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Biomedical subjects

W Finger

Publications and source records attributed to W Finger.

18 recordsLinked to original sources
PubMed1992

Influence of buffered and unbuffered acetylsalicylic acid on dental enamel and dentine in human teeth: an in vitro pilot study.

An in vitro study was conducted to investigate the erosive effect of buffered and unbuffered acetylsalicylic acid (ASA) on dental enamel and dentine in human teeth by scanning electron microscopy. In order to standardize the specimens and to improve comparability the dental enamel and dentine were superficially abraded. The enamel and dentine specimens were therefore particularly sensitive to the influences of acid agents. Concentrated solution of buffered chewable ASA tablets (500 mg ASA and 300 mg calcium carbonate in 5 ml water) showed no changes in the enamel surface structure after exposure times of 1 min, 5 min and 60 min. In contrast, minimal corrosive effects were already seen after exposure of the enamel surface to the unbuffered ASA solutions for 1 min. After exposure times of 5 min and 60 min erosion of the enamel was more pronounced. Immersion in the unbuffered ASA solution led to clearly visible micromorphological changes on the dentine surfaces even after exposure for 1 min. Exposure of the dentine specimens to the buffered ASA solutions led to only very slight changes in the surface morphology. Therefore, the scanning electron micrograph after exposure to buffered ASA is comparable to the picture of untreated dentine.

Aspirin↗
PubMed1990

Quantal secretion and loss of vesicles induced by veratridine at the crayfish neuromuscular junction.

Experiments were conducted in nerve-muscle preparations of small young crayfish (Austropotamobius torrentium, Astacus astacus). Application of veratridine in the superfusate induced strong quantal release of transmitter. After about 5 min when quantal release had declined to a low level preparations were fixed for electron microscopy. Unlike control preparations, veratridine-treated preparations revealed nerve terminals which were largely depleted of their synaptic vesicles. Our findings suggest that in the presence of veratridine the decline of quantal secretion results from the loss of vesicles caused by tonic nerve terminal depolarization. Moreover, our results indicate that during or after excessive quantal release triggered by veratridine synaptic vesicles may fuse with both the presynaptic membrane and each other.

Animals↗
PubMed1989

Quantal stores of excitatory transmitter in nerve-muscle synapses of crayfish evaluated from high-frequency asynchronous quantal release induced by veratridine or high concentrations of potassium.

At single voltage-clamped opener muscle fibres of crayfish claw, 10-100 mumol/l veratridine increased within a few seconds the rate of asynchronous quantal release, ñ, of excitatory transmitter from ñ less than 1 quantum/s to ñ congruent to 10,000 quanta/s. Thereafter ñ declined exponentially either with a single, tau(2) congruent to 50 s, or with two time constants tau(1) congruent to 19 s, tau(2) congruent to 50 s. In total (t----infinity), about 0.3 million quanta were released by veratridine in a single short fibre of about 1 mm length. These values were estimated by means of the noise analysis technique and they agreed with equivalent parameters of release when 100 mmol/l K+ were used as release stimulus. Strong quantal release could be elicited only once in a single muscle by veratridine. Furthermore, the effect of veratridine on quantal release could be completely prevented by pretreatment with tetrodotoxin. In another nerve-muscle preparation of crayfish, the abdominal superficial extensor muscle, up to 3 million excitatory quanta could be released by veratridine in a single fibre. In the latter muscle veratridine-induced asynchronous quantal release was strongly dependent on the extracellular concentration of Ca2+ whereas in the claw opener dependence of quantal release on extracellular Ca2+ was negligible.

Animals↗
PubMed1988

Prolonged time course of glutamate-operated single channel currents in neuromuscular preparations of small crayfish and a membrane current triggered by glutamate channel gating.

Single channel currents activated by glutamate were recorded by means of the patch-clamp technique in the abdominal superficial extensor muscle and the claw opener muscle of small (1-3 months old) and large (greater than 16 months old) crayfish. It was found that in small crayfish the time course of glutamate-operated single channel currents was prolonged by a factor of about 4 in these two preparations. In the abdominal superficial extensor muscle, single channel currents activated by 5 mmol/l glutamate had a mean burst length of tau = 2-3 ms in large crayfish and a mean burst length of tau = 8-9 ms in small crayfish. In the claw opener, for large crayfish tau congruent to 0.5 ms and for small crayfish tau = 1.5-2.5 ms resulted (500 mumol/l glutamate). Moreover, single channel currents with long time courses often slowly increased their amplitudes during the open time of the channel and current amplitudes did not decline completely to the baseline after channel closing. In addition, single channel currents with relatively constant amplitude were often followed by a small increasing and decreasing membrane current. The latter results suggest that glutamate channel gating might trigger a membrane current.

Animals↗
PubMed1988

Quisqualate-activated single channel currents in neuromuscular preparations of small and large crayfish.

