Hiroko Sasaki

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m-2 without city noise; (2) a calculating task on a VDT with luminance of 20 cd m-2 without city noise; (3) a calculating task on a VDT with luminance of 90 cd m-2 with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m-2 with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the highluminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.

Morphological factors of mandibular edentulous alveolar ridges influencing the movement of dentures calculated using finite element analysis

PURPOSE The aim of this study was to determine the importance of each morphological factor of edentulous alveolar ridges according to its influence on the movement of complete dentures. METHODS The shapes of casts and waxed complete dentures were digitized. The determined shapes of the ridges were uniformly divided circumferentially and radially. Principal component (PC) analysis was performed using the coordinates of the points on the grid as the variables (morphological PC). The denture movement under bilateral and unilateral loads was analyzed using a finite element (FE) model constructed from the digitized shape, following PC analysis of the displacement of representative points on the denture (displacement PC). The effects of the morphological PCs were evaluated by means of stepwise multiple regression analysis with displacement PC as a dependent variable. RESULTS The ridge height, clearance between the ridge and the occlusal plane, and various inclinations, were significantly selected as independent variables where the dependent variable was the displacement PC under a bilateral load. Under a unilateral load, the displacement PC was mainly influenced by the ridge height. The influence of morphological PCs of the non-loaded side tended to be larger than that of loaded side. CONCLUSION Under a bilateral load, ridge height, clearance to the occlusal plane, and inclination of the ridge are considered to account for denture movement. To evaluate the effect of the ridge morphology on denture movement under a unilateral load, it is effective to determine the partitioned shape together with the height in general.

Finite element model based on a mandibular cast and a waxed complete denture: Evaluation of the accuracy and the reproducibility of analysis

PURPOSE The purpose of this study was to evaluate a newly developed method to construct customized finite element models from the viewpoints of the accuracy of measurement and the reproducibility of calculated denture movement under loads. METHODS A cast of an edentulous mandibular alveolar ridge and a waxed complete denture were used. Measurement of the surface was done using a 3D-digitizer. After superposing, they were rotated so that the occlusal plane became level. The border of the alveolar ridge on the cast was decided in each buccolingual section. From a series of cross sections, the surface of the alveolar ridge was made. Based on the surfaces of the mucosa and denture, a finite element model consisting of the denture and underlying mucosa, which was given a uniform thickness, was constructed. This procedure and analysis under bilateral or unilateral loads on an artificial molar region were done repeatedly to evaluate its reproducibility and the error of the measurement of the surface. RESULTS The standard error of the measured shapes of spheres was estimated to be within 0.1mm. The error caused by superposing was estimated to be within 0.38 mm. The results of analysis showed that the coefficient of variation of the displacement of the denture at selected nodes was approximately 14.1% at most. CONCLUSIONS We conclude that this method has sufficient measurement accuracy and reproducibility for the calculated movement of dentures.

Zinc-Induced Excessive Glutamate Release may Cause Accelerated Senescence with Defect in Learning and Memory in Senescence Accelerated Mouse

Our results demonstrated that an abnormal glutamate neurotransmission caused by Zn deficiency induces neuronal cell injury in the hippocampus of SAMP 10. These neuronal disturbances may cause accelerated aging of brain of SAMP 10 with deficits in learning and memory (Fig. 2).