Biomedical subjects

W D McCall

Publications and source records attributed to W D McCall.

At least 19 recordsLinked to original sources

PubMed2003

Human masticatory muscle forces during static biting.

Muscle forces determine joint loads, but the objectives governing the mix of muscle forces involved are unknown. This study tested the hypothesis that masticatory muscle forces exerted during static biting are consistent with objectives of minimization of joint loads (MJL) or muscle effort (MME). To do this, we compared numerical model predictions with data measured from six subjects. Biting tasks which produced moments on molar and incisor teeth were modeled based on MJL or MME. The slope of predicted vs. electromyographic (EMG) data for an individual was compared with a perfect match slope of 1.00. Predictions based on MME matched best with EMG activity for molar biting (slopes, 0.89-1.16). Predictions from either or both models matched EMG results for incisor biting (best-match slopes, 0.95-1.07). Muscle forces during isometric biting appear to be consistent with objectives of MJL or MME, depending on the individual, biting location, and moment.

Adult↗

PubMed2002

Human masticatory muscle activity and jaw position under experimental stress.

The purpose of the present study was to determine whether stress induced a consistent pattern of increased electromyographic (EMG) activity in different masticatory muscles, and whether stress produced changes in jaw position. Thirty-five dental students at Taipei Medical College volunteered for this study. Mental arithmetic was used to create a stress condition and relaxation instruction was used to help relax the subjects. Subjects were asked to evaluate the stress they felt under each experimental condition with a visual analogue scale (VAS). Surface electrodes were used to monitor the EMG activities of the right masseter, right posterior temporalis and suprahyoid muscles. A kinesiograph was used to observe the jaw position. Data collected before mental arithmetic or relaxation monitored the baseline level. The VAS means were significantly increased during the stress condition and significantly decreased following relaxation, compared with the baseline. There was also a significant increase in EMG activity of all three muscles during mental arithmetic compared with baseline; different patterns of increased EMG activity were noticed in the three muscles under a continuous stress condition. Under stress, the incidence of tooth contact at intercuspal position was also increased.

Adult↗

PubMed2002

Effect of sustained contraction on motor unit action potentials and EMG power spectrum of human masticatory muscles.

The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift.

Action Potentials↗

PubMed2000

Amitriptyline treatment of chronic pain in patients with temporomandibular disorders.

Randomized clinical trials of amitriptyline will require data from pilot studies to be used for sample size estimates, but such data are lacking. This study investigated the 6-week and 1-year effectiveness of low dose amitriptyline (10-30 mg) for the treatment of patients with chronic temporomandibular disorder (TMD) pain. Based on clinical examination, patients were divided into two groups: myofascial and mixed (myofascial and temporomandibular joint disorders). Baseline pain was assessed by a Visual Analogue Scale (VAS) for pain intensity and by the McGill Pain Questionnaire (MPQ). Depression was assessed by the Beck Depression Inventory (BDI) short form. Patient assessment of global treatment effectiveness was obtained after 6 weeks and 1 year of treatment by using a five-point ordinal scale: (1) worse, (2) unchanged, (3) minimally improved, (4) moderately improved, (5) markedly improved. The results showed a significant reduction for all pain scores after 6 weeks and 1 year post-treatment. The depression scores changed in depressed but not in non-depressed patients. Global treatment effectiveness showed significant improvement 6 weeks and 1 year post-treatment. However, pain and global treatment effectiveness were less improved at 1 year than at 6 weeks.

Adult↗

PubMed1998

Psychophysiological assessment of stress in chronic pain: comparisons of stressful stimuli and of response systems.

Due to disparate findings across the published studies, the stress-hyperactivity hypothesis has never been fully accepted as a causal mechanism for chronic muscle pain. Two recent comprehensive reviews of the psychophysiological studies of chronic pain came to opposite conclusions about the viability of the hypothesis, which stemmed from differing importance placed on the experimental methodology: the adequacy of stress manipulation. The present study tested the hypotheses that the adequacy of stress manipulation is influenced by stress stimuli type, degree of personal relevance, and selection of criterion for verification of stress experience, and that these factors have a measurable impact on the related physiological responses in a manner that is consistent with a theory of stress applicable to clinical stress disorders. The three factors investigated were: task (imagery, reaction time), relevance (high, low), and manipulation criterion (autonomic, self-report). The tasks were presented to 16 chronic pain patients while muscle, electrodermal, and self-report responses were recorded. Reaction-time tasks and high-relevance conditions led to high muscle and electrodermal responses. Only the high-relevance imagery, however, produced high self-reported distress. Consistent with other research, the present overall data demonstrated differing physiological profiles for different stimuli types. More importantly, these data suggest that the manipulation type and the manipulation criterion influence outcomes of experimental tests of stress on physiological systems, which may directly lead to contrasting conclusions about causal relations between stress and chronic pain conditions.

