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Biomedical subjects

E Otten

Publications and source records attributed to E Otten.

36 records · Page 2Linked to original sources
PubMed1997

A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study.

The aim of the study was to determine and compare bending and torsion moments across mandibular fractures, for different positions of the bite point and different sites of the fracture. Three identical resin mandibles, each with a single fracture, were used. The fracture sites were in the angle, body and symphyseal regions. A polyethylene bone plate was used for fixation. Simulated bite forces were applied at 13 bite points. For each bite point, the displacements of the fragments were registered and converted into bending and torsion moments across the fracture. Positive bending moments were defined as those moments that caused compression at the lower border and tension at the alveolar side of the mandible; negative bending moments did the opposite. Angle fractures had relatively high positive bending moments. Body fractures had positive as well as negative bending moments and the highest torsion moments. Symphyseal fractures had negative bending moments only and relatively high torsion moments. It was found that angle, body and symphyseal fractures each have a characteristic load pattern. These load patterns should play a decisive role in the treatment of mandibular fractures with regard to number and positioning of plates.

Adult↗
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↗
PubMed1996

A three-dimensional study of loads across the fracture for different fracture sites of the mandible.

The loads across the fracture depend on variables such as position of the fracture and the bite point. Up to now, no study has described systematically the influence of these two variables on these loads. The aim of this study was to describe and compare value and direction of the loads across the fracture for different positions of fractures in the mandible. In a three-dimensional model, bending and torsion moments and shear forces were compared for five mandibular fractures. The fractures were located in, respectively, the angle, posterior body, anterior body, canine and symphysis region. Positive bending moments were defined to give compression at the border, negative bending moments to give compression at the alveolar side of the mandible. The angle and posterior body fracture have high positive bending moments, small torsion moments and high shear forces. The anterior body, canine and symphysis fracture have high negative bending moments and high torsion moments with similar maximum values. The number of bite points with negative bending moments were different for all fractures. These bite points were always located on the fractured side. It is concluded that mandibular fractures can be divided roughly into two groups with similar load patterns across the fracture. One group consists of angle and posterior body fractures, the other group consists of anterior body, canine and symphysis fractures.

Adult↗
PubMed1995

A model study on the influence of a slowly activating potassium conductance on repetitive firing patterns of muscle spindle primary endings.

The general mathematical model of Frankenhaeuser and Huxley, which describes the generation of action potentials in myelinated nerve fibres, has been used as a kernel for a model of a sensory nerve ending. Two types of modifications were implemented. First, the four original permeability constants (those of potassium, sodium, non-specific and leak) were changed simultaneously (using an automated tuning algorithm), in order to introduce low-frequency repetitive firing capability (down to 15 Hz), keeping the deviations from the original values as small as possible. Second, a slow potassium conductance was added, in order to model slow processes (like accommodation) with time constants longer than those required to simulate short-lasting action potentials. Sensory stimuli were simulated as changes in passive conductance. The model displayed the following properties, which are typical of many sensory endings in general and of muscle spindle primary endings in particular: (i) The range of sustained repetitive firing was extended into the domain of low discharge rates, so as to span the entire physiological range (from 2 to 700 sec-1). (ii) The relation between firing rate and receptor potential was roughly linear over the full range of firing. (iii) Following a step increase of stimulus, the firing rate showed adaptation with a time constant of about 70 msec. (iv) Sudden reduction of the stimulus was followed by post-release silence. (v) Following a step increase of stimulus, the receptor potential showed a short dynamic peak. (vi) Following a step decrease of stimulus, the receptor potential displayed a post-release undershoot and recovery with a time constant of approximately 100 msec. (vii) With sinusoidal stimuli the receptor potential showed band-pass filter properties with phase advance below and phase lag above 12 Hz and a peak in gain at about 20 Hz. Thus the present equations adequately describe a range of known properties of muscle spindle primary endings. Based on minimal modification and extension of the Frankenhaeuser-Huxley model of action potential generation in myelinated fibres, they constitute a theory of sensory encoding. This theory is further corroborated by the experimental evidence of the presence of calcium-activated potassium channels in numerous sensory--including primary spindle--endings.

