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Digital Imaging

Jeffery B. Price

1.1 Introduction

Imaging, in one form or another, has been used in the dental profession since the first intraoral radiographic images were exposed by the German dentist, Otto Walkhoff (Langland et al. 1984) in early 1896, just 14 days after W.C. Röntgen publicly announced his discovery of X-rays (McCoy 1919, Bushong 2008). Many landmark improvements have been made over the more than 120-year history of oral radiography (American Association of Oral and Maxillofacial Radiologists (AAOMR) 2021, Molteni 2021).

The first receptors were glass, but film set the standard for the greater part of the twentieth century until the 1990s, when the development of digital radiography for dental use was commercialized by the Trophy company who released the RVGui system (Mouyen et al. 1989). Other companies such as Kodak, Gendex, Schick, Planmeca, Sirona, and Dexis were also early pioneers of digital radiography.

The adoption of digital radiography by the dental profession has been slow but steady and seems to have been governed, at least partly, by the "diffusion of innovation" theory espoused by Dr. Everett Rogers (2003). His work describes how various technological improvements have been adopted by end-users of technology throughout the second-half of the twentieth and early twenty-first centuries. Two of the most important tenets of adoption of technology are the concepts of threshold and critical mass.

Threshold is a trait of a group and refers to the number of individuals in a group who must be using a technology or engaging in an activity before an individual adopts technology or engages in an activity. Critical mass is another characteristic of a group and occurs at the point in time when enough individuals in the group have adopted an innovation to allow for the self-sustaining future growth of adoption of the innovation. As more innovators adopt a technology, such as digital radiography, the perceived benefit of the technology becomes greater and greater to ever increasing numbers of other future adopters until eventually the technology becomes commonplace.

Digital radiography is the most common advanced dental technology that patients experience during diagnostic visits. According to the most recent dental office survey completed by the Conference of Radiation Control Program Directors in 2014-2015 and published in 2019, 86% of offices used digital imaging (Conference of Radiation Control Program Directors 2019). The numbers of dentists using digital imaging continue to increase. If you are still using film, the question should not be "Should I switch to a digital radiography system?" but instead "Which digital system will most easily integrate into my office?"

This leads to another question - What advantages do digital radiography offer the dental profession as compared with simply continuing with the use of conventional film? Let us look at them.

1.1.1 Digital Versus Conventional Film Radiography

The most common speed class, or sensitivity, of intraoral film has been D-speed film; the prime example of this film in the United States is Kodak's Ultra-Speed National Council on Radiation Protection and Measurements (NCRP 2012). The amount of radiation dose required to generate a diagnostic image using this film is approximately twice the amount required for Kodak's Insight, an F-speed film; in other words, F-speed film is twice as fast as D-speed film. According to Moyal, who used the 1999 NEXT data, the skin entrance dose of a typical D-speed posterior bitewing is ~1.7?mGy (Moyal 2007). According to NCRP Report #172, the median skin entrance dose for a D-speed film exposure is ~2.2?mGy, whereas the typical E-F-speed film dose is ~1.3?mGy, and the median skin entrance dose from digital systems is ~0.8?mGy (NCRP 2012). According to NCRP #145 and others, it appears that dentists who use F-speed film tend to over-expose the film and then under-develop it; this explains why the radiation dose savings with F-speed film is not as great as it could be since F-speed film is twice as fast as D-speed film (NCRP 2004, NCRP 2012). If F-speed film were used per the manufacturers' instructions, the exposure time and/or milliamperage would be half that of D-speed film and the radiation dose would then be half.

Why has there been so much resistance against the dental profession moving away from D-speed film and embracing digital radiography? First of all, operating a dental office is much like running a fine-tuned production or manufacturing facility; dentists spend years perfecting all the systems needed in a dental office, including the radiography system. Changing the type of imaging system risks upsetting the dentist's capability to generate comprehensive diagnoses. To persuade individual dentists to change, there has to be compelling reasons. Until recently, most of the dentists in the United States have not been persuaded to make the change to digital radiography. It has taken many years to reach the threshold and the critical mass for the dental profession to make the switch to digital radiography. And, in all likelihood, there are dentists who will retire from active practice before they switch from film to digital radiography.

There are many reasons to adopt digital radiography: decreased environmental burdens by eliminating developer and fixer chemicals along with the associated silver and iodide bromide chemical waste; improved accuracy in image processing of digital images; decreased time required to capture and view images with increased efficiency of patient treatment; reduced radiation dose to the patient; improved ability to involve the patient in the diagnosis and treatment planning process with co-diagnosis and patient education while viewing images on a computer monitor; and viewing software to dynamically enhance the image (Wenzel 2006, Wenzel and Møystad 2010, Farman et al. 2008). However, if dentists are to enjoy these benefits, the radiographic diagnoses for digital systems must be at least as reliably accurate as those obtained with film (Wenzel 2006).

Two primary co-factors seem to be more important than others in driving more dentists away from film and toward digital radiography - the increased use of computers in the dental office and the reduced radiation doses with digital radiography. These factors will be explored further in the next section.

1.1.1.1 Increased Use of Computers in The Dental Office

This book's focus is digital dentistry and later sections will deal with how computers interface with every facet of dentistry. The earliest uses of the computer in dentistry were in the business office and accounting. Over the ensuing years, computer use spread to full-service practice management systems with digital electronic patient charts, including digital image management systems. The use of computers in the business operations side of the dental practice allowed dentists to gain experience and confidence in how computers could increase financial efficiency and reliability in practice operations. The next step was to integrate computer applications developed for clinical uses. As a component of creating the virtual dental patient, initially, the two most prominent roles were electronic patient records and digital radiography. In the following sections, we will explore the attributes of digital radiography, including decreased radiation doses as compared with film, improved operator workflow and efficiency, fewer errors with fewer retakes, wider dynamic range, increased opportunity for co-diagnosis and patient education with the patient, improved image storage and retrievability, and communication with other providers (Farman et al. 2008, Wenzel and Møystad 2010). The virtual dental patient will be explored in later chapters.

1.1.1.2 Review of Basic Terminology

Conventional intraoral film technology, such as periapical and bitewing imaging, uses the direct exposure technique whereby X-ray photons directly stimulate silver bromide crystals to create a latent image. Today's direct digital X-ray sensor refers most commonly to a complementary metal oxide semi-conductor (CMOS) sensor that is directly cabled into the computer via a USB port. At the time of the exposure, X-ray photons are detected by cesium iodide or perhaps gadolinium oxide scintillators within the sensor, which then emits light photons. These light photons are then detected within the sensor pixel by pixel, which allows for almost instantaneous image formation on the computer monitor. Most clinicians view this instantaneous image display as the most advantageous characteristic of direct digital imaging.

The other choice for digital radiography today is an indirect digital technique known as photostimulable phosphor, or PSP plates; these plates resemble conventional film in appearance and clinical handling. During exposure, the latent image is captured within energetic phosphor electrons; during processing, the energetic phosphors are stimulated by a red laser light beam; the latent...