Biomedical subjects

J D van Willigen

Publications and source records attributed to J D van Willigen.

At least 19 recordsLinked to original sources

PubMed1998

The riddle of the large loss in bite force after fast jaw-closing movements.

In unloading experiments (in which the resistance to a forceful static bite is suddenly removed), it is shown that the residual bite force (when the jaw system is arrested shortly after the unloading) is remarkably small. For example, of a 100-N initial bite force, only 18 N is left after a jaw travel distance of 5.0 mm. The present experiments were designed to study whether the magnitude of the low residual bite force is dependent on the initial bite force, the initial degree of mouth opening, and the distance of jaw travel. Furthermore, we analyzed whether the low magnitude of the residual force can be attributed to reflex events of the jaw muscles or to the force-length properties of the jaw-closing muscles. It was found that the residual forces are largely dependent on the distance of jaw travel and are barely sensitive to variations in initial mouth-opening. The relative residual forces are independent of the magnitude of the initial bite force. The maximum residual forces are on the order of 25% of the initial bite force after a jaw travel of 4.5 mm. The low values of the residual forces cannot be attributed to reflex events, because it took about 80 ms for the masseter muscles to decrease their force to a 50% level after their excitation was switched off. Furthermore, it was shown that the force-length properties of the jaw-closing muscles are not responsible for the small values of the residual forces, since over the trajectories used in the present experiments, the sarcomere lengths of the jaw-closing muscles were beyond their optimum. It is suggested that the low residual forces are brought about by (1) a non-uniform sarcomere behavior of the jaw-closing muscles when contracting, or (2) a long-lasting change in the myofilament system of the closing muscles induced by the sudden shortening of muscle fibers.

Biomechanical Phenomena↗

PubMed1997

Contribution of the digastric muscles to the control of bite force in man.

The contribution of the (co-contracting) digastric muscles to the rapid decline in bite-force magnitude after unloading of a static bite was investigated by asking participants to perform two different biting tasks with sudden unloading, and correlating the degree of co-contraction of the digastrics (as derived from their electromyograms) with the impact force, the impact velocity (as measured after a travel distance of 5 mm), and the residual force when the jaw system was in static conditions again after the impact. Co-contraction of the digastrics was varied by asking participants to perform the biting task while controlling bite force (force-controlled experiments) or jaw position (position-controlled experiments). In half of the experiments, participants co-contracted their digastrics more strongly in the position-controlled than the force-controlled experiments. However, there was no clear relation between the level of co-contraction and the magnitude of the impact force, the impact velocity and the residual force. The results imply that co-contraction of the digastric muscles is not sufficient to explain the reduction in bite force and the low impact velocity after an unexpected jaw-closing movement. Two other possible mechanisms that reduce forces in an unloaded jaw system are: (1) force velocity properties of the activated jaw muscles in conjunction with creep of the aponeurotic sheets of the jaw muscles, resulting in a slow partial recovery of the biting force after impact: (2) force length properties of jaw-opening muscles, an activity not recorded here.

Bite Force↗

PubMed1997

Mathematical model of the human jaw system simulating static biting and movements after unloading.

When the resistance to a forceful isometric bite is suddenly removed in unloading experiments, the bite force drops to zero and the mandible reaches a constant velocity. This occurs at an initial bite force of 100 N after approximately 12 ms when the incisors have moved 4.5 mm. Reflex activity is far too slow to limit the velocity at impact. To explore the influence of other factors (cocontraction, force-length properties, and force-velocity properties of the muscles) on the velocity at impact, a numerical forward dynamic model of the jaw system is formulated. Unloading experiments in different experimental conditions were simulated with the model. Most parameter values of the model are based on physiological data, both from literature and a data basis from a human cadaver study. Other parameter values were found by optimally fitting the model results to data from the unloading experiments. The model analysis shows that the limitation of the jaw velocity mainly may be due to the force-velocity properties of the jaw-closing muscles. Force-length properties of the jaw muscles hardly contribute to the impact velocity. The compliance of tendinous sheets in the jaw muscles is unfavorable for the reduction in impact velocity, whereas cocontraction of jaw-opening and -closing muscles helps to limit impact velocity. The force-velocity properties of the muscles provide a quick mechanism for dealing with unexpected closing movements and so avoid damage to the dental elements.