Action Potentials↗
PubMed1993

Loss of asymmetric distribution of sarcolemmal phosphatidylethanolamine during simulated ischemia in the isolated neonatal rat cardiomyocyte.

In the present study we have investigated the reorganization of the sarcolemmal phospholipids during the first 60 minutes of simulated ischemia ("ischemia") as induced by anoxia, volume restriction, and nutrient deprivation. Experiments were carried out on [3H]acetate-labeled neonatal rat cardiomyocytes and isolated (nonradiolabeled) sarcolemmal membranes obtained from the same culture system. After 60 minutes of "ischemia," cellular high-energy phosphate (ATP) levels had decreased to approximately 40% of the control values, but no significant phospholipid hydrolysis was detected. Labeling experiments using the nonpermeant (primary amine-containing phospholipid) probe trinitrobenzenesulfonic acid and nonlytic treatment with (different) exogenous phospholipases A2 were both indicative of a shifted transbilayer distribution of the hexagonalII phase-preferring and fusion-promoting sarcolemmal phosphatidylethanolamine in favor of the outer membrane leaflet. This specific change in sarcolemmal phospholipid asymmetry preceded the loss of integrity of the sarcolemma, monitored by the release of lactate dehydrogenase as well as by scanning electron microscopy. It is proposed that, in addition to the previously reported lateral phospholipid reorganization, uncontrolled transbilayer movement of the non-bilayer-preferring phosphatidylethanolamine from the inner to the outer leaflet of the sarcolemma is an additional factor in destabilizing the lipid bilayer, eventually leading to the irreversible membrane damage seen after a prolonged period of ischemia.

Adenosine Triphosphate↗
PubMed1992

Three-dimensional visualization of the temporomandibular joint: a computerized multisectional autopsy study of disc position and configuration.

To demonstrate disc position and disc configuration of the temporomandibular joint, three-dimensional multisectional computer reconstructions were made of 20 autopsy specimens (11 female, 9 male; mean age, 40.4 years). The presence of a distinct occlusion was the only criterion for selection. Normal disc position was found in 13 joints, partial anterior disc position was found in 5 joints, and complete anterior disc position was seen in 2 joints. Fifteen joints had biconcave disc configuration and 5 joints had deformed discs. Considering the high incidence of disc position deviating from the normal superior position, it is suggested that in some cases a so-called abnormal disc position can be regarded as within the limits of anatomic and physiological variability.

Adult↗
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↗
PubMed1991

A muscle spindle model for primary afferent firing based on a simulation of intrafusal mechanical events.

1. A muscle spindle model for primary afferent firing is presented that contains two components representing a gamma d-dependent (bag1) and gamma s-dependent (bag2/nuclear chain) intrafusal fiber. Each of the intrafusal fibers is composed of a linear elastic element representing the sensory part and a muscle fiber representing the muscular part. 2. The muscular part of the bag1 was modeled as a slow twitch, that of the bag2 as a fast twitch muscle fiber. 3. The sensory regions were linear length transducers, generating a rising depolarization on increasing stretch. The input of both bags was fused by taking the largest depolarization to determine a generator potential. The rate of primary afferent firing depended on this generator potential as well as on its rate of change. 4. To simulate the high sensitivity of muscle spindles to small amplitudes of stretching, a model analogue of cross-bridge fixation (or stiction) has been included in the muscular part of the bag1 fiber. This makes use of one hundred cross-bridge regions that release one after the other, provided a certain breaking force is exceeded. 5. The values of the mechanical parameters that defined the model were selected by a computerized search procedure. 6. The values found by means of this procedure allowed the model to provide an accurate simulation of experimental data on ramp-and-hold stretches (for 6 different stretch velocities under variable conditions of fusimotor activity). 7. On sinusoidal stretches at a frequency of 1 Hz the spindle model responded with about one-half the discharge modulation reported in experimental studies. Its phase advance tended to be slightly lower than that observed for real spindles. 8. Frequency response curves showed the same high sensitivities at high frequencies as those observed in real spindles. 9. Close evaluation of the model compared with experimental results in literature reveal its merits as well as its limitations. Because the model is structural rather than phenomenologic, it provides insight into how intrafusal events may contribute to observed firing properties of real muscle spindles.

