By Scott Keating, VP Engineering, IMTEC (a 3M Company)
What is Cone Beam Computed Tomography (CBCT)?
When using CBCT imaging, clinicians have the most accurate anatomic information to plan the placement of dental implants in optimal sites by using technologically advanced digital imaging devices.
Computerized tomography is advancing rapidly. The imaging source-detector and the method of data acquisition distinguish cone beam tomography from traditional CT imaging. Traditional CT uses a high-output rotating anode X-ray tube, while cone beam tomography utilizes a low-power, medical fluoroscopy tube that provides continuous imaging throughout the scan. Traditional CT records data with a fan-shaped, helical X-ray beam onto image detectors arranged in an arc around the patient, producing a single slice image per scan. Each slice must overlap slightly in order to properly reconstruct the images. The advanced Cone Beam technology uses a coneshaped X-ray beam that transmits onto a solid-state area sensor for image capture, producing the complete volume image in a single rotation. The sensor contains an image intensifier and a CCD camera or an amorphous silicon flat panel detector.
The single-turn motion image-capture used in cone beam tomography is quicker than traditional spiral motion, and can be accomplished at a lower radiation dose as a result of no overlap of slices. This type of imaging exposes a patient to less radiation than traditional CT scanners. Manufacturers are designing Cone Beam Scanners with the physical space available in clinics and the patient’s comfort in mind. For example, upright seating is used in CBCT scanners with the X-ray tube and panel detector rotating around the patient’s head.
Current generation CBCT software capabilities
CBCT imaging provides important information about the 3-D structure of nerve paths, soft tissue and bone.
3-D software can shade images to differentiate varying densities of facial structures. Grayscale shading provides the ability to view the relationships of common internal anatomy. Traditional CT imaging renders an 8-bit grayscale (256 shades) or 12-bit grayscale (4,096 shades). Present-day scanners render images in 14-bit grayscale, providing 16,384 shades. Color coding the image by density further distinguishes anatomical structures, enabling the clinician to view pertinent anatomy while planning implant cases, such as nerves and nasal cavities, and mandibular and maxillary dimensions. Segmentation literally cuts the volume rendering, conceding top views, side views, and CT slices that produce unlimited axial, coronal and sagittal views. CBCT slices are as thin as 0.1 mm, compared to 1 mm for a conventional fan CT scan.
Image data may be obtained for a complete dental/maxillofacial volume or a limited region of interest. With the current generation of Cone Beam scanners, scan times for these types of images vary from about 20 to 40 seconds for the complete volume and as few as 8 seconds for the regional scan.
Several software programs on the market allow dentists to segment and transform the digital images into tessellated polygonal models, e.g., STL, which are used in the creation of surgical guides.
CBCT devices may be used for traditional forms of radiography, in addition to advanced 3-D volumetric renderings. Conventional cephalometric measurements may be obtained through 3-D volumetric images by rendering the image as a 2-D projection resembling a radiograph or a panoramic image. It is also possible to digitize cephalometric points in 3-D, resulting in the introduction of multiple analyses.
Non-conventional renderings are also realized using CT data. In fact, X-ray projections that are non-physical are possible. For example, a cephalogram can be created where the patient’s neck vertebrae have been omitted. The advantage of this type of rendering is that in a conventional ceph, the vertebrae may obfuscate the dentition, whereas in a non-conventional rendering, they do not.
Advantages of using CBCT in the specialty practice
CBCT imaging provides comprehensive data and the ability to dynamically manipulate that data, viewing anatomy from multiple perspectives. Diagnosis of TMJ condition and disorder or jaw pathology along with the evaluation of orthodontic cases, airways, impacted teeth and periodontal defects are all facilitated through the use of CBCT imaging.
A larger field of view CBCT is usually most appropriate in the specialty practice, due to the fact that compared to smaller field-of- view units, more of the patient’s maxillofacial anatomy is captured in each scan.
Advantages of using CBCT imaging in implant dentistry
CBCT imaging is the ideal radiological modality for implantology due to the high quality of the produced images, software capabilities, and lower doses of radiation exposure. Two of the hottest topics regarding CBCT and implantology are virtual surgery planning and surgical guides. A virtual surgery can be performed with special software applications that enable dentists to evaluate the quality of bone through density shading and dimensions of bone can be recorded accurately with 1:1 measurement tools. It identifies common internal anatomy needed to evaluate implant placement including the jaw boundaries, adjacent teeth, nasal fossa, mandibular canal, maxillary sinus, mental foramen, and incisive canal. It also detects pathology to be avoided for implant health. Therefore, before the surgery, the clinician can confirm the appropriate implant size, location and angulation, and that plan can be fed to a 3-D printer to produce a surgical guide or stent for use during the actual surgery.
CBCT imaging also has a positive impact on treatment acceptance rates, as it allows clinicians to illustrate recommended implant treatment plans to patients. The technology of the CBCT scanner and resultant images impress patients, facilitate a full understanding of the treatment options and aid in the selling of out-of-pocket implant treatment plans.
Raising the standard of care in implant dentistry
CBCT technology enhances patient trust and increases treatment acceptance. Possessing a CBCT scanner decreases implant case completion time while increasing the chances of implant success.
CT software and hardware options have been improved considerably, while the cost to own this technology has come down in recent years. This has resulted in many more doctors making the decision to implement CBCT into their practices.
CBCT is quickly increasing the quality and accuracy of radiographic dental care. Used in a wide variety of cases requiring additional information for treatment planning and detection of possible anatomical problems, CBCT scanners are rapidly changing the field of dentistry and quickly becoming the standard of care for implant treatment plans.
*Dr. Ronald A. Bulard graduated from the University of Oklahoma School of Dentistry.
The Iluma cone beam CT is currently not available in Canada