Factors affecting the accuracy of elastometric impression materials.

OBJECTIVES: The purpose of this study was to evaluate the effects of (1) various impression materials, (2) different storage times and (3) the proportion of inorganic filler on the accuracy and stability of elastometric impression materials. METHODS: The impression materials studied included three alginate impression materials (Algiace Z, CAVEX and Jeltrate), five commercial silicone impression materials (Aquasil, Exaflex regular type, Express, Coltex fine and Rapid liner) and two experimental silicone impression materials designed for this study (KE106A and KE106B). Impressions were made of 10 metal dies that mimicked prepared crowns. After an impression was taken, dental stone was immediately poured into the alginate impressions, while the silicone impressions was poured 30 min later and waited for 1 h for setting. The second and third stone dies were made 1 and 24 h later, respectively. The diameters of the occlusal surfaces of the metal dies and stone casts were determined using photographs of the surfaces taken with a Kodak DC 290 digital camera. The pictures were then measured using a photomicrograph digitized integration system to calculate any discrepancy. Because each impression was used to make three rounds of stone dies, two-factor mixed factorial ANOVA was used to evaluate the effect of materials and storage time on the accuracy of the stone casts. The simple effects analysis, combined with multiple comparisons considering the per family type I error rate, was performed following confirmation that an interaction between the two factors was significant. RESULTS: The results showed that: (1) there was a significant interaction effect between materials and storage times on the accuracy of the impressions. (2) Two addition type silicone materials, Aquasil and Exaflex, had the greatest accuracy and stability. (3) The experimental material KE106A had the least accuracy in the first and second rounds and the alginate impression material CAVEX had the least accuracy in the third round. (4) The stabilities of CAVEX and Jeltrate were the least consistent of the 10 materials and decreased significantly with storage time. (5) When the experimental material had a low proportion of filler (KE106A), there was a significantly greater dimensional discrepancy compared to the same material with a higher proportion of filler (KE106B). CONCLUSIONS: The accuracies varied among the 10 impression materials over three rounds. Of all the materials, the addition type silicone materials, Aquasil and Exaflex, had relatively greater accuracy and stability. The discrepancy of the alginate impression materials increased with storage time. The large loading of filler showed less discrepancy.

Centrally administered inhibitors of the generation and action of angiotensin II do not attenuate the increase in ACTH secretion produced by ether stress in rats.

The role of the brain renin-angiotensin system in the ACTH response to ether stress in rats was investigated by injecting the angiotensin II receptor blocking drug saralasin, the angiotensin II converting enzyme inhibitors enalaprilat and captopril, and the renin inhibitor L 363714 intraventricularly and measuring the ACTH and corticosterone concentration in plasma 10 min after ether stress. ACTH and corticosterone were elevated to at least the same level in rats treated with the inhibitors as they were in rats treated with the corresponding vehicles; indeed, ACTH values were somewhat greater in stressed rats treated with the converting enzyme inhibitors and the renin inhibitor. ACTH values in the absence of ether were not affected by saralasin, enalaprilat, and captopril and were increased by L 363714. The data do not support the hypothesis that the brain renin-angiotensin system is involved in the maintenance of ACTH secretion or that it mediates the increase produced by ether stress.

Some characteristics of the darkly stained area of the medial preoptic area of rats.

Male rats have larger darkly stained area (DSA) within the medial preoptic area (MPOA) than female rats and this sex difference appears at the age of day 5 and continues to persist up to senescence. This sex dimorphism seems to be independent of gonadal hormones in the adult. In male rats the DSA has higher neuron density and larger neurons than the surrounding non-DSA. The total neuron number in MPOA is not different between young male rats and young female rats. In old age, neuron number of MPOA decreased in female rats but not in male rats.

Age-dependent changes in the oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdaloid in rats.

The oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdala, of both sexes, ranging in age from 21-805 days for male rats and from 21-780 days for the estrus and diestrus female rats, was measured. The oxidative activity of the hypothalamus, hippocampus, and amygdala decreased rapidly from Day 21 until the 4th mo. and stabilized till the 27th mo. in the hippocampus and amygdala and gradually decreased from the 12th mo. to the 27th mo. in the hypothalamus. The cerebral cortex showed a different pattern which kept a constant level from day 21 to 12 mo. of age. There was no statistically significant change in any of the regions at the time of vaginal opening. Low oxidative activity of the hypothalamus and amygdala in old age was still observed in castrated/hypophysectomized male rats compared with young ones. Therefore, the decreased oxygen consumption in old age seems to be due primarily to changes in the brain tissue itself and not due secondarily to changes in the gonadotropin and sex hormone levels. Female rats had higher oxygen consumption values than males in the cerebral cortex, the hypothalamus, and the hippocampus. In the amygdala the males had a higher consumption. Estrus female rats showed significantly higher oxygen consumption than diestrus females only in the hypothalamus.