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Biomedical subjects

E Asmussen

Publications and source records attributed to E Asmussen.

At least 163 records · Page 9Linked to original sources
PubMed1978

The stability of water in the pores of acid etched human enamel.

A mechanism is proposed, explaining the fact that drying by compressed air for 5-10 sec. will remove acid and dissolved enamel from the relatively long and narrow pores of etched enamel surfaces. It is a consequence of the proposed mechanism that water in the liquid state is not stable in the pores, and accordingly, that condensation of water vapour on the etched and dried surfaces is not likely to occur. This was confirmed by studying tag formation in etched enamel surfaces under conditions where water vapour will condense on unetched tooth surfaces.

Acid Etching, Dental↗
PubMed1977

Regulation of respiration: "The Black Box".

A close relation between the state of wakefulness, the electroencephalogram, and the respiration has been demonstrated (Bülow 1963). In the present paper it was assumed that as opening and closing of the eyes influence the EEG and thus probably the state of wakefulness, the responsiveness of the respiratory center may likewise be influenced by the single act of closing the eyes. Seven subjects were studied in the steady state of rest breathing ambient air, 4-5% CO2 in air, or 11% O2 in nitrogen. In experimental periods of 4-5 minutes their pulmonary ventilation and alveolar PCO2 were measured while they randomly were either reading a book, or were blindfolded. It was found that in all three conditions closing of the eyes resulted in a mean decrease of VE of 8 to 14% with a concomitant increase of PACO2 of about 1 mmHg. It is tentatively suggested that other and stronger central or peripheral stimuli impinging on the reticular formation of the brain may explain the changed sensitivity of the respiratory center towards the chemical stimuli in conditions like exercise, chronic hypoxia etc.

Adult↗
PubMed1977

Penetration of restorative resins into acid etched enamel. I. Viscosity, surface tension and contact angle of restorative resin monomers.

It has been a controversial question whether an intermediate layer of low-viscous, non-composite resin between composite restorative and etched enamel is beneficial. It was the purpose of the present work to investigate some of the factors that govern the penetration of resins into the capillary pores of etched enamel surfaces. Viscosity, surface tension and contact angle on human enamel were measured using monomer mixtures similar to those found in commercial restorative resins. Employing a cylindrical model of relevant dimensions of the capillary pores, and on the basis of Poiseuille's equation the time of penetration was calculated for a relatively high-viscous and a relatively low-viscous monomer mixture. It was concluded that viscosity as such is not a limiting factor for the penetration of restorative resin monomers into the pores of etched enamel surfaces.

Acid Etching, Dental↗
PubMed1977

Penetration of restorative resins into acid etched enamel. II. Dissolution of entrapped air in restorative resin monomers.

Viscosity, surface tension and contact angle are factors that influence the penetration of restorative resins into acid etched enamel. Furthermore, as the resin is drawn by the capillary forces into the pores of the etched enamel the pressure of the entrapped air will increase. The increased pressure has the effect that air will dissolve in a resin that is saturated with air at one atmosphere. The purpose of the present work was 1) to investigate the rate of dissolution of included air bubbles at increased pressure, 2) to use the results to calculate the depth of penetration by means of a cylindrical model of the capillary pores, and 3) to check the results of the calculations by measurements of the tag lengths of restorative resins placed on acid etched enamel. The rate of dissolution was measured in monomers of varying viscosity in a glass syringe by means of a stereo microscope. The calculations showed that the depth of penetration decreases only slightly with viscosity. Thin sections of restorative resins placed on acid etched enamel were prepared whereafter the enamel was dissolved in hydrochloric acid. Tag lengths of 50 micron or more were observed with composite as well as non-composite resins.

Acid Etching, Dental↗
PubMed1977

Marginal adaptation of restorative resins in acid etched cavities.

