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Biomedical subjects

R M Verbeeck

Publications and source records attributed to R M Verbeeck.

At least 55 records · Page 3Linked to original sources
PubMed1989

Effect of carbonate content on the ESR spectrum near g = 2 of carbonated calciumapatites synthesized from aqueous media.

The ESR spectrum of X-irradiated carbonated apatites synthesized at low temperature was studied as a function of their carbonate content. Using 13C-enriched samples, four different carbonate-derived radicals and a surface O- ion could be identified. Isotropic CO3- and CO2- ions are present at a B site in the apatite lattice, and anisotropic CO3- and CO2- radicals are located at the surface of the crystallites. Only the isotropic ESR signals increase with increasing carbonate content. The anisotropic signal ascribed to a surface CO2- radical is mainly responsible for the so-called asymmetric ESR signal near g = 2. It is argued that this surface signal may still be composite and caused by several very similar CO2- ions. The consequences for phenomenological ESR studies of calcified tissues are discussed.

Apatites↗
PubMed1989

Plasma calcium difference between man and vertebrates.

1. Literature data about the plasma content of total calcium, ionized calcium and inorganic phosphate in healthy animals and man of different age and sex were collected. 2. It was established that under normal conditions ionized calcium is about 45% of total calcium. 3. The degree of saturation of these blood samples with respect to octocalcium phosphate OCP was calculated. 4. In young animals and man the blood plasma has a higher degree of saturation than in adult animals and man. 5. The blood plasma of healthy animals is supersaturated with respect to OCP during their whole life. 6. However, the blood plasma of healthy human adults is slightly undersaturated with respect to OCP.

Age Factors↗
PubMed1989

A systemic approach to the oral problem of mandibular resorption.

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. This pH difference is directly reflected by the degree of saturation of blood plasma with octocalcium phosphate. Calculation of these degrees of saturation of about 2000 data of blood plasma compositions given in the literature indicates that calcitonin injection, 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.

Animals↗
PubMed1988

On the prevention and treatment of calcification disorders of old age.

From several investigations it is known that magnesium oxide or hydroxide therapy causes a considerable delay of kidney stone recurrence in man. Further, it is known that the mortality of populations due to cardiovascular disease in areas with hard drinking water containing more magnesium and having a higher Mg/Ca ratio than soft water, is considerably lower than in soft water areas. In the present study a physiological model for the homeostasis of calcium and phosphate is given. It is shown that and why a slight magnesium deficiency causes the pH of bone extracellular fluid to decrease at or below the pH level of the other body fluids. This decrease makes the other body fluids supersaturated with octocalcium phosphate and this is the prime reason for calcification disorders in the soft tissues. Therefore, the hypothesis is proposed that soft tissue calcifications can be stopped and even prevented by magnesium therapy. However, they are not reversible and treatment with chelate therapy is contraindicated.

Acid-Base Imbalance↗
PubMed1987

The contribution of CO3(3-) and CO2- to the ESR spectrum near g = 2 of powdered human tooth enamel.

The ESR spectrum near g = 2 of powdered human tooth enamel from upper central incisors and lower canines was studied as a function of microwave power, irradiation, and storage time. The results clearly demonstrate that the ESR spectrum is composite with at least five paramagnetic species contributing to the signal. The main stable component is assigned to CO2-. Two other components arise from CO3(3-) radicals, one of which is demonstrated to be the same center as is present on a phosphate site in sodium- and carbonate-containing calciumapatite.

Carbonates↗
PubMed1987

Effects of acid-base status and fluoride on the composition of the mineral in developing enamel and dentine in the dog.

Developing molar teeth of the dog were sectioned, embedded in copper containing polymethyl methacrylate, polished and their Ca/P and Ca/Na molar ratios investigated with the electron microprobe. The teeth were obtained at 30 days from 9 pups fed regimes of different acid-base status with or without fluoride supplementation from birth to sacrifice at 30 days. No clear trends in their Ca/P or Ca/Na ratios with variation in the diet were observed. However, evaluation of the Ca/P ratio of the enamel as a function of depth revealed that this ratio was 0.80 +/- 0.15 at the mineralization front. This suggests that in enamel brushite rather than octacalcium phosphate is the precursor phase of the mineral.

