This review article introduces the revised WHO classification of cemento-osseous or cementum-containing lesions in comparison with the former classification of odontogenic tumours and bone lesions that are peculiar to the jaws. The most remarkable change is to combine the cementifying fibroma and ossifying fibroma into one entity under the designation of “ cemento-ossifying fibroma” and to place it in the category of benign osteogenic neoplasms. Cementifying fibroma and ossifying fibroma simply represent the ends of a continuous spectrum. Periapical cemental dysplasia (periapical fibrous dysplasia) and gigantiform cementoma (familial multiple cementomas, presently the preferred term is florid cemento-osseous dysplasia) have also been transferred from the subclassification of cementomas, i. e. odontogenic tumours, into the category of non-neoplastic bone lesions and are regarded to represent variants of the same reactive or dysplastic process grouped as “ cemento-osseous dysplasias”.Focal cemento-osseous dysplasia may occupy an intermediate portion of this spectrum between the periapical and florid cemento-osseous dysplasias. Consequently, only the benign cementoblastoma remains under the heading of “ neoplasms and other tumours related to the odontogenic apparatus ” and is categorized in the benign tumor group of odontogenic ectomesenchyme. The reasons or logical basis for these changes, particularly the current concept to regard the cementum and cementicles as a type of the bundle bone, are first outlined. Then, the disease concept, clinical, radiographic and histopathologic diagnostic features of each cemento-osseous lesion adopted in the present WHO classification are briefly explained. Points for differential diagnosis from each other or from other jaw lesions will also be discussed.

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The discoloration of dental X - ray film was examined by a spectrophotometric measurment and then digitally corrected using an image scanner and a computer. Discoloration was found to a decrease in transmittance over a comparatively wide range of wavelength. The decrease in transmittance was slight in red region andlarge in the blue region. RGB values of each pixel on a discolored film were measured. It seemed that discoloration progressed, and the B/R value decreased. Digital correction of the discoloration was made using a numerical correction function on the basis of B/R value. A couple of films stored in the same packet and having different discolored areas were used to evaluate the correction. In this evaluation, signal-to-noise ratio (SNR) of the image made by subtracting the digital corrected image from the non-discolored image was measured. High SNR was observed in this subtracted image. This correction was rcgarded to be almost reasonable.

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A nationwide survey in dental X-ray examination was performed in Japan and reported by UNS-CEAR, This time, we performed the nationwide survey using a questionnaire and estimated the frequency of radiographic examinations in Japan. The nominal tube voltage of the X-ray unit was usually, 60kV and a tube current of lOmA was most frequently used. Instant film with a speed group of C was most frequently used for intra-oral radiography. The frequency of using instant processing was similar to that of automatic processing in general hospital dental depart-ment and dental clinics, but automatic processing was used in all university hospitals. The fre-quency of X-ray examinations in dentistry in Japan was estimated 9287×104 for intra-oral expo-sures including 91.1×104 for bite-wing exposures and 3.9×104 for occlusal exposures in 1994, and 1104×104 for panoramic examination, The frequency of total of intra-oral and panoramic exami-nation was 10486×104 in 1994.

