Proper darkroom organization, film handling, and adherence to the time and temperature method of film processing play important roles in producing films of high quality.48 For the sake of expediency in the production of working films in endodontics, rapid processing methods are used to produce relatively good films in less than 1 to 2 minutes (Fig. 5-11).48,62 Although the contrast in using rapid-processing chemicals is lower than that achieved using conventional techniques, the radiographs have sufficient diagnostic quality to be used for treatment films and are obtained in less time and with less patient discomfort. Rapid-processing solutions are available commercially, but they tend to vary in shelf life, in tank life, and in the production of films of permanent quality.
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Figure 5-11 Chairside darkroom allows rapid processing of endodontic working films. (Courtesy Dentsply Rinn, Elgin, IL.)
To maintain the radiographic image for documentation, it is recommended that after an image has been evaluated it be returned to the fixer for 10 minutes more and then washed for 20 minutes and dried. An alternative is to reprocess the film by means of the conventional technique. Double film packets can also be used for working films: one can be processed rapidly and the other conventionally. Regardless of what method is used for working films, a controlled time and temperature method should be used for the diagnostic qualities desired in pretreatment, posttreatment, and recall radiographs. All radiographs taken during the course of endodontic treatment should be preserved as a part of the patient's permanent record
Radiographic Interpretation in Endodontics
Examination and Differential Interpretation
Radiographic interpretation is not strictly the identification of a problem and the establishment of a diagnosis. The dentist must read the film carefully, with an eye toward diagnosis and treatment. Frequently overlooked are the small areas of resorption, invaginated enamel, separated files, minute fracture lines, extra canals or roots, curved and calcified canals, and, in turn, the potential problems they may create during treatment (Fig. 5-12). If a thorough radiographic examination is conducted, problems during treatment, additional time, and extra expense can be avoided or at least anticipated. As mentioned earlier, additional exposures at various angulations may be necessary to gain a better insight into the three-dimensional structure of a tooth.
Many anatomic structures and osteolytic lesions can be mistaken for periradicular pathoses. Among the more commonly misinterpreted anatomic structures are the mental foramen and the incisive foramen. These radiolucencies can be differentiated from pathologic conditions by exposures at different angulations and by pulp-testing procedures. Radiolucencies not associated with the root apex will move or be projected away from the apex by varying the angulation. Radiolucent areas resulting from sparse trabeculation can also simulate radiolucent lesions. In such cases these areas must be differentiated from the lamina dura and periodontal ligament space.
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Figure 5-12 A, Maxillary left central incisor with history of trauma and thin walls in the apical one third of the tooth. Once an apical barrier is formed, pressures exerted during obturation could cause fracture. B, Maxillary right first premolar with three separate roots (arrows). C, Maxillary right central with history of trauma. Apical resorption and calcification of the canal system complicate treatment. D, Dilacerated root system on maxillary left canine. E, Maxillary left first molar with calcification of the chamber and root canal system. F, Endodontically treated mandibular second molar with apical root resorption (star on mesial root) and external root resorption (star on distal root); separated file in mesial root (arrow).G, Retrieved file. H, Completed retreatment. I, Angled radiograph showing evidence of another root (apical arrows) in an endodontically treated maxillary first premolar; coronal arrow indicates sealer in unprepared canal. J, Completed root canal treatment of two separate canals. K, Bifurcation (arrows) of the root canal system in a mandibular second premolar. (H, J,andKCourtesy Dr. Francisco A. Banchs.)
A commonly misinterpreted osteolytic lesion is periapical cemental dysplasia or cementoma (Fig. 5-13). The use of pulp-testing procedures and follow-up radiographic examinations will prevent the mistake of diagnosing this as a periradicular pathosis. The development of this lesion can be followed radiographically from its early, more radiolucent stage through its mature or more radiopaque stage.
Other anatomic radiolucencies that must be differentiated from periradicular pathoses are the maxillary sinus, nutrient canals, nasal fossa, and lateral or submandibular fossa. Many systemic conditions can mimic or affect the radiographic appearance of the alveolar process. A discussion of these conditions is beyond the scope of this chapter, but the reader is encouraged to read further in any oral pathology textbook.