Single channel currents elicited by 1-5 mumol/l quisqualate in neuromuscular preparations in large (greater than 16 month old) and small (1-3 month old) crayfish were recorded by means of the patch-clamp technique. In preparations from large crayfish single channel currents of variable amplitude (-1 to -12 pA) were induced by quisqualate. The mean burst lengths of these currents were tau approximately equal to 1-2 ms. In the opener muscle of the first walking leg and the contractor epimeralis muscle of small crayfish the mean burst lengths of single channel currents evoked by quisqualate were prolonged by a factor of about 4 (tau approximately equal to 5 ms). Moreover, in the opener muscle of the first walking leg of small crayfish single channel currents of small amplitude (-0.5 to -2.5 pA) were preferentially evoked by quisqualate. By contrast, in the contractor epimeralis muscle of small crayfish mainly single channel currents of large amplitude (-10 to -12 pA) were elicited by quisqualate. The results suggest that at the stage of neuromuscular development characterizing the small crayfish, gating properties of excitatory postsynaptic channels are different from those in adult crayfish. Furthermore, the results obtained in the opener muscle of the first walking leg of small crayfish are consistent with those obtained previously by means of the noise analysis technique.

Animals↗
PubMed1986

Repetitive axonal discharges elicited by serotonin and intracellular adenosine 3',5'-cyclic monophosphate in the crayfish neuromuscular junction.

Experiments were carried out in the opener muscle of the claw of small crayfish. After pretreatment of the preparation with serotonin (5-HT), application of the membrane permeant analogue of adenosine 3',5'-cyclic monophosphate (cAMP), 8-bromoadenosine 3',5'-monophosphate was capable of evoking reversibly repetitive discharges in the inhibitory and excitatory axon. Reducing phosphodiesterase activity with application of either 3-isobutyl-1-methylxanthine or theophylline also elicited repetitive axonal discharges after 5-HT treatment. Moreover, application of forskolin dissolved in ethanol caused repetitive axonal discharges. The chemically induced presynaptic action potentials were detected mainly by their postsynaptic effects, i.e. by recording inhibitory and excitatory postsynaptic currents in voltage-clamped muscle fibres. In addition, nerve spikes were recorded extracellularly. It is concluded that 5-HT and intraaxonal cAMP alter membrane properties of the efferent axons innervating crayfish muscle.

1-Methyl-3-isobutylxanthine↗
PubMed1979

Die-spacing technique by diffusion precipitation.

The present study has shown that it is possible by utilizing the principle of diffusion to precipitate on stone dies an adequate resin spacer of uniform and desirable thickness. Details and variables of the technique are described. The precipitation technique is simple and requires a minimum of time and equipment. This spacer technique opens up gateways for a new and improved casting technique cleared of most of the variables affecting the precision of the methods employed up till now. A new gypsum bonded investment for the new casting technique is being developed.

Acetone↗
PubMed1977

[Porosity of composite filling materials].

The porosity of composite materials was investigated. For the 5 materials tested the values varied between 5.9 and 2.2 vol. %. The volume of porosity could be reduced markedly by a short application of pressure upon the mixed material. Pressure and time of pressure were checked separately, and it could be shown that the percentage of porosity reduction was correlated almost completely with the viscosity of the composite.

Composite Resins↗
PubMed1976

[Inhibition of polymerization by oxygen in composite filling materials and enamel sealers].

The oxygen inhibition upon the polymerization of composite materials was investigated. The method permitted the avoidance of oxygen inhibition even in cases where the special matrix could not be used. The results can be summarized as follows: 1. The depth of inhibition, when atmospheric air is admitted, varies, according to different brands of composites, between 25 and 105 mum. 2. By conducting a protective gas over the surface of the polymerizing material, the contact of oxygen is avoided just as if a matrix were used. 3. Avoidance of oxygen is particularly important during the setting period of the material, i.e. the time between the end of mixing and the end of setting. 4. Polymerization under a protective gas makes it possible to polymerize even very thin layers of material and therefore widens the scope of use for sealants in caries prophylaxis.

Dental Materials↗
PubMed1975

[Mechanical-dynamic properties of prosthesis plastics].

Comparative studies on the mechanic and molecular properties of heat- and self-curing polymers (PMMA) showed the following results: 1. The glass-transition temperature of heat- and self-curing polymers clearly shows measurable differences also as a function of their storage conditions. However, this is hardly of any clinical or practical significance. 2. The modulus of elasticity values of heat and self-curing polymers are not significantly different in the range of the usually applied temperatures. However, water-uptake considerably reduces the rigidity. 3. Overloading or fatigue failures do not show any clear differences in morphological characteristics. The practical influence of smaller long-term inflation strength of self-curing polymers has not yet been sufficiently proven. 4. Heat and self-curing polymers are identical as basic materials for dentures from the point of view of material technology.

Cold Temperature↗
PubMed1975

[The cast structure after vacuum-pressure casting and centrifugal casting].

Evaluation of polished sections revealed the following: 1. Grain size in marginal areas of the crown is, in general, smaller than it is in the occlusal region. 2. Grain size varies depending on the casting method applied. Differences in hardness were found only to a limited extent. They were not always in line with the grain structure. This phenomenon deviating from the rule cannot satisfactorily be explained. The piping distribution was in accordance with observations made so far.

Crowns↗