Chapter 1
Digital Imaging

Jeffery B. Price and Marcel E. Noujeim

Introduction

Imaging, in one form or another, has been available to dentistry 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. Roentgen publicly announced his discovery of X-rays (McCoy, 1919; Bushong, 2008). Many landmark improvements have been made over the more than 115-year history of oral radiography.

The first receptors were glass, however, 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 (Rogers, 2003). His work describes how various technological improvements have been adopted by the endusers of technology throughout the second half of the twentieth century and the early twenty-first century. 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 interested individual will adopt the technology or engage in the 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 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 one leading manufacturer in dental radiography, digital radiography is used by 60% of the dentists in the United States (Tokhi, J., 2013, personal communication). 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 does digital radiography offer the dental profession as compared to simply continuing with the use of conventional film? What are the reasons that increasing numbers of dentists are choosing digital radiographic systems over conventional film systems? Let us look at them.

Digital versus conventional film radiography

The most common speed class, or sensitivity, of intraoral film has been, and continues to be, D-speed film; the prime example of this film in the US market is Kodak's Ultra-Speed (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 a randomly selected survey of 340 dental facilities from 40 states found in the 1999 NEXT data, the skin entrance dose of a typical D-speed posterior bitewing is approximately 1.7 mGy (Moyal, 2007). Furthermore, according to the National Council on Radiation Protection and Measurements (NCRP) Report #172, the median skin entrance dose for a D-speed film is approximately 2.2 mGy while the typical E-F-speed film dose is approximately 1.3 mGy and the median skin entrance dose from digital systems is approximately 0.8 mGy (NCRP, 2012). According to NCRP Report #145 and others, it appears that dentists who are using F-speed film tend to overexpose 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 because 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 (total mAs) would be half that of D-speed film and the radiation dose would then be half.

Why has there been so much resistance for dentists to move away from D-speed film and embrace 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; therefore, in order to persuade individual dentists to change, there has to be compelling reasons, and, 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. Moreover, in all likelihood, there are dentists today who will retire from active practice before they switch from film to digital.

There are many reasons to adopt digital radiography: decreased environmental burdens by eliminating developer and fixer chemicals along with silver and iodide bromide chemicals; improved accuracy in image processing; decreased time required to capture and view images, which increases the 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; 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 cofactors seem to be more important than others in driving more dentists away from D-speed and toward digital radiography - the increased use of computers in the dental office and the reduced radiation doses seen in digital radiography. We will explore these factors further in the next section.

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 efficiency and reliability in the financial side of their practices. The next step was to allow computers into the clinical arena and use them in patient care. 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 to film; improved operator workflow and efficiency; fewer errors with fewer retakes; wider dynamic range; increased opportunity for co-diagnosis and patient education; improved image storage and retrievability; and communication with other providers (Farman et al., 2008; Wenzel and Møystad, 2010).

Review of basic terminology

Throughout this section, we will be using several terms that may be new to you, especially if you have been using conventional film; therefore, we will include the following discussion of some basic oral radiology terms, both conventional and digital. Conventional intraoral film technology, such as periapical and bitewing imaging, uses a direct exposure technique whereby the X-ray photons directly stimulate the silver bromide crystals to create the latent image. Today's direct digital X-ray sensor refers most commonly to a complementary metal oxide semiconductor (CMOS) sensor that is directly connected to 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 emit light photons; these light photons are then detected within the sensor pixel by pixel, which allows for almost instantaneous image formation on the computer display. Most clinicians view this instantaneous image formation 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 energy stored in the phosphor electrons is released as a green light, which is captured, processed, and finally digitally manipulated by the computer's graphic card into images relayed to the computer's display. The...