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Biomedical subjects

F C Driessens

Publications and source records attributed to F C Driessens.

At least 91 records · Page 5Linked to original sources
PubMed1984

The use of electron spin resonance on human tooth enamel in relation to caries-susceptibility.

By means of the electron spin resonance technique it is possible to detect carbonate-related paramagnetic centers in human tooth enamel. Several arguments indicate that the radical formed after X-ray irradiation is a CO2- rather than a CO(3)3- center. There is experimental evidence that the distribution of the orientation of those centers is related to caries-susceptibility, but care has to be taken with regard to the interpretation of the results formulated in the literature. In our own preliminary research, we have studied the ESR-spectra of both bovine and human tooth enamel. As a model for human tooth enamel, the study of bovine enamel was unsatisfactory, because the signals were visibly different from the ones obtained on human tooth enamel. The reproducibility of the ESR-signals in human tooth enamel was carefully studied and found to be excellent. We also investigated the effect of heating these samples, and noted a drastic change in the spectra. Our numerical values for the R-parameter, as introduced by Cevc et al. (1976, 1980), are considerably lower than the ones they published. Clearly, additional information concerning the sample-preparation-technique and the etiological factors which determine the R-value, should be gathered.

Carbonates↗
PubMed1983

Synthetic apatites containing Na, Mg, and CO3 and their comparison with tooth enamel mineral.

Apatites containing Na, Mg, and CO3 in amounts occurring in tooth enamel mineral were synthesized by precipitation from aqueous solutions. The X-ray diffraction patterns showed only apatitic reflections, which were somewhat broader than those of enamel. X-ray Guinier photographs resulted in diffuse reflections from which the lattice parameters could not be determined. The infrared (IR) absorption spectrum of the synthetic samples was practically identical with that of tooth enamel. However, after heating the samples for 1/2 h at a temperature between 300 and 600 degrees C, no absorption peak was found at 2340 cm-1 as in the IR spectrum of tooth enamel after heating.

Apatites↗
PubMed1983

Diffusion in mammalian tooth enamel in relation to the caries process.

For the rate of demineralization of enamel during caries, three physicochemical processes are of importance: the diffusion into and out of the enamel, the dissolution of mineral and the complexation of ions. The interpretation of diffusion experiments in conjunction with artificial caries experiments and computer simulations is described. In the caries process, relevant diffusion coefficients of small ions and molecules are of the order of magnitude 10(-9)--10(-7) cm2 s-1.

Animals↗
PubMed1983

Effect of phytate and hexadecylamine on the permeability of bovine dental enamel.

The effect of hexadecylamine on the permeability of bovine dental enamel was investigated using a radiochemical diffusion technique. Treatment with an aqueous solution of hexadecylamine reduced the permeability of the enamel by about 20 per cent. Pre-treatment of the enamel with an aqueous solution of phytate followed by hexadecylamine yielded a reduction in permeability of approximately 70 per cent. The observed effects were similar for ionic (86Rb+ and 36Cl-) and non-ionic [( 3H]-sorbitol and [14C]-glycerol) compounds. The strong permeability-reducing effect of the combined phytate-amine treatment may also be anticariogenic.

Amines↗
PubMed1983

Remineralization in human premolars of different posteruptive age.

In human premolars with posteruptive ages varying from 6 months to 4 years demineralized enamel was remineralized for 3 days at 37 degrees C in a recalcifying medium containing 2 mM Ca2+, 1.2 mM phosphate, 0.05 mMF- and 150 mM NaCl (pH = 7). The Ca, P and Ca/P molar ratio of the mineral gained were determined at various distances from the enamel surface. Whereas, particularly at 30 micrometers from the surface remineralization was higher and more extensive in young demineralized enamel, no difference could be found in Ca/P molar ratio, suggesting precipitation of an apatitic mineral in both young and old demineralized human enamel. The probable nature of the precipitate is that of a fluoridated hydroxyapatite.

