Biomedical subjects

F Bosman

Publications and source records attributed to F Bosman.

At least 91 records · Page 5Linked to original sources

PubMed1993

Jaw-jerk reflex activity in relation to various clenching tasks in man.

In order to investigate whether the mandibular stretch (jaw-jerk) reflex is modulated in a task-dependent manner, jaw-jerk reflexes were elicited in eight subjects during clenching with unilateral and bilateral tooth support, respectively. The reflexes were examined in the electromyographic (EMG) activity recorded by means of surface electrodes and were elicited by means of small transient jaw displacements at a constant value of 80 microns. Low levels of background EMG were applied ranging from 1 to 30% maximal voluntary contraction (MVC) as controlled by means of visual feedback. Linear relationships were observed between reflex amplitude and level of background EMG. The slope in these relationships served as a measure of reflex gain. For the masseter as well as the anterior temporal muscles, the reflex gain, averaged over both sides, was larger during clenching with unilateral tooth support than with bilateral tooth support (P < 0.05). Furthermore, the gain was larger on the side without tooth support during unilateral clenching and larger on the side without visual feedback of elevator muscle activity during bilateral clenching. It can be concluded that the jaw-jerk reflex is modulated to subserve the stabilization of the mandible, with the reflex sensitivity being larger the more that alternative stabilizing factors such as mechanical tooth contact, visual feedback and feedback from periodontal pressure receptors around the teeth are lacking. The reflex modulation may be of functional importance in stabilizing the mandible during its movement in the chewing process, as the food is predominantly placed unilaterally between the antagonistic teeth during individual chewing cycles.

Adolescent↗

PubMed1993

Control of human jaw elevator muscle activity during simulated chewing with varying bolus size.

During chewing, a small part of the observed muscle activity is needed for the basic open-close movements of the mandible, and additional muscle activity (AMA) is needed to overcome the resistance of the food. The AMA consists of two contributions: a large peripherally induced contribution, starting after food contact and a small anticipating contribution, starting before food contact. We investigated whether the latencies of these contributions depend on the expected or actual bolus size. Subjects made rhythmic open-close movements near their natural chewing frequency controlled by a metronome. This frequency was determined while the subjects were chewing gum. Food resistance was simulated by an external force, acting on the jaw in a downward direction during part of the closing movement. Bolus size was simulated by the jaw gape at which the force started. Jaw movement and surface EMG of the masseter and anterior temporal muscles on both sides and the suprahyoid muscles were recorded during experiments in which the jaw gape at which the force started was varied. The peripherally induced contribution to the AMA started about 20 ms after the onset of the force, irrespective of the jaw gape at which the force started. It is concluded that the onset of this contribution depends solely on food contact in the actual cycle. The function of the observed mechanism for jaw elevator muscle control may be to enable a highly automatic control of the muscle activity required to overcome the resistance of food of different hardness and different size. The onset of the anticipating contribution to the AMA showed neither a relationship with the actual jaw gape at which force onset occurred nor with the expected jaw gape of force onset. It is suggested that the onset of the anticipating AMA is related to the jaw gape at the onset of closing. The function of this contribution may be the regulation of the mechanical response of the jaw after an expected disturbance of the closing movement by food contact, by tuning the muscle stiffness to the expected hardness of the food.

Adult↗

PubMed1993

Bilateral asymmetries in the jaw-jerk reflex activity in man.

In order to investigate whether there are bilateral differences in the sensitivity of the mandibular stretch (jaw-jerk) reflex between patients with a myogenous craniomandibular dysfunction (CMD) and healthy controls free from signs and symptoms of CMD, jaw-jerk reflexes were elicited under standardized conditions in two groups of 10 gender- and age-matched subjects. The reflexes were recorded bilaterally from the masseter and the anterior temporal muscles by means of bipolar surface electromyogram (EMG). Reflex amplitudes at a mandibular displacement of exactly 80 microns and at a background muscle activity of exactly 12% maximum voluntary contraction were determined from relations between reflex amplitude and jaw displacement. These were obtained at a visually controlled, constant clenching level. For both groups, comparisons were made between reflex amplitudes from the right- and the left-hand side. In CMD patients with predominantly unilateral jaw muscle pain, comparisons were also made between the pain and non-pain sides. Although significant side asymmetries were found in many individuals, no significant differences were found among bilateral asymmetries in reflex sensitivity between patients and controls. No influence of pain side on the asymmetries was found. It was concluded that neuromuscular factors do not cause significant bilateral differences in the sensitivity of the jaw-jerk reflex between patients with myogenous CMD and controls. In a control experiment, in which eight healthy control subjects participated, the influence of a possible asymmetry in jaw displacement on the reflex sensitivity was evaluated. To achieve this, reflexes were elicited not only by means of a bilaterally imposed mandibular load, but also by means of loading via a unilateral bite-fork, so that an equal, constant jaw displacement could be imposed successively on both sides of the mandible. As no significant differences were found in bilateral asymmetries in reflex sensitivity between unilateral and bilateral mandibular loading, the influence of a possible asymmetrical jaw displacement on side asymmetries in the jaw-jerk reflex sensitivity is negligible in our experimental model.