Adult↗

PubMed1996

Formalin induces biphasic activity in C-fibers in the rat.

While the formalin test is a widely used behavioral model of tonic chemogenic pain, little is known about the responses of primary afferent nociceptors to formalin. Formalin (2.5%, 50 microliters) was injected either directly in or adjacent to the mechanical receptive fields of single C-fibers isolated from the saphenous nerve of pentobarbital-anesthetized rats. The average formalin-evoked response in C-fibers (n = 29) over time was biphasic. This biphasic time course of the C-fiber response to formalin is similar to that of the behavioral response in the awake animal and is compatible with the hypothesis that increased C-fiber activity contributes to the behavioral response in phase 2, as well as in phase 1 of the formalin test.

Action Potentials↗

PubMed1996

Patterns of jaw muscle activity during voluntary chewing.

Mastication is controlled by central rhythm and burst generators, but whether this control is similar under automatic and voluntary chewing is not clear. Our first aim was to determine whether increased chewing frequency led to a proportional decrease in both the burst duration (the time of muscle activity) and the interburst interval (time of inactivity) of each muscle or to a minimal decrease in the burst duration and a substantial decrease in the interburst interval. Our second aim was to determine whether these two manifestations of control differed between the opening and closing muscles. Electromyograms from digastric, medial pterygoid, masseter and anterior temporalis muscles were obtained during gum chewing by five subjects at four frequencies. A nearly fourfold decrease in total cycle duration (TCD) with increased chewing frequencies was accompanied by minimal changes in burst duration in the digastric muscle but proportional changes in the jaw closing muscles. The onset latency of the digastric muscle as a percentage of TCD decreased and became negative (i.e. occurred before opening started) as the TCD decreased. The onset latencies of the jaw closing muscles remained roughly 10-20% of the TCD for the three lower chewing frequencies. Control of the opening muscle appears to differ from control of the closing muscles.

Chewing Gum↗

PubMed1995

Modelling of forces in the human masticatory system with optimization of the angulations of the joint loads.

Numerical models of the human masticatory system were constructed using algorithms which minimized non-linear functions of the muscle forces or the joint loads. However, the predicted solutions for isometric biting were critically dependent upon the modelled angular freedom of the joint loads. The most complete mathematical minimization of any objective function occurs when the joint load angles are predicted. However, the predictions have to be sensible in relation to the actual morphology of the joints. Therefore, the models were tested in terms of the angles of joint load predicted for a dry skull, using muscle vectors reconstructed from the geometry of the skull. The minimizations of muscle force were intrinsically incapable of predicting the angles of joint load. Such models must rely on constrained angles and this produces a restricted minimization and also an indeterminacy. In contrast, the minimizations of joint load predicted angles of joint load which varied appropriately with condylar position. The condylar movement was achieved with a positioning model which adjusted the angulation of the muscle vectors as the jaw was positioned. This model also generated the optimal sagittal shape of the articular eminence. Muscle predictions from the various models were not examined in detail, but the general nature of the predicted muscle force patterns was shown to be reasonable in some of the models and unreasonable in others. The results supported the hypothesis that the temporomandibular joint develops functionally to allow an approximate minimization of the joint loads during isomeric biting. This does not necessarily imply that the neurophysiological control is actually based on a minimization of joint load.

Algorithms↗

PubMed1995

Reliability of a portable electromyographic unit to measure bruxism.

This study evaluated the effect of different rates of increase of occlusal force and of removal and replacement of the electromyographic electrodes on the amount of occlusal force needed to trigger a modified electromyographic measuring unit. Seven subjects placed the electrodes on the masseter area on one side, and bit ipsilaterally on a bite force transducer. The electromyographic recorder was adjusted to be triggered only when the subject clenched. Occlusal force was recorded simultaneously with triggering of the electromyographic recorder. The subjects performed two series of five repetitions of clenching at each of four different rates of increase of force, by visual feedback from a second oscilloscope until the electromyographic recorder was triggered, and an occlusal force measurement was made from the first oscilloscope. Repeated measures of ANOVA analysis revealed no statistically significant differences among the different rates of increase in occlusal force or between the two recording series. Interaction between the two factors also was not significant. The intraclass correlation coefficient was large and statistically significant, indicating that this device was reliable for this method.