Lamina Dura: a Question of Integrity
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Figure 5-13 Variations in stages of periapical cemental dysplasia (i.e., cementoma) on the four mandibular incisors. All teeth are vital. (Courtesy Dr. Francisco A. Banchs.)
One key challenge in endodontic radiographic interpretation is understanding the integrity, or lack of integrity, of the lamina dura, especially in its relationship to the health of the pulp. Anatomically, the lamina dura62 is a layer of compact bone (i.e., cribriform plate or alveolar bone proper) that lines the tooth socket. Noxious products emanating from the root canal system can effect a change in this structure that is visible radiographically. X-ray beams passing tangentially through the socket must pass through many times the width of the adjacent alveolus, and they are attenuated by this greater thickness of bone, producing the characteristic "white line." If, for example, the beam is directed more obliquely so that it is not as attenuated, the lamina dura appears more diffuse, or it may not be discernible at all. Therefore the presence or absence and integrity of the lamina dura are determined largely by the shape and position of the root and, in turn, by its bony crypt, in relation to the x-ray beam. This explanation is consistent with the radiographic and clinical findings of teeth with normal pulps and no distinct lamina dura.56
Changes in the integrity of the periodontal ligament space, the lamina dura, and the surrounding periradicular bone certainly have diagnostic value, especially when recent radiographs are compared with previous ones. However, the significance of such changes must be tempered by a thorough understanding of the features that give rise to these images.
Buccal-Object Rule (Cone Shift)
In endodontic therapy it is imperative that the clinician know the spatial or buccolingual relation of an object within the tooth or alveolus. The technique used to identify the spatial relation of an object is called the cone or tube shift technique. Other names for this procedure are the buccal-object rule, Clark's rule, and the SLOB (same lingual, opposite buccal) rule.30,48,55,62 Proper application of the technique allows the dentist to locate additional canals or roots, to distinguish between objects that have been superimposed, and to distinguish between various types of resorption. It also helps the clinician to determine the buccolingual position of fractures and perforative defects, to locate foreign bodies, and to locate anatomic landmarks in relation to the root apex, such as the mandibular canal.60
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Figure 5-14 Objects may be localized with respect to reference structures by using the buccal-object rule (i.e., tube-shift technique). A and B, A straight-on view will cause superimposition of the buccal object (yellow circle) with the lingual object (red triangle). C and D, Using the tube-shift technique, the lingual object (red triangle) will appear more mesial with respect to the mesial root of the mandibular first molar, and the buccal object (yellow circle) will appear more distal on a second view projected from the mesial. E and F, The object (red triangle) on the lingual surface will appear more distal with respect to the mesial root of the mandibular first molar, and the object (yellow circle) on the buccal surface will appear more mesial on a view projected from the distal aspect.
The buccal-object rule relates to the manner in which the relative position of radiographic images of two separate objects changes when the projection angle at which the images were made is changed. The principle states that the object closest to the buccal surface appears to move in the direction opposite the movement of the cone or tube head, when compared with a second film. Objects closest to the lingual surface appear to move (on a film) in the same direction that the cone moved; thus the "same lingual, opposite buccal" rule. Fig. 5-14 shows three simulated radiographs of a buccal object (yellow circle) and a lingual object (red triangle) exposed at different horizontal angles. The position of the objects on each radiograph is compared with the reference structure (i.e., the mesial root apex of the mandibular first molar). The first radiograph (see Fig. 5-14, A and B) shows superimposition of the two objects; in this case the tube head was positioned for a straight-on view. In the second radiograph (see Fig. 5-14, C and D), the tube head shifted mesially, and the beam was directed at the reference object from a more mesial angulation. In this case the lingual object (red triangle) moved mesially with respect to the reference object, and the buccal object (yellow circle) moved distally with respect to the reference object. In the third radiograph (see Fig. 5-14, E and F), the tube head shifted distally and the beam was directed at the reference object from a more distal angulation; here the triangle moved distally with respect to the mesial root of the mandibular first molar, and the circle moved mesially. These radiographic relations confirm that the lingual object (red triangle) moves in the same direction with respect to reference structures as the radiograph tube and that the buccal object (yellow circle) moves in the opposite direction of the radiograph tube. Thus, according to the rule, the object farthest (i.e., most buccal) from the film moves farthest on the film with respect to a change in horizontal angulation of the radiograph cone. In an endodontically treated mandibular molar with four canals (Fig. 5-15), a straight-on view results in superimposition of the root-filled canals on the radiograph. If the cone is angled from mesial to distal, the mesiolingual and distolingual canals will move mesially and the mesiobuccal and distobuccal canals will move distally on the radiograph, when compared with the straight-on view.
