[Fundamental study of alveolar bone measurements in the hamster using an apparatus for intraoral radiography].

Morphometry of bone resorption in experimental periodontitis is performed primarily by radiography after sacrificing the animal or by microscopy of histopathologic specimens prepared from resected jaw bones. Both techniques are recognized as effective examinations. However, these are cross-sectional procedures involving resection of specimens, and for evaluation of changes in symptoms from reversible to irreversible, which are characteristic of periodontal diseases, or for follow-up of the aging process, application of standard radiography and a method to properly interpret the images obtained are needed. The author designed an apparatus that allows in site radiographic evaluation of individual animals, which has not been considered in conventional morphometric analyses of periodontal bone resorption. With this apparatus, radiograms are obtained by placing a soft X-ray film in the oral cavity and exposing it with a soft X-ray projector. As a fundamental study of the usefulness of this apparatus, author evaluated the optimal conditions of radiography for imaging of soft tissues, the accuracy of the measurements, and the method for bone measurement. Experimental bone resorption was induced in the mandibular alveolar bone of the hamster, the changing lesion was radiographed daily with this apparatus by the standard procedure, and measurements were attempted by the length measuring method and densitometry method. The following results were obtained: 1) The intraoral apparatus was designed to allow radiography of both sides of the mandibular molar regions of the hamster. The apparatus consisted basically of a film cartridge, an opening, and a fixing portion. The projection angle can be adjusted by the fixing portion so that soft X-ray is always projected orthoradially on the surface of the film, and the soft X-ray film can be kept attached to the hamster mandibular molar region by microadjustment of the opening and the calibrations for angle adjustment. With this apparatus, the percent enlargement was minute at 0.43%, and the reproduced image showed a correlation of 0.998 with the standard. (2) The radiographic conditions of a focus-film distance of 30 cm. acceleration potential of 40 kV, current of 2.5 mA, and projection time of 20 sec. were considered to be optimal in hamsters with regard to the quality of the image and stress to the animals. 3) Palladium used as a reference for densitometry was highly manipulatable with a maximum thickness of 0.1 mm and was appropriate for estimation of the mineral content of the hamster mandibular bone. 4) According to morphometry of the hamster lower jaw alveolar region by the length measuring method and the densitometry method in serial standard soft X-ray images, bone absorption was greater in the order of the diet + inoculation group, diet group and control group in a decreasing order. In the control group, the growth of the bilateral alveolar region reached a peak 23 weeks (about 165 days) after birth, and bone resorption probably due to aging was thereafter observed at the apex of the alveolar bone.