Dental radiographs are the traditional method used it) assess the destruction ot alveolar bone associated with periodontitis. Although radiographs cannot accurately reflect the bone morphology buccally and lingually, they provide useful information on interproximal bone levels. Moreover, they provide information on the periodontium that cannot be obtained by any other noninvasive methods (e.g., root length, root proximity, and presence of periapical lesions and estimates of remaining alveolar bone) (Fig 34-1, /». However, it is well known that substantial volumes ol alveolar bone must he destroyed before the loss is detectable in radiographs-'*; specifically, more than 30% of the bone mass at the alveolar crest must be lost for a change in bone height to be recognized on radiographs. " Therefore conventional radiographs arc very specific, but lack sensitivity. (See Chapters .32 and
Numerous cross-sectional and longitudinal epidemiologic studies have used radiographs as the principal method of determining the presence or absence of periodontal destruction. The primary criterion lor bone loss in these studies was the distance trom the cementoe-namcl junction (( .'I D to the alveolar crest »is measured from bite-wing radiographs, flu* threshold distance ol hone loss has varied Irom 1 mm to > mm, although most of the studies have used 2 mm as the criterion for bone loss.1 I'll¡s low degree of sensitivity is mainly due to the subjectivity of radiographic assessment and to the inherent sources of variability affecting the conventional radiographic technique, such as (I) variations in projection geometry; (2) variations in contrast and density due to differences in film processing, voltage and exposure time; and (3) masking of osseous changes by other anatomic structures (I'ig. 34-5). The variations in projection geometry can be reduced by the use of well-standardized long cone parallel radiographic techniques (Tig. t4-(>). lb standardize the radiographic assessment, radiographs should be obtained in a constant and reproducible plane, using film holders with a template containing some kind ol impression material, which is placed in a constant position on a group of teeth, and an extension arm that can be precisely attached to both the him holder and the x-ra\ tube 8 (l ig. 34-7). I he use of a parallel radiographic technique should be standard to all radiographic assessments tor periodontal diagnosis. I'he use of individualized film holders has been shown to be valid in evaluating bone changes in longitudinal studies and clinical trials.44
I he variations in image quality due to the variables inherent to conventional radiography can be reduced with the use ol digital intraoral radiography. Digital radiography enables the use of computerized images, which can be stored, manipulated, and corrected for under- and overexposures. Digital radiography may yield almost equal image properties compared with conventional radiographs, but through digital storage and processing, diagnostic information can be enhanced.lH Moreover, there is an important close reduction obtained with this technique (between \ to > of dose reduction compared vviih conventional radiographs).
Two digital radiography systems rely on the sensor the direct and indirect methods. Ihe direct method uses a charge coupled device (( CD) sensor linked with a liber optic or other wire to the computer system. I bis direct digital radiography obtains real-time imaging, offering both the clinician and the patient an improved visualization of the periodontium by image manipulation and comparison with previously stored images. Ihe main disadvantage of this technique is the limited sensor area, which is only large enough to depict one or two teeth. In addition, the sensor rigidity attached to a wire, which besides sterility issues, makes ideal image projection by using film holders very difficult.
Ihe indirect method (Digora System ) uses «i phosphor luminescence plate, which is a flexible fihnlike radiation energy sensor placed intraorally and exposed to conventional \-ray tubes. A laser scanner (lig. U-K) reads the exposed plates offline and reveals digital image data, which can be enhanced, stored, and compared with previous images. I he real advantage ol this indirect
492 PAR I .S ■ treatment af I'er'nnlantal Disease
Limitations in conventional periapical radiography. Examples of Ihe importance ot image projection in the diagnostic utility of oral periapical raciography. A, Radiograph taken without a paralleling technique showing a clear distortion of the root length relative to the crown. The alveolar bone height is and fills the interproximal space B, Image of the same tooth with a proper image projection showing the real alveolar bone height demonstrating severe bone loss in the distal of the upper first molar. C, Radiograph taken without a paralleling technique showing a clear distortion ot the root length relative to the crown Thealveo lar bone height is and fills the interproximal space. D, Image of the same tooth with a proper image projection showing the real alveolar bone height and the open interproximal space. (Courtesy Dr. Fredrico Herrero.)
method is clue to the plate size and llexibility, which is almost identical to conventional x-ray films. Therefore, a paralleling technique with the use of film holders can be easily applied.
