Biomedical subjects

F C Driessens

Publications and source records attributed to F C Driessens.

At least 37 records · Page 2Linked to original sources

PubMed1994

Chloride- and alkali-containing calcium phosphates as basic materials to prepare calcium phosphate cements.

Combinations of an alkali-containing calcium phosphate-like rhenanite, sodium whitlockite or calcium potassium phosphate and a chloride-containing calcium phosphate-like spodiosite or chloroapatite with or without additions of other calcium phosphates like monocalcium phosphate monohydrate, dicalcium phosphate or dicalcium phosphate dihydrate were made and mixed with water into pastes. The setting time of these pastes was determined. After soaking for a day in Ringer's solution at 37 degrees C the compressive strength and the diametral tensile strength were determined. Two of the combinations tried in this study resulted in the formation of cements at room temperature. One cement was of the type dicalcium phosphate, whereas the other gave octocalcium phosphate as the solid reaction product. The byproducts formed were an aqueous solution of NaCl and one of K2HPO4, respectively. Applications for bone repair and augmentation are envisaged.

Alkalies↗

PubMed1994

Compliance of an apatitic calcium phosphate cement with the short-term clinical requirements in bone surgery, orthopaedics and dentistry.

An apatitic calcium phosphate cement was developed containing a nucleator in its powder and an accelerator in the liquid and having an initial setting time of 7.5 min and a final setting time of 12.5 min according to testing with Gillmore needles at room temperature. At body temperature the initial setting time is 6 min, after which the wound can be closed. The dough time (during which it can be deformed without damaging its microstructure) is 4 min. Therefore, the time lost during an operation with this material is 2 min. The product does not shrink or expand during setting, neither is there a thermal effect; it does not swell or disintegrate upon exposure to aqueous fluids after initial setting. Upon soaking in Ringer's solution the product obtains a final compressive strength of 40 MPa and 65% of that strength is reached within 6 h at body temperature. Cytotoxicity is absent. Applications are envisaged in bone surgery, orthopaedics and dentistry, a.o. for acceleration of the osseointegration of metal endoprostheses.

Biocompatible Materials↗

PubMed1994

Theory about aging in humans and hypotheses about its possible delay.

Living beings can maintain their metastable state, e.g. can escape from the first law of thermodynamics by being open systems, by taking up high energy molecules and by dissipating waste products, heat and work. According to the present theory they can stay alive as long as they can escape from the external chaos which is due to the second law of thermodynamics. It is argued that aging is caused by penetration of this chaos into our body in the form of excess trace elements and as xenobiotic elements which either stop the functioning of our living cells or bring it out of neural or hormonal control. Aging might be delayed by the fact that sulfur metabolism maintains an H2S tension in the human body able to precipitate the xenobiotic elements from our tissues. For our defense we depend further on phagocytes to transport the precipitates to organs where they can be dissolved and excreted. It is suggested that the regular passing of kaoline, a natural cation exchanger, through the intestinal tract will help to extract the xenobiotic elements from the body. As far as cardiovascular diseases are concerned, they start with the inevitable tendency of triglycerides to form crystalline precipitates at the surface of the intima in the arteries and capillary vessels. It is hypothesized here that cholesterol serves as a complex former, together with yet unknown plasma protein factors to the triglycerides enabling the solubilization of the precipitates. It is supposed to act as a sort of hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗

PubMed1993

[Prevention of osteoporosis and pathological calcifications].