Bite Force↗

PubMed1997

Impact velocities of the teeth after a sudden unloading at various initial bite forces, degrees of mouth opening, and distances of travel.

A potentially dangerous situation arises when an individual bites on hard and brittle food which suddenly breaks, since the impact velocity of the lower teeth onto the upper teeth after the food is broken can be high and may cause dental damage. The present experiments were designed to study the magnitude of the impact velocity after a sudden unloading at various initial bite forces, degrees of mouth opening, and distances of travel. Subjects were asked to perform a static biting task during which the resistance to the bite was suddenly removed. The upward mandible movement was arrested after a certain distance. The velocity of the lower teeth at impact was calculated just before the mandible came to a standstill in combinations of 4 different bite forces (100, 80, 60, and 40 N), 4 different initial degrees of mouth opening (33.5, 30.5, 27.5, and 24.5 mm), and 3 different distances of travel of the mandible (4.5, 3.0, and 1.5 mm). We found that the bite force rapidly declined after the unloading, resulting in a small impact velocity of the lower front teeth. This impact velocity largely depended on the magnitude of the initial bite force and the distance traveled; it was barely sensitive to variations in degree of initial mouth opening. The maximal velocity of the lower teeth was 0.43 m/s (at an initial bite force of 100 N). This maximum was reached after a distance of travel of about 4 mm in 12 ms. The data suggest that the rapid decline in bite force coupled with a limitation of impact velocity is due to the force-velocity properties of the active jaw muscles and is not caused by neural control.

Biomechanical Phenomena↗

PubMed1995

Interneurones of the supratrigeminal area mediating reflex inhibition of trigeminal and facial motorneurones in the rat.

Whether sensory information from the inferior alveolar nerve is mediated by different types of interneurones in the supratrigeminal area (Su5) and whether different types of these interneurones have different inhibitory actions on jaw-closing motor neurones of the trigeminal motor nucleus was investigated. The intracellular responses of periodontal afferents in the mesencephalic trigeminal nucleus, Su5 interneurones and jaw-closing motor neurones were studied in response to graded, single-shock stimulation of the ipsilateral inferior alveolar nerve. It was found that the inhibitory action of afferent inflow from the inferior alveolar nerve to jaw-closing motor neurones is possibly mediated by two types of Su5 interneurones (T-I and T-II). These Su5 neurones were discriminated on the basis of their firing characteristics. The findings also indicated that: (1) T-I neurones are responsible for short-latency, low-threshold inhibitory postsynaptic potentials (IPSPs) observed in the trigeminal motor nucleus neurones; (2) T-II interneurones mainly contribute to the amplitude of these IPSPs at higher stimulus strengths; (3) the late part of plateau IPSPs in the jaw-closing motor neurones is induced by a characteristic firing of T-II neurones. It was also shown that afferent inflow from the inferior alveolar nerve, probably mediated by collaterals of T-I and T-II interneurones, also evokes IPSPs in neurones of the intermediate subnucleus of the facial motor nucleus. The characteristics of these IPSPs resemble those of the IPSPs recorded in the jaw-closing motor neurones.

Action Potentials↗

PubMed1994

Influence of visual feedback on human isometric bite-force tremor.

In contrast to recent reports, during an isometric short forceful bite, visual feedback had a significant influence on the force tremor spectrum. The value of a 'half-value frequency', being the frequency f1/2 at which, with increasing frequency, the amplitude of the spectrum for the first time drops to half its initial value, was used as an indicator for the spectral behavior. Under visual feedback, the amplitude contribution to the force spectrum in the 3-5 Hz frequency range was much larger than after deprivation of visual feedback. Elevations in the frequency range between 3 and 5 Hz in the force spectrum are interpreted as an expression of a visual feedback loop with a tau between 100 and 200 ms. This is supported by the visual/oral reaction times recorded, which were between 110 and 190 ms.

