[Basic studies on the measurement of bone mineral content of mandible by quantitative computed tomography]

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.