CBCT : Cone beam computed tomography for dental implants surgery
Introduction
Establishing an accurate dental implant diagnostic involves a painstaking clinical examination, often supplemented by additional radiological exams.
Cone Beam or CBCT (Cone Beam Computed Tomography), and also known as digital cone beam volumetric tomography, is a rapidly growing 3D sectional imaging technique. It can be harnessed to explore calcified tissues, i.e. bones and teeth.
This article will be examining this revolution in dento-maxillary imaging, which has been widely adopted in dental surgeries, opening up new horizons for diagnostics in dentistry.
Firstly, we’ll be defining Cone Beam technology and explaining the physical principle of this radiological process. We’ll then briefly review the differences between scanners and Cone Beam CT, followed by a discussion of the benefits and limitations of CBCT, still in comparison with scanners. Lastly, we’ll look at the clinical indications for use of this technique.
What is CBCT technology?
Definition
We can identify two different types of technique in dento-maxillary imaging: 2D panoramic or orthopantomographic (OPT) techniques, and more sophisticated 3D techniques such as scanners and, more recently, CBCT.
The advent of CBCT towards the end of the 1990s was seen as a major innovation in comparison to its predecessor, the scanner, as it introduced large scale matrix detectors that could scan a complete volume in just one rotation of the imaging system.
How does CBCT work?
Physical principle
As its name suggests, CBCT comprises an x-ray generator that emits an open conical radiation beam for sweeping the whole volume to be explored in a complete or semi-complete rotation, before being analyzed once the detection system has reduced it. The x-ray generator and detector are interdependent and aligned.
x-ray tube / conical x-ray beamflat sensor
With each rotational degree, the generator releases a pulse of x-rays that pass through the anatomical mass so that they are received by the detector, which then carries out a rotation at the same time as the source.
With each angular motion, a 2D image of the volume covered is recorded on the flat sensor.
Digital acquisitions take hundreds of images so that a volume can be created and 3D computer reconstruction can deliver a virtual view of the anatomical structures explored.
Tube / Object / Detector / Digitalization / Image memory / Reconstruction / Image processing / Console / Film / Digital image acquisition
Unlike with scanners, each unit or Voxel is isometric, creating a very high spatial resolution of around 100µ.
CBCT can be used to obtain a volumetric image of the area x-rayed, with a high image resolution for the various dimensions, by eliminating any overlapping of surrounding structures.
There are various types of CBCT, categorized according to their field of investigation:
– small fields: less than or equal to 8cm
– medium fields: between 9 and 15cm
– large fields: greater than 15cm
What happens in a CBCT dental examination?
The session is similar to that of a standard dental x-ray. The patient must stay motionless throughout the acquisition time, which lasts around 10 to 20 seconds. A computerized reconstruction is then carried out using dedicated software. Around 20 to 30 minutes is required for each examination, which is considerably more than the time taken by a scanner.
What is the radiation dose of a CBCT exam?
Cone Beam technology uses very different technical solutions, with radiation doses in ratios of 1:5.
It is defined by dosimetric studies as being the least irradiating of all sectional techniques. Cone Beam exposure doses are 1.5 to 12 times weaker than those used by conventional medical scanners. However, they are still 4 to 42 times stronger than panoramic imaging.
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