Adult↗

PubMed1993

Human jaw-elevator muscle activity and food comminution in the dentate and edentulous state.

Masseter and temporal surface electromyograms were obtained from seven dentate subjects and six complete-denture wearers during mastication, maximal voluntary clenching and measurements of bite force. The participants chewed two artificial test foods with different textures. The dentate subjects comminuted both foods much better than the denture wearers. In both groups, the softer food was comminuted better than the firmer food. The differences in particle-size reduction originated largely from differences in the numbers of particles fragmented per chewing stroke. The rhythm of mandibular movement was unaffected by food texture and dental state. No significant differences in the duration of bursts of electric muscle activity were found between either group. Peak amplitudes of activity during mastication and maximal voluntary clenching were more than twice as large in the dentate subjects as in the denture wearers. In both groups, chewing the softer food was associated with lower peaks of activity than with the firmer food. The peak amplitudes were weakly related to the reduction in particle size. In both groups, the peak forces determined from electromyographic activity were larger than the estimated forces required for fragmenting the particles between the teeth.

Adult↗

PubMed1993

A three-dimensional, finite-element analysis of bone around dental implants in an edentulous human mandible.

The design of dental superstructures influences the loading on dental implants and the deformation of the anterior interforaminal bone in an edentulous mandible. This deformation causes stress in the bone around the implants and may lead to bone resorption and loss of the implant. The stress distribution around dental implants in an edentulous mandible was calculated by means of a three-dimensional, finite-element model of an entire lower jaw. This model was built from data obtained from slices of a single human mandible and was provided with two endosseous implants in the interforaminal region. The implants were either connected with a bar or remained solitary, and were loaded with a horizontal bite force of 10 N, a vertical bite force of 35 N, or an oblique bite force of 70 N. The most extreme principal stresses in the bone were always located around the neck of the implant. Stress around the implant was, therefore, not only caused by the local deformation of the bone due to movement of the implant and interface relative to the surrounding bone but also by the bending of the mandible. The most extreme principal stress was found with oblique bite forces. The highest maximum and lowest minimum principal stresses were 7.4 and -16.2 MPa in the model without the bar and 6.5 and -16.5 MPa in the model with the bar. When differences in the amount of bite force were eliminated, the vertical bite force resulted in the lowest stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Bite Force↗

PubMed1993

The effect of missing postcanine teeth on chewing performance in man.

The masticatory performance of a group of subjects missing on average 5.7 postcanine teeth and of a control group with complete dentitions were compared. There were significant differences in performance between the two groups. Within the patient group the number of occluding units significantly influenced performance. The average number of chewing cycles needed to prepare the food for swallowing was significantly larger for the patient than for the control group. Despite this, subjects in the patient group swallowed, on average, significantly larger food particles. Correlations between chewing performance and the number of chews up to swallowing within each of the two groups did not reach significance. However, combining the data from the two groups and thus increasing the range of chewing performances yielded a highly significant correlation. Subjects with reduced performance needed more chewing cycles before swallowing the food. Significant correlations were also found between chewing performance and the size of the swallowed food; subjects with poor performance swallowed larger particles. The numbers of chewing cycles made to swallow a natural (peanut) and an artificial (Optosil) test food were highly correlated, indicating that both foods are suitable for testing chewing performance.

Adult↗

PubMed1993

Tooth formation in patients with oligodontia.

