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Biomedical subjects

M F Lyons

Publications and source records attributed to M F Lyons.

At least 19 recordsLinked to original sources
PubMed1999

Bite force, endurance and masseter muscle fatigue in healthy edentulous subjects and those with TMD.

It is well known that bite force and EMG activity are considerably reduced in edentulous patients, but the susceptibility of their jaw-closing muscles to localized fatigue is less certain. This information is even less clear for edentulous subjects who have TMD. Eleven healthy edentulous subjects and 10 edentulous subjects with TMD participated in this study. Maximum bite force was measured first, with the transducer placed on the canine-first premolar region bilaterally, and then two rapid relaxations were made from a brief voluntary clench to 50% of maximum. A sustained voluntary clench of 50% of maximum was then maintained and endurance time was noted. EMG was recorded from both masseter muscles and the median frequency of the power spectrum of the EMG from 2 s at the beginning of the sustained clench and 2 s at the end was subsequently calculated. Two more rapid relaxations from brief clenches were performed immediately after the sustained clench. The mean maximum bite force in the healthy group was 115 N (SD +/-41) and in the TMD group was 75 N (SD +/-22), this difference being significant (P = 0.0013). The mean endurance time in the healthy group was 86 s (SD +/-51) and in the TMD group was 63 s (SD +/-20). The percentage change in the median frequency in the healthy group as a result of the sustained contraction was 6% (left) and 8.6% (right) and in the TMD group was 13.9% (left) and 12.8% (right). The percentage change in the mean relaxation half time for the healthy group was 28.5% and for the TMD group was 72%, a significant difference (P = 0.0046). It was apparent that the maximum bite force was low in edentulous subjects and was further reduced in edentulous TMD subjects; endurance time was reduced in TMD subjects; fatigue resistance of the masseter muscles was reduced in TMD subjects.

Aged↗
PubMed1999

The study of jaw reflexes evoked by electrical stimulation of the lip: the importance of stimulus intensity and polarity.

The aim of this study was to investigate whether reported differences in the patterns of jaw reflexes which can be evoked by electrical stimulation of the lip might be related to the intensity or polarity of the stimuli. Constant-current stimuli were applied through bipolar electrodes clipped across the lower lip of 14 subjects while EMG recordings were made from a masseter muscle. During stimulation, the subjects sustained a level of masseter activity equivalent to 10% of their maximum. The stimuli were applied as multiples of sensory threshold. The EMGs were analysed following rectification, averaging and smoothing. A sequence of inhibitory, excitatory, inhibitory and excitatory responses could be produced in the muscle by both polarities of stimuli. The latencies of these four responses were generally in the ranges 10-20, 25-40, 40-55 and 80-100 ms, respectively. These latencies, particularly for the last two responses, tended to decrease at higher intensities of stimulation. The threshold for the long-latency inhibition was significantly lower than that for the short-latency inhibition when the cathode was outside the mouth but not when it was inside the mouth. In addition, the long-latency excitation had the lowest threshold of the four responses regardless of stimulus polarity. Since nerves are excited particularly around a cathode, we interpret these results as showing that stimulation of nerves supplying the skin outside the mouth evokes predominately long-latency jaw reflexes whereas shorter latency responses can be evoked by stimulating nerves supplying oral mucosa. Furthermore, long latency excitatory reflexes seem to be the most easily evoked by stimulation of the lip.

Adult↗
PubMed1999

The immediate effect of hard and soft splints on the EMG activity of the masseter and temporalis muscles.

The aim of this study was to compare the effects of hard and soft splints on the activity of the anterior temporalis and masseter muscles. Surface EMG recordings were made from these muscles during clenching at 10% of maximum, 50% of maximum and at maximum clench, both before and after insertion of a hard splint. This sequence was then repeated with a soft splint. The relative level of activity in the anterior temporalis and masseter muscles at all three activity levels was quantified by means of an Activity Index, which provides a measure of the balance of activity in the masseter relative to the activity in the anterior temporalis muscle. It was found that hard splints led to a decrease in EMG activity in relation to activity with no splint in both muscles at maximum clench and particularly the anterior temporalis. Soft splints produced a slight increase in activity of both muscles, but particularly the masseter muscle. The Activity Index indicated a shift in the balance of activity away from the anterior temporalis muscles with both splints, particularly at 10% of the maximum clenching level. It is possible that the decrease in activity of the temporalis muscles relative to the masseter muscles may be a factor in the therapeutic effect of both a hard and a soft splint, although the decrease is clearly greater with the hard splint.