Adult↗

PubMed1993

Inhibitory commissural connections of neurones in the trigeminal motor nucleus of the rat.

Physiological evidence is presented for the existence of commissural fibres that cross the midsagittal plane in the medulla of the rat at the level of the trigeminal motor nucleus (Mo5). These fibres, which have their origin in the Mo5, terminated in the contralateral Mo5. Small inhibitory postsynaptic potentials were recorded in jaw-closing motoneurones by electrical activation of the commissural fibres; jaw-opening and fusimotor neurones as well as the jaw-closing and jaw-opening reflex were not affected. Electromyographic recordings from jaw-closing and jaw-opening muscles in the unrestrained rat showed that masseter activity was inhibited by the commissural fibres. These trigeminal commissural connections might play a part in the co-ordination of bilateral activity of the jaw-closing musculature during unilateral chewing.

Animals↗

PubMed1993

Digastric muscle response as a function of knowledge of the task to be performed.

Whether the motor programme executed by the digastric muscles during a forceful bite is modified according to a subject's expectation that the resistance between the teeth will change was investigated. There were two experimental conditions: (1) tracking a ramp (drawn on an oscilloscope screen) by biting (isometrically) on a force transducer and holding it at 120 N, and (2) tracking the same ramp with a sudden unloading at 100 N. There were two groups of experiments: (1) control experiments in which subjects underwent a sudden and unexpected unloading of the jaw, and (2) experiments in which subjects were previously informed whether or not there was to be an unloading. In all experiments the subjects co-contracted their digastric muscles during the bite as compared to the state at rest. The subjects' responses fell into the three different types: (i) those who varied the level of tonic digastric activity only as a function of the experimental condition, (ii) those who co-contracted the digastric muscles at the same time as the masseter muscles, and (iii) those who changed the contraction pattern of the digastric muscles as a function of the experimental condition. If modulation of the digastric muscles occurred this is a 'feedforward' strategy mainly based on immediate past performance.

Bite Force↗

PubMed1993

Anterior digastric muscle responses to sudden unloading of the mandibular elevator muscles in younger and older adults.

The digastric motor responses in the unloading reflex were investigated in a sample of 10 younger and eight older dentate subjects. The occurrence of the pre-collapse digastric activity (PDA) and the reflex events (burst of activity) following the mandibular unloading (DB) were studied separately. PDA was nearly consistent in half of the subjects of both groups. DB was clearly identified in 60% of the younger subjects, but in 54.2% of the older subjects. The mean latency of DB found in the younger subjects was 32.4 +/- 9.5 ms but 34.5 +/- 8.8 ms in the older subjects. For the latencies found we can infer that they are related to polysynaptic pathways. Also a slight tendency for decreased frequency of occurrence and increased latencies of DB is observed in the older age group.

Adult↗

PubMed1993

Serotonin-immunoreactive terminals in the mesencephalic trigeminal nucleus of the rat: an electron microscopic immunocytochemical study.

The morphological characteristics and distribution of serotonin-immunoreactive terminals within the rat mesencephalic trigeminal nucleus (Me5) were studied using immunocytochemical electron microscopy. Fibers, immunostained by specific antibodies raised against serotonin, were distributed throughout the entire rostrocaudal portion of the Me5. Examination of 355 serotonergic terminals in the caudal part of the Me5 revealed that 93% formed synaptic contacts with dendritic shafts: 68% on small (< 1.5 micron diameter) and 25% on large (> 1.5 micron diameter) dendrites. The remaining 7% formed axosomatic synapses, about a third of which are in contact with small spinous processes (somatic spines). Serotonin was also present in vesicle-filled boutons lacking synaptic-membrane specializations. Our data indicate that of all the dendritic synaptic and nonsynaptic inputs observed in the Me5 nucleus, the serotonergic component amounted to between 15 and 27%. More than half (58%) of the somatic synaptic input on the Me5 cells appears to be serotonergic. This suggests that, of all the somatic synaptic input on the proprioceptive primary sensory neurons of the Me5, the serotonergic afferent input probably has the most significance for the functioning of Me5 neurons.