Age Factors↗
PubMed1982

X-ray diffraction of enamel of a freshly erupted human tooth.

Small slices were cut from enamel prepared from the labial surface of a freshly erupted human premolar. Consecutive slices (200 micrometers thick) were taken at distances 500 micrometers apart from each other. X-ray diffractograms were obtained from each slice in a Guinier camera. Only the slices cut from the outer 500 micrometers of human enamel resulted in distinct reflections. Typical lattice parameters were a = 9.462 A and c = 6.898 A for one slice and a = 9.457 A and c = 6.890 A for another slice of outer enamel. Non-apatitic reflections could not be detected. The line-broadening occurring in deeper layers was shown to be due either to intracrystalline strain or to inhomogeneities on the crystalline level. Theoretical models and submicroscopical findings of other authors are discussed in relation to the present findings.

Apatites↗
PubMed1982

X-ray diffraction of enamel from human premolars several years after eruption.

Small slices were cut from rods prepared from the labial surface of premolars extracted 4 and 5 years after eruption. Consecutive slices (200 microns thick) were taken at distances 500 microns apart from each other. X-ray diffractograms were obtained from each slice in a Guinier camera. Distinct reflections were obtained from slices up to depths of 2000 microns. The average depth of good cristallinity was 1000 microns in these older teeth in contrast to freshly erupted teeth where it is about 300 microns. No gradient could be detected in the lattice parameters from the surface layer towards the dentino-enamel junction in these older teeth. The average lattice parameters were a = 9.453 A and c = 6.890 A. Compared to data obtained on young teeth (Driessens et al., J. Biol. Buccale 10: 55, 1982) the crystallinity of the mineral appeared to increase with age in deeper layers. This result is consistent with the decrease of the caries susceptibility of human enamel with age postulated in the literature.

Age Factors↗
PubMed1982

Changes in calcium and phosphorus content in young human enamel during demineralization in vitro.

Premolars extracted about 6 months after eruption were divided into four parts by sectioning through the mesial- and distal midplanes. The enamel of each part was subjected to demineralization by hydroxy-ethyl-cellulose (H.E.C.) gel at pH 4 for periods varying between 2 and 24 hrs. The Ca and P contents of the gel as well as that of 10 microns slices prepared from the enamel after demineralization were determined. Then the Ca and P content of the HEC gel as well as that of 10 microns slices sequentially sectioned from the surface of the demineralized enamel inwards, were determined. The data indicate that initially, demineralization was predominant in the layers between 20 and 60 microns depth together with a reprecipitation in the surface 20 microns layer. After about 6 h of demineralization more mineral loss was found from layers deeper than 60 microns. Further, it was shown that the molar Ca/P ratio of mineral loss from these young teeth at depths of between 40 and 50 microns was extremely high (about 3) whereas in older teeth it was normal. This might be due either to preferential dissolution of carbonate containing mineral or to preferential precipitation of HPO4(2)--containing mineral or both especially at that depth.

Calcium↗
PubMed1981

Lattice parameters and cation distribution of solid solutions of calcium and lead hydroxyapatite.

Solid solutions of calcium hydroxyapatite (CaOHA) and lead hydroxyapatite (PbOHA) of the formula Ca10-x Pbx (PO4)6 (OH)2 were prepared by coprecipitation followed by heating at 800 degrees C in a steam of CO2-free water vapor of 1 atm. The samples were apatitic in the range 0 less than x less than 6 and contained lead phosphates as a second phase at higher Pb/Ca ratios. Lattice parameters and cation distribution of the apatitic samples were determined by X-ray diffraction. The lattice parameters varied linearly with x in the range considered, whereas all Pb2+ were located in the six-fold position for cations. There was a miscibility gap in the apatite series of solid solutions in the range 1 less than x less than 4, whereas apatites in the range 6 less than x less than 10 were not stable under the conditions of preparation. It is concluded that apatites in the range 4 less than x less than 6 represent a minimum in the free energy of solid solutions between CaOHA and PbOHA.

Calcium↗