CHAPTER 1 Introduction to Dental Radiography
Veterinary Dental Radiology
Dental and oral diseases, many of which cause discomfort and inflammation, are common in dogs and cats. These patients present a diagnostic challenge because they often show no outward sign of their discomfort. Furthermore, many of the methods that assist diagnosis in human patients, such as identification and localization of discomfort, thermal and electrical pulp testing, and local anesthesia testing, are not helpful in animal patients. In addition to these obstacles, most of the pathology-related tissues are below the gingival margin, hidden from direct visualization. So while radiography is a narrow method of adding additional information to that which we get during a physical examination, in the oral cavity it is a tremendously important one. In addition to diagnosing problems, dental and oral radiographs also provide critical information for treatment planning, treatment evaluation, and treatment success.
Basics of Radiographic Principles
Radiographs are images of shadows that are cast by tissues and structures of varying radiopacity. Structures that absorb x-rays are radiopaque, and those that transmit them are radiolucent. The final radiograph merges all the structures in a three-dimensional area into a two-dimensional image. It could be considered similar to taking all the slices of a computed tomography study and printing them all on top of each other on a single page. The interpreter needs to mentally reexpand the flat image into its original multilayered size to help make sense of the information on it. Interpretation of radiographs is often facilitated by evaluating two views taken at 90-degree angles. Unfortunately, due to the adjacent anatomy, radiographs of teeth cannot be made along the mesiodistal (side-to-side) axis. Veterinary dental radiographs are mostly taken along the facial-oral axis. When superimposition of structures interferes with radiographic interpretation, oblique projection radiographs should also be made by changing the horizontal angulation (tube shift) while keeping the vertical angulation the same (see “bisecting angle” technique in Chapter 12).
When evaluating a radiograph, always keep in mind the significance of multiple layers of overlapping structures. An important consequence of this is the “summation effect.” The summation effect is the result of superimposed structures and tissues either adding to the radiopacity (addition) or subtracting from it (subtraction) depending on their relative radiopacities (Figure 1-1
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