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Cone Beam CT: Comparison with 2D Imaging and 3D Applications
This is a summary of the webinar, hosted by Henry Schein Dental with featured speaker, Heidi Kohltfarber, DDS, MS, PhD. You may watch the webinar here.
Is 2D imaging enough in a general dental practice? How do you know when it’s time to move to 3D? As Dental Radiologist and Professor Dr. Heidi Kohltfarber explains, “3D is exactly what dentists need, because we can see so much more with it. We’re seeing many more lesions and quite a bit going on in the sinuses. This is great for patients, especially for dentists who are passionate about patient care as a whole. 3D imaging will become the standard of care to provide appropriate treatment for our patients.”
Dr. Heidi Kohltfarber, DDS, MS, PhD, FADI, FICD Diplomate ABOMR, is the owner of Dental Radiology Radiologists and is an adjunct professor at the University of North Carolina at Chapel Hill. She recently gave a webinar covering a comparative review between 2D and 3D technologies, diagnosing capabilities, and the ability for general dentists to do procedures in-house.
The History of Dental Imaging
Early dental radiographs (X-rays) were first discovered in 1895, but the first ever bitewings took 30 minutes to acquire. As we moved on to X-ray units in the 1920s, there were improvements, but less than ideal. In fact, the units had a live wire! The emergence of digital X-rays allowed dentists to process images much faster. However, this still involved the same geometry that had been used back in the 1890s.
The next big innovation was dental radiography and panoramic imaging. At the time, the extraoral imaging unit was stationary and the patient spun around.
“2D imaging did serve us well, but the problem is that perspective makes a big difference,” explains Dr. Kohltfarber. “When you can get to the third dimension, there are tremendous advantages for diagnosis and treatment. This is the foundation for digital dentistry. 3D imaging is also excellent for patient education. We’ve seen case acceptance go sky high. Patients love to see their own scans. You can also burn a CD for them to take home and you can put your logo on it and that’s great for marketing.”
Cone beam imaging has been around since the 1980s. The early systems in the 1980s took up a lot of room - today, CBCT systems are more compact and combine three technologies:
Ceph-arm fluoroscopy with image intensifiers or flat panel detectors
Tomography - algorithms for constructing the volumes
Panoramic radiography as a platform for the CBCT unit
The system rotates around the patient’s head, takes multiple images, and stitches them together, almost like a video. “The technology is software-driven, so we can continually get upgrades that help prevent the system from becoming obsolete,” says Dr. Kohltfarber.
How is CBCT Different from Conventional Medical CT?
“Conventional CT systems have little scatter and that’s why they show excellent soft tissue detail. This does come with a higher cost, as well as a higher dose to the patient. With CBCT imaging, there is a lot of scatter, so it’s not ideal for soft tissue detail but is excellent for hard tissue, which is what we want in dentistry,” explains Dr. Kohltfarber.
What Factors Should You Consider When Purchasing a CBCT?
What will you use it for? What fields-of-view and resolutions are needed for the task? An orthodontist, for example, would probably want a larger field-of-view while an endodontist would like a smaller, higher resolution field-of-view.
Is the software intuitive and easy to use? It’s important to choose a system that you’re comfortable with. Otherwise, you won’t get maximum use out of it.
What type of support is offered by the manufacturer? “This can often be overlooked, but if no one is able to fix your machine or answer your call, that's lost production time for you,” says Dr. Kohltfarber. “You will want very good support and customer service standing behind the machine.”
What Fields-of-View are Needed?
The field-of-view describes the anatomical area that will be included in the scan. There are several choices:
Large field-of-view: Shows the mandibular condyles, as well as airway space
Medium field-of-view: Shows maxible and mandible, but not the condyles. “This is often ideal for implant treatment planning. However, you won’t see the airway space unless you do two scans,” notes Dr. Kohltfarber.
Small field-of-view: Shows a few teeth in high resolution. “If you’re looking at a potential root fraction or widening of the periodontal ligament space, this size will work,” says Dr. Kohltfarber.
What are the Radiation Exposures with CBCT?
In general, the smaller the field-of-view, the lower the dose, although there are always outliers. On average, a CBCT with a 8x8” field-of-view would be one-third of the exposure of a film-based full-mouth series, and slightly more exposure than a digital full-mouth series. This is equal to 15 days of “background radiation” (background radiation is defined as what the average American is exposed to from natural background sources).
