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Several techniques such as intra-oral dental radiographs, dental panoramic radiographs, computed tomography and dual energy x-ray absorptiometry have been used to evaluate the effects of oral diseases such as periodontal disease and systemic diseases such as osteoporosis on quantity and quality of alveolar bone of the jaws. Advanced imaging such as magnetic resonance imaging might also be applied to evaluate them in the future. However, the analysis and evaluation of alveolar bone should be carefully performed in consideration of some limitations included in each technique.

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.

It is important to determine the changes in alveolar bone during periodontal treatments. At present, radiography is widely used to determine the changes. But small changes in alveolar bone cannot be detected on X-ray films. To detect these small changes, a direct observation system using gamma-ray from 133Ba was considered. Using a multi-channel analyzer, gamma-ray absorption through the bone was detected in this method. This method was compared with densitometric measurement on the films using sliced animal bone. The newly developed method detected the bone changes more accurately. To evaluate the influence of soft tissue, Mix-D was used in both measurements. 133Ba absorptiometry showed that soft tissue did not influence the measurement more than the densitometric method.

Dental radiographs can be important for examination, evaluation and diagnosis of periodontal disease, and they have been widely used by dentists. However, discrepancies between radiographs and existing clinical periodontal tissue have been found. The purpose of this study was to investigate the relationship between the existing alveolar bone level on a Xeroradiograph and the root surface area covered with a periodontal ligament. Alveolar bone blocks from human skulls (total 34 teeth) and 60 patients (total 165 teeth) were used for this study. Each human skull bone block was taken Xeroradiograph under three types of conditions. 165 teeth from patients with severe periodontal disease were taken Xeroradiograph by a parallel method. The following equation was used for measuring the teeth on the Xeroradiograph. alpha = Root area supporting the existing alveolar bone/Root area from periapical to C-E junction x 100 The root surface area of each of the teeth extracted from bone blocks and of the extracted teeth from patients were measured by the membrane technique and calculated as follows: beta = Root surface area covered with periodontal ligament/Root surface area x 100 There was no significant difference in equation alpha calculated on three types of Xeroradiographs in the human skull. Significant positive correlations between alpha and beta were obtained, and an empirical regression line was constructed to estimate the ratio of the root surface area covered with periodontal ligament from the existing alveolar bone level on the Xeroradiograph. The results suggest that the ratio of the area of periodontal ligament to the root surface area given by these methods provides useful data for examination, diagnosis and evaluation of periodontal disease.

This study was performed to evaluate the efficacy of digital subtraction radiography in detecting alveolar bone changes. In order to test the sensitivity of quantitative evaluation by subtraction radiography, a copper equivalent thickness obtained from digitized radiographs was compared with the actual mineral content of bone phantoms with 15 different minerals and 25 bone specimens. Results demonstrated that the copper equivalent thickness correlated well with the actual mineral content (bone phantoms: gamma s = 1.0, bone specimens: gamma s = 0.985). In order to test the ability of digitized subtraction radiography in assessing alveolar bone changes in vivo, subtraction images were compared with histological features. The experimental angular bony defects were treated with conservative periodontal therapy in 3 monkeys. The standardized radiographs were taken longitudinally after therapy, and subtraction images were made from the sequentially obtained radiographs. In addition, for fluorescent histomorphometrical evaluations of new bone formations, the animals were dosed with oxytetracycline, calsein solution and arizarin complex solution. Radiographic and histological evaluations were scheduled to provide healing periods of 2, 3, 4, 5, 6 and 9 weeks after periodontal therapy. Subtraction radiography offered an objective method to follow histological changes of alveolar bone, and the copper equivalent thickness obtained from subtraction radiographs correlated with the histometric bone volume (gamma s = 0.9023, p less than 0.01). The results of these studies indicated that subtraction radiography was useful in monitoring alveolar bone changes associated with periodontal disease and treatment and that the quanitative measurement of periodontal bone changes by subtraction radiography was feasible.

The basic studies were made in order to apply Quantitative Computed Tomography (QCT) to the measurement of mandibular bone mineral content. On the basis of the results, the bone mineral contents of the periapical region of the mandibular alveolar bone was measured in 10 normal subjects (5 male and 5 female: aged in their 20's). The obtained results were as follows. (1) The changes in CT numbers for 12 weeks under the same conditions of scanning were stable within the level of 1.0H.U. standard deviation. (2) The standard deviation of CT numbers obtained from the experiment with variable field sizes was under 14.5H.U.. The standard deviation of CT numbers obtained from experiments with subjects on various degrees of X-ray absorption was under 49.2H.U.. These results showed that CT numbers were considered to be unsatisfactory for use as a quantitative parameter. (3) The linearity of CT numbers and K2HPO4 liquid density was estimated by correlation coefficient. The linearity was proved to have a good correlation coefficient, above 0.999. And the correction made using a K2HPO4-QCT phantom considered to have a sufficient accuracy. (4) The accuracy of the measurement of the bone mineral density of the mandibular was estimated to be +/- 3.9mg/ml K2HPO4eq using a QCT phantom. (5) The bone mineral density of the total alveolar bone, the cortical and the spongy bone in the periapical region from premolar to molar was 503.5 +/- 55.7, 771.4 +/- 52.7 and 198.4 +/- 69.0mg/ml K2HPO4eq respectively. (6) No significant differences in bone mineral density depending on the location or sex were observed. (7) Significant differences in bone mineral surface density depending on the location were observed. The value was higher in molar than in premolar regions. But no significant difference between sexes was observed.