November 2012, Volume 8, Issue 11
Published by AEGIS Communications
It’s Time to Go Digital
Whether it’s a 2-D or 3-D system, to maximize the significant advantages of today’s digital intraoral imaging options, clinicians need to make choices based on their individual practice needs.
The first dental radiograph was exposed in 1896, a year after German physicist Wilhelm C. Roentgen first produced and subsequently detected what are now known as X-rays. However, it was not until about 1916 that dental X-ray units were commercially available and used in practice (Figure 1). Using this technology, an X-ray beam was directed through dental hard and soft tissues, and those that penetrated through exposed a piece of film, which was placed in a light-restricted pouch that was positioned intraorally. The next innovation did not come until the 1950s with the development of panoramic imaging. This was indeed a revolution, because it enabled clinicians to visualize the entire maxillary and mandibular dentition on a single film. The temporomandibular joints, as well as the floor of the maxillary sinuses and the entire maxilla and mandible, could be seen and evaluated. And, patients loved the fact that nothing needed to be put in their mouths. The panoramic radiograph became the standard of care in oral and maxillofacial surgery, especially because clinicians could see impacted teeth in their entirety, as well as their relationship to the mandibular canal and maxillary sinuses.
Two-Dimensional Digital Radiography
In 1994, digital radiography was introduced to dentistry. This technology obviated the need for a dark room and the use of toxic chemicals to process the images. In addition, less radiation was required to expose the sensor and obtain a good image. What’s more, imaging software enabled clinicians to enhance the on-screen image with brightness and contrast adjustments and colorization. The original intraoral sensors were bulky for patients and required a wire to connect them to the image-processing computer. Many of the sensors currently on the market are wireless and much more comfortable for patients.
Despite these radiographic innovations over time, there was one overlying issue that limited what clinicians could do with the images: radiographic images were all still 2-dimensional (2-D). This may not seem like a big deal to most dentists, who had to prove their 3-dimensional (3-D) aptitude to gain admission to and graduate from dental school. However, 2-D radiographs can be very easy to misinterpret due to overlap of anatomic structures (Figure 2). Pathology can be missed, and normal anatomy can be thought to be pathological because of superimposition and/or masking of adjacent structures.In addition, for periapical pathology to be evident radiographically, there must be destruction of the buccal or lingual bony cortex. Patients can go for months without a diagnosis of their odontogenic pain because radiographic signs of the problem are just not evident (Figure 3 and Figure 4). The problem was that, while patients existed in 3-D, dental imaging could only evaluate them in 2-D.
All this began to change in 1998, when the first cone beam computed tomography (CBCT) scan machine was introduced to the European dental market. Three years later, CBCT appeared in the United States. These radiographic units use a technology derived from conventional panoramic radiography to capture a 3-D image of a patient’s dentition and facial skeleton. This image can be manipulated so that the anatomy can be viewed from an infinite number of different angles and with varying thicknesses of tissue. Most CBCT units allow reconstruction of radiographic data to provide a cross-sectional, tangential, axial, sagittal, coronal, and 3-D view. A panoramic reconstruction can also be generated, but it differs in many ways from a conventional 2-D digital panoramic.
Cone beam CT differs from medical-grade CT in a number of ways. First, it uses a cone-shaped, as opposed to a fan-shaped, beam of X-ray photons to expose the image. Rather than a large detector, under which the patient must lie down, the CBCT unit uses a much small detector, which rotates around the head of the sitting or standing patient, similar to a panoramic machine. CBCT can be operated from a standard office PC computer system, and the cost of the equipment and the amount of radiation exposure to the patient is less about one tenth that of a medical CT scanner (Figure 5). These factors make CBCT a practical imaging system for many dental offices, both general practitioners and specialists. A conventional CT scan, with its high-energy dose and powerful computer, is designed to image both hard and soft tissue of the body. It can easily discern between various tissue densities in whatever is imaged. A CBCT uses much lower-energy photons and exposes the patient to considerably less radiation. Because of this, soft tissue is visualized as homogeneous soft tissue, and there is little variation in beam attenuation. Soft-tissue tumors can rarely be visualized. CBCT is optimal for evaluating only calcified structures, such as teeth and bones, which are what dentists are most interested in anyway. On the up side, because the beam is less powerful, scatter due to dental restorations is usually less of a problem with CBCT than with conventional CT.
3-D Imaging Selection Factors
Three-dimensional dental imaging is now commonplace due to the development of the CBCT scan, and will soon be the standard of care for the evaluation of jaw and dental pathology, facial trauma, and dental implantology.
There are well over a dozen CBCT units on the market. For clinicians considering this technology for their office, the decision-making process can be a daunting task. A number of factors that need to be considered when choosing a unit for the dental office are discussed below. They include: field of view (FOV); the amount of radiation emitted to expose a useful image; the time required to complete the scan; and the software used to evaluate the scanned volume and make a diagnosis.
