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Biomedical subjects

R Verbeeck

Publications and source records attributed to R Verbeeck.

At least 19 recordsLinked to original sources
PubMed2000

The effect of tooth size discrepancy on occlusion: An experimental study.

The purposes of this experimental study are the following: (1) to compare the anterior and overall tooth size ratios reported by Bolton to values reported in epidemiologic studies, (2) to assess the accuracy of tooth size discrepancy measurements, (3) to investigate to what extent generalized tooth size discrepancy affects occlusion, (4) to investigate the effect of leveling the curve of Spee, and (5) to evaluate the effect of extraction therapy of 4 premolars on occlusion. For the first part of the study, Bolton's mean anterior and overall tooth size ratio (as well as the extraction values) were compared with calculations derived from 4 publications reporting mean mesiodistal tooth width by using the t test (P </=.05). The second part of the study was carried out on a setup made from 1 dental cast of a male patient judged to have an ideal occlusion at the end of a nonextraction treatment. Our data reveal (1) no significant difference between the overall tooth size ratios of the Bolton values compared to 4 studies, but the anterior ratios were significantly different, (2) high reproducibility (99%) of tooth size discrepancy measurements, (3) that severe tooth size discrepancy affects the occlusion only a little, (4) that an excessive (6 mm) curve of Spee creates the poorest setup result, and (5) that extraction therapy only slightly affected the final occlusion. The effect of generalized tooth size discrepancy appears to be limited.

Dental Occlusion↗
PubMed2000

CerBeruS: a system supporting the sequential screening process

This paper describes the general design and application of CerBeruS, a computer-based system for supporting the process of sequential screening. CerBeruS stands for cluster-based selection, with cluster analysis forming the pivotal part of the system. CerBeruS uses the Ward's clustering method for partitioning the data set to be screened into smaller, more homogeneous subsets. One representative is picked from each subset and suggested as a screening candidate. Although the number of compounds submitted to screening is most often driven by the capacity of the assay, CerBeruS provides a statistical measure that computes the optimal number of clusters in the data set. This measure forms a point of reference for all screening experiments. Different hierarchies of subsets are stored in an Oracle database. Information about the size and content of a cluster can be retrieved from this database via a Visual Basic application. How these components work together in the CerBeruS system is demonstrated on a large data set. In addition, we show that, using the statistical measure, one can find an optimal trade-off between screening effort and number of hits.

Journal Article↗
PubMed1999

Dental wear in horses in relation to the microhardness of enamel and dentine.

The microhardness of enamel, primary dentine and secondary dentine was determined in the incisor teeth of 39 horses of three different breeds, trotter horses, Belgian draft horses and Arab horses. Using a microhardness tester fitted with a Knoop diamond indenter, the overall Knoop Hardness Number was determined for each tissue, and the influence of breed and age on the hardness were evaluated. Enamel and secondary dentine were significantly harder in Arab horses than in trotters and Belgian draft horses, but there were no significant differences between draft horses and trotter horses in the hardness of their enamel and dentine.

Age Factors↗
PubMed1998

The EASI project--improving the effectiveness and quality of image-guided surgery.

In recent years, advances in computer technology and a significant increase in the accuracy of medical imaging have made it possible to develop systems that can assist the clinician in diagnosis, planning, and treatment. This paper deals with an area that is generally referred to as computer-assisted surgery, image-directed surgery, or image-guided surgery. We report the research, development, and clinical validation performed since January 1996 in the European Applications in Surgical Interventions (EASI) project, which is funded by the European Commission in their "4th Framework Telematics Applications for Health" program. The goal of this project is the improvement of the effectiveness and quality of image-guided neurosurgery of the brain and image-guided vascular surgery of abdominal aortic aneurysms, while at the same time reducing patient risks and overall cost. We have developed advanced prototype systems for preoperative surgical planning and intraoperative surgical navigation, and we have extensively clinically validated these systems. The prototype systems and the clinical validation results are described in this paper.

Quality of Health Care↗
PubMed1996

Anaplastic (malignant) ganglioglioma arising from heterotopic grey matter nodules.

Anaplastic ganglioglioma is a rare malignant neoplasm. The short clinical course and the anaplastic histological features are characteristics of malignant ganglioglioma. Immunohistochemistry is necessary for the final diagnosis. The MRI appearances are described here for the first time in literature. Nodular grey matter heterotopias had been demonstrated and the patient developed an anaplastic ganglioglioma two years later, on the same place where the grey matter heteropias had been seen. This finding supports the hypothesis that these tumours may arise from grey matter nodules.