Animals↗

PubMed1992

Brainstem influences on biceps reflex activity and muscle tone in the anaesthetized rat.

This study analyzes the effect of electrical stimulation of the locus coeruleus (LC) and adjacent brainstem structures on the tonic reflex (TVR), the tonic stretch reflex (TSR) and on muscle tone (MT) in anaesthetized rat. Increases in TVR, TSR and MT of the m. biceps were evoked from regions rostrally and ventrally of LC, the caudal pontine reticular nucleus, the cuneiform nucleus and from the ventral parts of the colliculus inferior. Stimulation of the LC did not influence biceps EMG activity. The results indicate that the observed facilitation of muscle activity is due to stimulation of parts of the mesencephalic locomotor region. It is discussed that the recorded increase in TVR, TSR and MT possibly is due to an excitatory action on alpha motoneurones on one hand and to an enhanced fusimotor drive on the other.

Anesthesia, General↗

PubMed1992

Perception of forces exerted by jaw and thumb.

By comparing the results of force matching between the jaw and the thumbs, whether subjects have any knowledge about the magnitude of exerted forces irrespective of the motor system was studied. Subjects were asked to match isometric forces of their own choice exerted by flexion of one of the thumbs with the jaw, and the other way around. The results were compared with control experiments in which subjects matched forces exerted by flexion of one of the thumbs with the other thumb and vice versa. None of the subjects was able to match correctly in all experimental conditions. All subjects displayed inconsistent matching behaviour, showing a mixture of correct matching and mismatching. This holds both for absolute matches (in N), and for matches relative to the maximal forces. The results show that knowledge about the magnitude of exerted forces is different for the jaw and the thumbs. Sensations about isometric forces exerted by the jaw or the thumbs are different within each subject and from subject to subject.

Bite Force↗

PubMed1992

Computer-aided optimization of choice and positioning of bone plates and screws used for internal fixation of mandibular fractures.

The present study describes a biomechanical integrated model of the mandibular system in which the maxilla and mandible, the masticatory muscles, and the temporomandibular joints are regarded as one system. In this model, strains in plate-osteosynthesis devices for internal fixation of mandibular fractures can be minimized by optimizing their positions. The model evaluates maximal bite force strategies on all possible dental elements; it uses a linear programming technique and a muscle architecture model, resulting in muscle recruitment patterns. The shape of a "standard" lower jaw is digitized by means of a three-dimensional (3-D) coordinate retrieval device and drawn on a computer screen after its dimensions have been changed according to the clinical case at hand. The 3-D location of the fracture as well as the anatomic restrictions for screw placement can be indicated on the screen. Osteosynthesis devices can be indicated in terms of dimensions, number, and material properties.

Biomechanical Phenomena↗

PubMed1992

Distribution of synaptic boutons in the mesencephalic trigeminal nucleus of the rat--a quantitative electron-microscopical study.

The distribution of synapses and synaptic bouton types in the mesencephalic trigeminal (Me5) nucleus was examined in a quantitative electron-microscopical study. Of 588 terminal boutons that were counted in the compact caudal part of the Me5 nucleus, less than 8% formed synapses on the somata of the predominantly unipolar Me5 neurons. About 79% formed synapses on fibres located between the Me5 somata, while about 13% of the vesicle-containing terminals had no clear synaptic specialization. All of these non-synaptic terminals were G type boutons, with pleomorphic and large characteristic dense-core vesicles. Approximately 60% of the axosomatic synapses were of the S type, containing spherical vesicles and an asymmetrical or symmetrical synaptic specialization. About 20, respectively 15% of the axosomatic synapses, were of the F, respectively P type; both are symmetrical synapse types containing either a majority of flat or pleomorphic vesicles. Less than 10% of the axosomatic synapses were of the G type. Although some proportional differences were noted, an almost similar bouton type distribution pattern was found for the axodendritic synapses suggesting that the axosomatic and axodendritic synapses in the Me5 nucleus are part of the same afferent fibre plexus covering the Me5 nucleus.