Field of View
CBCT scanners can be simply divided into large, medium, and small field of view (FOV) units. The type of unit that is best depends on the clinician and what the clinical use will be. Large FOV units are most useful for orthodontics, orthognathic surgery, jaw pathology, temporomandibular joint evaluation, and maxillofacial trauma assessment. These tend to be the most expensive units, ranging from $150,000 to $200,000. The medium FOV units are the most popular with both general dentists and specialists. These are less expensive—in the $110,000 to $165,000 range—and have an average field size of 13 mm to 16 cm in greatest dimension. These are well suited to most indications, including TMJ evaluation, pathology and trauma of the maxilla and mandible, and evaluation of the maxillary sinuses and for planning dental implants. The small FOV units are popular because they are the lowest-priced machines available, at about $85,000 to $120,000. They first became popular in endodontics because they allowed high-resolution scanning of small areas. Many general practitioners are also buying these units, because of their low price point. However, these machines also can be limited in their usefulness because of their small field size, which requires that multiple scans be taken for evaluation of multiple areas of the jaws in the same patient.
The large FOV units are appropriate for the doctor who “wants it all” as far as image volume is concerned. A 15-cm FOV will generally capture most maxillofacial structures of importance, but will not include the back of the patient’s head, the sella turcica, frontal sinuses, or the neck. This may be an issue for some orthodontists and oral and maxillofacial surgeons. If these structures are part of the examination for every patient, a large FOV unit is appropriate; otherwise, supplementing a medium FOV with a conventional antero-posterior and lateral cephalometric projection will usually fill this information deficit when needed. The small FOV units are sufficient for applications involving only endodontics on a single tooth, but for most clinicians, the small field size will soon become a hindrance to patient care.
While it is desirable to expose patients to the lowest radiation dose possible for the sake of their health, there is a trade-off. The higher-energy the photons are, the less background noise will be present in the image, hence a clearer, more diagnostic image. Optimally, it is desirable to have a CBCT that delivers an outstanding image at less than 80 𝜇Sv of exposure. With a lower-end radiation dose like this, the sophistication of the diagnostic software plays a critical factor in the quality of the image.
Scan Completion Time
Those who own a panoramic machine are accustomed to asking the patient to “stand still” while the image is being exposed. With that in mind, a faster scan time lessens the chance for patient movement and distortion of the image. This is even more important for a 3-D CBCT image. Some machines take multiple exposures, then “stitch” them together to get the final image of the patient’s entire region of interest. If the patient has moved at all, this stitching process may not work properly and an aberrant image will result. Ideally, a single rotation of the X-ray source and sensor around the patient in 15 seconds or less will ensure a diagnostic image most of the time.
Software for Evaluation and Diagnosis
Perhaps most important of all is the software, which must be intuitive to use and allow visualization of the patient’s anatomy from a variety of orientations without needing an advanced radiology degree. If intensive training and a steep learning curve are required to perform the most basic imaging functions, this sizeable investment in new technology is likely to end up as a coat rack. Because dentists are very familiar and comfortable with the panoramic radiograph, it is important that the imaging software include an easily generated panoramic reconstruction that can be used for navigation and orientation of the cross-sectional, tangential, axial, and other slices (Figure 6). This will facilitate diagnosis of both normal and abnormal structures. Finally, because most dentists invest in CBCT to help them evaluate patients and provide them with tooth replacement using dental implants, the software should be able to easily export its DICOM files to the various implant planning programs. Better yet, the CBCT diagnostic software should have its own implant-planning module, so transition between these two functions is seamless. To evaluate the anatomy of patients, who exist in 3-D, for the placement of dental implants, 2-D radiography should no longer be acceptable. The true ridge height and width, location of adjacent roots, nerve canal, and the maxillary sinus should only be determined with the accuracy of cone beam CT.
Going Digital—The Author’s Own Experience
When I graduated from dental school in 1982, there were two options for a dental office radiography system in the United States—a film system made by Kodak and a film system made by any one of a number of other companies. When I entered a hospital-based GPR in that same year, we used the Kodak film-based imaging system, which was considered the standard of the day, for both our intraoral and extraoral imaging needs. Because I had used Kodak in dental school and in my residency, I selected Kodak when I set up my private practice in 1984.
However, today’s practitioner faces many more choices and the financial impact is far-reaching. This I know from my own experience, which picks up again in the late 1990s, when I built a new office building.
After seeing a colleague using a digital radiography management system that integrated with his computerized practice management system, I decided to build my new office without a darkroom, thereby committing to both an intraoral and extraoral digital imaging system in the late 1990s—quite a leap of faith, given the state of technology at the time. I chose the Trophy RVG intraoral (CCD based) and Trophy extraoral systems at that time primarily because I saw another practitioner using the intraoral RVG system. I knew that the intraoral system worked and that it was not “vaporware” or still in “beta” testing. In the 15 years since then, approximately 50% of all US dentists now use digital radiography; there is no longer any question of diagnostic accuracy, precision, or reliability with the major digital systems on the market.
