Biomedical subjects

H W van der Glas

Publications and source records attributed to H W van der Glas.

At least 19 recordsLinked to original sources

PubMed2006

Oral physiology and mastication.

Mastication is a sensory-motor activity aimed at the preparation of food for swallowing. It is a complex process involving activities of the facial, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation and the crushing of food between the teeth. Saliva facilitates mastication, moistens the food particles, makes a bolus, and assists swallowing. The movement of the jaw, and thus the neuromuscular control of chewing, plays an important role in the comminution of the food. Characteristics of the food, e.g. water and fat percentage and hardness, are known to influence the masticatory process. Food hardness is sensed during mastication and affects masticatory force, jaw muscle activity, and mandibular jaw movements. When we chew for instance a crispy food, the jaw decelerates and accelerates as a result of resistance and breakage of food particles. The characteristic breakage behaviour of food is essential for the sensory sensation. This study presents a short review of the influence of oral physiology characteristics and food characteristics on the masticatory process.

Animals↗

PubMed2005

The influence of orthognathic surgery on masticatory performance in retrognathic patients.

Surgical correction of retrognathism may influence chewing performance and its underlying mechanisms selection and breakage of food particles. In this study we examined the hypothesis that treatment of this anomaly improves chewing performance. Furthermore, we determined to what extent this change can be attributed to selection and breakage of food particles. Eleven patients were tested before and 1-1.5 years after surgery. To determine chewing performance, eight cubes of 8 mm of a silicone rubber (Optosil) were used as a test food. Selection and breakage were determined in one-chew experiments using three particle sizes. On average, no differences were found for chewing performance, selection or breakage. However, on an individual basis, patients with a poor chewing performance before surgery tended to improve, whereas no improvement was observed for patients with a good chewing performance. The change in chewing performance was mainly due to a change in breakage of the food particles.

Adult↗

PubMed2004

Exteroceptive reflexes in jaw-closing muscle EMG during rhythmic jaw closing and clenching in man.

Exteroceptive jaw reflexes might play a role in normal functions of the mouth such as mastication. Until now these reflexes have only been studied under isometric conditions. The aim of this study was to compare exteroceptive reflexes in jaw muscle EMG during the closing phase of rhythmic open-close movements and clenching, at the same jaw gape and with similar muscle EMG. Reflexes consisting of successive waves of decreased and increased muscle activity (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by light noxious electrical stimulation of the vermillion border of the lower lip, were recorded from the jaw closing muscles of 17 subjects. Differences between the two tasks occurred in two phases of the PSEC: (1) in an early phase, around the R wave, there was significantly less EMG during jaw closing (mean EMG ratio between jaw-closing and clenching 0.71), and (2) in a late phase, around the transition between the S to the T wave, there was significantly more EMG during jaw closing (mean EMG ratio: 1.40). The decrease in EMG activity around the R wave during jaw closing may be due to a change in reflex sensitivity at an interneuron level. The increase in EMG activity around the transition between the S and T waves during jaw closing might, at least in part, be due to a proprioceptive stretch reflex. This reflex is mediated by muscles spindles that are activated by the deceleration of the jaw evoked by the lip stimulus. The finding of inhibitory reflex mechanisms that predominate more during rhythmic jaw movements than during clenching in an early phase of the PSEC might be related to protecting oral tissues from trauma when the jaw is closing with potentially a large muscle force. In contrast, when food is held between the teeth, a possible inhibitory influence of light noxious stimuli is diminished.

Adolescent↗

PubMed2002

Masticatory performance in patients with myasthenia gravis.

Masticatory muscle electromyograms (EMGs) were recorded while patients with bulbar myasthenia gravis chewed artificial food and compared with those of patients with ocular myasthenia gravis, patients in clinical remission who had previously suffered from bulbar myasthenia gravis and healthy individuals. Masticatory performance and EMGs were significantly smaller in the bulbar group. There were no indications of subclinical masticatory muscle weakness in patients with bulbar myasthenia gravis in remission and in patients with ocular myasthenia gravis. Patients with bulbar myasthenia gravis barely compensated for muscular weakness by chewing at a higher percentage of their maximal EMG. These quantitative findings, when combined with subjective reports of masticatory muscle weakness, show that a need to support the jaw is characteristic of patients with bulbar myasthenia gravis who produce low EMG activity.

