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Biomedical subjects

J Klimek

Publications and source records attributed to J Klimek.

At least 37 records · Page 2Linked to original sources
PubMed1991

[Effects of an incremental application technique on the polymerization of two light-activated composite filling materials].

The influence of the use of an incremental technique on the polymerization depth of two light-activated composite resins (hybrid composite resin, microfilled composite resin) was investigated in vitro. Of each of the two materials specimens were produced using variable increments and different polymerization times. Polymerization depth was determined by means of a microhardness tester (Vickers hardness). At the bottom of the cavity hardness values were significantly higher in samples produced in small increments (2 mm) than in samples with thicker layers (3 mm). A polymerization time of 20 s resulted in a significantly poorer polymerization at the bottom of the cavity than longer polymerization times. Hardness values decreased within each layer from the surface to the bottom. Irrespective of the material and the duration of illumination SEM pictures showed the presence of a line in the interface of the layers. The use of incremental technique in class II restorations resulted in differently polymerized zones that are exposed to the varying conditions of the oral cavity.

Composite Resins↗
PubMed1990

Cytochrome P-450 involvement in the NADPH-dependent lipid peroxidation in human placental mitochondria.

The NADPH-dependent lipid peroxidation in human placental mitochondria has been found to be inhibited strongly by amphenone B, aminoglutethimide and carbon monoxide, inhibitors of cytochrome P-450-mediated reactions, but was hardly affected by respiratory chain inhibitors. Cytochrome c, an exogenous electron acceptor which is known to compete with cytochrome P-450 for the reducing equivalents, showed an inhibitory effect on NADPH-dependent lipid peroxidation. The observed NADPH-dependent superoxide generation was also strongly inhibited by amphenone B and aminoglutethimide. Moreover, the lipid peroxidation in placental mitochondria was demonstrated to be stimulated by xanthine/xanthine oxidase added as superoxide generating system. This peroxidation was not affected by amphenone B and aminoglutethimide. On the other hand, the superoxide dismutase was found to inhibit both the xanthine oxidase- and NADPH-dependent lipid peroxidation. These data provide evidence that cytochrome P-450 is involved in NADPH-dependent mitochondrial lipid peroxidation. It is suggested that superoxide liberated from cytochrome P-450, in combination with iron, may be responsible for initiation of NADPH-dependent lipid peroxidation in human placental mitochondria.

Aminoglutethimide↗
PubMed1990

[In situ fluoride uptake of initial caries lesions following application of two children's toothpastes].

Cylindrical blocks of enamel with initial caries lesions were brushed twice a day for 6 days using amine fluoride or monofluorophosphate children's toothpaste (250 ppm F-). Some of the enamel samples were left in the oral cavity for three further days after the end of the trial, during which time a fluoride-free toothpaste was used for daily oral hygiene. Half of the enamel blocks showed plaque formation during this period. The other half were kept clean. Fluoride soluble in KOH was only detected on the enamel blocks that had been brushed with amine fluoride children's toothpaste. The amount of solidly bound fluoride was significantly higher following the use of amine fluoride children's toothpaste than with monofluorophosphate children's toothpaste. The amounts of KOH-soluble fluoride and solidly bound fluoride fell again 3 days after discontinuation of fluoride application. But only the drop in the amount of KOH-soluble fluoride in demineralised tooth enamel after application of the two children's toothpastes can be explained by the differing reaction mechanisms of the two fluoride compounds.

Dental Enamel↗
PubMed1990

[Identification of children with high risk of caries related to caries occurrence in the past].

In several studies high correlations were found when the prevalence of caries in the past was correlated with future caries risk in children and adolescents. The practical value of this method for the identification of children with high risk for caries can be assessed by measurement of the ability of the method to recognize subjects who will develop caries (sensitivity) and to exclude those who will not (specificity). Taking into consideration worldwide studies from recent years the problems of this method were pointed out and discussed.

Child↗
PubMed1990

[Mercury release of silver amalgam fillings in vitro].

In vitro mercury release from silver amalgam fillings was analyzed by ICP (Inductively-coupled-plasma-atomic-emission-spectroscopy). Within 14 days 63.2 micrograms Hg and 41.5 micrograms Hg respectively, were released from unfinished and finished amalgam fillings (n = 5). The amounts of mercury found in this study were several times higher compared with the results from other in vitro-studies.

Dental Amalgam↗
PubMed1989

[Influence on de- and remineralization of dental enamel by toothbrushing with a dental salt].

In the study in question, tests were made to determine whether a dental salt, with or without the addition of fluoride, can improve the remineralization effect of the saliva. The experiments were performed in vitro by applying a method in which the dental enamel was softened and rehardened several times within a short period. The Knoop hardness of the enamel surface was used to determine the degree of de- and remineralization. The results clearly confirm the remineralization-promoting effect of the fluoride added to the dental salt.

Dental Enamel↗
PubMed1989

[In vivo retention of KOH soluble and firmly bound fluoride in demineralized dental enamel].

Cylindrical enamel blocks with initial carious lesions were treated for one hour with Duraphat or Fluor-Protector. After removal of the fluoride varnishes the enamel blocks were kept in the mouths of 3 probands for 5 days. Plaque was allowed to accumulate on half of the enamel cylinders, while the other half was kept clean. Part of the enamel cylinders were retained as fluoridated controls. Compared with Duraphat the application of Fluor-Protector resulted in a significantly higher uptake of KOH soluble and firmly bound fluoride. During the 5 days of the experiment the amount of KOH soluble fluorides decreased in both groups. In the presence of plaque the fluoride loss was higher. The amount of firmly bound fluoride increased both in the plaque covered and in the clean enamel. The durable cariostatic effect of fluoridated varnishes seems to be due to the slow dissolution of Ca F2-like precipitates on the enamel surface and the concomitant fluoride uptake in the underlying demineralized enamel.

