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Biomedical subjects

F C Driessens

Publications and source records attributed to F C Driessens.

At least 73 records · Page 4Linked to original sources
PubMed1986

The vulnerability of unexposed human dental roots to demineralization.

Crowns and roots of human molars, the roots from which had not been exposed to the oral environment, were exposed for 0, 3.5, 7, and 14 days to buffer solutions which were undersaturated or supersaturated with respect to hydroxyapatite. Densitometric measurements on contact-microradiograms of transverse sections of the crowns and of the cervical parts of the roots yielded plots of the mineral content as a function of the distance to the outer surface. From these plots, the rate of demineralization was calculated. It was found that the mineral of the roots dissolved even in buffer solutions which were supersaturated with respect to hydroxyapatite. Comparison of the results obtained from the crowns with those from the roots showed that the root hard tissues were more vulnerable to demineralization than was the dental enamel.

Buffers↗
PubMed1986

The dynamics of bone mineral in some vertebrates.

In the literature octocalcium phosphate as well as brushite have been proposed as the precursor phase for bone mineral in the higher vertebrates. In this study it is shown that the situation is more complex. A sodium and carbonate containing apatite (NCCA) and a magnesium whitlockite (MWH) are present from the beginning of mineralization together with octocalcium phosphate. Upon further bone development the NCCA and the MWH phase are deposited in amounts proportional to the amount of mineral deposited. However, the octocalcium phosphate is transformed slowly in a heavily carbonated defective hydroxyapatite. From the available experimental data it can be derived that the time of this transformation is smaller than four weeks under in vivo conditions.

Aging↗
PubMed1986

The microcrystal alignment in human tooth enamel from carious and non-carious teeth in relation to caries susceptibility.

The degree of microcrystal alignment in the intact enamel from carious and non-carious upper incisors, lower incisors and upper canines was determined by means of electron paramagnetic resonance. The results show that a low degree of alignment is not a generally valid indication for caries-susceptibility. Upper canines have a high degree of crystallite alignment whereas lower incisors have a relatively low one. With the exception of the upper central incisors no differences in microcrystal alignment are found between the intact enamel from carious and non-carious lower incisors and upper canines. These results indicate that a possible caries-susceptibility of tooth enamel reflected by low R-values is not solely determined by the degree of microcrystal alignment.

Crystallization↗
PubMed1986

Some aspects of artificial caries lesion formation of human dental enamel in vitro.

Investigations of artificial carious lesion formation of human dental enamel showed great variability in caries susceptibility. Human specimens were demineralized in acid buffers with Ca and phosphate ions, undersaturated with respect to hydroxyapatite. Under nearly all conditions the results varied from no lesion formations to etching. This may be due to properties of the surface layer such as fluoride content and permeability.

Decalcification Technique↗
PubMed1985

Dolomite as a possible magnesium-containing phase in human tooth enamel.

A solid-state chemical model is derived to estimate the solubility of dolomites having different degrees of cation ordering. It is shown that the solubility of dolomites formed by precipitation at ordinary temperatures is such that it allows for the formation of dolomite in tooth enamel during in vivo mineralization.

Calcium Carbonate↗
PubMed1985

Effect of time, degree of saturation, pH and acid concentration of buffer solutions on the rate of in-vitro demineralization of human enamel.

The rate of demineralization of the artificial caries-like process was measured using two methods. The rate calculated from microradiography of the demineralized enamel appeared to be equal to the one calculated from calcium and phosphate analysis of the demineralizing buffer. In small volumes of demineralizing solution, the rate of demineralization decreased with time, due to the increase in saturation of the solution during the demineralization of the enamel. With increasing saturation, with respect to hydroxyapatite, and with increasing pH the rate of demineralization decreased. Increasing acid concentration had a marked influence only at the lower concentrations; a further increase had no effect on the rate of demineralization.

Buffers↗
PubMed1984

The effect of undissociated acetic-acid concentration of buffer solutions on artificial caries-like lesion formation in human tooth enamel.

A chemical system for lesion production was used. The influence on lesion characteristics of the concentration of undissociated acetic acid in a calcium and phosphate-containing buffer solution was investigated. Artificial lesions obtained after demineralization in buffers with a pH of 4.0, 4.5, 5.0 or 6.0 at 5 or 6 different acid concentrations for different demineralization times were investigated micro-radiographically. The lesion characteristics studied were: the mineral content of the surface layer; the mineral content of the body of the lesion; and the depth at which these mineral levels were reached; the depth of the lesion. The concentration of undissociated acetic acid had little effect on the lesion characteristics at low pH. When lower concentration buffers at pH 6.0 were used, the effect was more pronounced. At this level, the buffer capacity of the acetic acid/acetate buffer is small.

Acetates↗
PubMed1984

A phenomenological interpretation of the frequency-dependent impedance behaviour of bovine dental enamel.

The permeability of dental enamel can be estimated by means of diffusion measurements with radio-isotopes. Because of the low intrinsic permeability of enamel membranes, determination via this route may take two weeks. A much faster electrochemical method is presented, in which the real and imaginary part of the membrane impedance are measured at discrete intervals in the frequency-range 1 Hz-1 MHz. Using the principles of network-analysis, a phenomenological interpretation of these electrochemical data in terms of a 6-parameter model is given. The model contains R0, the intrinsic membrane resistance, R infinity, the residual membrane resistance and the four parameters, necessary to describe the postulated enamel diffusion impedance, which bears strong resemblance to the Warburg impedance. Starting from this model, optimal estimates (with standard-errors) of a membrane's R0 and vmax (the log of the frequency where the imaginary part of the membrane impedance is maximal) were derived. These parameters were predictors of the permeability of enamel.

Animals↗