Oligodontia is defined as the congenital absence of many teeth. The aim of the present study was to evaluate tooth formation in patients with oligodontia who were missing six or more teeth. The oligodontia sample was compared to a control group matched for race, sex and age. Calcification stages of the teeth of the left side of the mandible were rated. Patients with oligodontia showed a tendency for delayed tooth formation. Significant differences in tooth formation were found between males with oligodontia and the control group for several stages of tooth formation. In females only stage 5 of the second mandibular molar showed a significant difference. Because of the great individual variation in tooth formation in patients with oligodontia, tooth formation in patients with oligodontia should be individually examined before starting treatment.

Adolescent↗

PubMed1993

A comparison of three finite element models of an edentulous mandible provided with implants.

The stress distribution in an edentulous mandible provided with two implants in the interforaminal region was calculated by means of three different finite element models. The implants were connected with a bar or remained solitary. The first model was a three-dimensional representation of the entire mandible, the second model of the interforaminal region of this same mandible, whilst the third model was a two-dimensional representation of the interforaminal region. The differences in stress distribution around the connected implants and the solitary implants between these three models were analysed. It can be concluded that for a parameter study the stress distribution around the dental implants following from a three-dimensional finite element model of only the interforaminal region of an edentulous mandible can be used. For such studies therefore, benefit can be gained from the advantages of reduced modelling and calculation time.

Bite Force↗

PubMed1993

Comminution of two artificial test foods by dentate and edentulous subjects.

An experimental artificial test food with low fracture strength (Optocal) was compared with Optosil with respect to the comminution during mastication by complete denture wearers and subjects with natural dentitions. The comminution of both test foods revealed large differences between the denture wearers and the dentate subjects. These differences were larger with Optosil than with Optocal. The differences in comminution between Optocal and Optosil were larger in the denture wearers than in the dentate subjects. The differences in comminution between the denture wearers and the dentate subjects as well as the differences in comminution between Optocal and Optosil within each group were largely established in less than 20 chewing strokes. The results indicate that differences in selection contributed substantially to the differences in comminution. Since Optocal appeared to be much easier to chew than Optosil, it may be preferred to Optosil for measuring masticatory performance in complete denture wearers.

Adult↗

PubMed1993

Taurodontism and length of teeth in patients with oligodontia.

Taurodontism and a reduced tooth length are reported to occur in patients with oligondontia. The aim of this study was to evaluate the occurrence of these factors in Dutch patients with oligodontia. Panoramic radiographs of 117 patients with oligodontia and 91 controls were collected. Taurodontism of the mandibular first molars was recorded and the length of cuspids, bicuspids and first molars of the mandible were measured. In patients with oligodontia 28.9% showed taurodontism of one or two mandibular first molars. The prevalence of taurodontism in normal Dutch subjects was 9.9%. No significant differences were found between the two sexes in both groups. Neither was there a significant difference in the unilateral and bilateral occurrence of taurodontism. The present findings supported the hypothesis that taurodontism may be the result of an ectodermal defect and a manifestation of developmental instability in patients with oligodontia. The length of mandibular cuspids and first molars in females were significantly reduced. In males only the lower right first molar was significantly reduced. The reduced length of the teeth may also be the result of a defect in ectodermal cells. Both taurodontism and a reduced length are of importance considering dental therapy.

Adolescent↗

PubMed1993

A comparison of methods to assess marginal bone height around endosseous implants.

3 methods of measurements of marginal bone level on intra-oral radiographs of endosseous implants are described: measurements with a computerized image analysis system, with a magnifying-glass and with a digital sliding gauge. The accuracy of each of these methods was investigated and compared. The intra- and inter-observer error analysis showed that determining the precise bone height on the image is responsible for a large standard deviation for each method. It is concluded that measurements with a digital sliding gauge are preferable because it is easy to put into practice, and in addition, accuracy matches the accuracy of the other methods.

Alveolar Bone Loss↗

PubMed1993

Characteristics and treatment outcome of diagnostic subgroups of CMD patients: retrospective study.