Based on physiological data about the influence of magnesium compounds on the degree of saturation of blood plasma with calcium phosphates, we have hypothesized in 1988 that magnesium deficiency is the real cause of osteoporosis and pathological calcifications. The incidence of these diseases is among the elderly as high as 40%. These diseases are the reason that there is such a discrepancy between the morbidity and mortality curve for the elderly as a function of age. Meanwhile it has been proven that a. in all osteoporotic patients the intracellular magnesium content of the erythrocytes is lower than in controls, b. this content can be restored to normal by oral magnesium supplementation without increasing the serum magnesium level, c. by this supplementation the bone density in perimenopausal women increases and d. this supplementation keeps the blood plasma and probably also the other extracellular fluids undersaturated with octocalcium phosphate so that it is impossible for pathological calcifications to occur or to progress. The possible benefits for dentistry are the following: a. perhaps mandibular resorption is retarded or inhibited by oral magnesium supplementation and b. this treatment may also help to inhibit or diminish dental calculus formation in heavy calculus formers. Since both aspects are accessible to experimental clinical investigation, we will soon have the answer to these questions.

Aged↗

PubMed1992

Acid-susceptibility of lesions in bovine enamel after remineralization in the presence of fluoride and/or carbonate.

After de- and subsequent remineralization at 0.03 and 1.0 ppm fluoride and either 0, 1, 10, 20 or 25 mM carbonate, artificial lesions in bovine enamel were demineralized again. The amount of secondary demineralization was determined after 15, 30 and 70 h of demineralization by means of quantitative microradiography. The results showed that fluoride incorporated during the remineralization period retards lesion formation during secondary demineralization. Carbonate incorporated during the remineralization period enhances secondary demineralization. An interaction between both ions was observed.

Animals↗

PubMed1992

Influence of fluoride and pH on in vitro remineralization of bovine enamel.

Subsurface lesions in bovine enamel slices were remineralized. The remineralization solutions contained either 0.03, 0.3, or 1.0 ppm fluoride at either pH 5.5 or 6.8. The amount of remineralization was determined after periods of up to 610 h, using quantitative microradiography. The results showed that after 126 h of remineralization in the presence of 0.03 ppm fluoride significantly (p less than 0.05) more remineralization occurred at pH 6.8 than at pH 5.5. At 0.3 and 1.0 ppm fluoride no significant differences between pH 5.5 and pH 6.8 were observed. An interaction between fluoride and pH was observed. The observed differences in the rates of remineralization are explained by the formation and subsequent transformation of the precursors octacalcium phosphate (pH 6.8) and brushite (pH 5.5) into (fluor)apatites.

Animals↗

PubMed1992

The influence of various amphiphilic phosphates on in vitro caries lesion formation in human dental enamel.

Some newly designed surface-active phosphates were investigated with respect to their capacity to inhibit caries lesion formation in vitro. On the labial or buccal surfaces of sound human third molars, windows were prepared for investigation. One half of each window was treated with the test compound at pH values of 7.5, 5.5, or 3.5. The other half served as a control. Both halves were demineralized and the generated caries lesions in both parts were compared by means of quantitative microradiography. Mono-, bis- and trisphosphates differed only marginally in their effect on the demineralization. The compounds diminished the demineralization down to 30% of that of untreated enamel. Per molecule at least one long alkyl chain (more than 12 C atoms) was required for achieving decreased demineralization, indicating the importance of a low surface tension. The results suggest that some of the tested compounds have promising properties for their use as anticaries agents, especially when applied in combination with fluoride.

Dental Caries↗

PubMed1991

In vitro remineralization of caries lesions treated with surface-active phosphates.

Intact human enamel was demineralized in vitro to obtain artificial caries lesions. Part of the lesions was then treated with different surface-active compounds and remineralized with a remineralizing solution. The other part of the lesions was de- and remineralized in the same way, but was not treated with a surface-active compound. The results indicate that none of the surface-active compounds do affect the remineralization of the caries lesions. Possible applications of the tested compounds in combination with fluoride, for the prevention of dental caries, are discussed.

Dental Caries↗

PubMed1991

Effect of 2-O-stearoyl glycerol-1,3-bisphosphate on in vitro demineralization of dental root surfaces.