Acrylic Resins↗
PubMed1999

Using sector endoluminal ultrasound to identify the normal pancreas when axial computed tomography is falsely positive.

RATIONALE AND OBJECTIVES: Little has been reported on the ability of endoluminal ultrasound (EUS) to identify a normal pancreas after an abnormal axial computed tomogram (CT). Many clinicians still use axial technology, as opposed to helical or spiral CT, which differ in scanning speed. Spiral CT and EUS are considered equal in their ability to diagnose pancreatic tumors. Although this is not the case with axial CT, the complementary role by EUS has not been defined. This study reports on the ability of EUS to identify the "true-negative" pancreas deemed abnormal by axial CT. METHODS: Sixty-five consecutive patients suspected of having a small pancreatic lesion were studied by comparing axial CT and EUS examinations, using each patient as his or her own control. Identification of a normal pancreas was reviewed using surgery, biopsy, and long-term clinical follow-up as the standard of truth. RESULTS: Thirty-three patients were documented as having small pancreatic lesions; the remaining 32 were normal. The sensitivity and specificity, respectively, were 91% and 41% for axial CT and 88% and 88% for EUS. The positive and negative predictive values, respectively, were 61% and 82% for CT and 88% and 88% for EUS. The statistical differences between axial CT and EUS were significant. CONCLUSION: An axial CT positive for a small pancreatic mass requires confirmation with additional imaging before invasive management. The specificity of EUS--twice that of CT--is strong evidence that EUS can fulfill this role. Review of the literature supports the conclusion that EUS should be required in the workup of small pancreatic lesions identified at axial CT.

Chronic Disease↗
PubMed1998

Pilot study of a semi-flexible intra-oral appliance for the control of snoring.

OBJECTIVE: To determine the effectiveness and acceptability of an intra-oral appliance in the reduction of snoring, with construction and fitting as a 1-visit process. DESIGN AND SETTING: This was a prospective study. Patients were attending a hospital sleep breathing disorders clinic and appliances were made at a dental hospital. This work was carried out in the UK during 1996 and 1997. SUBJECTS AND METHODS: Patients were selected from those referred to a sleep breathing disorders clinic with socially disruptive snoring. MAIN OUTCOME MEASURES: Patients were assessed by means of limited sleep studies and by questionnaires before and after fitting of the appliances. The sleep studies consisted of monitoring respiratory variables (principally oronasal airflow and nocturnal oxygen saturation). A respiratory disturbance index was assigned. Questionnaires were completed by both patients and sleep partners, with many of the responses being marked on visual analogue scales. RESULTS: 16 male patients, mean age 49 years, were included in the trial. 14 were able to wear the appliance and their level of snoring, as assessed by their sleep partners, reduced from a mean of 8.8 out of 10 to 4.2 out of 10 (P = 0.0003, paired t-test). CONCLUSION: It is concluded that the semi-flexible intra-oral appliance is effective in the control of snoring.

Adult↗
PubMed1998

The variability of bite force measurement between sessions, in different positions within the dental arch.

The effect of measuring bite force with different patterns of transducer on different occasions was studied. Maximum voluntary bite force was measured in eight volunteers. Three transducer positions, each with a different pattern of transducer, were used; between the anterior teeth, between the second premolar and the first molar on one side and between the second premolars and first molars on both sides. Visual feedback of force was provided. Two sets of five maximum clenches were recorded with a rest period in between. This sequence was repeated for each transducer and the experiment was repeated on three different days. The highest forces were measured with the bilateral posterior transducer (mean 580 N, s.d. 235) and the lowest on the anterior transducer (mean 286 N, s.d. 164). The standard deviations of the bite force mean values were used as an indication of the variability and were subjected to a non-parametric anova (Kruskal-Wallis). The forces recorded with each transducer position were significantly different between the transducers (P < 0.01) and the maximum bite force showed least variability when measured between the posterior teeth on one side only. There was little difference in bite force between the three different sessions (P > or = 0.05) when measured in the same position within the dental arch, whichever of the three positions that may be.