Acidosis↗
PubMed1986

Solubility of calcium oxalate monohydrate and hydroxyapatite in EDTA solutions.

The effect of the addition of a buffer to an ethylenediaminetetracetic acid (EDTA) litholytic solution on the solubility of calcium oxalate monohydrate and hydroxyapatite is investigated. The experiments show that the addition of triethanolamine as a buffer to EDTA solutions at pH 8 and 8.5 enhances the solubility of these salts, confirming theoretical predictions. The solubility of calcium oxalate monohydrate at 25C in solutions with varying ratios of buffer to EDTA concentrations and an osmolality of 0.9 was determined. The solutions resulting in the highest solubility were finally tested for their litholytic ability at 37C. At pH 8 solubilities of 22.5 g X l-1 for calcium oxalate monohydrate and 20.2 g X l-1 for hydroxyapatite were obtained. The corresponding solubilities at pH 8.5 were respectively 24.5 g X l-1 and 19.2 g X l-1.

Calcium Oxalate↗
PubMed1986

Screening of chelating agents for chemolysis.

The solubility of calcium oxalate monohydrate and calcium hydroxyapatite was calculated as a function of pH in the presence of different chelating agents and was compared with the solubilities in EDTA- or CDTA-containing solutions. An analysis of the solubility curves for 19 chelating agents showed that 5 of the complexing agents considered result in a high solubility for calcium phosphate and oxalate at pH 8 or higher. For these complexing agents the solubility curves of struvite were also calculated. EGTA and HEDTA showed rather low solubilities for struvite due to their low tendency to form complexes with magnesium. On the basis of the calculated solubility curves, the expected litholytic effectiveness for the inorganic kidney stone compounds could be classified in the following decreasing order: CDTA approximately equal to EDTA approximately equal to EGTA greater than EEDTA greater than DTPA greater than UDA approximately equal to HEDTA. With the exception of EGTA and HEDTA for struvite stones, solutions based on these compounds show high solubilities for all the inorganic kidney stone compounds at a solution pH of 8 or higher and therefore have good prospects as litholytic agents.

Chelating Agents↗
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↗
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

Solubility of inorganic kidney stone components in the presence of acid-base sensitive complexing agents.

Computation methods used to calculate the solubilities of the main inorganic kidney stone components in the absence or presence of acid-base-sensitive complexants as a function of pH are described. The solubilities of whewellite, brushite, whitlockite, octocalcium phosphate, hydroxyapatite and struvite were calculated in the presence of ethylenediaminetetraacetate (EDTA), trans-cyclohexane-1,2-diaminetetraacetate (CDTA), citrate, tripolyphosphate and alpha-hydroxyisobutyrate. The results explain why kidney irrigations with citrate give extremely variable results. The calculated solubility curves show that only EDTA and CDTA solutions with a pH of 8 or higher will have good litholytic properties for all compounds concerned. The computation methods presented in this paper can be used to calculate the solubility of a large number of salts. These salts may contain non-acid-base-sensitive cations capable of forming complexes, acid-base-sensitive anions, hydroxyl ions, hydrogen ions or other acid-base-sensitive cations (e.g. NH4+), and the solubilities can be calculated in the presence or absence of acid-base-sensitive complexing agents.

Calcium Oxalate↗
PubMed1985

Apatite crystallite alignment in sound human tooth enamel studied by E.S.R.

The degree of microcrystal alignment in enamel of clinically sound upper and lower central incisors, canines and premolars was determined by means of electron paramagnetic resonance. The results show that the degree of alignment depends on the individual properties of the enamel as determined by biological variations, tooth morphology and tooth position. Upper incisors and canines have a much higher degree of crystallite alignment as compared to all other teeth investigated. These results indicate that the caries susceptibility of tooth enamel is not defined only by the degree of microcrystal alignment.

Apatites↗
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↗
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↗