Cone Beam Computed Tomography
Computed tomography (CT), and the three-dimensional images it provides, was developed in 1973. The technology, while primitive, was amazing to the practitioners involved. Those practitioners where at a loss of how to apply CT, and had no idea of the profound effect it would have on the surgical and medical community. It took several years of development and a new segment of the specialty of radiology, but CT has become an integral part of surgical treatment of the patients of today.
Oral and maxillofacial surgeons utilized CT routinely in the management of trauma and pathology, and are accustomed to the technology. In a dental practice, practitioners depend almost entirely on two-dimensional imaging utilizing plain films. The advantages of CT technology has been unrealized in the dental practice.
Cone beam CT (CBCT) was initially used in angiography. The advantages for head and neck imaging were quickly realized. The first CBCT developed specifically for dentistry was the NewTom 9000 in 1998 (Quantitative Radiology, Verona, Italy). Currently, there are several companies with versions of the CBCT scanner.
Medical CT scanners and CBCT scanners have two main differences. CBCT scanners use a low-energy fixed anode tube, similar to the tube used periapical or panoramic radiographs. CBCT scanners also only rotate around the patient once, exposing the patient to a cone-shaped x-ray beam to capture the images. These two differences result in a less-expensive, smaller device that exposes the patient to approximately 20% of the radiation of a typical helical CT. This is equivalent to the radiation from one full-mouth series of x-rays. The radiation dose from a multidetector row helical CT is 458 mSv, versus 1.19 mSv from a typical CBCT.
The different CBCT scanners are largely identical in their technology. The only major difference among CBCT scanner manufacturers is the type of detector used. All manufacturers use either an amorphous silicon flat-panel detector or a combination of an image intensifier and a charge-coupled device camera. Both provide accurate, reliable, high resolution images adequate for dental medicine.
The introduction of new technology in any field raises many questions. You must first identify the practical applications and benefit to the patient when compared to existing technology. In the end, the most important consideration may be the effect on the standard of care. There are several applications for the CBCT that are encountered daily in an oral and maxillofacial surgery practice: implant dentistry, oral and maxillofacial pathology, temporomandibular joint disorders, impacted teeth, orthognathic surgery, and traumatology.
The advantages of CBCT in implant dentistry are obvious. The ability to accurately visualize the alveolus and surrounding structures of the maxilla and mandible is invaluable. While traditional two-dimensional panoramic radiographs produces approximately 25% of magnification, overlap of vital structures, and an inability to provide information about bone volume, CBCT provides the practitioner with a virtual image of the patient. CBCT images measure one-to-one compared to patient anatomy. CBCT allows volumetric and even qualitative evaluation of the patient’s planned implant site preoperatively. Implant surgery can even be performed virtually preoperatively, and produce a computer aided surgical guide. Abutments and prostheses can even be fabricated preoperatively and placed the day of surgery. Utilizing CBCT, it is far less likely to have to change a surgical plan intraoperatively because of anatomy that was not visualizable preoperatively.
CBCT is indicated in maxillofacial pathology. Traditionally, oral and maxillofacial pathology has been visualized with multidetector helical CT, exposing the patient to a large dose of radiation. CBCT produces higher resolution images and delivers a fraction of the dose of radiation. This allows the surgeon to obtain detailed imaging of cysts and tumors without fear of excessive radiation exposure, allowing more specific preoperative surgical planning for grafting, reconstruction, or stereolithographic model fabrication.
CBCT provides detailed evaluation of the TMJ. Magnetic resonance imaging (MRl) is the gold standard for evaluating the intraarticular soft tissnes of the TMJ. Bony evaluation has been by plain film. CBCT allows more accurate evaluation and diagnosis of the TMJ with radiation exposure equal to plane film.
Orthognathic surgery and orthodontic therapy have relied on plain film lateral cephalometry. Since the landmark studies of the mid-1970’s, evaluation of facial growth and development has been based on standard plain film skeletal landmarks. Lateral cephalometric analysis with plain films is inadequate in severe facial assymetries such as hemifacial microsomia, or skeletal occlusal canting. CBCT skeletal and soft tissue imaging makes all of the data available for complete facial analysis. To date, it is unclear how CBCT can be better utilized in orthognathic surgical planning and orthodontic treatment. With further clinical research, CBCT will become the standard in preoperative surgical orthodontic treatment planning.
Surgical retrieval of impacted teeth is fraught with potential complications. CBCT evaluation allows for more thorough identification, evaluation, and treatment planning with the three-dimensional view. CBCT allows better evaluation or impacted teeth and surrounding vital structures, be it nerves, sinus, cortical border, or other teeth. This results in less invasive and more efficient surgery, resulting in a better outcome.
CBCT is a relatively new but highly applicable technology for dentistry and oral and maxillofacial surgery. Patients are treatment planned more accurately, which provides the ability to operate more accurately and efficiently. The greater diagnostic information will also give the capability for more detailed research in treatment of the head and neck. The lower radiation dose makes this technology more appropriate for imaging in the outpatient setting than traditional helical CT. CBCT will become an invaluable tool in head and neck evaluation.