The records of 193 randomly chosen patients with CMD referred 2.5 yr previously were examined retrospectively for anamnestic, clinical and radiological findings and observations related to treatment. These data were supplemented with information from questionnaires sent to all treated patients in which their opinion on the treatment outcome was asked. Within the patient group, four diagnostic subgroups were distinguished. Three subgroups consisted of patients with the diagnoses CMD with a mainly myogenous component, osteoarthrosis and internal derangement respectively, whereas the fourth subgroup consisted of patients who did not fit into one of these categories. Differences between the four groups were found concerning mean age, the prevalence of a limited range of motion, headache, psychosocial factors, loss of posterior tooth support and objective treatment outcome. The patients with CMD with a mainly myogenous component showed the highest percentages of CMD associated disorders, the least successful treatment outcome and the highest percentage of renewed treatment. The patients with internal derangement showed the lowest mean age, the highest prevalence of a limited range of motion and the best treatment outcome. The patients in the osteoarthrosis group showed the highest mean age and the highest percentage of loss of posterior tooth support. It may be concluded that the evaluation of diagnostic subgroups of CMD patients has to be preferred in the assessment of a heterogeneous group of patients with CMD.

Adult↗

PubMed1993

Serodiagnosis of toxoplasmosis by using a recombinant form of the 54-kilodalton rhoptry antigen expressed in Escherichia coli.

A 330-residue carboxy-terminal antigenic fragment of the Toxoplasma gondii 54-kDa rhoptry protein (ROP2) was expressed in Escherichia coli as a fusion polypeptide containing a 48-amino-acid sequence derived from phage lambda protein Cro and E. coli protein LacI followed by six consecutive histidyl residues. Metal chelate affinity chromatography provided an easy way to isolate the recombinant product in a highly purified form (> 95%). When this material was used to develop an immunoglobulin G (IgG) enzyme-linked immunosorbent assay for diagnosis of toxoplasmosis, the test reached a sensitivity of 89%. The sensitivity of the assay was similar whether the sera contained T. gondii-specific IgM or were devoid of such IgM. It was also found that ROP2 is a conserved antigen since antibodies against the recombinant antigen could be detected in mice experimentally infected with 11 independent T. gondii isolates originating from infected human tissues tested. Thus, the 54-kDa rhoptry antigen could advantageously complement other previously described T. gondii antigens for the development of more-sensitive and more-informative recombinant antigen-based tests for toxoplasmosis diagnosis.

Animals↗

PubMed1993

The effect of an occlusal stabilization splint and the mode of visual feedback on the activity balance between jaw-elevator muscles during isometric contraction.

The aim of the present study was to gain an insight into the influence of a vertical bite-rise (clenching in intercuspal occlusion vs. clenching on an occlusal stabilization splint), the mode of visual feedback (VF; obtained from the compound masseter signal, from the compound anterior temporalis signal, or from the compound signal of both masseter and anterior temporalis muscles) and the EMG clenching level (10% MVC and 50% MVC) on the muscle balance between the masseter and the anterior temporalis muscles. The muscle balance was quantified as the logarithmic value of the ratio between the summated mean rectified EMG activity of the masseter muscles and this activity of the anterior temporalis muscles. The muscle balance was influenced significantly by the mode of VF (p < 0.01), the muscle balance shifting toward the group of muscles from which VF was obtained. When VF was obtained from the masseter muscles, a decrease in the anterior temporalis EMG activity was observed when the vertical dimension was increased (p < 0.05-0.01). When VF was obtained from the anterior temporalis muscles, the activity of the masseter muscles was raised with respect to that of the anterior temporalis muscles during clenching with a vertical bite-rise (p < 0.05-0.01). When VF was obtained from both groups of muscles, the masseteric EMG activity increased, whereas the anterior temporalis EMG activity decreased. Hence, regardless of the mode of VF, a relatively lower activity level of the anterior temporalis muscles was achieved after insertion of an occlusal stabilization splint.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Diagnostic value of orthopedic tests in patients with temporomandibular disorders.

For a better definition of diagnostic subgroups of patients with temporomandibular disorders (TMD), clinical orthopedic tests have been developed for the masticatory system, for use together with the commonly used active movement tests and palpation. In the present study, the characteristics and additional diagnostic value of four orthopedic tests--namely, passive opening, the joint play test, compression, and the static pain test--were determined for a patient group, diagnostic subgroups, and a control group. Significant differences among the scores of the tests in the different groups indicated that all six orthopedic tests contributed to the diagnostic process. Because of the close functional relationship of the masticatory system, most information was obtained when patients indicated where pain occurred during the different tests. Logistic regression techniques were used for determination of the relative diagnostic value of each orthopedic test in the diagnostic process. Active movement was the most powerful test for distinguishing the different subgroups. Palpation and passive opening were additionally useful for distinguishing between patients and control subjects and between the subgroups of arthrogenous and myogenous patients. Besides active movement, both compression and the joint play test played a minor role in the distinction of subgroups of arthrogenous patients. It may be concluded that in routine clinical practice, besides history taking and conventional radiography, a functional examination consisting of active movements, passive opening, and palpation provides valuable diagnostic information. In patients with a specific diagnostic problem, one of the other additional tests might be indicated.