Adult↗

PubMed2002

The influence of orthodontics on selection and breakage underlying food comminution in pre-orthognathic surgery patients.

Comminution of food is the composite result of selection and breakage. Selection is characterized by the chance that a food particle will at least be damaged by the teeth during a chew. For any particle size, this chance equals the ratio between the weight of damaged and broken particles and that of all initial particles. The breakage process refers to fracturing of selected particles. Since orthodontic treatment applied to patients before orthognathic surgery has an effect on the position and orientation of teeth, it may alter chewing efficiency by influencing selection and/or breakage. The effect of such orthodontic treatment on chewing efficiency was examined using eight cubes of 8.0 mm of a silicone-rubber (Optosil) as a test food for determining the number of chews required to halve the initial particle size (N(1/2)) in 12 patients. Three particle sizes (2.4, 4.8 and 8.0 mm) were used for determining selection and breakage in one-chew experiments. Orthodontic treatment had no effect on the chewing efficiency and the selection chances of all particle sizes whereas the degree of breakage was significantly (P<0.05) increased only for a particle size of 8.0 mm. These findings suggest that presurgical orthodontics has only a minor effect on food comminution.

Adult↗

PubMed2002

[Repair and revision 9. Peripheral trigeminal nerve injury].

A review is given about long-term incidence of sensory disturbance in the areas of innervation of the n. trigeminus for different types of trauma and/or treatment. Diagnosis, clinical course and possible types of treatment are in addition reviewed. Regarding diagnosis, the outcome of a test on sensory function is not always related to the degree of nerve damage because methods differ in the type of afferent nerve fibers of which function is tested, and some specificity might occur in nerve damage, i.e. either thick or thin afferent fibers might be predominantly affected at a particular time. An initial quick testing of sensory function is recommended. This testing includes examining two sensory modalities, which are related to functioning of thick and thin afferent fibers respectively and which have a dichotomous yes/no outcome on the incidence of a pronounced sensory disturbance.

Humans↗

PubMed2001

Controlled study of EMG activity of the jaw closers and openers during mastication in patients with myasthenia gravis.

Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.

Adult↗

PubMed2001

Chewing efficiency of pre-orthognathic surgery patients: selection and breakage of food particles.

Comminution of food is the composite result of selection and breakage. Selection is characterised by the chance that a food particle will at least be damaged by the teeth during chewing. For any size, this chance equals the ratio between the weight of damaged or broken particles and that of all initial particles. The breakage process refers to fracturing of selected particles. The aim was to examine whether a reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of selection, breakage or both. Eight cubes of 8.0 mm of the silicone-rubber Optosil " were used as a test food to determine chewing efficiency for 12 patients (skeletal Angle Class II and dental Angle Class II, subdivision 1) and 12 controls (class I molar relation). Selection and breakage were determined in one-chew experiments using various particle sizes. Chewing efficiency was significantly lower for the patients than for the controls. The selection chance was significantly smaller for the patients, in particular for smaller (< or = 4.8 mm) particles. The degree of breakage was lower for the patients, in particular for medium-sized particles of 4.8 mm. These findings suggest that the reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of both selection and breakage.

Adult↗

PubMed2000

What's in a smile?: Quantification of the vertical smile of patients with myasthenia gravis.

Many patients with myasthenia gravis who experience bulbar symptoms show a vertical smile, which may have a considerable, and often underestimated, impact on social life. Peri-oral muscle function can be quantified by calculating lip-length and snout indices, which indicate the degree to which a person is capable of smiling and of pursing the lips, respectively. In the present study patients with bulbar myasthenia gravis were compared to patients with ocular myasthenia gravis, patients now in remission (but previously suffering from bulbar myasthenia gravis), and healthy subjects. The lip-length and snout indices of patients with bulbar myasthenia gravis were significantly lower than those of the other groups. The facial impairments were no longer detectable in patients with bulbar myasthenia gravis in remission and no subclinical impairments in lip-length and snout indices were found in the ocular myasthenia gravis group. These findings were consistent with the patients' reports of impairment of smiling and other oral functions. The patients suffering from a vertical smile or other oral impairments were well aware of their condition, most probably because of the social consequences of being unable to smile. The indices could be of importance in the longitudinal evaluation of therapy in individual patients and in pharmacotherapeutical research. We found a low correlation between the lip-length and snout indices, which reflects the capricious pattern of involvement of separate muscles in myasthenia gravis. Therefore both indices deserve special attention if they are used for monitoring myasthenic symptoms.

