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J W van Dijk

Publications and source records attributed to J W van Dijk.

32 records · Page 2Linked to original sources
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

The mineral content of human enamel studied by polarizing microscopy, microradiography and scanning electron microscopy.

The total observed birefringence and mineral content of the outer 300 micron of longitudinal sections of sound buccal premolar enamel were measured and three-dimensional contour maps were made. Using similar contour maps of calcium, carbonate and magnesium content from the literature, it seemed possible to explain the differences between the contour maps of total observed birefringence and mineral content. Scanning electron micrographs provided information about the orientation of the prisms. The cervical part of the enamel had a high intrinsic birefringence which may explain the difference between mineral content and total observed birefringence. This high intrinsic birefringence may be caused by a high carbonate content in cervical enamel.

Bicuspid↗
PubMed1980

On the physical chemistry of tooth enamel and the caries process.

A model is presented for the pathway of reactions of the mineral of tooth enamel during caries. It is based on a mathematical simulation of the caries process (van Dijk, Borggreven and Driessens, 1979) and knowledge about the variable solubility behaviour of calcium phosphates (Driessens, van Dijk and Borggreven, 1978). According to this model the surface of the crystals in the intact superficial layer of enamel will transform into a relatively pure fluor-hydroxyapatite; in the lesion a mineral with a brushite- or monetite-like composition will be formed, while at the bottom of the lesion an increasing amount of the original carbonatoapatite will be found. The experimental studies of Arends and Davidson (1975) and of Featherstone, Duncan and Cutress (1978) corroborate these results. The model also explains why demineralization take place at some distance under the enamel surface, and predicts that the intact superficial layer of enamel over a lesion becomes thicker with increasing pH of the plaque fluid and with its degree of saturation with respect to fluor- and hydroxyapatite (Larson, 1974 b). Sobel's finding (1960) that high-carbonate teeth are more susceptible to caries than low-carbonate teeth is consistent with the present model.

Apatites↗
PubMed1978

Biological calcium phosphates and their role in the physiology of bone and dental tissues I. Composition and solubility of calcium phosphates.

Variations in the composition of bone and tooth mineral are consistent with the model that the constituents are a mixed microcrystalline apatite (AP)-octocalcium phosphate (OCP) like phase and an amorphous or submicrocrystalline calcium phosphate (ACP) like phase whereby these phases can occur in different proportions. An appropriate model for a description of the variable composition and the solubility behavior of the apatite phase is given by the formula (formula: see text) in which the compositional parameters x, y, z, and u each account for one type of defect mechanism. Other point defects are formed as well by incorporation of minority amounts of ions such as Cl-, K+, and F-; a number of trace elements can substitute for Ca2+ ions under in vivo conditions. It is suggested that the incorporation of ions in or loss from the crystals in contact with aqueous solutions is reversible. Literature data are used to show the direction in which the solubility product of the apatite phase shifts by incorporation of the different physiologically relevant ions. A quantitative evaluation of the available literature data revealed that Na+ and CO3= incorporation is the main cause for shifts in the solubility product of biological apatites.

Apatites↗
PubMedDate not supplied

Degree of saturation of blood plasma in vertebrates with octocalcium phosphate.

In previous papers it has been shown that octocalcium phospate OCP occurs in bone mineral of vertebrates. Although this compound is not stable, there is a continuous new-formation of OCP due to bone turnover. Literature data of the calcium and phosphate concentrations in the blood plasma of vertebrates were collected and the degree of saturation with OCP was calculated. The results show that blood plasma of vertebrates is almost saturated with OCP. This fact indicates that OCP is the solubility controlling phase in the mineral of vertebrates. Further it verifies the expectation based on physicochemical theory that the interaction between body fluids and bone mineral is important in the calcium and phosphate homeostasis.

Animals↗