Adult↗

PubMed1993

[Chewing: a matter of selection and breakage].

The masticatory performance of subjects can objectively be determined by describing the particle size distribution of a comminuted test food (cubes Optosil). After a fixed number of chewing strokes the particles are collected and sorted with a stack of sieves. The size distribution can be characterized with two parameters; the median particle size and the broadness of the distribution. The rate of reduction of the median size is used to characterize the chewing performance. The chewing process can be described as the result of two processes: selection and breakage. The parameters of these two processes can be derived from the chewing result using a mathematical model. The differences in chewing performance between subjects with a natural dentition and subjects with a complete denture occurs already in the first 20 chewing strokes. Experimental results indicate that especially the selection chance is smaller in denture wearers.

Dentures↗

PubMed1992

A selection model to estimate the interaction between food particles and the post-canine teeth in human mastication.

Food comminution during chewing is the composite result of selection and breakage. In the selection process, every food particle has a chance of being placed between the antagonistic post-canine teeth and being subjected to subsequent breakage. The selection chance, being the ratio between the number of selected and offered particles, has been mathematically described as a function of the number of particles offered, in terms of the number of breakage sites available on the teeth and particle affinity, i.e. the fraction of breakage sites occupied by one particle. The assumption has been made that particles are successively selected during a jaw-closing phase and that the selection chance of subsequent particles having the opportunity to occupy a breakage site proportionally decreases with the unoccupied fraction of the breakage sites left. The number of selected particles of a single size then asymptotically approaches the total number of breakage sites available for that size, when the number of particles offered increases. The critical particle number, derived from the measure of particle affinity, indicates the number of particles by which the breakage sites become saturated. The selection model for single particle sizes has been successfully applied to describe one-chew experiments, using various numbers and sizes of particles made of a silicone-rubber. After pseudo-chewing movements the subjects were unexpectedly instructed to carry out a real chew on particles (half-cubes). Undamaged, hence non-selected half-cubes could afterwards be distinguished from broken particles. The model has been extended to a particle mixture to describe the selection of particles of a certain size while other particles of different sizes are present. If a two-way competition between smaller and larger particles is assumed, the model predicts that the ratios of the selection chances between different particle sizes do not depend upon the numbers of the particles in the mixture.

Food↗

PubMed1992

Cytomegalovirus infection induces vascular injury in the rat.

The role of cytomegalovirus (CMV) in the early development of atherosclerosis was studied in a rat model. Arterial samples derived from virus-infected normo- and hypercholesterolaemic animals were investigated by light microscopy at 1, 4, 8 and 16 weeks post infection. Early atherogenic lesions comparable to those seen in non-infected hypercholesterolaemic rats were found in CMV-infected normocholesterolaemic and hypercholesterolaemic animals, starting at 1 week post infection. The changes consisted of minimal endothelial cell damage, as shown by the en face technique, and a more than 10-fold increase in the number of leukocytes adhering to the aortic intima. The increased adhesion of leukocytes was observed in infected normocholesterolaemic rats but only in the non-infected rats which were hypercholesterolaemic. The infection of hypercholesterolaemic rats did not enhance this effect although it resulted in increased migration of the leukocytes into the subendothelial space. CMV infection of normocholesterolaemic rats induced lipid accumulation in the endothelium. In these animals approximately 1% of the endothelial cells contained lipid at 1 week post infection. In the non-infected hypercholesterol-fed animals 10% of the cells contained lipid. CMV infection in these rats induced an extra increase of the lipid-containing endothelial area. The changes in the CMV infected animals largely corresponded with the intimal injury observed in the hypercholesterolaemic rats. These results support the hypothesis that CMV may be one of the factors involved in atherogenesis.

Animals↗