Dale A. Miles, BA, DDS, MS, FRCD(C)

Diplomate, ABOM and ABOMR

Digital radiography—making the most of your image

Abstract

The contemporary general dental practitioner is already integrating digital intraoral videocameras, digital panoramic and cephalometric images, digital clinical still cameras, and even transparency scanners into the practice. These digital devices allow for more convenient image storage and image retrieval, better image display, improved patient educational experiences, and faster and more convenient remote consultation. This article discusses the advantages of using digital radiography in the dental practice, explores several of the imaging software “tools” available that can be used to aid and enhance diagnoses, and explains why “going digital” is something every dentist, regardless of his or her career stage, should invest in and develop an understanding of this technology.

Learning Objectives

After reading this article, you should be able to:

• discuss the advantages of incorporating digital radiography into the dental practice.
• describe the different types of digital radiography available today.
• explain some of the tools used with digital radiography to improve disease diagnoses.
• define feature extraction and explain how it can be used to diagnose dental disease.

 The advantages of producing and using digital images in the dental practice are well established. This author has presented these advantages in various articles since 1993.^1-4 However, the principle advantage, that of “feature extraction,” has been lost in the “market rhetoric” until more recently.^5-8

Commercial vendors often talk about “software tools.” Largely because the term is commonly used in reference to photography, dentists talk more about “image manipulation.” What we are all really doing when we apply these software tools (computer algorithms or filters) to our digital images is “electronic image processing” (EIP). Altering these initial images actually is necessary and desirable for improving disease detection. The current medically accepted terminology for this task is “feature extraction.”

Table 1, reprinted from an article on my website posted in 2002, contains a list of the positive attributes of digital imaging systems.⁹ It is important to explain the third attribute, “better disease detection.” This is feature extraction; that is, improving the detection of a disease attribute by using digital image processing.

The imaging of lesions in dentistry, unlike medicine, requires very few image-processing tools because we deal with few diseases on a daily basis. In medicine, imaging of the entire body is required to visualize and detect pathology from diverse sources such as infection, tumor, systemic disease, and trauma. Lesions in body parts such as the lungs, heart, and colon are not nearly as accessible as they are in the jaws. While we still deal with the same pathologic processes cited above, we need only to image dental caries and their sequelae (periapical lesions), periodontal bone changes, and occasional temporomandibular joint (TMJ) problems on a routine basis. Certainly we see odontogenic lesions and some systemic changes, but not nearly as frequently as they are discovered in other parts of the body and, in the oral cavity, they are not nearly as difficult to image.

 Medical radiologists need plain films, computed tomography (CT), ultrasound, interventional contrast studies, scintigraphy (nuclear scanning), magnetic resonance imaging (MRI), and even PET (Positron Emission Tomography) scans to detect and delineate various diseases and disorders with any certainty. They use all of these imaging modalities to help their diagnoses. It is interesting to note that many of these imaging modalities share a common technology—the imaging software.

 Today, dentists can use the same imaging software technology to process the digital image and to improve disease detection capability. Finally, we can employ digital technology to help us help our patients. But we can do this only if we “go digital” and learn to understand and use the helpful tools and digital imaging products commercially available. Dentists and specialists increasingly have intraoral x-ray systems, panoramic x-ray systems, clinical digital still cameras, digital videocameras, and even cone beam CT (specifically designed for dental use) at their disposal. The technology is here, it’s the education and understanding that is lacking.

 Who should adopt digital x-ray imaging – and when is it time to buy?

 There are three “stages” in the typical clinician’s career:

1.  the recent graduate (in practice 1-5 years)
2.  the “mid-career” dentist (in practice more than 10 years)
3.   the “soon-to-be-retired” dentist (getting ready to sell the practice).

Which of these groups needs to go digital? In my opinion, all three. And when should they buy? Immediately!

 Today, the recent graduate was exposed to many new technologies in dental school and has a basic understanding of the various technologies and tools available. This is the easiest group to convince to go digital—they are computer literate and understand the benefits and improved productivity that technology offers.

 Mid-career dentists have acquired technical skills, have mastered their “business,” and are looking for ways to improve their productivity and make clinical decisions easier and more precisely. They have adopted many other digital “technologies” and have converted to sophisticated practice management systems, but often do not understand the use and benefits of the newest digital x-ray systems. They need to be exposed to digital radiography and have their comfort level challenged. After they try the systems, after they adopt the technology and use it themselves, they often become vocal proponents of the technology and wonder how they ever managed without it.

