Biomedical subjects

R M Verbeeck

Publications and source records attributed to R M Verbeeck.

At least 37 records · Page 2Linked to original sources

PubMed1997

Setting reaction and hardening of an apatitic calcium phosphate cement.

The combination of self-setting and biocompatibility makes calcium phosphate cements potentially useful materials for a variety of dental applications. The objective of this study was to investigate the setting and hardening mechanisms of a cement-type reaction leading to the formation of calcium-deficient hydroxyapatite at low temperature. Reactants used were alpha-tricalcium phosphate containing 17 wt% beta-tricalcium phosphate, and 2 wt% of precipitated hydroxyapatite as solid phase and an aqueous solution 2.5 wt% of disodium hydrogen phosphate as liquid phase. The transformation of the mixture was stopped at selected times by a freeze-drying techniques, so that the cement properties at various stages could be studied by means of x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Also, the compressive strength of the cement was measured as a function of time. The results showed that: (1) the cement setting was the result of the alpha-tricalcium phosphate hydrolysis, giving as a product calcium-deficient hydroxyapatite, while beta-tricalcium phosphate did not participate in the reaction; (2) the extent of conversion of alpha-TCP was nearly 80% after 24 hr; (3) both the extent of conversion and the compressive strength increased initially linearly with time, subsequently reaching a saturation level, with a strong correlation observed between them, indicating that the microstructural changes taking place as the setting reaction proceeded were responsible for the mechanical behavior of the cement; and (4) the microstructure of the set cement consisted of clusters of big plates with radial or parallel orientations in a matrix of small plate-like crystals.

Bone Cements↗

PubMed1996

Genetic polymorphisms and erythrocyte sodium-lithium countertransport in essential hypertension.

Erythrocyte sodium-lithium countertransport (SLC) activity is elevated in essential arterial hypertension. With the growing attention to the genetic substrate of disturbed biochemical tests associated with essential arterial hypertension, we were particularly interested in the involvement of key genes for the regulation of SLC, possibly related to the pathophysiology of essential arterial hypertension. Consequently, the aim of the present study was to investigate SLC and its determining factors in essential hypertension. The influence of haptoglobin (Hp)-polymorphism, insertion/deletion polymorphism of angiotensin converting enzyme (ACE-I/D) and MNS blood group system on the regulation of SLC was studied. SLC activity was studied in a cross-sectional case-control study including 90 Caucasians: 60 patients with essential arterial hypertension who had been treated for at least 1 year and 30 normotensive controls. In essential hypertension, the SLC activity is significantly higher (P = 0.00005) than in controls. In normotensive patients, no differences in SLC are observed for the different polymorphisms studied. However, in the hypertensive group, SLC activity is higher (P = 0.003) in Hp 2-1 phenotype and independent of ACE-I/D genotyping and MNS blood group polymorphism. Multifactor analysis of variance in essential hypertension reveals significant (P = 0.001) differences in SLC activity for the presence or absence of Hp 2-1 phenotype and for body weight (P = 0.0003). Multivariate regression analysis shows the same parameters to be independent determining factors of SLC in essential arterial hypertension. No relation is found between SLC activity and target organ damage which includes coronary artery disease, peripheral arterial occlusive disease, left ventricular hypertrophy and cerebrovascular accident. We conclude that erythrocyte SLC activity is elevated despite pressure-lowering therapy. In essential arterial hypertension, individuals of Hp 2-1 phenotype show higher SLC activity than patients of other Hp-types, suggesting genetic heterogeneity of essential arterial hypertension. The presence or absence of Hp 2-1 phenotype is an independent determining factor of SLC activity whereas body weight codetermines SLC activity in essential hypertension.

Adult↗

PubMed1996

Kinetic study of the setting reaction of a calcium phosphate bone cement.

The setting reaction of a calcium phosphate bone cement consisting of a mixture of 63.2 wt % alpha-tertiary calcium phosphate (TCP)[alpha-Ca3(PO4)2], 27.7 wt % dicalcium phosphate (DCP) (CaHPO4), and 9.1 wt % of precipitated hydroxyapatite [(PHA) used as seed material] was investigated. The cement samples were prepared at a liquid-to-powder ratio of: L/P = 0.30 ml/g. Bi-distilled water was used as liquid solution. After mixing the powder and liquid, some samples were molded and aged in Ringer's solution at 37 degrees C. At fixed time intervals they were unmolded and then immediately frozen in liquid nitrogen at a temperature of TN = -196 degrees C, lyofilized, and examined by X-ray diffraction as powder samples. The compressive strength versus time was also measured in setting samples of this calcium phosphate bone cement. The crystal entanglement morphology was examined by scanning electron microscopy. The results showed that: 1) alpha-TCP reacted to a calcium-deficient hydroxyapatite (CDHA), Ca9(HPO4)(PO4)5O H, whereas DCP did not react significantly; 2) the reaction was nearly finished within 32 h, during which both the reaction percentage and the compressive strength increased versus time, with a strong correlation between them; and 3) the calcium phosphate bone cement showed in general a structure of groups of interconnected large plates distributed among agglomerations of small crystal plates arranged in very dense packings.

