Michael K. Shrout

American Academy of Oral and Maxillofacial Radiology executive opinion statement on performing and interpreting diagnostic cone beam computed tomography

The American Academy of Oral and Maxillofacial Radiology (AAOMR) is the professional organization representing oral and maxillofacial radiologists in the United States. The Academy is a nonprofit professional society the primary purposes of which are to advance the science of radiology, improve the quality and access of radiologic services to the patient, and encourage continuing education for oral and maxillofacial radiologists, dentists, and persons practicing oral and maxillofacial imaging in allied professional fields. The AAOMR embraces the introduction of cone beam computed tomography (CBCT) as a major advancement in the imaging armamentarium available to the dental profession. The AAOMR is currently in the process of developing a position paper on appropriate application of CBCT to provide evidence-based guidelines. In the interim, the Executive Committee (EC) of the AAOMR considers it necessary to provide an opinion document addressing the principles of application of CBCT as it relates to acquisition and interpretation of maxillofacial imaging in dental practice.

Quantitative evaluation of digital dental radiograph imaging systems.

Two digital imaging systems, a video camera and analog-to-digital converter, and a charge-coupled device linear photodiode array slide scanner, were tested for their suitability in quantitative studies of periodontal disease. The information content in the original films was estimated, and digital systems were assessed according to these requirements. Radiometric and geometric performance criteria for the digital systems were estimated from measurements and observations. The scanner-based image acquisition (digitization) system had no detectable noise and had a modulation transfer function curve superior to that of the video-based system. The scanner-based system was equivalent to the video-based system in recording radiographic film densities and had more geometric distortion than the video-based system. The comparison demonstrated the superiority of the charge-coupled device linear array system for the quantification of periodontal disease extent and activity.

Differentiation of periapical granulomas and radicular cysts by digital radiometric analysis

It is generally accepted that two of the most commonly seen radiolucencies, the periapical granuloma and the radicular cyst, cannot be differentiated radiographically. The purpose of this investigation was to determine the feasibility of identifying radiometric differences in these two pathologic conditions by analyzing the patterns of the gray-level distributions of digitized radiographic images. Radiographs used in the study had been sent by practitioners to the School of Dentistry with tissue specimens. Radiographs of lesions identified as periapical granulomas and radicular cysts in the mandibular posterior quadrant were included in the study. The radiographs were digitized and regions of interest were drawn to include the lesions. Frequency distributions (histogram) with 256 gray-scale intervals and a cumulative percent histogram were computed. The typical histograms of the dental granulomas had narrower ranges and lower gray-scale values than did cysts. The results of this study indicate that it is feasible to radiometrically differentiate between lesions that are visually indistinguishable on radiographs.

35-mm film scanner as an intraoral dental radiograph digitizer: I: A quantitative evaluation

A 35-mm slide scanner digital imaging system was tested for its suitability in digitizing intraoral dental radiographic film for quantitative studies. The system (Nikon model LS-3510AF Nikon Electronic Imaging, Nikon, Inc., Melville, N.Y.) uses a charge-coupled device linear photodiode array. The data content in the original film images was evaluated, and the system performance assessed objectively with the use of specially designed test films. Radiometric and geometric performances for the digitizing system were extracted from measurements and observations, and these were compared with published data for two other film digitizing systems (video camera DAGE MTI, Michigan City, Ind. and Barneyscan 35-mm film digitizer Barneyscan, Berkeley, Calif.). The techniques used to evaluate this system are easy and suitable for evaluation of any digitizing system. This scanner system (Nikon) was superior to previously evaluated systems in transforming and recording radiographic film densities across the range (0.3 to 2.0 optical density units) of clinically relevant optical densities. The scanner offers substantial advantage over the other digitizing systems for gray scale information from clinically important optical densities.

A retrospective study of Angle Class I malocclusions treated orthodontically without extractions using two palatal expansion methods

The correction and relapse of mandibular anterior crowding was evaluated in a population of 58 patients with Angle Class I malocclusion who were treated orthodontically without extraction of permanent teeth. The subjects were retrospectively evaluated from records taken before treatment, posttreatment, and postretention. The postretention period averaged 8 years (minimum of 4 and maximum of 20 years). All cases in Groups A and B were given orthopedic treatment to develop the maxillary apical base in the transverse and anteroposterior planes. Group A was treated with expansion of the inner bow of the face bow appliance (Kloehn), and Group B was treated with the Haas palatal expansion appliance. Both groups were then treated orthodontically with tandem mechanics. The response variables measured were: overbite, overjet, intercanine distance, intermolar distance, and irregularity index. Study groups A and B were not significantly different for subject age, retention, or postretention time. Moreover, the groups did not show significant difference for any of the response variables before treatment. However, there was a statistically significant difference in the treatment times (P =.0133). A statistically significant treatment effect was observed for most response variables in the groups. Overbite, overjet, and irregularity index were significantly reduced, intermolar distance was significantly increased, and intercanine distance showed no significant change in Groups A and B. In the postretention period, there was a tendency for variables to change slightly toward their before treatment values but no compromise of orthodontic correction was noted. The irregularity index in Group A was corrected from 4.8 to 1.1 mm and remained at 1.1 mm in the postretention period. The irregularity index in Group B was corrected from 5.1 to 1.2 mm (P =.0001) and changed slightly from 1. 2 to 1.7 mm (P =.0540) in the postretention period. We concluded that mandibular incisors tended to become more crowded postretention. However, in contrast to previous reports, we calculate this relapse to be small. Neither before treatment nor posttreatment variables were predictive of relapse.