Adult↗
PubMed1998

Acoustic myography, electromyography and bite force in the masseter muscle.

Acoustic myography (AMG) offers some advantages over electromyography (EMG) in certain circumstances, but the use of AMG on the jaw-closing muscles has not been fully tested. The purpose of this study was to examine the relationship between AMG, EMG and force in the masseter muscles of nine healthy male subjects. The AMG was recorded using a piezoelectric crystal microphone and the EMG was recorded simultaneously with surface electrodes. Force was recorded between the anterior teeth with a strain-gauge transducer. Analysis showed that Pearson's correlation coefficient was 0.913 for force/AMG and 0.973 for force/EMG in all subjects, indicating a linear relationship between force, AMG and EMG at the four different force levels tested (25-75% of maximum). It is apparent that AMG may be used as an accurate monitor of masseter muscle force production, although some care is required in the technique.

Acoustics↗
PubMed1997

A great position before a great 'package'.

Should employment agreements (EAs) be the deciding factor in considering a new position? EAs are details--important details, but background just the same--to the key issue: Do you want the job? And because of the way many health care organizations create their EAs, there really is little room for negotiation. Perceptions persist that this is an entirely open area, a blank canvas upon which each physician executive, in each situation, must don his or her battle gear and fight fiercely for the best possible deal. And yet, this is an area in which you are unlikely to have control.

Humans↗
PubMed1997

Health care is sales.

Health care is all about sales--everyone today in the competitive arena of health care is a salesperson. Your selling days began when you applied to medical school. Your product was yourself, and you worked hard to sell it. That was only the beginning. In your daily work as physician executives, you are selling yourself and your ideas-your ideas about relationships, management structures, partnership issues, merger questions, etc. It's a complicated world, and the concepts are often abstract and difficult. But it is your job to communicate with others to get things done. It is the most important part of your job. It is selling, in fact, at a sophisticated level. How do you communicate and sell yourself and your ideas effectively? Here, some ideas on how to listen and communicate.

Commerce↗
PubMed1996

Twitch interpolation in the assessment of the maximum force-generating capacity of the jaw-closing muscles in man.

The method of twitch interpolation was employed to study the maximum potential bite forces of humans. Transcutaneous electrical stimuli were applied to parts of one or both masseter muscles in eight volunteers while they bit with a variable but controlled isometric force on a unidirectional force transducer held between the anterior teeth. In all participants the twitch force produced by a single 1-ms pulse, of 25 50 mA intensity, was inversely and linearly related to the voluntary bite force. For each participant the slope of the regression between twitch force and bite force depended on the stimulus intensity and not on whether the stimulus was applied to one or both masseters. Extrapolation of the regression lines to zero twitch force showed that they converged towards a bite-force value that, for any given participant varied only a small amount between different stimulus intensities. For most participants this bite force lay above the maximum that they produced voluntarily: voluntary maximum bites ranged from 153 to 593 N, while the extrapolations predicted a narrower and higher potential range of 282-629 N. It was concluded that, for the masseters at least, there is often spare force-generating capacity which individuals are either unable or not prepared to utilize. This method is non-invasive and may help to define better the maximum bite-force potential of humans.

Adult↗
PubMed1996

Properties of a custom-made hinge clasp compared with a conventional circumferential clasp.

The use of the hinge clasp in removable partial denture design, together with the design of a custom-made hinge unit, is discussed in this article. Tests of the retention provided by these custom-made hinge clasps were made, together with conventional clasps, and the results were compared. Six custom-made hinge clasps were constructed and attached to blocks of acrylic resin. The forces required to open these clasps and the effect of wear on the clasps were measured. Six conventional cast clasping units were also constructed and tested. The results indicated that the average force required to open the hinge clasps was 8.13 N (SD 1.99). After a period of simulated wear, the mean value of force required was 7.70 N (SD 2.33) and there was no statistically significant deterioration caused by wear. The mean forces required to withdraw these clasps vertically from a tooth were 30.25 N (SD 6.51) for the conventional clasps and 49.67 N (SD 18.69) for the hinge clasps. It was also found that the hinge clasps had to be withdrawn further from their seated position than the conventional clasps before retention was finally lost. However, neither of these differences were statistically significant.

Dental Clasps↗
PubMed1996

Breaking the rules.

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Contract Services↗