Bone Cements↗

PubMed1996

Fluoride release profiles of restorative glass ionomer formulations.

OBJECTIVES: The amounts of fluoride released by different glass ionomer formulations were compared on the basis of individual fluoride release profiles in order to derive the effect of the physical and chemical formulation on the fluoride release process. METHODS: The fluoride release profiles of each of five specimens of ten glass ionomer cements setting by an acid-base reaction were investigated. The profiles were obtained by determining the amount of fluoride released [F] after equilibrating the samples at 37 degrees C in distilled water for 140 d. The [[F],t]-profiles were compared with a Multivariate Data Analysis on the basis of a Principal Component Analysis. RESULTS: The Multivariate Data Analysis reveals that eight of the ten glass ionomers can be classified into four distinct groups. When the cumulative amount of fluoride released by each sample, [F]c, is calculated and fitted as a function of time, a regression analysis (r > 0.99) reveals that [F]c for all samples is most adequately represented by [F]c = ([F]l x t)/(t + t1/2) + beta x square root of t, indicating that two kinetic processes are responsible for the fluoride release profiles. SIGNIFICANCE: A comparison of the parameters of this equation shows that the physicochemical rationale for the classification of the glass ionomers conforms to differences in the kinetics of these processes which are determined by the qualitative and quantitative chemical composition as well as by the presentation (hand-mixed vs. capsules) of the glass ionomer. From the classification, it becomes apparent that different formulations can result in the same fluoride release profiles.

Analysis of Variance↗

PubMed1996

Comparative shear bond strength of some orthodontic bonding resins to enamel.

The aim of this study was to compare the in vitro bond strength, to bovine enamel measured in shear, of the orthodontic adhesives Lee Insta-bond (LiB), Rely-a-Bond (RaB), Right-on (Ro), Concise precoating method (Cc), Concise mixed method (CaB), Super-C (Sc), and Orthon (Or), and of the glass ionomer cement Ketac-Cem (KC). The fracture surfaces after debonding were also examined in order to determine the sites of failure. The results indicate that there is a significant difference between the shear bond strength obtained with the different adhesives so that the mean shear bond strength decreases in the order [Ro approximately Cab approximately Sc] > [LiB approximately RaB approximately Cc] > Or > KC. Moreover, for Cab and Sc it was found that the shear bond strength varies depending on the location on the bovine tooth. The failure site was essentially at the resin-bracket interface, except for Concise, where only 50 per cent of the cases failed at the resin-bracket interface.

Adhesives↗

PubMed1995

Infrared spectrometric analysis of endemic bladder stones in Niger.

The composition of 42 bladder stones from young children in Niger has been determined by infrared spectrometry. Nucleus and subsequent layers were analyzed separately. The major constituents of the stones were ammonium acid urate (AAU) and calcium oxalate monohydrate (COM). The nucleus consisted of nearly pure AAU in 17 stones (40%) and it was found to be the major constituent of the nucleus in 8 other stones (19%). Furthermore, it was present as a minor constituent of the center in another 9 stones (21%). In only 3 calculi (7%) the nucleus consisted of pure COM. This study suggests that (a) AAU is the initiating material for nucleation in this stone type in Niger, and (b) the incidence of endemic bladder stone disease is higher in Africa than previously reported.

Adolescent↗

PubMed1994

The integumental profile: a reflection of the underlying skeletal configuration?

The aim of this study was twofold: (1) to evaluate the importance of the level of training in orthodontics when estimating skeletal configuration by visual inspection of the soft tissue profile, and (2) to evaluate a possible discrepancy between integumental profile (IP) and skeletal class (SC). Four test groups comprising 10 orthodontists (O), 10 senior assistants (S), 10 junior assistants (J), and 10 dentists (D) assessed horizontal and vertical skeletal pattern from a series of slides of 100 patients. The assessments were repeated after a 1-month interval. Cephalometric analysis was also carried out by using a number of conventional analyses. Analysis of the results with Levene's test, two factor mixed-design variance analysis, and Newman-Keuls' Multiple-Range test showed that (1) orthodontists, independent of their level of training, are more consistent in assessing an IP than dentists; (2) assessments were more consistent for sagittal profile than for vertical profile; (3) sagittally the Wits' appraisal corresponds best with IP, and (4) vertically the Steiner analysis corresponds best with IP.

