Biomedical subjects

T M van Eijden

Publications and source records attributed to T M van Eijden.

At least 19 recordsLinked to original sources

PubMed2001

Action potential shape of rabbit masseter motor units and jaw angle.

Action potentials of rabbit masseter motor units (n = 42) were registered at different jaw angles to examine whether the shape of the action potential is related to length of muscle fibers in motor units and depends on the intramuscular location of the motor unit. Twitches were elicited by stimulating motoneurons in the trigeminal motor nucleus. During jaw opening (0-21 degrees), the duration of the action potentials increased by about 10%. Anteriorly located motor units showed an increase in duration larger than that of more posteriorly located units, which was probably due to a larger stretching of the more anteriorly located units.

Action Potentials↗

PubMed2001

Mechanical properties of single motor units in the rabbit masseter muscle as a function of jaw position.

Positions and contractile properties of rabbit masseter motor units were investigated at different jaw gapes. Twitch responses were measured at gapes ranging from dental occlusion (0 degree) to maximum opening (21 degrees), in steps of 3 degrees. The twitches were elicited by stimulating motoneurons extracellularly in the trigeminal motor nucleus. The units appeared to produce a large variety of force vectors. On average motor units in the deep parts of the masseter produced considerably less twitch force (average: 25-30 mN) than those in the superficial parts (average: 45-50 mN) and anteriorly located motor units were slower than posteriorly located units. With an increase of jaw angle, twitches became slower, reflected by an increase (30%) of the twitch contraction time. Most motor units had a parabolic-like active jaw angle-force relationship. A large variation in the shape of the curves was found. The average optimum jaw angle was reached at 12 degrees jaw opening. In general, force output was relatively low (20-60% of maximum force) at occlusion and relatively high (60-100% of maximum force) at maximal jaw opening. Anteriorly and posteriorly located motor units differed significantly in their angle-force curves. Anteriorly located motor units produced less relative force at occlusion, showed a steeper increase of force with an increase of jaw angle, reached maximum force at larger jaw angles and produced larger forces at maximum jaw opening. The larger force changes in the more anterior units are probably related to their longer distance from the axis of jaw rotation. The large variability of motor unit properties and angle-force curves suggests that a fine gradation of both force magnitude and direction is possible within the masseter and that the angle-force curve of the whole muscle or of whole muscle parts is broader than that of individual motor units. This broadening may be considered as a mechanism to sustain active muscle force throughout a large movement range.

Animals↗

PubMed2001

A longitudinal electromyographic study of the postnatal maturation of mastication in the rabbit.

At 2 weeks of age, infant rabbits show chewing movements that resemble those of the adult animal. Previous studies have shown that, at that stage, the accompanying masticatory motor pattern is clearly similar to the suckling motor pattern. As early as 4 weeks, chewing muscle activity is indistinguishable from the adult chewing motor pattern. These reports suggest that the adult chewing motor pattern is developed from the suckling motor pattern. In this study, the chewing motor pattern in the intermediate period (between 2 and 4 weeks of age) was investigated by means of fine-wire electromyography and jaw tracking. Maturation of masticatory movements was found to have two phases. Maximum gape increased in the first few days and was followed by strong development of transverse jaw excursions after the age of 17 days. The increase in jaw excursions was brought about by changes in motor behaviour and facilitated by the development of smooth occlusal surfaces. The changes in motor behaviour were: (1) the level of activity of the balancing-side muscles became more equal to that of the working side; (2) the timing of digastric muscle activity became asymmetrical at the age of 17 days; (3) the peak activity of masseter, temporalis, medial pterygoid and lateral pterygoid muscle portions was gradually shifted or prolonged into the power-stroke phase. It can be concluded that the masticatory contraction pattern shifts from one derived from the suckling contraction pattern at the age of 14 days to one almost similar to the adult chewing pattern at the age of 23 days.

Animals↗

PubMed2001

Mechanical properties of cancellous bone in the human mandibular condyle are anisotropic.

The objective of the present study was (1) to test the hypothesis that the elastic and failure properties of the cancellous bone of the mandibular condyle depend on the loading direction, and (2) to relate these properties to bone density parameters. Uniaxial compression tests were performed on cylindrical specimens (n=47) obtained from the condyles of 24 embalmed cadavers. Two loading directions were examined, i.e., a direction coinciding with the predominant orientation of the plate-like trabeculae (axial loading) and a direction perpendicular to the plate-like trabeculae (transverse loading). Archimedes' principle was applied to determine bone density parameters. The cancellous bone was in axial loading 3.4 times stiffer and 2.8 times stronger upon failure than in transverse loading. High coefficients of correlation were found among the various mechanical properties and between them and the apparent density and volume fraction. The anisotropic mechanical properties can possibly be considered as a mechanical adaptation to the loading of the condyle in vivo.

Aged↗

PubMed2001

A method to predict muscle control in the kinematically and mechanically indeterminate human masticatory system.