The examples cited previously involve application of the buccal-object rule, using changes in horizontal angulation. The clinician should be aware that this rule also applies to changes in vertical angulation (Fig. 5-16). To locate the position of the mandibular canal relative to mandibular molar root apices, radiographs must be taken at different vertical angulations. If the canal moves with or in the same direction as the cone head, the canal is lingual to the root apices; if the mandibular canal moves opposite the direction of the cone head, the canal is buccal to the root apices. The clinician should recognize the wide range of applicability of the buccal-object rule in determining the buccolingual relationship of structures not visible in a two-dimensional image.
Digital Radiographic Techniques
The replacement of traditional radiographic film with digital sensors offers many advantages to radiography. The evolution of computer technology for radiography has allowed for nearly instantaneous image acquisition, image enhancement, storage, retrieval, and even transmission of images to remote sites in a digital format. The major advantages of using digital radiography in endodontics are that radiographic images are obtained immediately and radiation exposure is reduced from 50% to 90% compared with conventional film-based radiography.51,62 The primary disadvantages of digital imaging systems are their high initial cost and potential for reduction in image quality when compared with conventional radiography.
Digital imaging systems require an electronic sensor or detector, an analog-to-digital converter, a computer, and a monitor or printer for image display.62 (See Chapter 26 for a further discussion of digital imaging systems and how they function.)
Digitization of ionizing radiation first became a reality in the late 1980s with the development of the original RadioVisioGraphy (RGV) system by Dr. Francis Mouyen.51 This system has evolved into the RVGui (Trex Trophy, Danbury, CT). Other available systems include Dexis Digital X-Ray (Provision Dental Systems, Redwood City, CA) and Computed Dental Radiography (CDR) (Schick Technologies, Long Island City, NY) (Fig. 5-17, A and C). The FDA has approved all these systems.
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Figure 5-15 Comparison of straight-on and mesial-angled views of an endodontically treated mandibular molar with four canals. A to C, Straight-on view of the mandibular molar shows superimposition of the root canal fillings. D to F, Mesiodistal angulation produces separation of the canals. The mesiolingual (ML) and distolingual (DL) root-filled canals move mesially (i.e., toward the cone), and the mesiobuccal (MB) and distobuccal (DB) root-filled canals move distally (i.e., away from the cone) on the radiograph.
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Figure 5-16 Examples of the buccal-object rule using shifts in vertical and horizontal angulations. A, Bite-wing radiograph (straight-on view with minimal horizontal and vertical angulation) depicts amalgam particle superimposed over the mesial root of the mandibular first molar. To determine the buccolingual location of the object, the tube-shift technique (buccal-object rule) must be applied. B, The periapical radiograph was taken by shifting the vertical angulation of the cone (i.e., the radiograph beam was projected more steeply upward). Because the amalgam particle moved in the opposite direction to that of the cone (compared with the bite-wing radiograph), the amalgam particle lies on the buccal aspect of the tooth. C, The periapical radiograph was taken by shifting the horizontal angulation of the cone. (The radiograph was taken from a distal angle.) Compared with both A and B, each taken straight-on with minimal horizontal angulation, the amalgam particle moved opposite the direction of movement of the cone or tube head, confirming that the amalgam particle lies on the buccal aspect of the tooth.
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Figure 5-17 Digital imaging systems. A, Dexis Digital X-Ray System. B, Special shape of Dexis sensor. C, Schick desktop digital system with wireless sensor. D, Clinical placement of wireless sensor. E, Schick wired sensor covered by plastic sheath for infection control. (AandBCourtesy Provision Dental Systems, Redwood City, CA. CtoECourtesy Schick Technologies, Inc., Long Island City, NY.)