Adult↗
PubMed1996

[Evaluation of long-term release of fluoride by type II glass ionomer cements with a conventional hardening reaction].

As a part of a fundamental investigation on the fluoride release of glass ionomer cements (GIC), this study investigates the operator dependency of the fluoride release. In this respect the GIC fluoride release of a classical powder-liquid based system (Fuji II) and a capsule-based system (Fuji Cap II) in water during 14 days was determined on the hand of 5 specimens per formulation, made by 5 different operators. The data reveal that the variance on the fluoride release as well as the mean fluoride release at a given time are independent of the operator for both Fuji II and Fuji Cap II. In order to derive fundamental factors affecting the GIC fluoride release, the long-term fluoride release of 10 conventional setting type II GIC is investigated. In this respect the fluoride release profiles (FRP) of each of 5 cylindrical specimens (d = 6 mm, h = 3 mm) of Fuji II (FP), Fuji Cap II (FC), Miracle Mix (MM), Chemfil II (CP), Chemfil II in caps. (CC), Chelon-Fil (CF), Ketac-Fil (KF), Shofu II (SH), Chelon-Silver (CS) and Ketac-Silver (KS) were determined. The specimens were made according to the manufacturer's instruction and equilibrated at 37 degrees C in 25 mL distilled water up to 140 days. The water was regularly renewed and the fluoride concentration [F] of the equilibrated solution determined. A Multivariate Data Analysis of the ¿[F]],t¿-profiles on the basis of Principal Component Analysis (PCA) reveals that the FRP can be classified into 4 distinct groups: ¿CS,KS,FP¿ - ¿FC,CC¿ - ¿CF,KF¿ and ¿MM¿, leaving SH and CP apart as unclassifiable. When the cumulative amount of fluoride released ([F]c) for each individual sample is calculated and fitted as a function of time, a regression analysis shows that [F]c is most adequately fitted (r > 0.99) by [F]c = [F]I/t + t1/2 + beta. Square root of t, indicating that 2 kinetic processes are responsible for the FRP. A comparison of the parameters of this equation ([F]I, t1/2 and beta) shows that the physicochemical rationale for this classification of the GIC conforms to differences in the kinetics of these processes. From the classification, it becomes apparent that different formulations can result in the same FRP.

Dental Caries↗
PubMed1996

[Evaluation of the long-term release of fluorides from type II glass ionomer cements with conventional setting reactions].

As a part of a fundamental investigation on the fluoride release of glass ionomer cements (GIC), this study investigates the operator dependency of the fluoride release. In this respect the GIC fluoride release of a classical powder-liquid based system (Fuji II) and a capsule-based system (Fuji Cap II) in water during 14 days was determined on the hand of 5 specimens per formulation, made by 5 different operators. The data reveal that the variance on the fluoride release as well as the mean fluoride release at a given time are independent of the operator for both Fuji II and Fuji Cap II. In order to derive fundamental factors affecting the GIC fluoride release, the long-term fluoride release of 10 conventional setting type II GIC is investigated. In this respect the fluoride release profiles (FRP) of each of 5 cylindrical specimens (d = 6 mm, h = 3 mm) of Fuji II (FP), Fuji Cap II (FC), Miracle Mix (MM), Chemfil II (CP), Chemfil II in caps. (CC), Chelon-Fil (CF), Ketac-Fil (KF), Shofu II (SH), Chelon-Silver (CS) and Ketac-Silver (KS) were determined. The specimens were made according to the manufacturer's instruction and equilibrated at 37 degrees C in 25 mL distilled water up to 140 days. The water was regularly renewed and the fluoride concentration [F] of the equilibrated solution determined. A Multivariate Data Analysis of the [[F], t]-profiles on the basis of Principal Component Analysis (PCA) reveals that the FRP can be classified into 4 distinct groups: [CS,KS,FP]-[FC,CC]-[CF,KF] and [MM], leaving SH and CP apart as unclassifiable. When the cumulative amount of fluoride released ([F]c) for each individual sample is calculated and fitted as a function of time, a regression analysis shows that [F]c is most adequately fitted (r > 0.99) by [F]c = [F]I/t+t1/2 + beta, square root of t, indicating that 2 kinetic processes are responsible for the FRP. A comparison of the parameters of this equation ([F]I, t1/2 and beta) shows that the physicochemical rationale for this classification of the GIC conforms to differences in the kinetics of these processes. From the classification, it becomes apparent that different formulations can result in the same FRP.

Capsules↗
PubMed1995

An EPR study of intact and powdered human tooth enamel dried at 400 degrees C.

