Biomedical subjects

M Beek

Publications and source records attributed to M Beek.

9 recordsLinked to original sources

PubMed2003

Human temporomandibular joint disc cartilage as a poroelastic material.

OBJECTIVE: The hypothesis was tested that a poroelastic material model is potentially able to describe the mechanical behavior of cartilaginous tissues in dynamic indentation experiments.Design. This hypothesis was tested by comparing the results from model predictions with results obtained from cyclic indentation experiments. BACKGROUND: The characteristics of cartilaginous tissues in general and of the temporomandibular joint disc in particular are generally identified by static confined or unconfined indentation experiments, while under physiologic circumstances these tissues are mostly loaded dynamically. METHODS: Dynamic indentation experiments were simulated using an axisymmetric finite element model. The results from the simulations were qualitatively compared with the experiments. RESULTS: The simulations showed several similarities with the experiments when the solid matrix was assumed to be hyperelastic. Both the maximum stress and the amount of energy dissipated decreased in each subsequent cycle. Furthermore, a similar dependency on the indentation frequency and amplitude was found. CONCLUSIONS: This qualitative study showed that a poroelastic material model can describe the dynamic behavior of the temporomandibular joint disc, provided that the solid matrix is modeled as hyperelastic. RELEVANCE: Temporomandibular disorders are presumably related to joint load distributions. Besides large static, dynamic loads are considered as a risk factor for cartilaginous wear. Dynamical loads, however, are also considered to stimulate the biosynthetic activity of cartilaginous tissues. Biomechanical analysis can be applied to estimate nonmeasurable joint loads. This enables to understand the underlying mechanisms of temporomandibular disorders, necessary to develop methods to prevent, diagnose and cure joint disorders. The present study shows that a poroelastic material model can be applied successfully to model the dynamical behavior of the temporomandibular joint disc in such analyses.

Cartilage, Articular↗

PubMed2001

Dynamic properties of the human temporomandibular joint disc.

The cartilaginous intra-articular disc of the human temporomandibular joint shows clear anteroposterior variations in its morphology. However, anteroposterior variations in its tissue behavior have not been investigated thoroughly. To test the hypothesis that the mechanical properties of fresh human temporomandibular joint discs vary in anteroposterior direction, we performed dynamic indentation tests at three anteroposteriorly different locations. The disc showed strong viscoelastic behavior dependent on the amplitude and frequency of the indentation, the location, and time. The resistance against deformations and the shock absorbing capabilities were larger in the intermediate zone than in regions located more anteriorly and posteriorly. Because several studies have predicted that the intermediate zone is the predominantly loaded region of the disc, it can be concluded that the topological variations in its tissue behavior enable the disc to combine the functions of load distribution and shock absorption effectively.

Aged↗

PubMed2001

Three-dimensional finite element analysis of the cartilaginous structures in the human temporomandibular joint.

While the movability of the human temporomandibular joint is great, the strains and stresses in the cartilaginous structures might largely depend on the position of the mandible with respect to the skull. This hypothesis was investigated by means of static three-dimensional finite element simulations involving different habitual condylar positions. Furthermore, the influence of several model parameters was examined by sensitivity analyses. The results indicated that the disc moved together with the condyle in the anterior direction without the presence of ligaments and the lateral pterygoid muscle. By adapting its shape to the changing geometry of the articular surfaces, the disc prevented small contact areas and thus local peak loading. In a jaw-closed configuration, the influence of 30 degrees variations of the loading direction was negligible. The load distribution capability of the disc appeared to be proportional to its elasticity and was enhanced by the fibrocartilage layers on the articular surfaces.

Aged↗

PubMed2000

Three-dimensional finite element analysis of the human temporomandibular joint disc.

A three-dimensional finite element model of the articular disc of the human temporomandibular joint has been developed. The geometry of the articular cartilage and articular disc surfaces in the joint was measured using a magnetic tracking device. First, polynomial functions were fitted through the coordinates of these scattered measurements. Next, the polynomial description was transformed into a triangulated description to allow application of an automatic mesher. Finally, a finite element mesh of the articular disc was created by filling the geometry with tetrahedral elements. The articulating surfaces of the mandible and skull were modeled by quadrilateral patches. The finite element mesh and the patches were combined to create a three-dimensional model in which unrestricted sliding of the disc between the articulating surfaces was allowed. Simulation of statical joint loading at the closed jaw position predicted that the stress and strain distributions were located primarily in the intermediate zone of the articular disc with the highest values in the lateral part. Furthermore, it was predicted that considerable deformations occurred for relatively small joint loads and that relatively large variations in the direction of joint loading had little influence on the distribution of the deformations.

Aged↗

PubMed2000

The accuracy of joint surface models constructed from data obtained with an electromagnetic tracking device.