Adolescent↗

PubMed1994

Analysis of urinary calculi.

Urinary calculi are often small (< 5 mg) and can be composed of many very different constituents. The highly variable composition has lead to the development of many different methods of calculi analysis. In general the analytical methods can be divided in chemical and physical methods. Chemical methods are destructive and need several mg of sample. The smallest stones can not be analyzed with chemical methods. Qualitative and semi-quantitative chemical analysis methods are not accurate and can lead to clinical significant errors. Quantitative, instrumental, chemical analysis is accurate and makes no clinical significant errors, but these consume too much sample. None of the chemical methods of stone analysis makes it possible to distinguish the mineral constituents with similar chemical composition, e.g. the calcium phosphates, from one another and they usually can not identify "unexpected" stones. Physical methods need less sample than chemical methods and physical methods can distinguish the different minerals in the stones. Thermal analysis can give quantitative results but needs relatively much sample. Optical methods can analyze a few grains of stone but gives only qualitative results. Both methods can not be used to analyze an "unexpected" stone. Best suited methods for the analysis of calculi are X-ray diffractometry and IR spectroscopy. X-ray diffractometry can detect crystalline minerals in low concentrations. IR spectroscopy can detect both crystalline and amorphous minerals. Both methods can be used for semi-quantitative stone analysis and can analyze less than one mg of stone sample. X-ray diffractometry and IR spectroscopy are also the best methods to identify "unexpected" stone constituents.

Calcium Oxalate↗

PubMed1993

ESR study of 13C-enriched carbonated calciumapatites precipitated from aqueous solutions.

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied at carbonate contents ranging from approximately 5.4 up to 12.4 wt%. 12C- as well as 13C-enriched samples were prepared and examined with ESR after dying until constant weight at 25 degrees C and 400 degrees C. In these carbonated apatites, two CO3(3-) radicals were detected, one of which is derived from B-type carbonate situated at a phosphate lattice site. The other CO3(3-) most probably arises from CO3(2-) ions situated at OH- lattice sites. In contradistinction to the B-type contribution, the A-type contribution to the overall ESR signal decreases in absolute terms with increasing carbonate concentration. In addition, the line shape and the complete set of principal g-values of the A1-signal found in previous studies could be determined, corroborating the assignment of A1 to a surface O- ion.

Apatites↗

PubMed1993

The short-term fluoride release of a hand-mixed vs. capsulated system of a restorative glass-ionomer cement.

The present study investigated whether variability in fluoride release was reduced by use of a capsulated system as compared with a hand-mixed system based on the same qualitative and quantitative glass-ionomer formulation. Five operators independently prepared five disks of each type of glass-ionomer restorative filling material. The amount of fluoride released in water by each specimen after 1, 2, 3, 7, and 14 days was determined. The variance and the mean value of the fluoride release at a given time were independent of the operator, regardless of the glass-ionomer system considered. However, the variance and the mean value of the fluoride release at a given time were considerably greater for the capsulated system than for the hand-mixed system. A regression analysis further showed that the cumulative amount of fluoride released, [F], as a function of the time t conformed to [F] = a[1 - exp (-bt)] + ct0.5 for each glass-ionomer specimen, suggesting the simultaneous occurrence of two processes. Whereas the parameter b was the same for the hand-mixed and capsulated system and was independent of both a and c, the latter parameters were positively correlated. Moreover, the values for a and c were significantly greater for the capsulated system. On the basis of these results, it is concluded that the mixing process drastically influences the short-term as well as the long-term fluoride release.

Capsules↗

PubMed1993

Spectrum decomposition through maximum likelihood common factor analysis of the EPR spectra of Na+ containing carbonated apatites dried at 400 degrees C.

X-irradiated carbonated apatites precipitated from aqueous solutions and dried at 400 degrees C until constant weight are investigated with electron paramagnetic resonance (EPR). The carbonate content of the samples studied ranges from 8.12 to 21.0 wt%. The observed multicomponent EPR spectra are analyzed with maximum likelihood common factor analysis (MLCFA), a multivariate statistical technique. Once the correct number of constituents are determined and the factor spectra estimated by MLCFA, a minimization procedure is performed in order to transform the abstract factor spectra linearly into an equal number of real EPR powder spectra. The spin hamiltonian parameters of the component spectra thus obtained are used to characterize and identify the different paramagnetic radicals. A comparison with values from the literature is made. A spectrum decomposition study of all the observed multicomponent EPR spectra in terms of the isolated constituents is successfully performed as a function of the carbonate content of the samples.

Analysis of Variance↗

PubMed1992

Low-voltage coagulation for welding sutures watertight: an experimental study.