Adult↗

PubMed2000

Maximal bite force and surface EMG in patients with myasthenia gravis.

Masticatory muscle strength was quantified in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in clinical remission (whether or not pharmacological) who previously suffered from bulbar myasthenia gravis, and healthy subjects. Maximal bite force and maximal activity of the masseter and temporalis muscles and of the submental muscle complex were measured. Bite force was decreased in the patients with bulbar myasthenia gravis, but was normal in the patients in the clinical remission group and in the ocular group. These findings were consistent with the results of electromyographic data. Although subjective reports of masticatory muscle weakness provide valuable information, quantitative measurements provide more information about the degree of muscle weakness of individual muscles. This is especially important for longitudinal evaluation of therapy in individual patients and for pharmacotherapeutic research.

Adult↗

PubMed2000

Mechanisms underlying the effects of remote noxious stimulation and mental activities on exteroceptive jaw reflexes in man.

Successive inhibitory, excitatory, inhibitory and excitatory reflexes (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by applying non-painful taps to an incisor tooth, were recorded from the jaw-closing muscles of 15 subjects. The effects on these reflexes of the subjects undertaking mental exercises (MEx) in the form of arithmetic calculations were compared with those of remote noxious stimulation (RNS; application of 3 degrees C to a hand). This was done to investigate whether the previously established effects of RNS were likely to be related to a change in the subject's mental state and/or to direct nociceptive mechanisms. Both MEx and RNS caused increases in EMG activity around the Q-R and S-T transitions of the PSEC, which resulted principally from shortenings of the inhibitory Q and S waves. Reducing the intensity of the tap stimuli, which mimicked condition-induced disinhibition, caused shortenings of the inhibitory waves at latencies similar to the shortenings induced by MEx or RNS. The magnitude of the RNS-induced effect on the ST segment of the PSEC was greater (P<0.01) than that on the QR segment. By contrast, MEx induced similar effects on both segments. Regression analyses were performed for the relationship between condition-induced changes in amplitude of the excitatory waves and their control amplitudes. These analyses were performed to reveal any condition-induced inhibition or facilitation of the tap-induced influences on the motoneurons. Overall, the evidence suggested that: (1) mental exercise induced a similar degree of inhibition of the two tap-induced inhibitory jaw reflexes and a facilitation of the excitatory ones, and (2) remote noxious stimulation induced an inhibition of the second tap-induced inhibitory reflex which was greater than that of the first one, and an inhibition of the first excitatory reflex. Thus, although factors related to altered mental activity could play a role in the modulation of jaw reflexes by RNS, the differences between the effects of MEx and RNS suggest that alternative or complementary mechanisms are also likely to be involved.

Adult↗

PubMed2000

Tongue force in patients with myasthenia gravis.

OBJECTIVES: The aim was to study tongue force in patients with bulbar myasthenia gravis and compare it with that of patients with ocular myasthenia gravis, patients in clinical remission who previously suffered from bulbar myasthenia gravis, and healthy subjects. MATERIAL AND METHODS: Tongue force was measured with a tongue force transducer in cranial and lateral directions, which coincide with the directions in which the tongue exerts force during swallowing, speech, and mastication. RESULTS: Tongue force in lateral direction was significantly decreased in patients with bulbar myasthenia gravis. In addition, our findings suggest an incomplete recovery of lateral tongue force in the patients of the remission group. CONCLUSION: Our tongue force measurements may be useful for longitudinal evaluation of therapy in individual patients and also in studies of therapy efficacy in matched groups of patients if the influence of factors such as age, dental state, and sex is taken into account.

Adult↗

PubMed2000

[Comparison of treatment options for myogenous temporomandibular dysfunction].

A randomized clinical trial which included a follow-up of one year was applied to 118 myogenous TMD-patients. The therapies investigated were: physiotherapy of the masticatory system or splint therapy for patients without occlusal interferences, and occlusal adjustment therapy or the combination of splint and occlusal adjustment therapy for patients with pronounced occlusal interferences. Counseling, which yielded a reduction of 27% of the scored pain intensity, will most likely eliminate any further need for treatment of patients with a low level of myogenous TMD signs and symptoms. Otherwise, physiotherapy might be preferred as a starting option with respect to splint therapy because of 1. A similar efficacy; 2. A shorter treatment duration so that either chronic facial pain is earlier relieved or a patient can undergo a second type of therapy earlier; and 3. Lower costs. One third of the patients selected had pronounced occlusal interferences. Using stringent criteria it might be possible to apply occlusal adjustment therapy without involvement of splint therapy yielding a similar therapy efficacy and with advantages of a shorter treatment duration and lower costs. All types of therapy diminished not only facial pain but also pain of neck and shoulder areas.