Adult↗

PubMed1994

Spontaneous palpebromandibular synkinesia: a localizing clinical sign.

In the classical corneomandibular reflex (CMR), corneal stimulation elicits a bilateral eyelid blink and a brisk anterolateral jaw movement. We here describe 14 patients with a spontaneous palpebromandibular (eyelid-jaw) synkinesia (SPMS) in whom jaw movements, similar to those in CMR, regularly accompanied spontaneous eye blinks without an external corneal stimulus. Eleven of the patients with SPMS also had CMRs on corneal stimulation. Four patients had clinical and imaging evidence of brainstem lesions above the mid-pons, 5 patients had autopsy or imaging evidence of both bilateral cerebral and upper brainstem lesions, and 5 patients had clinical or imaging evidence of bilateral cerebral dysfunction. Topical corneal anesthesia administered to patients who had both CMR and SPMS blocked the CMR but had no effect on the SPMS. In patients with both SPMS and CMR, measurements of latency from onset of orbicularis oculi electromyographic activity to onset of lateral pterygoid EMG activity, and mandibular kinesiography of jaw velocity and direction showed that the eyelid-jaw synkinesias of CMR and SPMS had similar characteristics. We conclude that SPMS is pathophysiologically the same as the eyelid-jaw synkinesia of CMR and both synkinesias originate centrally, probably in the pons. In CMR, the jaw movement is primarily related to the blink rather than the corneal stimulus, but corneal stimulation may be necessary to overcome a higher threshold for expression of the synkinesia than in patients with SPMS. Like CMR, SPMS emerges in patients with upper brainstem or bilateral cerebral lesions and SPMS may therefore be a useful localizing clinical sign.

Adult↗

PubMed1993

Kinematics of jaw movements during chewing at different frequencies.

The three-dimensional jaw movement trajectory and its velocity profile were investigated to provide information regarding the motor control of chewing. This was done on a cycle-by-cycle basis across three voluntarily guided chewing frequencies to test the lack of invariance at the velocity level and the evidence for a cost function. The data revealed that an increase in chewing frequencies resulted in a significant reduction of the three-dimensional path, being significantly higher in opening than closing. The ratio of peak speed/three-dimensional distance, a kinematic index of stiffness, increased with increase in chewing frequency; higher stiffness being associated with faster chewing, the stiffness being significantly higher in opening than in closing. The ratio of peak velocity to mean velocity decreased as a function of increase in chewing frequency only at the highest frequency and this decrease again was different in opening than in closing. The results demonstrated that the velocity profile of chewing movements, like that of speech movements, lacked invariance. Rather than minimizing one cost function, the system used an efficient trade-off between time, space and effort, based on the objective of movements.

Adult↗

PubMed1991

Electronic technology for clinical prosthodontics.

A review of the literature on electrodiagnostic devices indicates that current studies have not substantiated claims regarding the utility of these devices in clinical dentistry. Research design problems, such as inadequate control subjects and use of inappropriate statistical tests, limit the conclusions that can be drawn from the results of these studies. Further research, including measurements of sensitivity and specificity, is needed in order to indicate the diagnostic utility of jaw tracking or electromyography in clinical dentistry.

Diagnosis, Oral↗

PubMed1990

Effects of chewing frequency and bolus hardness on human incisor trajectory and masseter muscle activity.

Nine adults with no orofacial dysfunctions were instructed to chew a standardized piece of soft or hard gum on the right side in time with a metronome set at 46, 100 or 160 beats/min. Jaw movements were recorded with a Myotronics kinesiograph and masseter electromyograms were detected with surface electrodes. The chewing patterns on either gum were not significantly different in any of their spatial or temporal aspects, in mean or peak opening or closing velocities, or in the timing or level of activity in either masseter at any of the three chewing frequencies. These findings suggest that during metronome-paced chewing the change in sensory feedback resulting from a change in gum hardness exerts little or no effect on either the spatial or temporal aspects of masticatory motor output.

Electromyography↗

PubMed1990

Devices for the diagnosis and treatment of temporomandibular disorders. Part I: Introduction, scientific evidence, and jaw tracking.