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 cm H2O, i.e. statistically significantly lower than the mean leak pressure of the conventional suture, which is 14.1 cm H2O. 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.

Animals↗

PubMed1991

The effect of carbonate content and drying temperature on the ESR-spectrum near g = 2 of carbonated calciumapatites synthesized from aqueous media.

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied as a function of their carbonate content and drying temperature. When the latter increases from 25 to 400 degrees C, the ESR spectrum is gradually modified and becomes similar to the spectrum of carbonated apatites, synthesized at high temperatures by solid state reactions. The latter ESR spectrum is dominated by CO3(3-)-contributions whereas the spectrum of precipitated samples dried at 25 degrees C can mainly be interpreted in terms of CO2-, CO3-, and O- ions. The behavior of these earlier-reported CO2-, CO3-, and O- centers is now studied as a function of drying temperature. In addition, the Spin Hamiltonian parameters of the CO3(3-) centers are determined and some other new paramagnetic radicals are discussed. It is shown that a CO3(2-) ion at a phosphate lattice site (B-type substitution) may give rise to either a CO2-, CO3-, or CO3(3-) radical on X-irradiation, depending on the sample preparation conditions. A surface CO3(2-) ion may cause a surface CO2-, CO3-, or O- radical. From the reported results it is not unambiguously clear whether the CO3(3-) ion detected in the samples with the relatively lowest carbonate content should be located on the surface or on a hydroxyl lattice site (A-type substitution). An important result is that the absolute concentration of the B-type CO3(3-) ion increases with increasing carbonate content as was also the case for the earlier reported B-type radicals (isotropic CO2- and CO3-). On the other hand, the absolute concentration of the surface radicals decreases with increasing carbonate content. The reported results show that similar deconvolution techniques can be applied in the future for the study of ESR spectra of calcified tissues. This will allow a more efficient phenomenological investigation of the latter.

Apatites↗

PubMed1991

Compressive strength of some polyalkenoates with or without dental amalgam alloy incorporation.

The present study compares the compressive strength after one week of some conventional glass-ionomer restorative materials with that of glass ionomers reinforced by the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder. Apart from the commercially available Ketac Silver and Miracle Mix, experimental mixtures of Fuji II glass-ionomer powder, the old as well as the new version, with various amounts of either a spherical or lathe-cut amalgam alloy were investigated. For the conventional glass ionomers, the mean compressive strength based on all measurements amounts to 159.9 +/- 4.5 MPa. Both formulations of Fuji II have a comparable strength after one-week maturation. The compressive strength of Ketac Silver does not differ significantly from that of Ketac Fill or from that of the conventional glass ionomers investigated. The effect of admixing amalgam alloy on the compressive strength is found to be determined by the shape and the amount of the alloy particles. Moreover, both parameters are interactive with the formulation of the Fuji glass ionomer used for preparation of the mixture. The results indicate that when dental amalgam alloy is added to the glass ionomer, lathe-cut particles are to be preferred but only in an amount up to 20% by weight.

Analysis of Variance↗

PubMed1990

The use of 'Fluor Protector', a fluoride varnish, as a caries prevention method under orthodontic molar bands.

The aim of this study was to determine whether Fluor Protector, a fluoride varnish, applied to molars before orthodontic banding could prevent white spot formation. In the in vitro study 93 human premolars were used, divided in five different groups, representing different clinical situations. Each tooth was sliced in half, one as a control and the other as a test specimen. All tooth halves were stored in a demineralizing solution, in an attempt to induce white spot formation. In the in vivo study 104 molars (52 controls and 52 tests) of 28 orthodontic patients were involved. The 'split-mouth technique' was used. After evaluation of the results of both studies, it is evident that Fluor Protector is very effective in the prevention of white spot formation under molar bands.

Dental Caries↗

PubMed1990

Is systemic treatment of osteoporosis and mandibular resorption possible?

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 with octocalcium phosphate. Calculation of these degrees of saturation of about 2000 data of blood plasma compositions given in the literature learned that calcitonin injections, 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.

Bone Resorption↗

PubMed1990

Aluminium in tooth pastes and Alzheimer's disease.

Epidemiological studies from Norway and England suggest a relation between the frequency of Alzheimer's disease and the concentration of aluminium in the drinking water. Estimates, made in this study, show that the role of aluminium from tooth pastes may be even more important than that from the drinking water. For that reason we determined in samples of tooth pastes taken from the BENELUX market which brands contained aluminium. This appeared to be the case for about 22% of the brands which according to the manufacturers cover about 60% of the market.

Aluminum↗

PubMed1990

[The use of aluminum-containing toothpaste and its potential risk].

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.

Aluminum Hydroxide↗