Electric Stimulation↗
PubMed1991

Three-dimensional computer reconstruction of the eustachian tube and paratubal muscles.

A new method of anatomic dissection and image reconstruction using computer techniques for better understanding of eustachian tube (ET) functioning is presented. Coronal sections of two noncleft fetal skulls were photographed and projected on a graphic tablet. Contours of the pertinent structures were digitized using a mouse. Coordinates of all digitized points were entered into a special computer program. The data were transformed into three-dimensional representations of anatomic structures. The levator veli palatini muscle (M-LVP) was found to have a close relationship with the ET running underneath it and passing at the inside of the pharyngeal edge of the medial cartilage before entering the soft palate. On M-LVP contraction, this part of the medial ET cartilage appears to be the sole point of impact for ET opening. The tensor veli palatini muscle (M-TVP) is connected with the lateral cartilage of the ET and leaves the ET, rounding the pterygoid hamulus before entering the palatal aponeurosis. On this anatomic basis, action of the muscle by isotonic contraction appears to be more likely than isometric contraction.

Cartilage↗
PubMed1989

Mathematical and philosophical reflections on motor control systems.

In line with the tradition of the Dutch school of functional morphology, an attempt is made to integrate numerical models of sarcomeres, muscle fibres, muscles, bone-connective-tissue systems, joints, muscle spindles and neural networks into one model simulating motor control. There are two purposes for this attempt. Firstly, to indicate whether numerical properties of the organs forming a system of motor control can be explained in terms of its motor functions. Secondly, to indicate properties that emerge from the integration of the organs into a system of motor control: how much more is an integrated motor system than the sum of its functional components. The motor control system of chewing has been taken as an example, particularly that in rats.

Animals↗
PubMed1987

Optimal design of vertebrate and insect sarcomeres.

This paper offers a model for the normalized length-tension relation of a muscle fiber based upon sarcomere design. Comparison with measurements published by Gordon et al. ('66) shows an accurate fit as long as the inhomogeneity of sarcomere length in a single muscle fiber is taken into account. Sequential change of filament length and the length of the cross-bridge-free zone leads the model to suggest that most vertebrate sarcomeres tested match the condition of optimal construction for the output of mechanical energy over a full sarcomere contraction movement. Joint optimization of all three morphometric parameters suggests that a slightly better (0.3%) design is theoretically possible. However, this theoretical sarcomere, optimally designed for the conversion of energy, has a low normalized contraction velocity; it provides a poorer match to the combined functional demands of high energy output and high contraction velocity than the real sarcomeres of vertebrates. The sarcomeres in fish myotomes appear to be built suboptimally for isometric contraction, but built optimally for that shortening velocity generating maximum power. During swimming, these muscles do indeed contract concentrically only. The sarcomeres of insect asynchronous flight muscles contract only slightly. They are not built optimally for maximum output of energy across the full range of contraction encountered in vertebrate sarcomeres, but are built almost optimally for the contraction range that they do in fact employ.

Animals↗
PubMed1987

A myocybernetic model of the jaw system of the rat.

A dynamic model of the jaw system of the rat has been formulated. The model consists of several units: (1) A static muscle fiber model, relating force with fiber length, based on sarcomere morphometric information. (2) A static skeletal muscle model, relating muscle force with muscle length based on myomorphometric information and the static fiber model. (3) A dynamic skeletal muscle model, relating muscle force with muscle length, contraction velocity and stimulation rate, based on fiber type data, calcium dynamics and velocity-force relations and on the static skeletal muscle model. (4) A kinematic model of the jaw system, relating the possible movements of the jaw system with the morphometrics of the bones, joints and connective tissue. (5) A three-dimensional reconstruction package, devised to analyze and display the morphometrics of the jaw system and to show the model results in terms of force vectors, positions and movements of the jaw system. EMG data of chewing rats and myomorphometric data (from unit 5) are fed into unit 3 resulting in muscle forces. The trajectories of the lower jaw and hyoid resulting from these velocity-dependent forces are calculated using unit 4, taking inertias and gravity into account. The calculated movements are remarkably similar to those that have been observed experimentally. The force-velocity relation of the muscles is highly important in stabilizing the velocities of the elements.

Animals↗