Today, there are 2D imaging technologies and more developed 3D techniques such as CT and more recently the Cone Beam CBCT, which revolutionize dento-maxillary imaging.

In this article, we will detail the limits of 2D imaging, the principle of the Cone Beam technique, its applications and its comparison to the scanner technique, and its interest in implantology.

2D imaging: principle and limits

2D imaging is a first-line exam. It can be extra oral with panoramic radiography (or OPT orthopantomography) or intraoral with retro-alveolar and retro-coronary radiography.

Panoramic radiography: the extra-oral technique

The panoramic X-ray shows the dental arches, sinuses, jaws, joints and lesions that can not be detected during a first clinical examination.

Taking a dental panoramic is done by a flat sensor that allows to obtain a scanned image on a computer.

In comparison to 3D radiography, 2D radiography has certain limitations. It is often subject to a phenomenon of enlargement, distortions, distortions and artifacts: we speak of geometric limits.

The radiological apparatus is programmed for a theoretical arcade shape that is superimposed only exceptionally to that of the patient, so that the quality of reproduction of the anatomical structures is not homogeneous over the entire image.

This imaging technique does not allow absolute measurements, which limits its indications especially in implantology and endodontics.

An intraoral examination is then performed.

Retro-alveolar and retro-coronary radiography: the intraoral technique

To complete the dental panoramic, an intraoral examination can be performed. Originally, the technique was conventional film but it was dethroned by digital technique. The image processing method has been modified with two main advantages:

- the possibility of avoiding the stage of development of the cliché in the dark room

- The digital image can undergo image processing (changes in brightness, contrast ...) that improve visual perception and allow to focus on the region of interest that interests us, depending on the pathology observed.

Thanks to the use of angulators and the taking of images under different incidences (for example eccentric to highlight the entire anatomy of the canal network), the intra-oral images can present a definition 4 times greater than the panoramic shot.

After proper use of the standard two-dimensional dentistry examinations described above, the use of three-dimensional techniques including the Cone Beam (CBCT) can be performed.

The Cone Beam, reference in 3D imaging

The Cone Beam, also called Conical Beam Computed Tomography (CBCT), is a three-dimensional radiological examination at the interface of orthopantomography (OPT panoramic radio) and CT (computed tomography).

CBCT (Planmeca)

Physical principle of the Cone beam

The Cone Beam technique consists of an X-ray generator that emits a conical beam through the object to be explored before being analyzed after attenuation by a detection system. The X-ray emitter and the detector are integral and aligned.

At each degree of rotation, the transmitter releases an X-ray pulse that passes through the anatomical body to be received on the detector.

CBCT technique

The CBCT works with a conical open beam which allows a single resolution to scan the entire volume to explore. In addition, it has the ability to produce high resolution images in multiple planes of space by eliminating overlays of surrounding structures.

To answer all indications in odonto-stomatology, there are different CBCTs according to their field of exploration:

- small fields: less than 10cm,

- the average fields: between 10 and 15 cm,

- large fields: greater than 15 cm.

Like its ancestor CTCT, the CBCT allows to obtain reconstructions in three dimensions, which are compared to the scanner for their spatial resolution of mineralized hard tissues namely the bone and the teeth but the Cone beam remains rather technically different from the scanner .

Differences in the acquisition between a Cone Beam and a scanner

Cone beam scanner

X-ray beam source flattened (fan-shaped) Conical X-ray beam

Intercepted by a generally elongated shape sensor Collected by a flat sensor

Acquisition requiring multiple rotations Acquisition requiring only one rotation around the patient

The general shape of the devices (extended position required) General shape approaching the generator of the panoramic radio: simpler acquisition

Patient comfort -

Patient comfort

Voxel Parallelepiped Rectangle: Anisotropic Volume Cubic Voxel: Isotropic Volume

Irradiation 300 to 1300 uSv Irradiation 50 to 250 uSv

Benefits of the Cone Beam

The Cone Beam is now recognized as the gold standard in dento-maxillofacial imaging.

From a single acquisition, we have different views on the same image, namely frontal, sagittal, oblique coronal slices, which represent an undeniable advantage of the CBCT. Due to obtaining images from an isotropic voxel, in terms of magnification, we obtain images with a ratio of 1: 1. The resolution power is equivalent or even better than that of the scanner. The Cone beam is also less subject to metal artifacts (especially root canal).

CBCT is a 'low dose' technique which gives good image quality with irradiation lower than that of a CT scan. Indeed, it is much less irradiant than conventional CT since it delivers a much lower dose of radiation.