There are also low-dose protocols that have radiation that is less than a set of bitewings. “Notably, the chances of defects from in-utero exposure to CBCT is zero,” says Dr. Kohltfarber.
What are the Applications of CBCT Imaging?
The driving force for CBCT imaging is implant imaging and treatment planning. “With CBCT, you can also see developmental abnormalities, third molar/canal relationships, periapical and periodontal findings, TMJ imaging, trauma, as well as pathological findings. This technology is also useful for airway and sleep apnea applications as well as orthodontic applications and segmentation,” says Dr. Kohltfarber.
How do You Know When to use 3D Imaging?
3D imaging should be used when 2D imaging doesn’t give you enough information to properly manage that patient. For example, 2D imaging consistently underestimates the amount of bone loss and overestimates bone gain. Some dentists will take a panoramic series and if they can’t diagnose the patient’s pain or planning an implant, they will do a 3D scan.
A position paper by the American Academy of Oral and Maxillofacial Radiology recommends radiology in dental implantology with an emphasis on cone beam computed tomography (CBCT). Specifically, they recommend that “cross-sectional imaging be used for the assessment of all dental implant sites and that CBCT is the imaging method of choice for gaining this information."
“One of the great reasons to use CBCT is as a surgical guide,” says Dr. Kohltfarber. “This is especially helpful if you are first starting out with dental implants. You can have a recipe to follow and there's often an accuracy attached for that ...guided surgery takes the guesswork out. Even though you have a huge area in which to plan your implant, you can't always place it the way you want to. We see this all the time.”
Patient Examples
Dr. Kohltfarber reviews numerous patient cases and the profound differences in findings when comparing 2D and 3D imaging.
Watch the webinar to learn about the case studies.
Early Detection of Apical Periodontitis
New research¹ shows that there is a connection between apical periodontitis and an increased risk of cardiovascular disease. Anytime there is a chronic inflammatory process, there is an increased risk of cardiovascular disease. In addition, the size of the lesion at the time of discovery and at the time of treatment will determine the success of treatment. In other words, the larger the lesion, the greater the risk for failure of the treatment. “If there is a bone loss, it might be better to do an extraction and add an implant, instead of trying heroics to try and save the tooth,” says Kohltfarber.
Additional Applications of CBCT Imaging
There are many additional applications of CBCT, including:
Assessment of osteoarthritic changes in temporomandibular joints
Identification of cysts, surface erosion, osteophyte, or generalized sclerosis
Trauma, including identification of fracture lines
Pathological findings
Airway analysis for potential sleep apnea
Orthodontic applications, enabling you to look at the orientation, morphology, and path of alignment of the teeth, as well as the relationship to other teeth
What is the Prevalence of Incidental Findings?
“Often these are self-reported surveys, but we can extrapolate this data to show how it might impact your office,” says Dr. Kohltfarber. Findings include:
Survey of a young patient population, largely orthodontics: Incidental findings 25% of the time (The largest was airway issues).
Survey of older patients, many with dental implants: Roughly three incidental findings per scan. 16% of these needed treatment, 16% needed active monitoring, and the rest did not need intervention.
Survey of young patients, many with sinus or airway issues: Roughly two incidental findings per scan, with 10-50% being actionable (i.e., requiring treatment, other diagnostic tests, or referral).
Who is Responsible for the CBCT Data?
The dentist who obtains the volume is responsible. “From a legal and ethical standpoint, the dentist needs to examine the entire scan volume,” says Dr. Kohltfarber. “You need to be able to recognize abnormalities and refer appropriately. The good news is there is training offered by Cerecdoctors, and there are oral and maxillofacial radiologists who can help you. There are also CBCT anatomy and pathology courses available, as well as radiology CE courses coming out late this year.”
“What’s exciting is that we now have a dental radiology diagnostics button right in the CBCT system. This scan goes right into our HIPAA-compliant secure server and we can read that for you.”
What type of Insurance Coverage can be Expected for CBCT?
“We know patients need cone beam, yet insurance companies are not keen to pay for this technology,” says Dr. Kohltfarber. “I expect this will change as our standards in the dental society start to change… A lot of people are looking into medical billing because that will pay for cone beam. Other dentists will charge it as an included fee in the implant, or will charge it as a pan if it's a large field of view and does get the condyles. We are seeing insurance start to pay for those through medical billing.”
The Future of CBCT
“What we’ve seen for opportunities in digital dentistry is just the tip of the iceberg,” concludes Dr. Kohltfarber. “The uses for improving patient health will continue to grow.”