Animals↗

PubMed1991

Origin, distribution and morphology of serotonergic afferents to the mesencephalic trigeminal nucleus of the rat.

We have studied the localization, the morphology and sources of serotonergic input on the primary afferent neurons in the mesencephalic trigeminal nucleus (Me5) of the rat with light and electronmicroscopy immunocytochemistry and with anterograde and retrograde neuroanatomical tract tracing methods. Me5 neurons were found to receive a serotonergic input that is part of a serotonergic fibre plexus extending over the neighbouring parabrachial nucleus and locus coeruleus. These serotonergic afferents originate predominantly from serotonergic cells in the dorsal raphe nucleus.

Animals↗

PubMed1991

Tissue responses to degenerative changes in the temporomandibular joint: a review.

The articular cartilage covering of the mandibular condyle and the articular eminence, as well as the tissue of the articular disc, may be affected by degenerative changes associated with osteoarthrosis. Degenerative changes of cartilage alter its physical properties and, as a result, affect its ability to withstand compressive and shearing stresses. Increased friction between the articular surfaces may impair joint movement and may elicit compensatory or pathologic responses of the cartilage and the adjacent tissues, such as capsule and ligaments, synovial membrane, subchondral bone, and associated musculature. In this review, these structural changes are described and related to common signs and symptoms of craniomandibular dysfunction, such as clicking, locking and instability, pain and tenderness, restricted ranges of mandibular motion, crepitation, deformity, muscle wasting, and changes of occlusion.

Adaptation, Biological↗

PubMed1991

Ultrastructure of the rat mesencephalic trigeminal nucleus.

The subcellular morphology of the mesencephalic trigeminal (Me5) nucleus in the rat was studied by transmission electron microscopy. Most neurons in the thin rostral as well as in the major caudal part of Me5 appeared as large (40-50 microns), round- to ovoid-shaped unipolar cells. A few neurons (estimated 5%) appeared to be multipolar, usually bipolar. The Me5 neurons had a large, round, centrally located nucleus, and their cytoplasm was characterized by a dense network of lamellar granular endoplasmic reticulum, an abundant Golgi apparatus, many mitochondria and neurofilaments suggesting very active cells with a high rate of synthesis and axoplasmatic transport. Numerous small spinous processes covered the surface of the Me5 neurons. Clustering of 2 or 3 cells was accomplished by maculae, i.e. zones of gap junctions and close cell appositions. Boutons contacting the soma of Me5 neurons and boutons contacting large and small dendrites were defined as axosomatic and axodendritic synapses, respectively. Four types of synaptic boutons were distinguished: (1) S boutons, with round vesicles and asymmetrical as well as symmetrical synapses, (2) F boutons, with pleomorphic admixture of flattened and spherical vesicles and asymmetrical synapses, (3) P boutons, which resembled the F-type boutons but contained predominantly spherical vesicles and symmetrical synapses, and (4) G boutons, characterized by a heterogeneous population of vesicles. This description of the Me5 nucleus is particularly useful for future studies that attempt to correlate the structure of a particular synapse with its function.

Animals↗

PubMed1990

Dopaminergic afferents to the mesencephalic trigeminal nucleus of the rat: a light and electron microscope immunocytochemistry study.

The localization and sources of dopaminergic projections on the primary afferent neurons in the mesencephalic trigeminal nucleus (Me5) of the rat were studied using light and electron microscopic immunocytochemical staining techniques combined with anterograde and retrograde neuroanatomical tract tracing methods. Me5 neurons were found to receive a dopaminergic input that is part of a dopaminergic fibre plexus extending over the neighbouring nucleus parabrachialis and locus coeruleus. These dopaminergic afferents originate from the substantia nigra, the ventral tegmental area and the medial hypothalamus.

Animals↗