 Some might think that the final group—the “about-to-retire” dentists—would be the least likely to adopt digital imaging technology. They are nearing the end of their careers and have built tremendous good will in their practices, which they hope to convert to cash to help the retirement transition. Actually, they should consider adopting digital radiography even more than the mid-career types. Why? Because new graduates, out looking for a practice to acquire, will not be as interested in practices that are not digital. If a graduate is comparing three practices and two have adopted contemporary digital technology, they will consider those first. The “old-fashioned” practice will require a lot more initial investment, so it will be relegated to the bottom of the list in many cases. Thus dentists in this last category must research systems and give serious consideration to digital adoption if they want to compete for the new graduates’ dollars.

 Which tools are useful for which tasks?

Any digital image, including those obtained with solid-state detectors, allows the dentist to perform EIP. This capability is not just a marketing tool or hype. When we perform a filtration (apply a software tool), or electronic image processing step, it is with the expectation that the disease process or disease feature will be made more visible, more detectable.

This diagnostic application, “feature extraction,” is finally available to all dentists. Manufacturers have given us sophisticated tools that allow us to:

• detect disease more readily

• display the disease features more conveniently to patients

• display the disease features more prominently for treatment decisions

• be more confident of our diagnosis because of these capabilities.

 Those using digital radiography have found that patients love it, and, increasingly, they expect it. It is an excellent tool for treatment planning, explaining the treatment plan to patients, and, ultimately, patient acceptance. Feature extraction tools that can be used for certain tasks are outlined in Table 2. They include image inversion, image embossing, regional histogram equalization, and optimization of contrast and density (brightness).

Figure 1 demonstrates the usefulness of these enhanced diagnostic capabilities in detecting several of the common dental diseases listed in Table 2.

Interproximal caries detection – which tools for this task?

Probably the most frequently performed task in the dental office is using bitewing (BW) images to detect interproximal carious lesions. The image detector used may be either a solid-state sensor (direct digital), a phosphor plate (indirect digital), or conventional x-ray film. Film images can actually be indirectly converted to digital images by scanning them into a computer using a flatbed transparency scanner.¹⁰ Regardless of the mode used, once an image is in the computer, the most useful procedures (in my opinion) for diagnostic purposes are “contrast and brightness optimization” and “embossing.” Many commercial dental imaging programs employ this process before the image is displayed; that is they “pre-process” the image for optimal display characteristics using computer algorithms before you see it on your monitor. The Image 4.0 (Dentrix), Schick CDR (Schick Technologies), Dixi2 Digital Imaging (Planmeca), Prof. Suni (Suni Imaging), and Dental Imaging Software (Eastman Kodak) are examples of several manufacturers’ systems that employ this method. Kodak’s software (formerly Trophy) defaults to a high-contrast, high-“edge” filter for initial display (Figure 1D). This gives the initial image a very sharp, “digital” appearance.

Each of these systems also includes an embossing filter program, although most use one preselected “embossing” direction. The embossing filter should be customizable, as it is in Adobe Photoshop^TM, to allow the clinician to change the direction of the shadowing for optimal interproximal caries visualization.

 Alveolar crestal bone height – how high is really high?

Another very common task in the evaluation of the dental patient is to measure the periodontal attachment depths around all teeth. These measurements are then correlated with the bone levels seen in images of the teeth to determine the patient’s periodontal health status. Healthy bone levels are assigned to patients whose alveolar bone levels are within 1-2 mm of the cementoenamel junctions (CEJs) of the teeth. In many cases, the patient’s BW or periapical images are too dark to make accurate height assessments (Figure 2). With digital images, optimizing contrast and brightness can help measure alveolar bone height, but “image reversal,” in this author’s opinion, can help make this determination even more precise.

 

Figure 2

The bone anterior to tooth #29 is easily visible with “inversion”.

 In addition to this height determination, image reversal seems to allow better visualization of the periodontal ligament (PDL) space (Figure 3), furcation areas (Figure 4), and even the pulp canals (Figures 5). All vendors include this tool as part of their image-processing software programs. Figures 3-5 provide examples of inverted images.

 

Figure 3

 

Figure 4

 

Figure 5

Periodontal ligament width – how wide is really wide?

Although the estimation of PDL space and thickness of lamina dura (apparently thickened in hyperparathyroidism) may be over-rated¹¹ as clinical diagnostic aids, dentists do derive some clinical information about the patient’s periodontal health status and, in some cases, systemic health status (for example, the symmetrical widening of the PDL in progressive systemic sclerosis or scleroderma) from more apparent changes in these structures.

