Acquiring Pediatric Bitewing Radiographs

Direct and Indirect Digital Radiography

Regarding the performance of dental  radiography, the adoption of digital intraoral imaging receptors, such as solid-state sensors and photostimulable phosphor (PSP) plates has been slow but steady in the United States.³ These faster receptors have been adopted primarily to reduce patient radiation dose, increase patient comfort, improve overall image quality by eliminating chemical processing, and increase practice productivity-all of which are all positive goals. Because of its potential to reduce radiation dose, it is recommended that all dental practices adopt digital intraoral x-ray imaging.² Two main types of digital intraoral systems are available: direct and indirect.

Direct systems utilize solid-state sensors that are directly connected to the computer via a cable or wireless connection, and the resulting image is immediately rendered on the computer. Typically, the matrix of a direct sensor is composed of several parts, including the electronic substrate, the chip, the fiber-optic faceplate, and the scintillator screen, which are all enclosed within a plastic housing to protect the components from the oral environment.

Indirect systems utilize PSP plates that, once exposed to radiation, capture an image that will then be "uncovered" by a scanner, converted to a digital image, and finally, displayed on a computer. Introduced to dentistry in the 1990's, PSP plate systems employ a phosphorous coated plate that is composed of a plastic base with a layer of europium-activated barium fluorohalide. When a red light (ie, around 600 nm) from a plate scanner stimulates the electrons "trapped" during exposure, the barium fluorohalide releases them, and light is released and converted into electrical energy.³ The variations in voltages output from PSP plates correspond to variations in stimulated light intensity from the latent image.

At an average of 1 mm in thickness, PSP plates (Figure 1) are only slightly thicker than film, which is approximately 0.77-mm thick. Despite this, PSP plates offer some flexibility and can be slightly bent to increase patient comfort (Figure 2). This is a critical advantage of PSP plates when compared with harder, solid-state sensors. This benefit translates into patient acceptance, especially with pediatric patients (Figure 3), and can lead to less retakes and, ultimately, less radiation for the patient.

Depending on several factors, such as storage conditions, PSP plates can retain their information for 12 to 24 hours. Once the information has been obtained from the plate, the system erases the image, and the plate is ready to be reused. Depending on a practice's needs, scanners are available in the market that can process one plate or multiple plates at the same time.

Case Report

A boy aged 3 years and 11 months presented to the office of a family dentist for a recall appointment. An examination revealed clinical evidence of occlusal caries on the mandibular right primary second molar (ie, tooth T). The interproximal spaces between the primary molars were closed tight, making it impossible to visually determine if there were any interproximal caries lesions. To aid in diagnosis, the dentist decided to obtain bitewing radiographs using PSP plates (ScanX^® Intraoral Phosphor Plates [size No. 2], Air Techniques). These PSP plates are manufactured in the same common sizes as film (ie, size No. 0, 1, 2) but are also available in larger sizes (ie, size No. 3, 4). A size No. 2 film is 35 mm x 45 mm, whereas the size No. 2 plate is 30 mm x 40 mm, which is smaller in the patient's mouth. However, because 100% of the surface area of a PSP plate is active, the size of the active area of the No. 2 PSP plate is nearly identical to the size of the active area of the No. 2 film. Both the right side (Figure 4 through Figure 6) and left side bitewing radiographs were obtained without any issue. No interproximal caries lesions were noted in the right side image (Figure 7).

Benefits of Indirect Digital Radiography

When compared with solid-state sensors, PSP plates are lower in contrast. However, with the use of image enhancement tools, even low exposures with PSP plates can produce relatively high contrast images.⁴ PSP plates can have effective resolutions ranging from 7 LP/mm to 18 LP/mm. Without magnification, the human eye is capable of distinguishing only about 6 LP/mm, which is obviously well within in the range of the resolving power of PSP plates.⁴

Undoubtedly, a fundamental factor that differentiates PSP plates from solid-state sensors is the patient's comfort during placement.^5,6A 2009 study examined the comfort levels of patients who underwent radiographic examination using solid-state sensors, PSP plates, and traditional film.⁷ According to the results, the most comfortable experiences were found to be the ones using the PSP plates.

Helping clinicians visualize small caries lesions is one of the most important tasks of digital intraoral radiography systems. During the last 20 years, several studies have compared the ability of solid-state sensors with that of PSP plates in differentiating small interproximal caries lesions.³ Besides positioning errors, for which the unfortunate consequence is often retakes, both systems perform similarly in their ability to help clinicians recognize small caries lesions.

Images from solid-state sensors can be seen immediately, and it has been recognized by the profession that some operators with insufficient training, primarily dental assistants, can be tempted to take multiple images in order to present the "best one" to the dentist. This practice is counterproductive to the goal of reducing patient exposure to ionizing radiation. The use of PSP plates, which employ a film-like workflow, can help to prevent the incidence of unnecessary repeated exposure.

Conclusion

All dentists in all dental practices should educate their teams in proper positioning techniques and safe radiographic imaging practices to eliminate unnecessary retakes and limit patients' lifetime exposure to ionizing radiation. It is a good practice to maintain a logbook to keep track of any films that are retaken. It has been reported that as many as 7% to 13% of all dental radiographs taken are retakes.⁸ Many of these retakes could be eliminated and the patients' overall exposure reduced through the use of patient-friendly intraoral receptors, such as PSP plates, as well as the implementation of intraoral positioning devices and rectangular collimators. 

About the Author

Juan F. Yepes, DDS, MD, MPH, MS, DrPH
Diplomate
American Board of Pediatric Dentistry
Professor
Department of Pediatric Dentistry
Indiana University
School of Dentistry
Indianapolis, Indiana

Private Practice
Indianapolis, Indiana