Digital retro-alveolar view: 4 to 6 14568 uSv,

- Digital Panoramic X-ray: 10 to 15 uSv,

- Cone beam: 50 to 250 uSv,

- Medical scanner: 300 to 1300 uSv.

The irradiation dose depends on the size of the area examined. A Cone beam examination of 3 teeth is obviously less irradiating than an examination of 2 complete arches. In general, the Cone beam delivers an average of 2 to 4 times less x-rays than the scanner.

Cost

In addition, the Cone Beam is much less expensive than the scanner.

The indications of the Cone Beam

The CBCT is now of interest in almost all areas of dento-maxillary imaging.

dentistry

The CBCT is indicated in odontostomatology whenever the information provided by the clinic and 2D radiology are not sufficient to establish an accurate diagnosis and a 3D image is essential:

in endodontics for finding and locating an additional root canal,

for a pre-surgical periapical assessment particularly in the posterior maxillary region or in the region of the foramen mentonnier

in the case of traumatic lesions

in oral surgery before extraction of wisdom teeth to see the ratio of the roots with the lower alveolar nerve

for the assessment of a root pathology, type of fracture, internal and external resorption, periapical or latero-radicular

in pathology to evaluate the extension and the reports of the cystic and tumoral lesions of the jaws

for a pre-implant assessment and an estimate of the bone volume at the implant site, following bone grafts, for therapeutic follow-up in periodontology and implantology ...

ENT and Maxillofacial

The Cone beam presents other indications in ENT and Maxillofacial especially in the following cases:

- achievement of an assessment of TMJ (temporomandibular joint)

- exploration of the maxillary sinuses and nasal cavities,

- exploration of the rock because less radiating. It has proven to be effective for studying the different structures of the middle ear and the optic capsule, as well as for post-operative follow-up of middle ear or cochlear implants.

Implantology is greedy biometrics, sectional imaging given by the Cone Beam has become a tool of choice in the issue of bone volume available.

The Cone beam is indeed a mandatory examination in implantology except in the case where the indication to implant placement is formally challenged by panoramic radio and clinical examination. It is considered in implantology as the reference examination to establish a preoperative diagnosis and sometimes even for postoperative follow-up.

The pre-implant assessment

It is performed by the practitioner and includes a thorough general and local clinical examination, an OPT radiological examination and a CBCT.

The Cone Beam allows the indication in implantology if there is any doubt or to confirm the impossibility or dangerousness of implant placement.

Moreover, it is this imaging technique, by facilitating the exploitation of anatomical data in 3D, which allowed the development of the concept of guided surgery either in a static way, by a guide printed in 3D, or by a dynamic way.

The Cone Beam allows the optimal visualization of bone volumes, the appreciation of the quantity and quality of the bone by an appreciation of the density of cancellous bone.

CBCT (Planmeca)

In addition, planning software has reduced surgical errors and the limitations of implantology have been pushed back. This leads to a considerable reduction in implant failures, as the selection of the case is based on increasingly reliable information.

Post-surgical follow-up

Therapeutic monitoring is essentially clinical and radiological standard but this does not exclude the use of CBCT at the slightest doubt of complication (defective immediate osteointegration, peri-implantitis ..) after implant placement or following a pre-treatment. implant by grafts, or sinus-lift ... The Cone beam allows the estimation with great accuracy of the success of bone grafts and their sites of sampling.

Choice of Cone Beam devices

The Morita® device is still at the top of the charts in the Cone Beam comparisons because of the overall quality of the material and the image produced, other brands are increasingly competing with it, among others, Carestream®, and well on Sirona® but also Newtom® and Planmeca®.

The choice of the Cone Beam radio device depends on the surgical specifications: some devices perform better in implant surgery, others are oriented more towards diagnosis in pathology and oral surgery or in endodontics.

Implantology has pioneered the field of sectional imaging, but this imaging can and should be used in other areas of dentistry: periodontics, endodontics, oral surgery, orthodontics. Cone beam

The Cone Beam is today the benchmark 3D examination in dentistry due to its technical and dosimetric performance which is prescribed when the study of soft tissues is not required.

However, its prescription should not be systematic because it should rather be considered as a complementary examination of the standard radiology (OPT and retroalveolar and retro-coronary images), itself complementary examination of the clinic.

Indeed, the CBCT is a less invasive examination than the scanner. It makes it possible to obtain 3D images at a lower cost with less radiation and with an image resolution equivalent to or even greater than that of scanners, hence the need to democratize it.