The purpose of the present work was to investigate the wall-to-wall polymerization contraction of restorative resins placed in acid etched cavities and to study the effect of water absorption and temperature changes on the formation of marginal gaps on such fillings. Fillings made in extracted human teeth were examined microscopically. Before filling the cavities including 1.5-2 mm peripheral enamel were etched with 35% H3PO4. When polished and examined immediately after setting, fillings of a number of brands showed no marginal gaps. Gaps due to continued polymerization were formed around some of these fillings after 1 day's storage in water at 37 degrees C. These gaps did not close as a consequence of hygroscopic expansion of the fillings. Around fillings after 1 day's storage in water at 37 degrees C. These gaps did not close as a consequence of hygroscopic expansion of the fillings. Around fillings of the brands where no gaps present immediately after setting, gaps were formed by cooling from 37 to 23 degrees C. One day's storage in water at 37 degrees C before polishing generally reduced the frequency of marginal gaps both directly and after cooling. Heating of the fillings increased the risk of gaps being formed by a subsequent cooling.

Acid Etching, Dental↗
PubMed1976

Mechano-elastic properties of human muscles at different temperatures.

The effect of changes in the muscle temperature on their ability to store elastic energy was studied by having 5 trained subjects perform maximal vertical jumps on a force platform, with and without counter movement, at muscle temperatures between about 32 degrees C and 37 degrees C. The results showed that the heights of vertical jumps were considerably reduced at lowered temperature, but the gain in height after a counter movement in the form of a jump down from a height of 0.4 m over the force platform, was significantly higher in the cold condition. T o test whether this was due to an increased stiffness of the muscles, experiments with imposed sinusoidal length variations at 14 Hz were performed. Delta force XDelta length-1 (i.e.stiffness) increased with isometric tension independent of muscle temperature. Experiments in which the rate of tension development and relaxation in voluntary maximal isometric contractions were measured at different muscle temperatures showed that maximal isometric tension changed by less than 1% per degree but the rate of tension development and relaxation by 3-5% and 5% per degree, respectively, in the temperature range studied (30 degrees to 40 degrees). These data may be explained by the hypothesis that the series elastic components of the active muscle are located in the cross-bridges between myosin and actin filaments. The storage of elastic energy would be enhanced if the rate of breaking of these bridges were decreased at lower temperatures.

Body Temperature↗
PubMed1975

A follow-up longitudinal study of selected physiologic functions in former physical education students-after forty years.

Reported is the continuation of follow-up investigations of certain physiologic functions in former physical education students. The first follow-up study was conducted about 30 years after the initial measurements. The present follow-up study concerned a re-investigation of the same group (23 men and 11 women), 10 years later, i.e., about 40 years after the first examination. Resting values for heart rate, blood pressure and metabolism were determined, as well as values for lung volume, hand-grip strength, and reaction time. During moderately hard exercise, measurements were made of oxygen uptake, ventilatory equivalents, and heart rate. By extrapolation of these heart-rate determinations to "maximal heart rate," the maximal oxygen uptake was estimated and expressed as L times min-1 and as ml x min-1 and as ml times kg-1 x min-1. The data show a general deterioration in practically all the physiologic functions studied, most pronounced during the last 10 years of the 40-year period.

Adult↗
PubMed1975

Enamel damages caused by contracting restorative resins.

Several observations have shown that contraction stresses in restorative resins bonded to the enamel of cavity walls readily broke the enamel surrounding the cavities. The forces studied were caused by polymerization contraction, thermal contraction or elastic hysteresis. The bonding was obtained mainly by etching the cavity walls by phosphoric acid.

Acrylic Resins↗
PubMed1975

NMR-analysis of monomers in restorative resins.

A study on the composition of the resin component of the several brands of composite resin has not been published so far. It was the purpose of the present work to fill out this gap in our knowledge of this important group of restorative materials by analyzing the monomers of the materials as delivered by the manufacturers. 24 brands of restorative resins were investigated by means of a Nuclear Magnetic Resonance spectrometer at 90 MHz. Spectra were taken of deuterated chloroform solutions of the organic part of the filling materials and compared with spectra of pure monomers that were conceivable constituents of the investigated brands. It was found that the BIS-GMA containing brands all contain at least one other monomer, most often TEDMA, in varying concentrations. The brands with MMA as main component in most cases also contain other monomers.

Acrylic Resins↗