Ronald Verbeeck - Academia.edu (original) (raw)

Papers by Ronald Verbeeck

Journal of Dental Research, 1998

Berichte der Bunsengesellschaft für physikalische Chemie, 1980

Fluorhydroxyapatites were synthesized by solid state reaction at 1000°C. They contain vacancies i... more Fluorhydroxyapatites were synthesized by solid state reaction at 1000°C. They contain vacancies in the OH sublattice and are, in this respect, a good model for tooth enamel mineral. The presence of fluoride at the 0.1 to 1 ppm level reduced the solubility of these defective apatites with a factor 8 in the caries relevant range 4 < pH < 5. The simultaneous presence of Ca2+ ions, till a level similar to that in saliva, together with the F− ions in the physiological range 6.5 < pH < 7.5 suppressed the eventual decrease in solubility of these defective apatites caused by the presence of F− ions alone. Thus, the combined effect of Ca2+ and F− ions on the solubility behaviour of defective apatites is supposed to be relevant to the caries process and the caries reducing capacity of extra F− additions.

$Research paper thumbnail of X-ray diffraction of enamel of a freshly erupted human tooth$

Journal de biologie buccale, 1982

Small slices were cut from enamel prepared from the labial surface of a freshly erupted human pre... more 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.

Journal de biologie buccale, 1984

By means of the electron spin resonance technique it is possible to detect carbonate-related para... more 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 ...

Journal de biologie buccale, 1986

The degree of microcrystal alignment in the intact enamel from carious and non-carious upper inci... more 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.

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Revue belge de médecine dentaire, 1990

Epidemiological studies from Norway and England suggest that there is a relation between the freq... more Epidemiological studies from Norway and England suggest that there is a relation between the frequency of Alzheimer's disease and the concentration of aluminum in the drinking water. A recent Dutch study suggests further that the role of aluminum from tooth pastes may be even more important than that from drinking water. For this reason we determined in samples from the Belgian market which tooth pastes contained aluminium oxyhydroxide as abrasive. This happened to be the case in 5 out of 27 brands. It is not know to us which part of the market these tooth pastes represent.

Biomaterials Engineering and Devices: Human Applications

Calcium phosphate bone cements (CPBCs) consist of a powder and an aqueous liquid, which are mixed... more Calcium phosphate bone cements (CPBCs) consist of a powder and an aqueous liquid, which are mixed to form a paste that sets at room or body temperature under the formation of a precipitate that contains at least one calcium phosphate (CaP) (1–4). In the system, Ca(OH)2-H3PO4-H2O, a limited number of CaPs can precipitate (5,6; Table 1). Among these CaPs, monocalcium phosphate monohydrate precipitates only from very acidic aqueous solutions, which are for that reason cytotoxic. Moreover, octacalcium phosphate precipitates only after very long induction times, which are impractical to form CPBCs. The composition of the apatite can vary continuously from CDHA to hydroxyapatite (HA), so that no definite border between the pH ranges exists at which a Ca-deficient or stoichiometric apatite precipitates. If the system contains also Na+ and/or Co 3 2− ions, these ions will be incorporated at least partially into the apatite precipitate Finally, there is no easy way to distinguish between amorphous calcium phosphate (ACP) I and ACP II. For these reasons, the CPBCs known are of the brushite type, the apatite type, or the ACP type.

Quintessence international (Berlin, Germany : 1985), 2008

To determine the hardness versus depth profile of several polyacid-modified composite resins (PAM... more To determine the hardness versus depth profile of several polyacid-modified composite resins (PAM-Cs) as a function of shade (A2, A4) and compare the depth of cure (DoC) based on these profiles with that previously obtained with the scraping and penetrometer methods. Samples of 6 PAM-Cs (Hytac, 3M ESPE; F2000, 3M ESPE; Glasiosite, Voco; Dyract, Dentsply DeTrey; Dyract AP, Dentsply DeTrey; Compoglass F, Vivadent) and 3 composite resins (Herculite Enamel XRV, Kerr; Z100, 3M ESPE; Durafill VS, Heraeus Kulzer) with shades A2 and A4 were light-cured in bulk in split stainless steel molds (thickness ranging from 0.5 to 3.5 mm in steps of 0.5 mm). The Knoop hardness of the irradiated top (KHN(surface)) and nonirradiated bottom (KHN(bottom)) surfaces was determined as a function of sample thickness using a microhardness tester. Regression analysis demonstrated that for a given material, KHN(bottom) equals KHN(surface) up to a specific depth (= DoC) depending on the material and shade and th...