A method is proposed to generate muscle activation patterns for goal-directed movements of the human masticatory system. This system is special because apart from a larger amount of muscles than degrees of freedom its joints do not restrict its movements a priori. Therefore, each muscle is able to influence all six degrees of freedom which makes the system kinematically and mechanically indeterminate. Furthermore, its working space is principally determined by the dynamical properties of its muscles and not by passive constraints. The presented method determines the contribution of each degree of freedom to a movement of a reference point on the mandible. It avails of straightforward mathematical techniques like Linear Programming. It does not require a separate trajectory planning step. It was applied in a six degrees of freedom dynamical mathematical model of the human masticatory system. This model which was based upon rigid-body dynamics incorporating skull morphology and muscle architecture including dynamical properties. Movements were exclusively defined by a goal position of the mandibular reference point. The method proved to be robust in generating muscle activation patterns for both feasible and infeasible movement tasks. Generally, they were accomplished faster than habitually observed. If the task was infeasible the movement stopped at the outer boundary of the working space at the side of the unreachable goal. The method, therefore, enables to explore the working space of the mandible and the factors that are relevant for its boundaries.

Biomechanical Phenomena↗

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

The three-dimensional active envelope of jaw border movement and its determinants.

The sagittal and frontal active envelope of border movement is applied regularly as a clinical tool in functional examinations of the human masticatory system. In contrast, the three-dimensional movement area has hardly been examined. Furthermore, the determinants of this area are not established unambiguously. In the present study, the three-dimensional envelope of incisor movement was predicted with a three-dimensional mathematical model of the human masticatory system, which included the morphology of the system and the fine architecture of its muscles. With this model, the influence of the temporomandibular ligaments and the passive muscle tensions on the envelope were estimated. The predicted three-dimensional active envelope of border movements was limited in horizontal directions, predominantly by the temporomandibular ligaments. The passive tensions of the masticatory muscles influenced, although marginally, its vertical extension. It appeared unlikely that, in a normal situation, active muscle tensions (casu quo muscle reflexes) contribute to the shape of the envelope.

Computer Simulation↗

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↗

PubMed2001

Morphology and physiology of masticatory muscle motor units.

Motor unit territories in masticatory muscles appear to be smaller than territories in limb muscles, and this would suggest a more localized organization of motor control in masticatory muscles. Motor unit cross-sectional areas show a wide range of values, which explains the large variability of motor unit force output. The proportion of motor unit muscle fibers containing more than one myosin heavy-chain (MHC) isoform is considerably larger in masticatory muscles than in limb and trunk muscles. This explains the continuous range of contraction speeds found in masticatory muscle motor units. Hence, in masticatory muscles, a finer gradation of force and contraction speeds is possible than in limb and in trunk muscles. The proportion of slow-type motor units is relatively large in deep and anterior masticatory muscle regions, whereas more fast-type units are more common in the superficial and posterior muscle regions. Muscle portions with a high proportion of slow-type motor units are better equipped for a finer control of muscle force and a larger resistance to fatigue during chewing and biting than muscle portions with a high proportion of fast units. For the force modulation, masticatory muscles rely mostly on recruitment gradation at low force levels and on rate gradation at high force levels. Henneman's principle of an orderly recruitment of motor units has also been reported for various masticatory muscles. The presence of localized motor unit territories and task-specific motor unit activity facilitates differential control of separate muscle portions. This gives the masticatory muscles the capacity of producing a large diversity of mechanical actions. In this review, the properties of masticatory muscle motor units are discussed.

Animals↗

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↗

PubMed2000

EMG power spectrum and motor unit characteristics in the masseter muscle of the rabbit.

Masticatory muscles contain a large variety of motor units with different physiological and morphological properties. In this study, we tested the hypothesis that a relationship exists between the mechanical and myo-electric properties of single motor units in the masseter muscle of the rabbit. It was expected that faster-contracting motor units, which usually have a relatively large number of fibers with large diameters, should have faster action potentials with larger amplitudes than slower motor units. Single motor units were stimulated. A two-dimensional force transducer registered mechanical parameters of the units. EMG electrodes were used to determine amplitude and frequency parameters of the action potentials of the same units. The results showed that faster-contracting motor units indeed produced action potentials with higher conduction velocities. However, faster motor units had no significant larger amplitude of the action potential. Small but significant positive correlations were found between the tetanic peak force and the amplitude of the action potentials. Little difference was found among the various frequency and amplitude parameters, respectively, making them equally suitable to describe the action potential. Surprisingly, a negative correlation between the amplitude and frequency parameters of the action potential was found, which may result from variability in arrival times of action potentials at the electrode site. Regional differences in the frequency parameters were found between the anterior and posterior parts of the superficial masseter.

Action Potentials↗

PubMed2000

The three-dimensional cancellous bone architecture of the human mandibular condyle.