An EPR study of human tooth enamel dried at 400 degrees C is presented. Enamel blocks as well as powdered samples were investigated. The discussion deals mainly with three different spectral components, i.e., a CO3(3-) and two different CO2- signals. Using the anisotropic enamel block spectra, a convincing differentiation between the latter two radicals was possible. The first CO2- signal shows no dependence on the orientation of the enamel blocks, disappears from the spectrum upon heating, and was assigned to a surface radical. The second CO2- component is mainly responsible for the angular variation of the enamel blocks and is assigned to a bulk position. For the CO3(3-) ion, the (pseudo) angular variation of its isolated spectrum is presented and discussed. By means of the results presented in this study, earlier interpretation problems are considerably reduced.

Apatites↗
PubMed1995

The use of magnetic resonance angiography in stereotactic neurosurgery.

The authors discuss the advantages and disadvantages of the use of magnetic resonance (MR) angiography images in stereotactic neurosurgery. Current computer programs designed to assist the neurosurgeon in the planning of stereotactic neurosurgical interventions use intraarterial digital subtraction angiography images to visualize the blood vessels. Magnetic resonance angiography is a recent technique with a number of advantages over the digital subtraction method: it is less invasive and less prone to complications; it provides truly three-dimensional data sets that can be viewed from any direction; and it can visualize both stationary and flowing tissues with the same imaging device and localizer frame. Although digital subtraction images are still superior in contrast and vascular detail, state-of-the-art high-resolution MR angiography sequences provide sufficient vascular detail for planning surgery. Contrast-enhanced MR angiography images were acquired using adapted gradient-echo sequences to compensate for flow-induced distortions; postacquisition distortion correction was not necessary. Five methods to integrate and inspect a possible trajectory in the MR angiography data are discussed. Initial clinical experience with eight patients led to the conclusion that MR angiography is a valuable imaging modality that can be integrated reliably into a stereotactic neurosurgery planning procedure.

Adult↗
PubMed1994

How does the stereotactic workstation help the neurosurgeon?

At the KUL University of Leuven a workstation for the planning of neurosurgical stereotactic procedures has been developed. Its benefits are illustrated in three exemplary cases. The CT and/or MR images, acquired under stereotactic conditions, are transmitted via a PACS network (picture archiving and communication systems) directly to the stereotactic workstation in the operating theater. Target and entry point can be accurately defined on zoomed images. The trajectory can be checked and modified on all registered data sets and on resliced images along any plane. Maximum intensity projection of magnetic resonance angiography data sets along any arbitrary direction show the relative position of the blood vessels and the trajectory. During the preceding 32 months 29 patients were operated on using the stereotactic workstation. Postoperatively no new neurological deficit was observed in any of these patients. The workstation improves patient safety and increases the accuracy of neurosurgical stereotactic operations, because it helps the neurosurgeon to avoid blood vessels and/or important functional areas.

Adult↗
PubMed1994

Chemolysis of calcium containing urinary calculi. A review.

A review of current literature and research on chemolysis of calcium containing urinary stones is made. The type of chemolytic solution is dependent upon the composition of the stone. Calcium phosphates can be desolved with Suby or Renadecin solution although it is often tedious and time consuming procedure. Calcium oxalate, the major urinary stone component, can not be dissolved by these solutions. EDTA and other strong calcium chelators cannot be used because of their local toxicity. Certain enzymes can digest the organic matrix of the stone. The indication to chemolysis of stones are rather restricted.

Calcium↗
PubMed1993

Watertight sutures with fibrin glue: an experimental study.

A rat model was developed to test the watertightness of sutures and used to evaluate the value of fibrin glue (Tissucol, Immuno France, Tisseel, Immuno U.S., Inc.) in making conventional sutures watertight. Fibrin glue raised the mean hydrostatic pressure to which the skin suture resisted from 9.1 to 26.3 cm H2O, thus indicating that it enhances suture watertightness immediately after surgery. After 3 and 6 days, the pressure was increased, respectively, from 24.8 to 47.9 and from 56.5 to 73.3 cm H2O. For bladder sutures, the results are comparable.

Animals↗
PubMed1992

Rationale for local toxicity of calcium chelators.

Calcium chelating agents, such as ethylenediaminetetraacetate are toxic to urothelium. Their capacity to form complexes with calcium ions, which is the basis for their chemolytical effectiveness, also determines their toxicity. A decrease of chemolytical effectiveness by prior saturation of the chelator with Ca2+ or by lowering the pH to levels unfavourable for calcium binding significantly diminishes tissue injury. Exchange of Mg2+ ions does not, however, diminish tissue damage. The clinical use of calcium ligands is therefore unsafe.

Animals↗