Electromagnetic tracking devices are widely used in biomechanics. In this article a method is evaluated to construct models of articular surfaces using an electromagnetic tracking device. First, the accuracy of the space tracker was examined and optimised. Then, from several joint surfaces random points were measured and eighth degree polynomials were fitted to these measurements. To check if the fit converged well, plots of cross sections of the model with corresponding data points were examined. The accuracy of the models was determined by comparing them with computed tomography data and by reproducibility tests. All the fits converged well to the data. The root mean square (RMS) error of the models varied from 0.07 to 0. 18mm, and was proportional to the size and complexity of the surface. This was mainly due to systematic errors made by the space tracker, which were also proportional to the size and complexity of the surface.

Biomechanical Phenomena↗

PubMed1999

Fitting parametrized polynomials with scattered surface data.

Currently used joint-surface models require the measurements to be structured according to a grid. With the currently available tracking devices a large quantity of unstructured surface points can be measured in a relatively short time. In this paper a method is presented to fit polynomial functions to three-dimensional unstructured data points. To test the method spherical, cylindrical, parabolic, hyperbolic, exponential, logarithmic, and sellar surfaces with different undulations were used. The resulting polynomials were compared with the original shapes. The results show that even complex joint surfaces can be modelled with polynomial functions. In addition, the influence of noise and the number of data points was also analyzed. From a surface (diam: 20 mm) which is measured with a precision of 0.2 mm a model can be constructed with a precision of 0.02 mm.

Joints↗

PubMed1991

Patient education about cough: effect on the consulting behaviour of general practice patients.

The aim of this general practice study was to examine how the consulting behaviour of patients with a cough was affected when the tasks and responsibilities of patients, practice nurses and general practitioners were reorganized. In four 'average' single-handed general practices the effects on the consulting behaviour of patients of a rational practice policy on cough and the provision of systematic patient education on cough were compared with patient behaviour in four matched control practices. Changes of behaviour were measured in 548 patients who consulted for cough at least twice, in two successive autumn-winter periods. Significantly more patients in the experimental practice changed their behaviour to follow the practice guidelines than did patients in the control practices (56% versus 30%, P less than 0.001). The proportion of patients who continued to consult in the approved manner was greater among patients receiving intervention (66% versus 29%, P less than 0.001). This was equally true for patients who had suffered less than four episodes of cough or more than four episodes. The more often the patients received the education, the more effective it was. All patients who consulted the general practitioner for cough during the first autumn-winter period filled in a cough diary during the second period. From this it appeared that the intervention did not result in patients delaying consultation when they had a cough lasting longer than three weeks or one with 'serious' symptoms. It would appear that a rational practice policy and the provision of patient education can stimulate patients to modify their consulting behaviour. This could result in a reduction in the costs of health care.

Adolescent↗

PubMed1990

Feasibility and effects of a diabetes type II protocol with blood glucose self-monitoring in general practice.

A diabetes protocol characterized by self-monitoring of blood glucose was introduced in four general practices with the aim of making the frequency of consultations dependent on the metabolic regulation and emphasizing body weight reduction. The feasibility of the programme was investigated and the results after 1 year were compared with those of conventional care in four control practices. In the experimental practices, 13 patients switched from a medical specialist's to a general practitioner's supervision, 20 remained under supervision of their GP and 33 started self-monitoring. The self-monitoring rate, the consultation frequency according to protocol, the low number of dropouts and inadequate referrals and adherence to the therapeutic scheme showed that the protocol was feasible for both the GPs and the patients. At the initial assessment, the regulation of the diabetes was worse in patients of the experimental group, compared with those of the control group (mean HbA1 9.7% vs 8.9%; p less than 0.05). On average, patients in the experimental group (n = 56) lost 0.4 kg of body weight, whereas those in the control group (n = 73) gained 0.1 kg (n.s.). The mean change in HbA1, adjusted for the initial value, was -0.4% in the experimental and +0.5% in the control group (p less than 0.05). The results of the protocol can be attributed to a combination of greater participation of the patient, the individualized consultation frequency and the prescription of oral hypoglycaemic agents according to body weight development.

Administration, Oral↗

PubMed1985

Work satisfaction of general practitioners and the quality of patient care.

The emotional reactions of 57 general practitioners to three aspects of work was assessed by means of questionnaires. The quality of patient care was assessed by means of observations of general practice consultations, assessment of audiotaped consulting hour contacts and an analysis of the referral and prescription figures. A distinction was made between the degree of positive and the degree of negative feelings general practitioners have about their work. Many positive feelings (satisfaction, feeling at ease) correlated with more openness to patients, more attention to psychosocial aspects of the complaints but also with a higher rate of referral to medical specialists. On the other hand, many negative feelings (frustration, tension, lack of time) correlated with a high prescription rate and with giving little explanation to patients. To some extent the way that work is experienced by general practitioners correlated with the quality of care for the patients, but what constitutes cause and effect requires further study. A reflection of a doctor's own feelings about work should become part of training, continuing education and medical audit programmes.

Drug Prescriptions↗