Implant site assessment using panoramic cross-sectional tomographic imaging

OBJECTIVES The purpose of this study was to evaluate the ability of two different panoramic imaging systems to produce cross-sectional images with accurate vertical dimensions of the posterior mandible. STUDY DESIGN Three partially edentulous human cadaver mandibles were used for this study. On each mandible, three potential implant sites were arbitrarily identified in an area between the mental foramen and the ascending ramus. Each site was imaged using two different panoramic machines. Using each image, the mandibles outline, cortical thickness, and position of the mandibular canal were traced on clear acetate film. The mandibles were then sectioned at each site to serve as a gold standard. The cadaver sections and tracings (corrected for magnification) were measured, recording the overall mandibular height, distance from the crest of the ridge to the superior aspect of the mandibular canal, and the thickness of the cortical bone at the most inferior aspect of the mandible. RESULTS There were no significant differences between either of the systems image measures and the gold standard when considering the distance between the crest and the mandibular canal. Differences were noted between the systems measures and the gold standard in the assessment of the cortical bone thickness and the overall mandibular height. CONCLUSIONS Both imaging systems can be useful for vertical measurements of a potential implant site in the posterior mandible.

Radiometric Classification of Alveolar Bone Health

A radiograph-based classifier for discrimination between normal and diseased alveolar bone was developed. The alveolar bone health of dry mandibles was rated, by consensus of two trained observers, as normal or diseased. Bitewing radiographs of mandibular quadrants were digitized and regions of interest (ROIs) of the alveolar bone between the first and second permanent molars outlined. Gray-scale histograms for the ROIs were computed, and a classifier based on these histograms was developed. Two observers (independently) used only the classifier to rate the bone as being normal or diseased. These ratings were compared with the original ratings of trained observers who viewed and scored the actual alveolar bone. The sensitivity (the ability to detect diseased alveolar bone), specificity (the ability to detect normal alveolar bone), and accuracy were 0.90 or greater, indicating good agreement with subjective visual assessments of dry mandibles. These results suggest that this procedure may be applicable for evaluations of bone health in humans.

Reproducibility of beam alignment using different bite-wing radiographic techniques

Longitudinal radiographic assessment of crestal alveolar bone plays an important role in the diagnosis and long-term evaluation of periodontal disease in patients. Because practitioners use several radiographic techniques to obtain bite-wing radiographs, horizontal and vertical alignment errors could adversely affect the diagnostic impression gained from this type of radiographic examination. The objective of this study was to determine the alignment reproducibility of three different clinical techniques used to acquire bite-wing radiographs. Patients who require bite-wing radiographs as part of a dental school screening process were radiographed with modified standard bite-wing tabs and two different intraoral positioning devices. Horizontal and vertical angular deviations were measured and alignment errors were calculated for each radiograph. The mean total angular alignment error for the standard bite-wing tab technique was 6.2 degrees, whereas the mean alignment error for both positioning devices was less than 1.8 degrees. The results of this study suggest that an intraoral positioning device for acquiring bite-wing radiographs should be used.

35-mm film scanner as an intraoral dental radiograph digitizer. II: Effects of brightness and contrast adjustments

Typical 35-mm slide scanners use a photodiode array and software that allows for digital and analog controls that are manually adjustable. The digital controls provide brightness and contrast adjustments, whereas corresponding analog controls adjust the exposure time and black level that determines the clamping level of the charge-coupled device for the maximum black in the image. The objective of this study was to determine the effects of these controls on the radiometric data of intraoral dental radiograph images, to establish recommended settings, and to set specific standard guidelines for the digitization process. Three approaches were used. The results of this study demonstrate that brightness and contrast control alterations on the digitizer produces different optical densities and modulation transfer function values. The impact of these results is unresolved yet must be considered in analysis on quantitative radiometric studies.

Effects of region of interest outline variations on gray-scale frequency distributions for alveolar bone

Normalized cumulative percentage gray-scale distributions from digitized radiographs of dry skulls can be used to evaluate alveolar bone health. With this method, manually defined regions of interest are used to identify the area of the image to be analyzed. The purpose of this study was to determine if variations in the dimensions of the regions of interest affect the gray-scale distributions. Two approaches were used. The effect of region of interest outline variations on (1) the ability to differentiate between various sized bone chips and (2) the ability to distinguish between two groups of skulls with the alveolar bone subjectively rates as normal or diseased were investigated. Four different regions of interest, which consisted of outline and area variations to a basic region, were used. Ninety-one percent of the cumulative histograms that represented chips were sufficiently separated from nonchip plots to be distinguished. Bone health was correctly assessed with a numeric classifier for 37 of 44 quadrants, for an accuracy of 84%, a specificity of 79%, and a sensitivity of 90%. Although ROI size and shape consistency in longitudinal studies are important in radiometric analyses, small variations had minimal impact in this study.