This three-part series of articles summarizes the uses of several devices or groups of devices intended for the diagnosis or treatment of temporomandibular disorders (TMD) and compares their claimed clinical usefulness with the present scientific evidence. Part I of this review defines TMD; discusses the principal criteria for evaluating published scientific clinical evidence such as reliability, validity, sensitivity, and specificity; gives a rationale for the clinical "gold standard" against which diagnostic and therapeutic devices must be compared; and evaluates the status of jaw tracking for the diagnosis of TMD. This review and evaluation led to the conclusion that, at the present time, the claim that jaw-tracking devices have a diagnostic value for TMD is not well supported by the scientific evidence.

Evaluation Studies as Topic↗

PubMed1990

Devices for the diagnosis and treatment of temporomandibular disorders. Part II: Electromyography and sonography.

This second article in the three-part series on temporomandibular disorder (TMD) devices compares the claimed diagnostic usefulness of electromyography and sonography with the present scientific evidence. This review concludes that there is no evidence to support the use of either surface electromyography or silent period duration for the evaluation or diagnosis of TMD. Furthermore, in view of the available evidence, sonography and Doppler ultrasound have no particular advantage over a conventional stethoscope or direct auscultation.

Auscultation↗

PubMed1989

The effect of L-tryptophan supplementation and dietary instruction on chronic myofascial pain.

Effects of L-tryptophan supplementation and dietary manipulation were tested on patients with chronic myofascial pain around the temporomandibular joints. In this study, however, reduction of chronic pain reported in previous similar studies was not duplicated. No significant reduction in pain was noted in the groups receiving tryptophan and dietary manipulation compared with control groups.

Dietary Carbohydrates↗

PubMed1989

Interrater reliability in masticatory muscle palpation.

Muscle palpation is an important procedure in screening for TM disorders and assessing results of treatment outcome studies, but interpretation of response may be subjective and vulnerable to examiner bias. Masticatory muscle palpation scoring was evaluated with respect to interrater agreement on 31 myofascial pain-dysfunction patients participating in a medication study. Two clinicians independently palpated the temporomandibular joints, muscles of mastication, and related head and neck musculature on three different occasions over the 6-week period of the study. Standardization of palpation technique and initial protocol for interpretation of subject response were discussed prior to the first examination. Further clarification and reinforcement of examination methodology and scoring were carried out prior to the second examination, 1 week later. Another 5 weeks passed, with no further standardization, before the third and last examination. A behaviorally anchored scoring system (0 to 3) was used to rate response to palpation. Results indicate that two investigators can achieve a fair degree of reliability when carefully standardized, further interrater standardization can result in higher reliability, and reliability can be maintained over at least a 5-week period of time.

Humans↗

PubMed1988

Comparison of automatic and voluntary chewing patterns and performance.

Chewing, like respiration, is ordinarily performed as an automatic motor act, yet both can be voluntarily controlled. No in-depth analyses of voluntary chewing exist. Therefore, we have analyzed on a cycle-by-cycle basis voluntarily controlled chewing, and compared it with automatic chewing. We assessed the performance during voluntarily controlled chewing by obtaining constant error and variable error scores. Nine healthy adults with full dentition were subjects (Ss). Their three-dimensional jaw movements and movement times were derived from Kinesiograph recordings obtained while chewing a standard piece of gum on the right side of the mouth. Burst durations and onset latencies of masseter activity were obtained from surface-recorded EMGs. Frequency during automatic chewing was obtained from data recorded while the subject viewed a film. Next, the subject chewed in time with a metronome set at this "automatic" rate. Intrasubject variability among 30 consecutive chewing cycles during voluntary was less than during automatic chewing. In every S gape and ipsilateral jaw excursions and the variability of burst durations of masseter activity were less during voluntary than during automatic chewing, showing that both the spatial and temporal aspects of the two types of chewing differ significantly. Ss varied in ability to follow the metronome. A S's constant error might be small, yet his variable error might be large, as if feed-back-based corrections influenced cycle-to-cycle variability. Fast chewers had smaller constant and variable error scores than did slow chewers, suggesting a speed-accuracy relationship. In summary, both temporal and spatial aspects of voluntary chewing were modified compared with those of automatic chewing. During voluntarily controlled chewing, cycle-to-cycle variability was less compared with automatic chewing due to reductions in variability of occlusal phase and the masseter's burst durations, and total jaw excursions were less because gapes and ipsilateral deviations during closing were reduced.

Adult↗