The effect of 2-O-stearoyl glycerol-1,3-bisphosphate (Glydip) on caries lesion formation in root surfaces of sound human third molars was investigated in vitro. For this purpose parts of the root surfaces were treated with Glydip. Adjacent parts of the surfaces were not treated and served as control. Lesions were obtained by demineralization with an acetate buffer of pH 5.0. It was found that Glydip had no inhibiting effect on the rate of lesion formation. Additionally, pretreatments were performed with lauryl sulphate, a chloroform-methanol mixture, an aqueous solution of sodium hypochlorite, and collagenase prior to the treatment with Glydip to enhance the accessibility of the tissue for Glydip. None of these pretreatments or combinations of them revealed an inhibiting effect of Glydip on the rate of caries lesion formation. This result is in contrast to the effect of Glydip on the demineralization of enamel.

Acid Etching, Dental↗

PubMed1991

The distribution of magnesium in developing rat incisor dentin.

Previous studies have shown that rat incisor dentin contains a considerable amount of magnesium that is distributed heterogeneously. The cementum-related dentin, especially its incisal portion, is richest in magnesium. It was the purpose of the present study to investigate the changes that occur in the magnesium content during dentin maturation. Cross-sections were prepared from rat incisors at the apical, middle, and incisal levels. By means of an electron microprobe, tracings were made of the Ca-, Mg-, and P- signal frequencies. Comparison of corresponding dentin layers within and between the cross-sections showed that the Mg/P molar ratio was always higher in the cementum-related dentin (CRD) than in the enamel-related dentin (ERD) and increased from the apex toward the incisal edge. Especially in the incisal cross-section, an increase in Mg/P was found from the older (peripheral) toward the younger (central) dentin layers. As the Mg/P ratio varied from 0.07 to 0.33, the Ca/P ratio was found to fluctuate from 1.48 to 1.15. The two ratios appeared to be highly correlated (r = -0.97; p less than 0.001), suggesting that Mg replaces Ca and is bound to phosphate.

Animals↗

PubMed1991

Influence of fluoride and carbonate on in vitro remineralization of bovine enamel.

The influence of fluoride, carbonate, and fluoride in combination with carbonate on the in vitro remineralization of bovine enamel was investigated with the use of a sandwich technique. After demineralization, enamel slices were subjected for 610 h to remineralizing solutions with 0.03 or 1.0 ppm fluoride. At each fluoride level, either 0, 1, 10, 20, or 25 mmol/L carbonate was tested. After 0, 22, 62, 126, 192, 329, and 610 h of remineralization, contact microradiographs were made by Cu K alpha-radiation. At 0.03 ppm fluoride, carbonate had an inhibiting influence on remineralization. At 1.0 ppm fluoride, the inhibiting influence of carbonate changed into a stimulation of remineralizatization at 20 and 25 mmol/L carbonate. At 0, 1, and 10 mmol/L carbonate, fluoride had an inhibiting influence on remineralization. The differences in remineralization between the groups were explained by events concerning crystal growth, i.e., different types of minerals might have precipitated with differences in precipitation rates, and retardation of a precipitation step might have occurred under the various remineralization conditions. There was a mutual influence of fluoride and carbonate on the remineralization process. We conclude that the composition of the remineralizing solution with respect to fluoride and carbonate concentrations is important for the remineralization process.

Animals↗

PubMed1991

Acid-susceptibility of lesions in bovine enamel after remineralization at different pH values and in the presence of different fluoride concentrations.

Artificial caries lesions were created in sound bovine enamel slices demineralized at pH 5.0. The lesions were then remineralized at either pH 5.5 or pH 6.8 in solutions containing either 1.5, 15, or 50 mumol/L fluoride. The remineralized slices were then demineralized at pH 5.0 for investigation of acid-susceptibility by means of quantitative microradiography. The results indicated that fluoride, incorporated during the preceding remineralization, had a retarding effect on the demineralization after remineralization, and that for the lowest concentration of fluoride in the remineralizing solution, the inhibitory influence of fluoride depended on the pH of the remineralization solutions used.

Acids↗

PubMed1991

The effect of 2-O-stearoyl-glycerol 1,3-bisphosphate on the demineralization of dental enamel in vitro.