Assessing PDL width may be over-rated simply because many PDL spaces interpreted as wide may really just be more apparent in some cases because the x-ray beam happened to pass through the space at 90 degrees (or a perfect right angle) as a result of projection geometry, while other spaces appear narrower or absent because the beam was not perpendicular (Figure 6).

Figure 6

That being said, the evaluation of changes in the PDL may best be accomplished by using EIP and the software’s image inversion and embossing tools (Figures 7 and 8). The PDL on the distal aspect of tooth #5 is more visible with either tool.

  

Figures 7 and 8

Early periapical changes – how soon is soon?

When the pulp dies, one of the earliest changes dentists seek to correlate with symptoms is the widening of the PDL at the apex of the suspected symptomatic tooth. Only perfectly exposed and processed conventional x-ray film images will help with this evaluation. Digital images may help make this determination sooner, or more accurate. Although many dentists and endodontists still believe that about 30% of the cortical bone must be destroyed before a periapical lesion can be detected, we have demonstrated that this may not be the case when using digital-image processing and digital solid-state detectors.¹² Early changes may be found sooner with digital radiography technology, especially those employing solid-state technology. Figure 9 illustrates this possibility.

  

Figure 9.

Early apical lesion on tooth #24 (left central incisor) made more “apparent” by inversion and embossing.

Digital imaging – it’s not just for x-rays!

 Digital imaging can be applied to almost all aspects of general and specialty dental practice. Clinical images, cosmetic images, video camera images, x-ray images, scanned x-ray images, CAD/CAM images, implant images, TMJ images, and cone beam CT images…all of these digital tools have become integral parts of contemporary dental practice. While readers may not be using all of these modalities, they are probably using some. Digital imaging technologies come in many flavors. The devices listed in Table 3 are driven by solid-state detector technology—see how many you have.

 As the reader can probably discern from this list, the contemporary general dental practitioner is already integrating digital intraoral videocameras, digital panoramic and cephalometric images, digital clinical still cameras, and even transparency scanners into the practice. It is puzzling why many practitioners are slow, if not reluctant, to adopt intraoral digital x-ray systems. Tables 4, 5, 6, and 7 list many of the systems available. (Table 6 is included for the sake of completeness, but the devices listed are used primarily in radiology clinics/labs by referral.) Cone beam technology (CBT) is included because it uses solid-state detectors.

The “skinny” on phosphor plates

For many dentists, phosphor plate systems, called photostimulable phosphor plates (PSPs) or reuseable phosphor plates, are attractive because they do not have a wired connection, they are as thin as film, and they even look like conventional film. A distinct advantage is that they have a wide exposure latitude; that is, they can be exposed for a short time or long time and still result in a diagnostically acceptable image. These systems also seem to be less expensive initially. However, the PSPs do require infection control procedures just like film (individual wrapping and unwrapping, clean gloves for processing, etc.), they need to be handled carefully and are susceptible to scratching, which can render them nondiagnostic in as little as 50 uses.¹³ PSPs require discharging before re-use. They are uncomfortable for patients, just like film. They are not nearly as “productive” (in terms of speed) because of all the steps described above. For some offices this time loss may not be that critical, for others, rapid image production is critical.

 The new Optime system from Soredex (GE/Instrumentarium), introduced in 2004, showed instant utility. In my opinion, it is ideal for endodontic practices and emergency patient evaluation in general dental offices. The plate can be read in 5 to 7 seconds in the single image reader, and is returned to the operator fully discharged, all with minimal handling. It is not loaded on a drum scanner, which can slow the processing down. It does not require a special “lightbox” or to be placed on a dental x-ray viewbox to be discharged. It is actually a very rapid system, although it is still time-consuming to use for a full-mouth series (12 to 20) of images. Figure 13 shows this system and a sample image.

 I have postulated the reason(s) for slow adoption in several previous articles. some of the reasons. ^3,4  Perhaps some of the hesitation is because of the seemingly vast number of systems available. Or, perhaps the principle reason for slow adoption is because dental staff members, rather than dentists themselves, are the people taking x-rays. The task of rapid and precise x-ray acquisition is often delegated to auxiliaries. If dentists had to pick up an image detector and use it daily like a handpiece, laser, or air abrasion unit, they might adopt digital detectors more quickly. It may be a matter of “out of site, out of mind.” I say, give auxiliaries the best tool(s) for the job and then get out of their way. With digital tools, the staff will be able to take better images faster and the whole office will be more productive.

What’s really new – how advanced is advanced?

