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Biomedical subjects

F C Driessens

Publications and source records attributed to F C Driessens.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1980

Contribution to the physicochemical rationale for the caries reducing effect of fluoride.

The effect of fluoride on the stability of apatites containing Na+ and CO3(2)- ions is described qualitatively. Also the boundaries of the apatite stability field in the quasi-septary system CaO - P2O5 - H2O - Na2O - CO2 - NaF - MX are presented. At these boundaries brushite (or monetite), octocalciumphosphate, calcite and calcium fluoride can become stable solid phases. As a consequence, certain mechanisms for the caries reducing effect of fluoride gain probability over other proposed mechanisms. First, it is likely that endemic fluoride yields more fully mineralized enamel which in turn results in a lower initial rate of the caries process. Second, after eruption the mineral in the tooth superficial layer is bound to accumulate fluoride on the surface of its crystals. This causes a slower rate of the crystal surface dissolution at that site and, hence, a thicker and denser intact superficial layer over the lesion. Finally, the formation of a precipitate of fluorhydroxyapatite and perhaps also of calcium fluoride is promoted in the plaque during cycles of metabolic activity. Subsequent dissolution of the CaF2 and transformation of the fluorhydroxyapatite sets free Ca+ and F- ions. Both of these ions promote the remineralization of the lesion during periods of metabolic rest whereby brushite or monetite are transformed back into apatite.

Apatites↗
PubMed1979

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

Solid solutions of strontium and calcium hydroxyapatite were synthesized by solid-state reaction. Lattice parameters of these compounds were determined using two types of Guinier cameras. They vary linearly with the molar percentage of strontium hydroxyapatite. The distribution of Ca and Sr ions over the fourfold and sixfold positions in the apatite structure was determined by comparing experimental and calculated values for the intensity ratios of suitable reflections. A slight, although significant, preference of Sr for the sixfold position was found. An ideal behavior is predicted for these solid solutions.

Calcium↗
PubMed1979

[Adhesion of restoration materials to hard tooth structures].

Adhesion occurs in dentistry in many situations. The demand for an adhesive restorative material becomes increasingly pressing. After a general treatment of the physico-chemical principles of adhesion the materials and technics for adhesion to dental enamel are reviewed. Only materials on a polymer basis are being developed for new indication areas and tried out in clinical investigations. Microretention to dental enamel obtained by etching with phosphoric acid, is the leading technic. As follows from a survey of clinical investigations on fissure sealants and adhesive restorations in front teeth, this technic yields the desired result only in the hands of well-trained researchers. Recently, Smith (1975) succeeded in developing a polymer system adhering chemically to dentine, but it is not yet available on the market. Whether this system is the answer to the demand of a truly adhesive restorative material, is doubtful due to the work of Hoppenbrouwers and Borggreven (1977).

Acid Etching, Dental↗
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↗
PubMed1977

Chemical adhesion in dentistry.

The terms used in the chemistry of adhesion are reviewed as well as the role played by surface energies, viscosity, surface roughness, etc. The similarity of chemical bonds in substrate and adhesive which favours adhesion in general, is very rare in dentistry. It is shown how and when a chemical bridge between two different types of materials works in dentistry. Finally, it is made evident why binding to dental hard tissues will not be permanent.

Adhesiveness↗
PubMed1975

Dimensional behavior of curing bone cement masses.

The curing of bone cements is accompanied by release of polymerization heat and, hence, by a temperature rise of the curing cement mass. This temperature rise causes expansion of enclosed air bubbles and evaporation of the volatile monomer. An overall expansion of 3 to 5 vol % has been mentioned in the literature. It has often been stated that this expansion favours the fixation of metal endoprostheses in the marrow cavity of bone. To check for the influence of this expansion on linear dimensions of the cured cement mass we filled stainless steel cylinders with a precision bore of 22,000 +/- 0,005 mm and a length of 120 mm with bone cement. After curing of the cement in a environment of 37 degrees C the resulting cement rod was released from the cylinder and the diameter of the rod was measured at 37 degrees C. The influence of the "foaming effect" on the transverse dimensions of the rods was studied by curing the cement at 37 degrees C and 2 atm air pressure in a high-pressure-vessel. This method of curing eliminates porosity in the cement almost completely, so that curing shrinkage is to be expected rather than expansion of the cement mass. The results indicate that a volumetric expansion of the cement during curing of cylindrical rods in laboratory experiments, can be accompanied by a linear diametrical shrinkage of the cement mass. The explanation of this phenomenon is to be sought in the fact that the volumetric expansion takes place at a time when the cement is still plastic; by the formation of gas bubbles, the cement is forced in longitudinal direction into the cylinder and when the temperature of the mass has passed through a maximum, the cooling of the cement mass results in a thermal shrinkage of approximately 0.4% linearly. Extrapolating this laboratory result to clinical situation one might doubt whether the overall expansion of bone cements during curing will result in a permanent positive pressure on the walls of marrow cavity and whether it will contribute to a better fixation of endoprostheses than in the case of a, still hypothetical, nonporous cement.

Bone Cements↗