Should You Take the Plunge?
Until one experiences the advantages of never again having to hunt through paper charts for a FMX taken 2 years ago to compare a set of current bitewings, or a peri-apical from last August to see what the apical PDL space looked like 6 months ago, etc, you really have no idea how much going digital will improve your professional life. The sooner the transition is made, the sooner you will learn what you’ve been missing in terms of increased efficiency and pure practice enjoyment. Then, too, there is the positive impact it has on your bottom line over the next several years as you grow to use your digital system in ways that you cannot imagine possible.
Direct vs. Indirect Intraoral Receptors
After making the decision to transition to digital, the clinician needs to determine which image-capturing technology to purchase—indirect digital (phosphor storage plates [PSP]) or direct digital (CCD/CMOS [charge coupled device/complementary metal oxide semiconductor]).
Between my use of PSP, which was the primary system in the undergraduate radiology clinic when I was in dental school, and the many systems I was able to use during my oral and maxillofacial radiology residency in 2008, I have first-hand theoretical knowledge and clinical use of the two types of digital image capturing technologies available to dentists today.
Technology—In film systems, the latent image is stored in silver atoms within the emulsion on the film; through chemical processing with fixer and developer solutions, the final image can be seen. In PSP systems, energetic phosphor electrons absorb X-ray energy during the exposure and store this energy until stimulated by a laser beam during the scanning process; when this excess energy is released, the scanner and computer software transform this released light energy from these electrons into the visible image seen on the computer monitor; the time required for processing the PSP plates is the reason for the delay between exposure and image visualization in the PSP system. The CCD and CMOS direct digital systems are faster because the receptors are either plugged directly into the computer or the signals are transmitted wirelessly; and, as soon as the exposure is complete, the electrical signals correlated to each pixel in the digital sensor send the exposure information immediately to the imaging software and the image is visible on the monitor within seconds.
Size—In both film and PSP systems, the receptors capture only the latent image, while in CCD and CMOS systems, the receptors not only capture the image, they also perform image transfer duties; therefore, digital receptors also have all the electronics necessary for each pixel to capture and transmit exposure information to the computer. The bigger CCD/CMOS receptors do not yield diagnostically better images; but because they deliver images to the computer monitor more quickly, diagnoses can be made more quickly as well, so that you can make your diagnosis faster.
Which to Choose
Determining whether to purchase direct digital (CCD/CMOS) or indirect digital (PSP) should be based on the primary diagnostic and treatment tasks performed on a daily basis in your practice, those that will be required of your intraoral system. The choice between a direct and indirect system depends on the clinician’s unique practice requirements.
Family dentists—For family dentists, who typically see patients of all ages, it makes sense to have a PSP system for young patients who don’t like big, bulky CCD/CMOS sensors in their mouths. PSP plates are thinner and therefore more likely to be more accepted by young patients than CCD/CMOS receptors (Figure 7). However, those also doing endodontic procedures and/or implants with any regularity at all should consider having both PSP and CCD/CMOS systems. In the long run, the flexibility will be worth the added investment.
Super generalists—Super generalists might do a molar root canal treatment in the morning followed by a single-tooth implant placement, and in the afternoon may see orthodontic patients. These dentists need to have a very fast image acquisition and processing turnaround time for tasks such as molar endodontics and implant placement, and the CCD or CMOS sensor is likely to be their workhorse sensor. Depending on the number of child patients in the practice, the super generalist may or may not seriously consider the time, cost, and maintenance issues required to run a PSP system as well.
Advanced restorative dentists—Advanced restorative dentists may manage restorative cases ranging from 3-unit bridges to single-tooth implants and full-mouth reconstruction cases. Those placing implants or performing any endodontic procedures share the fast image acquisition needs of the “super generalist” and will most likely choose the direct imaging options of CCD/CMOS. On the other hand, for those not placing implants or performing a significant number of endodontic procedures, the PSP system may be the optimal system.
The Bottom Line
The final choice between the two systems comes down to this. The PCP is the right choice for clinicians who want a system that physically looks like film, handles like film in the mouth, and requires the easiest transition with the smallest technology budget for a film to digital transition—especially those who do not already own operatory computers.
A direct digital system, ie, CCD/CMOS, would be the way to go for those who want a system that will speed up many of their clinical procedures, such as endodontics and implant placement, and who do not see a lot of children.
You owe it to yourself and your future practice health and professional enjoyment to make the transition to digital imaging. But first, you should take the time to understand your own needs to select a system that will best work for your practice.
About the Authors
Jay B. Reznick, DMD, MD
Diplomate, American Board of Oral and Maxillofacial Surgery
Jeffery B. Price, DDS, MS
Meharry Medical College School of Dentistry
Diplomate, American Board of Oral & Maxillofacial Radiology