Parts of the buccal and lingual enamel surfaces of sound human third molars were treated with a test compound, and the non-treated parts served as control. After the treatment both parts were demineralized, and the artificial caries lesions were analyzed by means of quantitative microradiography. Treatment during only 1 minute with an aqueous solution of 1.5 mmol/l of the surface active compound 2-O-stearoyl-glycerol 1,3-bisphosphate (Glydip) resulted in a decrease in the rate of enamel demineralization by about 60%. When Glydip was dissolved in a toothpaste/water slurry it inhibited the demineralization by about 30%. When the enamel was covered by a salivary pellicle prior to the application of the slurry, the inhibition of the demineralization disappeared. However, when Glydip was applied in an aqueous solution, the presence of a salivary pellicle did not interfere with the decreasing effect of Glydip on the demineralization. It is concluded that Glydip has promising properties for its use as an anti-caries agent, in combination with fluoride.

Dental Caries↗

PubMed1990

Zinc deficiency-induced changes in the lipid composition and ultrastructure of rat incisor teeth.

The lipids and ultrastructure of the forming, maturing and erupted parts of incisors were compared in rats fed a zinc-deficient diet for 28 days, pair-fed rats and control rats. The lipid levels in the forming portions of zinc-deficient incisors were 30-50% below control levels and were associated with longer Tomes' processes in the secretory ameloblasts, porosities in the forming enamel and fewer malachite green-aldehyde-phospholipid aggregates in the predentine. No marked structural changes were seen in the erupted portions of the teeth, although variations in lipid composition were detected both in the maturing and erupted parts. No differences were found between teeth from the 3 groups of animals for Na, Mg, Cl, Ca and P signals with the electron microprobe.

Animals↗

PubMed1990

Influence of fluoride on in vitro remineralization of artificial subsurface lesions determined with a sandwich technique.

Remineralization experiments of bovine enamel with subsurface lesions were carried out with the use of a sandwich technique. The remineralizing solutions contained no or 2 ppm fluoride added to the solution. The amount of remineralization was determined after remineralization periods up to 324 by means of quantitative microradiography. After 84 h the group with fluoride showed significantly (p less than 0.05) less remineralization than the nonfluoride group. This inhibition of fluoride on the remineralization may be explained by the inhibiting effect that fluoride at certain concentrations has on the crystal growth of apatites.

Animals↗

PubMed1990

Effect of X-ray irradiation on the permeability of bovine dental enamel.

To estimate permeability properties of bovine dental enamel, complex impedance measurements and radioisotope diffusion experiments were carried out before and after X-ray irradiation (single dose, 72 Gy) of enamel specimens. Neither impedance measurements nor diffusion experiments showed significant changes in permeability.

Animals↗

PubMed1990

Is systemic treatment of osteoporosis and mandibular resorption possible?

It is argued that mandibular resorption can be considered as osteoporotic in nature. This calls for a systemic approach in its treatment. One aspect mostly neglected is the tendency of bone to bind calcium and phosphate ions. A direct measure for this tendency is the difference in pH between the bone extracellular fluid and blood plasma with octocalcium phosphate. Calculation of these degrees of saturation of about 2000 data of blood plasma compositions given in the literature learned that calcitonin injections, estrogen replacement and magnesium supplementation increase the tendency of bone to bind calcium and phosphate ions and, hence, should be used in the therapy of mandibular resorption and of bone resorption in general.

Bone Resorption↗

PubMed1990

Aluminium in tooth pastes and Alzheimer's disease.

Epidemiological studies from Norway and England suggest a relation between the frequency of Alzheimer's disease and the concentration of aluminium in the drinking water. Estimates, made in this study, show that the role of aluminium from tooth pastes may be even more important than that from the drinking water. For that reason we determined in samples of tooth pastes taken from the BENELUX market which brands contained aluminium. This appeared to be the case for about 22% of the brands which according to the manufacturers cover about 60% of the market.

Aluminum↗