Perhaps the most exciting imaging technology now available to dentists is cone beam CT. Four manufacturers are currently providing this technology to the profession (Table 6). There are three “sit-down” panoramic-type and one traditional “table-gantry” type of cone beam CT units available in dentistry. These devices allow oral radiologists to acquire images of only the head and neck region of the patient, at greatly reduced absorbed x-ray doses compared to conventional medical CT, with full three-dimensional volume-rendering capability. These images can be used by dentists and dental specialists for a variety of purposes, including:

  §         pre-surgical implant assessment

§         TMJ imaging

§         orthodontic assessment

§         airway assessment

§         endodontic tooth morphology

§         paranasal sinus evaluation

§         surgical planning for odontogenic lesions.

 Examples of CBCT images for some of the applications listed above appear in Figures 10 through 12.

Conclusions

Digital technology is already everywhere in the dental office. The reality is that most dentists probably will adopt digital intraoral x-ray imaging systems in the very near future. The last hurdle to the integration of digital intraoral x-ray imaging is learning how to expertly apply the tools, specifically feature extraction, that will allow dentists to visualize dental disease more precisely. Hopefully, through this supplement, dentists who are hesitant to adopt these systems will gain a better understanding of the power of this technology, the usefulness of the software, and the ease of its application to help their clinical decision-making. As with most new technology, it is not a matter of whether dentistry will adopt digital x-ray imaging, it’s just a matter of when.

Disclosure

Dr. Miles is a consultant for Dentrix Dental Systems and other digital radiography manufacturers. He is also Director of Radiology for ClearSCAN Imaging in Phoenix, AZ.

References

1.      Miles DA: Imaging Using Solid State Detectors. Dent Clin North Am. 1993, 37(4):531-40.

2.      Miles DA and Davis E: Electronic Imaging in the Dental Office. J Canadian Dent Assoc 1993, 59(6): 517-521.

3.      Miles DA, Langlais RP and Parks ET: Digital X-rays Are Here; Why Aren’t You Using Them?  JCDA, 1999, 27 (12):926-934.

4.      Miles DA, Razzano MR:  The Future of Digital Imaging in Dentistry Applications of Digital Imaging Modalities for Dentistry. Dental Clinics of North America 2000, 44(2)427-438.

5.      Miles DA: Advances in Imaging in Oral Medicine, Alpha Omegan 2001, 94 (2): 21-25.

6.      Miles DA:  “The Deal on Digital: Radiographic Imaging in the New Millennium” Compendium 2001 22(12): 1057-1064.

7.      Li G, Yoshiura K, Welander U, Shi XQ, and McDavid WD: Detection of approximal caries in digital radiographs before and after correction for attenuation and visual response. An in vitro study. Dentomaxillofac Radiol. 2002, 31(2):113-6.

8.      Svanaes DB, Moystad A, and Larheim TA: Approximal caries depth assessment with storage phosphor versus film radiography. Evaluation of the caries-specific Oslo enhancement procedure. Caries Research 2000 34(6):448-53.

9.      Miles DA: "Radiology in a Digital Age: No Escaping Reality", 2002, www.LearnDigital.net.

10.  Miles DA: “Much Ado about Scanners”, 2001, www.LearnDigital.net.

11.  Berry HM Jr: The lore and the lure o' the lamina dura. Radiology. 1973, 109(3):525-8.

12.  Tirrell BC, Miles DA, Brown CE Jr, Legan JJ: Interpretation of chemically created lesions using direct digital imaging. J Endod. 1996, 22(2):74-8.

13.  Bedard A, Davis TD, Angelopoulos C: Storage phosphor plates: how durable are they as a digital dental radiographic system? J Contemp Dent Pract. 2004, 5(2):57-69.

Table 1—Positive attributes* of digital imaging

 

Table 2—Electronic image processing tools and tasks

Table 3—Commonly used devices that employ digital technology

Digital photographic cameras (e.g., Kodak DX7590, 5 megapixel)

            Intraoral videocameras (e.g., Dentrix ImageCam 2.0)

            CAD/CAM milling lathes (e.g., Sirona Cerec3^TM)

            Intraoral digital sensors (see Table 4)

            Panoramic digital machines (see Table 5)

            Cone beam CT  (CBCT) x-ray machines (see Table 6)

            Photostimulable phosphor plates (see Table 7)

            Flatbed scanners (e.g., Umax, Microtek, etc.)

            Fax machines

Table 4—Solid-state intraoral x-ray systems (CCD* or CMOS**)