Direct digital systems have three components: (1) the "radio" component, (2) the "visio" component, and (3) the "graphy" component. The "radio" component consists of a high-resolution sensor with an active area that is similar in size to conventional film. However, length, width, and thickness vary slightly depending on the respective system (see Fig. 5-17, B and E). The sensor is protected from x-ray degradation by a fiberoptic shield, and it can be disinfected. Specially designed multiple types of sensor holders are available; for infection control, disposable plastic sheaths are used to cover the sensor when it is in use (see Fig. 5-17, E). Wireless CDR sensors have recently become available through Schick Technologies, Inc. This technology provides cable-free sensors to allow enhanced mobility at chairside (see Fig. 5-17, C and D). CDR Wireless is the first wireless direct digital radiography system. Wireless sensors provide greater mobility at chairside while reportedly providing the same level of image quality acquired with conventional CDR systems. Sensors instantly transmit images directly from the mouth. The image is automatically transmitted to the computer via radio waves. Images do not need to be processed as with traditional film and storage phosphor plates. Chemical processing as with traditional film is not needed. Also, sensors do not need to be downloaded, erased, or reset between shots.
The second component of a direct digital system, the "visio" portion, consists of a video monitor and display-processing unit (see Fig. 5-17, A and C). As the image is transmitted to the processing unit, it is digitized and stored by the computer. The unit magnifies the image for immediate display on the video monitor; it also can produce colored images and display multiple images simultaneously, including a full mouth series on one screen. Because the image is digitized, further manipulation of the image is possible; this includes enhancement, contrast stretching, and reversing. A zoom feature is also available to enlarge a portion of the image up to full-screen size.
The third component of a direct digital system is the "graphy," a high-resolution video printer that provides a hard copy of the screen image, using the same video signal. In addition, a digital intraoral camera can be integrated with most systems. Indirect digital imaging or cordless systems, such as Digora (Soredex-Finndent, Conroe, TX) and DenOptix Digital Imaging System (Dentsply/Gendex, York, PA), involve the use of a reusable filmlike plate without wires. The image to be scanned by a laser (to digitize it before viewing on the computer) is recorded on this plate. Although indirect digital imaging still incorporates reduced radiation exposure and image manipulation, it usually takes slightly longer before the image can be viewed.
The advantages of both direct and indirect digital radiography seem numerous, but the primary ones include the elimination of standard radiograph film and processing chemicals, a significant reduction in exposure time (i.e., 80% to 90% reduction, when compared with D-speed film), and rapid image display. Virtually all systems can be linked with electronic record systems so that patient data can be stored, accessed, and transmitted easily. An exposure time in the range of hundredths of a second is all that is needed to generate an image.62 One study showed that digital radiographic resolution was slightly lower than that produced with silver halide film emulsions, but the radiographic information may be increased with the electronic image treatment capabilities of the system.51 These systems appear to be very promising for endodontics and for general dentistry.
Digital subtraction radiography53 is a sensitive method for detecting changes in radiographic density over time. In endodontics, digital subtraction radiography may be especially useful for evaluating osseous healing after treatment and as an aid in diagnosis. By definition, subtraction radiography requires that two images have nearly identical image geometry; specialized positioning devices and bite registrations aid in matching the images. The subtracted image is a composite of the images, representing their variations in density. By subtracting all anatomic structures that have not changed between radiographic examinations, changes in diagnostic information become easier to interpret. Any change is displayed on the resultant image against a neutral, gray background. Recently, advances53 in computer technology have incorporated built-in algorithms to correct for variations in exposure and projection geometry. These advances have also enabled colorization of density changes so that hard tissue gain is represented by one color and hard tissue loss is represented by another color
Orascopy and Endoscopy
Orascopy6 (Fig. 5-18, A), or endoscopy, is a new method for enhanced visualization in endodontics using a flexible, fiberoptic endoscope. These fiberoptic probes are available in various diameters; the probes provide a large depth of field, and refocusing is not needed after the initial focus. Once the probe is applied, the clinician views the conventional or surgical site from the magnified image displayed on the monitor. Endoscopic endodontics allows the clinician to have a nonfixed field of vision, and probes can be manipulated at various angles and distances from an object without loss of focus or image clarity. With orascopy, finite fracture lines, accessory canals, missed canals and isthmuses, and apical tissues can be viewed (see Fig. 5-18, B to E). Evolving technology will likely enhance the precision and accuracy of the fiberoptic probes.