In the present study, we tested the hypothesis that the cancellous bone of the mandibular condyle is inhomogeneous and anisotropic. For this purpose, 11 mandibular condyles from embalmed human cadavers were scanned in a micro-CT system. Within each condyle, 9 volumes of interest were selected from different mediolateral and supero-inferior regions. Several bone parameters were calculated to describe the morphology. It appeared that the cancellous bone of the condyle could be approximated by parallel plates. These plates were almost vertically oriented at an angle of 17 degrees relative to the sagittal plane, i.e., perpendicular to the condylar axis. In the superior regions of the condyle, the cancellous bone had the largest bone volume fraction (0.19), associated with the thickest trabeculae (0.11 mm), and the highest trabecular number (1.72 mm(-1)). The lowest bone volume fraction (0.15) was found more inferiorly. The degree of anisotropy increased from superior to inferior across the condyle. No mediolateral differences in bone morphology were found, but superiorly central regions contained more bone than peripheral regions. The plate-like trabeculae could indicate that the condyle is optimally adapted to sustain loads from all directions in a plane perpendicular to the condylar axis. The high bone mass and lower anisotropy in the superior regions could enable the condyle to sustain multiple load directions. Toward the collum, the trabeculae are more aligned. This could point to stresses acting predominantly in one direction.

Aged↗

PubMed2000

Biomechanics of the mandible.

In this review the biomechanical behavior of the mandibular bone tissue, and of the mandibular bone as a whole, in response to external loading is discussed. A survey is given of the determinants of mandibular stiffness and strength, including the mechanical properties and distribution of bone tissue and the size and shape of the mandible. Mandibular deformations, stresses, and strains that occur during static biting and chewing are reviewed. During biting and the powerstroke of mastication, a combination of sagittal bending, corpus rotation, and transverse bending occurs. The result is a complex pattern of stresses and strains (compressive, tensile, shear, torsional) in the mandible. To be able to resist forces and bending and torsional moments, not only the material properties of the mandible but also its geometrical design is of importance. This is reflected by variables like polar and maximum and minimum moments of inertia and the relative amount and distribution of bone tissue. In the longitudinal direction, the mandible is stiffer than in transverse directions, and the vertical cross-sectional dimension of the mandible is larger than its transverse dimension. These features enhance the resistance of the mandible to the relatively large vertical shear forces and bending moments that come into play in the sagittal plane.

Animals↗

PubMed1999

Three-dimensional dynamical capabilities of the human masticatory muscles.

Many habitual human jaw movements are non-symmetrical. Generally, it is observed that when the lower incisors move to one side the contralateral condyle moves forwards onto the articular eminence, whereas the ipsilateral condyle stays in the mandibular fossa, moving slightly to the ipsilateral side. These jaw movements are the result of contractions of active masticatory muscles and guided by the temporomandibular joints, their ligaments and passive elastic properties of the muscles. It is not known whether the movements are primarily dependent on passive guidance, active muscle control or both. Therefore, the objective of this study was to analyse the interplay between these factors during non-symmetrical jaw movements. A six-degrees-of-freedom dynamical biomechanical model of the human masticatory system was used. The movements were not restricted to a priori defined joint axes. Jaw movement simulations were performed by unilateral activity of the muscles. The ligaments or the passive elastic properties of the muscles could be removed during these simulations. Laterodeviations conform to naturally observed ones could be generated by unilateral muscle contractions. The movement of the lower incisors was hardly affected by the absence of passive elastic muscle properties or temporomandibular ligaments. The latter, however, influenced the movement of the condyles. The movements could be understood by analysing the combination of forces and torques with respect to the centre of gravity of the lower jaw. In addition, the loading of the condyles appeared to be an important determinant for the movement. This analysis emphasizes that the movements of the jaw are primarily dependent on the orientation of the contributing muscles with respect to this centre of gravity and not on the temporomandibular ligaments or passive elastic muscle properties.

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↗

PubMed1999

Contribution of jaw muscle size and craniofacial morphology to human bite force magnitude.

The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometrics and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalometric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.

Adolescent↗

PubMed1998

A model for mylohyoid muscle mechanics.

The purpose of the present study was to develop a mathematical model of the mylohyoid muscle allowing to analyze the complex mechanics of the muscle during jaw movement. The model was based on muscle morphology and physiological properties. Bending of fibers was incorporated into the model by pulleys located along the upper lateral border of the anterior belly of the digastric muscle. The dynamical properties of the muscle portions, i.e. force length and force velocity relationships, were related to sarcomere length changes. In addition, the effective force component produced by each portion in the sagittal plane was calculated. The model provided information on the geometrical changes of the muscle portions and the concomitant effect on sarcomere length, dynamical properties and effective force component as a function of jaw opening angle. Muscle configuration changed drastically and non-uniformly during jaw opening. However, sarcomere length changes were relatively small and differed but slightly between the muscle portions. The muscle portions all operated near optimum length regarding to their force-length relationship. In all muscle portions effective muscle force was the smallest (10-20% of maximum isometric force) in the beginning of the opening movement. With an increase of jaw angle effective muscle force gradually increased to 60-70% of maximum isometric force in the posteriormost muscle portion and to 20% in the anteriormost portion. Muscle fiber bending appeared to increase the sagittal plane component of the muscle force substantially.

Biomechanical Phenomena↗