Zeitschrift für anorganische und allgemeine Chemie, 1983

Mixtures of CaHPO4, CaCO3, and Na2CO3 were heated at 870°C under steam or under dry CO2 until pha... more Mixtures of CaHPO4, CaCO3, and Na2CO3 were heated at 870°C under steam or under dry CO2 until phase composition and weight were constant. According to chemical analysis and X‐ray diffractometry the stability field of the β‐Ca3(PO4)2 phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β‐Ca3(PO4)2 and a new whitlockite with the composition Ca10Na(PO4)7. The IR spectrum of these solid solutions shows that the point symmetry of the PO4 groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β‐Ca3(PO4)2 and whitlockite. The composition of these solid solutions suggests that Na+ ions can replace H+ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.

Urological Research, 1992

A rat model was developed to test the watertightness of sutures. In this model it was proved that... more A rat model was developed to test the watertightness of sutures. In this model it was proved that welding by use of low-voltage coagulation current did not improve on the watertightness obtained with conventional skin suturing. The mean leak pressure after welding was about 4.2 cmH20 , i.e. statistically significantly lower than the mean leak pressure of the conventional suture, which is 14.1 cmH20. Neither addition of protein solder nor an additional conventional suture improved these results. It is therefore concluded that low-voltage coagulation is unsuitable for welding tissues.

Zeitschrift für Physikalische Chemie, 1980

Zeitschrift für Physikalische Chemie, 1981

Diagramme wurde die relative Stabilität der schwer löslichen Strontium-Orthophosphate ß-SrHP04, S... more Diagramme wurde die relative Stabilität der schwer löslichen Strontium-Orthophosphate ß-SrHP04, Sr6H3(P04)5 2 H20, Sr3(P04)2 und Sr5(P04)3(OH) abgeleitet und ihr Löseverhalten diskutiert.

International Endodontic Journal, 2012

AimTo evaluate the strengthening effect of two different types of fibre‐reinforced composite (FRC... more AimTo evaluate the strengthening effect of two different types of fibre‐reinforced composite (FRC) posts in an ex vivo experimental model.MethodologyCompact and hollow bone samples from bovine femurs were used as standardized samples. A total of 80 hollow samples were divided into two groups and filled either with a prefabricated FRC post or with individually adapted FRC posts. For each group, half of the samples were subjected to thermocycling (5–55 °C, 5000×). The remaining samples were kept for 24 h at 37 °C at 100% relative humidity. All samples were loaded diametrically until fracture. The null hypothesis tested was that the fracture resistance of standardized bone samples is not influenced by the type of FRC post, independently of the exposure to thermocycling. Results were evaluated by anova, and subsequent multiple comparisons were performed.ResultsThe samples filled with the individually adapted FRC posts were more resistant to fracture than the prefabricated ones (P < 0...

Inorganic Chemistry, 1984

The solubility of MgHP04.3H20 is determined in the ternary system Mg(OH)2-H3P04-H20 at 25 "C in t... more The solubility of MgHP04.3H20 is determined in the ternary system Mg(OH)2-H3P04-H20 at 25 "C in the range 5.0 C pH < 7.3. The solubility behavior can consistently be described by taking into account the formation of the ion pairs of MgH2P04+ and MgHPO,,. The thermodynamic solubility product of MgHP04.3H20 and the thermodynamic association constants for MgH2P04+ and MgHP04 with their standard error are determined as (1.67 * 0.03) X lod mo12/L2, (1.89 f 0.17) X 10 M-I, and (7.12 * 0.23) X lo2 M-I, respectively. was calculated from the molar activities ax of the species X in solution