Adult↗

PubMed1999

Differentiating condition-induced facilitation, inhibition and disinhibition in a complex series of reflexes in an electromyogram.

In man, the principal exteroceptive reflexes evoked by intra-oral stimulation involve the jaw-closing muscles and include inhibitory and excitatory responses [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.]. These reflexes can be observed in electromyograms (EMGs) recorded with bipolar surface electrodes. The likelihood that these reflexes play important roles in the integrative actions of the jaw has led to interest in the physiological control mechanisms by which they may be modulated. It has been reported recently that the complex series of jaw reflexes evoked by non-painful tapping on human teeth can be modulated by the application of noxious stimulation to the hand [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, Effects of remote noxious stimulation on exteroceptive reflexes in human jaw closing muscles, Brain Res. 726 (1996) 189-197.] or by exercises which produce a change in mental state [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, The influence of attentional factors on short- and long-latency jaw reflexes in man, Arch. Oral Biol. 41 (1996) 995-998.]. The effects of remote noxious stimuli and mental exercises usually involved transient increases in electromyographic (EMG) activity around the interfaces between the successive inhibitory and excitatory reflexes. As the mechanisms underlying the tap-induced inhibitory and excitatory reflexes may show some temporal overlap [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.], these condition-induced increases in EMG activity could, in the simplest hypothesis, have been due to either (i) a condition-induced inhibition of the tap-induced inhibitory influences on the motoneurones (i.e., disinhibition) and/or (ii) a condition-induced facilitation of the tap-induced excitatory influences underlying the subsequent excitatory reflexes. In the present protocol, we describe how it is possible to differentiate between these different underlying mechanisms. The method includes a regression analysis of the relationship between condition-induced changes in amplitude of a reflex and the reflex amplitude under control conditions after taking account of the effect of chance. The analysis is applied on reflex data pooled from various subjects. Although this method of data analysis is illustrated with trigeminal reflexes, it is potentially of use for other complex extracellular recordings including those in other fields of motor control (e.g., EMGs from muscles other than jaw ones).

Adult↗

PubMed1999

Comparison of external load compensation during rhythmic arm movements and rhythmic jaw movements in humans.

Experiments were performed on human elbow flexor and extensor muscles and jaw-opening and -closing muscles to observe the effect on rhythmic movements of sudden loading. The load was provided by an electromagnetic device, which simulated the appearance of a smoothly increasing spring-like load. The responses to this loading were compared in jaw and elbow movements and between expected and unexpected disturbances. All muscles showed electromyographic responses to unexpected perturbations, with latencies of approximately 65 ms in the arm muscles and 25 ms in the jaw. When loading was predictable, anticipatory responses started in arm muscles approximately 200 ms before and in jaw muscles 100 ms before the onset of loading. The reflex responses relative to the anticipatory responses were smaller for the arm muscles than for the jaw muscles. The reflex responses in the arm muscles were the same with unexpected and expected perturbations, whereas anticipation increased the reflex responses in the jaw muscles. Biceps brachii and triceps brachii showed similar sensory-induced responses and similar anticipatory responses. Jaw muscles differed, however, in that the reflex response was stronger in masseter than in digastric. It was concluded that reflex responses in the arm muscles cannot overcome the loading of the arm adequately, which is compensated by a large centrally programmed response when loading is predictable. The jaw muscles, particularly the jaw-closing muscles, tend to respond mainly through reflex loops, even when loading of the jaw is anticipated. The differences between the responses of the arm and the jaw muscles may be related to physical differences. For example, the jaw was decelerated more strongly by the load than the heavier arm. The jaw was decelerated strongly but briefly, <30 ms during jaw closing, indicating that muscle force increased before the onset of reflex activity. Apparently, the force-velocity properties of the jaw muscles have a stabilizing effect on the jaw and have this effect before sensory induced responses occur. The symmetrical responses in biceps and triceps indicate similar motor control of both arm muscles. The differences in reflex activity between masseter and digastric muscle indicate fundamental differences in sensory feedback to the jaw-closing muscle and jaw-opening muscle.

