The dental surgeon must be explicit in prescribing a CBCT examination. His indications must allow the radiologist not to make a mistake. Thus, he must specify :
- The reason for the examination;
- The location of the area to be explored;
- The number of the tooth (if the examination concerns a particular tooth);
- The dental arch concerned;
- The patient’s state of health;
- The desired reconstructions (standard or adapted)…
- The desired field of exploration (small, medium or large) must also be indicated.
What are the limits of this technique?
Despite its many advantages, the CBCT technique has some limitations. The first one concerns cases where the patient has a crown or any other metallic element in the mouth at the time of the examination. This usually results in artifacts during digital acquisition. Reading of the images then becomes difficult, sometimes even impossible.
The second limitation of the Cone Beam is related to soft tissue. Since its dosimetry is low, a volumetric cone beam tomograph is generally not very effective for their observation.
What to remember? 3D sectional imaging is a complementary examination that provides the dental surgeon with more information about the oral structure of his patient. It is painless, minimally invasive and above all very effective.