Digital intraoral radiography is in a slate of rapid development. Sensors, as well as computer hardware and software, are continually modified and improved. Due to the clear advantage ot real or almost real images that can be improved and to the important educational component ol online images presented to the patient, it is expected that digital radiography will soon replace conventional radiography in modern daily practice. However, certain improvements should be expected in order to overcome some of the current limitations.
Subtraction radiography, a well-established technique in medicine, has been introduced as a technique in periodontal diagnosis. I his tec hnique relies on the conversion of serial radiographs into digital images. The serially obtained digital images can then be superimposed and the resultant composite viewed on a video screen. Changes in the density and/or volume of bone can be detected as lighter areas (bone gain» or dark areas (bone loss). Quantitative changes in comparison with the baseline images can be detected using an algorithm for gray-scale levels. Ibis is accomplished by means of a computer (computer assisted subtraction radiography) (l ig. 34-9). I his tec hnique requires a paralleliza-tion technique to obtain a standardized geometry and accurate superimposahle radiographs. Radiographs taken with identical exposure geometry can then be scanned using a microphotometer that determines a gray-scale value for each picture point. After superimposition of two subsequent radiographs, this technique can show differences in relative densities. Studies using this technique have shown (I) a high degree of correlation
Advanced Diagnostic Techniques ■ CHAPTER 34 493
Fig. 34-6 Radiographic paralleling technique. A, Position of the film holder relative to the teeth. B, Position of the film holder relative to the paralleling device C, Position of the paralleling device to the radiograph long cone tube. D, Obtained x-ray with proper image projection. (Courtesy Dr. Fredrico Herrero.)
between changes in alveolar bone determined by subtraction radiography and attachment level changes in periodontal patients after therapyts and (2) increased de-tectahilitv of small osseous lesions compared with the conventional radiographs from which the subtraction images are produced. ' Grondahl et al,2H using subtraction analysis, showed nearly perfect accuracy at a lesion depth corresponding to 0.49 mm of compact bone, whereas a lesion must be at least three times larger to be detectable with a conventional radiology technique. Subtraction radiography has also shown a degree of sensitivity similar to that for I1" absorptiometry.-16 It can detect a change in bone mass of as little as 5%.66
Subtraction radiography has been applied to longitudinal clinical studies. Hausmann et al detected significant differences in crcstal bone height of 0.87 mm/ and Jeffcoat et al41 showed a strong relationship between probing attachment loss detected using sequential measurements made with an automated periodontal probe and bone loss detected with digital subtraction radiography. Subtraction radiography is a technique that fa cilitates both qualitative anil quantitative visualization of even minor density changes in bone by removing the unchanged anatomic structures from the image. This enhances the detection of bone structures with true density change and significantly improved the sensitivity and accuracy of the evaluation. The main disadvantage of digital subtraction radiography techniques is the need to be close to identical projection alignment during the exposure of the sequential radiographs, which makes this method very impractical in a clinical setting. Recently, new image subtraction methods (diagnostic subtraction radiography |1)SK |) have been introduced combining the use ot a positioning device during film exposure with specialized software designed for digital image subtraction using conventional personal computers in dental Offices (see I ig. .34-9). This image analysis software system applies an algorithm that corrects for the effects of angular alignment discrepancies and provides some degree of flexibility in the imaging procedure. Recently, the use ot the DSK technique has been compared with the conventional subtraction radiography technique and with the conventional intraoral radiography technique yielding statistically significant gains in diagnostic accuracy over conventional radiographs and no differences against the classical subtraction radiography technique.64
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.