Adult↗

PubMed1999

Speed-dependent control of cyclic open-close movements of the human jaw with an external force counteracting closing.

Previous work with open-close movements of the jaw in which food resistance was simulated by an external force has shown that additional activity of the jaw-closing muscles to overcome the force is mainly of sensory origin. When the force was expected, a small anticipatory response was also observed, starting before the onset of the force. The movement rates in these experiments corresponded to natural chewing rates of about 60 cycles per minute. Our aim was to investigate how anticipatory and peripherally induced muscle activity change with movement speed. Peripheral feedback to the muscles may increase at higher movement speed, possibly resulting in stronger reflex activity. On the other hand, when the force is expected, more preprogrammed muscle activity may be generated with faster movements, in anticipation of the force. Three movement rates were studied: 30 cpm (slow), 60 cpm (normal speed), and 120 cpm (fast). The results show that muscle activity to move the jaw increases sharply with movement speed. Extra muscle activity needed to overcome the force also increases with movement speed. However, the contribution by peripherally triggered muscle activity does not increase. In contrast, preprogrammed extra muscle activity in anticipation of the force increases sharply with movement speed. It is concluded that the control strategy for these movements is speed-dependent, with a shift to relatively more anticipatory muscle activity at higher movement speeds, making the movement more ballistic.

Adult↗

PubMed1998

A comparison of jaw-opener and jaw-closer muscle activity in humans to overcome an external force counteracting jaw movement.

In contrast to the jaw-closer muscles, no or very few spindles are present in the jaw-opening digastric muscle. Therefore sensory feedback to the digastric muscle may be different from feedback to the jaw-closer muscles, resulting in a different reaction when jaw movement is perturbed. This possible difference was investigated by comparing the reaction of the digastric muscle when jaw opening is perturbed, with the reaction of the masseter muscle when jaw closing is perturbed. Subjects made rhythmic, 1-Hz open-close movements of the jaw under control of a metronome. During jaw opening (digastric muscle) or, in the other experiments, during jaw closing (masseter muscle), an external force counteracting jaw movement could appear. Series of movements without the force were unexpectedly alternated by series with the force. In both muscles sensory induced activity started approximately 25 ms after the onset of the force and consisted of two phases. In the masseter muscle the maximum of the first increase was reached significantly sooner (37 +/- 2 ms SEM) than in the digastric muscle (54 +/- 3 ms). The second increase appeared much sooner in the masseter muscle (73 +/- 4 ms) than in the digastric muscle (159 +/- 10 ms). When the force was expected, in both muscles an increase in preprogrammed muscle activity was observed. Also an increase in reflex activity, generated before 120 ms after the onset of the force, was observed, compared with when the force appeared unexpectedly. The relative increase in reflex activity was approximately 2 times larger than the relative increase in preprogrammed activity. Therefore, the increase in reflex activity when the force was expected may have been caused not only by an increase in recruitment, but also by an increase in the gain of the reflex loops. Reflex activity relative to preprogrammed activity was on average 4 times larger in the masseter muscle than in the digastric muscle. This indicates that the masseter muscle can react more adequately to disturbances of jaw movement than the digastric muscle.

Adult↗

PubMed1998

Information on infraorbital nerve damage from multitesting of sensory function.

Sensory disturbance following orbitozygomatic complex fractures was studied in 65 patients from 4 treatment groups which represented potentially varying degrees of sensory disturbance. The fracture-type-dependent treatments were: no surgical intervention (n = 20), closed reduction with or without wire fixation (n = 17), open reduction with miniplate fixation (n = 15) and/or reconstruction of the orbital floor (n = 13). In order to assess the sensory function of different classes of afferent fibres, several methods of sensory testing were applied. On average 6.3 months after treatment, the patient's report was obtained, and tests regarding touch, two methods of two-point discrimination, and cold were applied on the cheek and upper lip. The degree of sensory disturbance was method-dependent. In patients who underwent closed reduction, pronounced levels of positive correlation occurred between results from different tests or from both test sites. The levels of these correlations were, in general, low for all other treatments. These findings suggest that afferent fibres of both large and small diameter tended to be permanently damaged in the patient group with closed reduction. In contrast, the types of sensory afferent fibres that were involved in the trauma and/or their recovery were highly variable within patients and sites for all other treatment groups.

Adolescent↗