A Dental Hygienist’s Guide to Digital Radiography

Digital radiography has been revolutionizing dentistry since its introduction two decades ago in 1987.¹ This technology is gaining in popularity and in the past five years, the use of digital radiography has more than doubled from 10 percent in 2000 to 22 percent in 2005.² A recent national survey of pediatric dentists revealed that 28 percent utilize some form of digital radiography.³ According to Dr. Steven Morrow, Director of Patient Care Services and Clinical Quality Assurance at the Loma Linda School of Dentistry, “no other topic seems to generate greater interest, and confusion, than digital radiography."⁴ While most dental practitioners understand analog or film-based radiography, it is equally as important for clinicians to have a basic understanding of digital radiography.

Digital Image

Digital radiography is technology that uses a sensor, computer and monitor to acquire, process, store, retrieve and display the radiographic image. In some cases, a scanner is required. Unlike a conventional radiograph, a digital radiographic image has no physical form. The dental radiograph seen in film-based radiography is analogous to a painting, where colors blend continuously to create the finished canvas. In filmless digital radiography, the image is more like a mosaic, tiny pieces put together to make the final portrait. These tiny dots of information, called pixels, are short for “picture elements.” The more pixels that are present, the higher the resolution, greater the sharpness and an overall better quality image is produced. Each pixel is assigned a number in the computer from 0 to 255, each representing a specific shade of gray, from pure black at 0 to pure white at 255. This gray scale displayed by the monitor is another important characteristic of a digital image because it is critical in our ability to diagnosis or interpret oral conditions. Despite the 256 shades of gray available, the human eye can only detect 32-shade levels unaided.⁵

Most digital systems use a conventional dental x-ray unit as the source for x-radiation. With digital radiography, we “acquire” an image rather than “take” a radiograph like in film-based radiography. Digital radiography requires 50 percent to 80 percent less radiation exposure in order to achieve an image, depending on the speed of film currently being used in the practice.⁶ Besides the required computer and monitor, basic components of digital systems include imaging software, image-recording device and scanner if needed. Many systems are available today and include intraoral, panoramic and cephalometric systems.

Types of Dental Images

There are three basic means to acquire a digital image:

• Direct: This is the fastest method to acquire an image and requires a specially coated electronic receptor, called a sensor, which records the image. The sensor is placed in the oral cavity in a similar manner as you would place a film packet. When exposed to x-radiation, the sensor converts the x-rays to an electronic form that is read by the computer almost immediately. Intraoral sensors are comparable in size to an intraoral film packet and may be wired or wireless. Wired sensors are connected to the computer via a fiberoptic cable and wireless sensors communicate with the computer via a radio frequency. (Currently only Schick Technologies sells a wireless sensor.)
• Indirect: This is the slowest method and requires a conventional dental radiograph. The film-based radiograph is converted into a digital image using a x-ray film scanner with a transparency adapter option and transferred to a computer for display and storage. A digital still or video camera can also be used to take a photograph of the dental radiograph. The resulting image is considered a copy of the original.
• Semi-indirect: This method requires a special sensor called a photostimulable phosphor plate (PSP) and a special scanner. The sensor is coated on one side with reusable phosphorus that stores the x-radiation until a scanning device converts it into a digital image. The PSP plate looks and handles like dental film, and the image is acquired when exposed to x-rays. Step two involves placing the plate in a special scanner, specific to the imaging software, to convert it to a digital image. This method is not as fast as the direct method, but quicker than the indirect method. The image stored on the plate is erased by exposing it to bright light. Once the plate is cleared, it can be used again. Some systems offer a scanner that also clears the plate, while other systems require the plate to be placed separately in bright light.

Advantages

There are several advantages to implementing digital radiography into clinical practice:

• Eco-friendly: No film, darkroom, chemicals or processing equipment needed. No hazardous chemical, silver salts or lead foil waste generated.
• Reduced radiation exposure: Digital sensors and PSP plates are more sensitive to x-radiation and require 50 percent to 80 percent less radiation dose than film. This technology supports the ALARA principle, “As Low As Reasonably Achievable” which promotes radiation safety.
• Efficiency: With the direct method, an instant image appears on the computer monitor; in the semi-indirect method, an image is visible on the monitor in less than half the time it takes to process a conventional radiograph.
• Lower cost per image: No darkroom, film, processing chemicals or waste disposal costs. No darkroom processing errors. Dental personnel are more efficient and productive as less time is needed to acquire images.
• Superior gray scale resolution: Digital radiography uses up to 256 shades of gray compared with the 16 to 25 shades seen on conventional film.⁶ This allows for contrast and density enhancement, which aids in the detection of disease.
• Visibility: Several features are available to assist in interpretation. Darkening or lightening the image, colorizing, 3-D, sharpness, flip and magnifying features help to highlight conditions. Digital subtraction, the reversal of the gray-scale, where radiolucent images appear more radiopaque and vice versa, can be used to assist in diagnosis and educate the patient.
• Ease of information transfer: Digital images can be sent electronically to insurance companies, referring dentists or consultants. They are easily stored in the patient’s electronic chart record.
• Enhanced patient education: Viewing the digital image on a computer monitor is an effective educational tool and can lead to increased patient understanding of their oral condition.

Concerns

• Upfront cost: The initial start up cost of purchasing a digital system has dropped significantly but still averages almost $10,000. This does not include the cost of the dental x-ray unit or maintenance and service repairs. To add or replace image receptors is costly, ($4,000-$10,000 for sensors and $30 each PSP plate). These costs, however, can be quickly recouped and lead to greater profitability in the long run.
• Sensor size: Some direct systems have sensors that are thicker and bulkier than dental film. This may be more uncomfortable for patients and more difficult for gaggers. The digital sensor is smaller than a standard #2 film, so the area covered by the image is less. In addition, the wire can be cumbersome. But these obstacles can be overcome with proper placement technique. Although PSP plates are thinner than film packets, they are more fragile and prone to damage from bending. Frequent replacement is often necessary.
• Infection control: Most digital sensors and PSP plates cannot be sterilized. Therefore, plastic barriers are required. These barriers must be changed between patients to prevent cross contamination and careful handling of these items is critical in maintaining asepsis.
• Infrastructure: Digital radiography is only as good as the system and hardware your practice has in place. Ensure that you have enough processing and storage capability, including a back up storage plan to protect files from data corruption or computer malfunction. System compatibility may be an issue when transmitting or transferring images.
• Legal concerns: Legal issues have been raised regarding the ability to manipulate digital images. Many manufacturers have addressed this by requiring a manipulated image to be saved as a copy or by marking the original image with an embedded, invisible watermark, making fraudulent modification more difficult.

Technique Tips

• The paralleling technique is the preferred method of exposure. Sensor holding devices are available to assist the clinician in stabilizing the sensor in the mouth and acquiring a diagnostic image. A poorly placed sensor or PSP plate results in a poor image. New disposable holding devices are also available.
• Digital sensor aids are available to ease patient comfort and prevent sensor slippage as well as add a barrier cover to the wired sensor. A finger cot can also be used to cover a sensor if the patient is not allergic to latex. These adhesive sponge pads can also be attached to the PSP envelope to add rigidity and help protect it from damage during exposure.
• Despite less x-radiation exposure, lead or lead-free aprons are still needed to protect patients, this includes thyroid shields for intraoral exposures.
• Continue to follow the FDA/ADA guidelines for prescribing dental radiographs.

Clinical practice is moving away from the era of film-based radiography. Clinicians of the 21st century need to have a basic understanding of the essentials of digital radiography in order to produce an image that can be used in the assessment, diagnosis, planning, treatment and evaluation of oral conditions and disease.

1. Wenzel A. Two decades of computerized information technologies in dental radiography. J Dent Res 2002; 81(9):590-3.

2. Dental Products Report (DPR). Radiography: A DPR survey report. Dental Products Report. 2005 May; Accessed on July 23, 2007.

3. Russo JM, Russo JA, Guelmann M. Digital radiography: a survey of pediatric dentists. J Dent Child (Chic). 2006 Sep-Dec;73(3):132-5.

4. Marrow, SG. Digital radiography: examining the choices. Loma Linda University Dentistry. Winter/Spring 2006;17(1):12.

5. Bushong SC. Radiologic science for technologists: physics, biology and protection. 7th edition. St Louis, MO: CV Mosby., 2001, 374.

6. Haring J, Howarten L. Dental Radiography Principles and Techniques. 3rd ed. Philadelphia, PA: Elsevier; 2006, 351-2.