Dental Caries↗
PubMed1989

[Clinical comparison of newly introduced toothbrush with two presently available toothbrushes].

The cleansing effect of a newly introduced toothbrush, which is characterized by a thin, permanently elastic neck for reduction of abrasion pressure and an especially flat brush head, was clinically compared with two tested toothbrushes. Under identical experimental conditions, 30 subjects tested all three toothbrushes. Plaque was determined by the plaque index for toothbrush studies. On the whole, no significant differences were demonstrable with regard to the cleansing effect among the toothbrushes. Reduction of abrasion pressure, therefore, does not have a negative effect on the cleansing effect of these toothbrushes.

Adolescent↗
PubMed1988

The involvement of superoxide and iron ions in the NADPH-dependent lipid peroxidation in human placental mitochondria.

Incubation of human term placental mitochondria with Fe2+ and a NADPH-generating system initiated high levels of lipid peroxidation, as measured by the production of malondialdehyde. Malondialdehyde formation was accompanied by a corresponding decrease of the unsaturated fatty acid content. This NADPH-dependent lipid peroxidation was strongly inhibited by superoxide dismutase and singlet oxygen scavengers, markedly stimulated by paraquat, but was not affected by hydroxyl radical scavengers. Catalase enhanced the production of malondialdehyde by placental mitochondria. The effects of catalase and hydroxyl radical scavengers suggest that the initiation of NADPH-dependent lipid peroxidation is not dependent upon the hydroxyl radical produced via an iron-catalyzed Fenton reaction. These studies provide evidence that hydrogen peroxide strongly inhibits NADPH-dependent mitochondrial lipid peroxidation. The inhibitory effect of superoxide dismutase and stimulatory effect of paraquat, which was abolished by the addition of superoxide dismutase, suggests that superoxide may promote NADPH-dependent lipid peroxidation in human placental mitochondria.

Female↗
PubMed1987

Inhibition by hydroxymalonate of malate dependent biosynthesis of progesterone in the mitochondrial fraction of human term placenta.

It has been shown that the conversion of cholesterol to progesterone by human term placental mitochondria incubated in the presence of malate or fumarate was inhibited by hydroxymalonate--an inhibitor of malic enzyme. No inhibition was observed when mitochondria were incubated in the presence of citrate or isocitrate. The degree of inhibition by hydroxymalonate of partly purified NAD(P)-linked malic enzyme activity was identical to that of both malate dependent pyruvate and progesterone formation by intact mitochondria. These data strongly support a previous suggestion that malic enzyme plays an important role in the malate dependent progesterone biosynthesis by human placental mitochondria.

Cholesterol↗
PubMed1987

The influence of plaque on reaction mechanism of MFP and NaF in vivo.

A modified Intra-oral Cariogenicity Test was used to study the influence of plaque on the reaction mechanism of sodium monofluorophosphate (MFP) or sodium fluoride (NaF) in either sound or demineralized enamel in vivo. Volunteer students, wearing mouth appliances holding enamel blocks, rinsed their mouths with MFP or NaF solution (1,000 ppm F-) three times a day. The amount of loosely-bound and acquired fluoride was determined after an experimental period of five days in plaque-covered, demineralized (PCD); clean, demineralized (CD); plaque-covered, sound (PCS); and clean sound enamel (CS). While no measurable loosely-bound fluoride could be found after MFP treatment, NaF caused deposition of a significant amount of alkali-soluble fluoride in all experimental groups. After MFP rinses, fluoride concentration in the enamel was increased in the following order: CS, PCS, CD, and PCD. After NaF treatment, demineralized enamel exhibited a higher fluoride acquisition when compared with sound enamel. Plaque had a minor effect on F- acquisition. It is concluded that demineralization of enamel enhances F- uptake from both NaF and MFP solutions. In the presence of plaque, F- acquisition was additionally increased only after MFP rinses in vivo.

Adult↗
PubMed1986

Correlation between the malate dependent progesterone and citrate biosynthesis in the mitochondrial fraction of human term placenta. The stimulatory effect of ADP and ATP.

The relationship between malate dependent conversion of cholesterol to progesterone and citrate biosynthesis in human term placental mitochondria has been investigated. It has been shown that ADP and ATP (but not AMP) stimulate, significantly, both progesterone and citrate formation. The stimulatory effect of these adenine nucleotides was dependent on the presence of Mn2+ in the incubation medium. When Mn2+ was omitted or replaced by Mg2+ only negligible stimulatory effect of ADP and ATP was observed. Atractyloside and oligomycin were without effect on ADP and ATP stimulated progesterone and citrate production. Other dinucleotides tested as: GDP, UDP and CDP stimulated both progesterone and citrate formation only slightly. In all the experiments presented the rate of progesterone biosynthesis was found to be significantly correlated with the rate of citrate production. The experimental results presented in this paper suggest that the stimulatory effect of ADP and ATP on malate dependent progesterone biosynthesis is a consequence of an increased conversion of malate to tricarboxylic Krebs cycle intermediates. The possible mechanism by which ATP and ADP stimulate the citrate formation in human placental mitochondria is discussed.

Adenosine Diphosphate↗