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Magnetic resonance imaging is becoming ever more essential in stomatognathic examination and diagnosis. MR images, however, may be affected by artifacts caused by certain dental mate-rials. To analyze possible metal-induced artifacts developed in dental MR images, quantitative analyses were done in a basic experiment using a medium intensity magnetic field (0.3 tesla). To simplify the relationship between the skull and dental restorations, we prepared metal (6 types: Nickel-chromium alloys, Cobalt-chromium alloys, Titanium alloys, Au alloys, Ag-Pd-Cu-Au alloys, silver) as well as acrylic resin specimens as 5 mm cubes and as a phantom. MR images of each metal specimens were compared to those of acrylic resin specimens. Imaging conditions were fast spin echo T2 weight, spin echo T2 weight, spin echo proton density weight, spin echo Ti weight and gradient echo T2*, and imaging directions were transverse, sagittal and coronal. Therefore, 645 different combinations were possible. The area of each resulting image was calculated. Nickel-chromium alloys, Cobalt-chromium alloys and Titanium alloys showed artifacts when compared with the acrylic resin control. Au alloys, Ag-Pd-Cu-Au alloys and silver did not show a consistent tendency, and images obtained tended to differ from those of the acrylic resin control depending on imaging conditions and direction. The order of artifact development range was Nickelchromium alloys, Cobaltchromium alloys, Titanium al-loys, Ag-Pd-Cu- Au alloys, Au alloys and silver. The strongest and weakest artifacts were ob-served under the condition of spin echo T2 weight and spin echo Ti weight, respectively. There was no consistent tendency observed among imaging directions: in Nickel-chromium alloys, Cobalt-chromium alloys and Titanium alloys, the artifact area increased in proportion to the increase in the number of specimens. In silver, Au alloys and Ag-Pd-Cu-Au alloys, the artifact area increased in proportion to the increase in the number of specimens, but only when speci-mens were arranged parallel to the imaging direction. In Nickel-chromium alloys, Cobalt-chro-mium alloys and Titanium alloys, artifacts were larger in the horizontal imaging direction than in the vertical direction. This finding was reversed in silver, Au alloys and Ag-Pd-Cu-Au al-loys. Quantitative artifact analysis revealed that the artifact area differed depending on the type of metal, imaging condition and direction. It is important to be aware that metal artifacts can create misleading images, so careful attention should be paid to the interpretation of raw dental MR images.

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Panoramic radiography is a unique projection technique for producing a single image of both maxillary and mandibular arches and many other anatomical structures. To obtain a similar panoramic image without panoramic radiography system, a modified three-dimensional (3D) CT imaging technique was designed. A set of CT slice image data extending from the chin to the orbit was used for 3D reconstruc-tion. The CT machine used in this study was the X-Vision (TOSHIBA, Japan). The helical scan technique was used. The slice thickness of reconstructed image was one or 1.5 mm. The occlusal plane or Frankfort horizontal (FH) plane was used as the reference line. The resultant slice image data was stored on a magnetic optical disk and then used to create panoramic 3D-CT images on a Macintosh computer systems (Power Macintosh 8600/250, Apple Computer Inc., USA). To create the panoramic 3 D-CT image, the following procedure was designed: 1: Design a curved panoramic 3D-CT imaging layer using the imaging layer and the movement of the x-ray beam in panoramic radiography system as a template. 2: Cut this imaging layer from each slice image, then the trimmed image was transfor-med to a rectangular layer using the “still image warping” special effect in the Elastic Reality special effects system (Elastic Reality Inc., USA). 3: Create panoramic 3D-CT image using the Voxel View (Vital Images Inc., USA) rendering system and volume rendering technique. Although the image quality was primitive, a panoramic view of maxillofacial region was obtained by this technique.

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The purpose of this study was to evaluate intraoral digital images converted to aluminum-equivalent images and their characteristics. Using DixelR, pixel value distributions were mea-sured for various exposure doses and the average pixel values calculated. Image of radiograph with aluminum wedge was transferred to a personal computer and converted to an aluminum-equivalent image. The original digital and aluminum-equivalent images were evaluated by four observers for the detection of hole on the aluminum block phantoms. As a result, there was no effect of the exposure time on the pixel values for dark current. The dose - response curves of the Dixel systems indicated that the pixel values increased in proportion to the radiation expo-sure. The original digital image changed according to exposure dose, however aluminum-equiva-lent images showed constant quality in the range of exposure time from 0.07 to 0.17sec. Furthermore, there was no effect of the exposure time on the aluminum-equivalent values of enamel, dentin, alveolar bone and pulp cavity. Aluminum-equivalent images were superior to the original digital images by visual evaluation using ROC analysis.

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