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Biomedical subjects

R Yemm

Publications and source records attributed to R Yemm.

At least 19 recordsLinked to original sources
PubMed1997

Electromyographic evidence for a digastric reflex evoked by perioral stimuli in humans.

Electromyographic recordings (EMGs) were made using skin surface electrodes placed over the anterior digastric muscle in seven subjects. In every case, short bursts of electrical stimuli to the upper lip produced a response in the EMG that had a minimum latency of 62.0 +/- 10.8 ms (mean +/- SD). By contrast, no responses were seen when single pulse stimuli were applied. In 6/7 subjects, the minimum stimulation intensity that produced the reflex was described as being sharp or painful. In three additional experiments, single motor units were recorded within the digastric muscle using needle electrodes. In two of these experiments, there was evidence of reflex activity 60-110 ms after the application of painful electrical stimuli to the lip. These findings confirm that perioral stimuli can evoke a digastric reflex in humans and suggest that this reflex requires the summation that results from successive volleys of impulses in a large number of nociceptive afferent neurones.

Electric Stimulation↗
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

Removable partial denture production in Scotland.

Removable partial denture production in Scotland was studied by analyzing photographs taken of consecutive casts and dentures and reviewing prescriptions of 539 cases at a large dental laboratory. Of the casts, 70.4% were maxillary and 29.6% mandibular. The mean number of teeth present was 9.9 in the maxilla and 8.4 in the mandible. Of the partial dentures studied, 33.6% were acrylate dentures without any framework. None of these had occlusal rests, and 5.6% had clasps. Of the framework-retained maxillary dentures, the palatal strap (12.9%), horseshoe (15.8%), and anterior palatal bar (18.9%) designs were the most frequent. In the mandible, lingual bars (32.7%) and lingual plates (32.7%) predominated. Of the acrylic dentures, 89.3% were made without any instruction from the dentist. The corresponding figure for prostheses with cobalt-chromium frameworks was 15.0%.

Denture Design↗
PubMed1993

Changes in human jaw muscles with age and dental state.

The effects of ageing and dental state on the cross-sectional area and density of two jaw muscles, the masseter and medial pterygoid, were investigated using computed tomography. The study involved 84 male and 70 female subjects between the ages of 20 and 90 years. The cross-sectional area of both muscles showed a significant reduction with age; values for female subjects being found in the lower range of the distribution. When consideration was given to the presence or absence of a natural dentition, the cross-sectional area of both muscles in edentulous subjects showed a greater decrease throughout the age range studied. There was a significant decrease in the density of the muscles with increasing age. Previously, this has been interpreted to indicate a progressive increase in fat and fibrous tissue. Subject gender and the absence of teeth appeared to have little effect on this parameter. Changes in the cross-sectional area and density of these muscles would appear to be consistent with a general age related change of muscle tissue in the body as a whole and may specifically indicate a reduction in the masticatory forces which can be or are being utilised by ageing patients, many of whom have no remaining natural dentition.

Adult↗
PubMed1992

The structure and function of the temporomandibular joint.

Although characterised by having a synovial membrane lining the nonarticulating surfaces within the joint capsule, in some ways the temporomandibular joint (TMJ) is an atypical joint. This paper highlights the differences between the TMJ and other movable joints with a description of the structure, innervation blood supply and musculature. Also included are details of how the TMJ moves--the effectors of movement and the various reflexes controlling movement of the joint.

Cartilage, Articular↗
PubMed1991

Replacement complete dentures: no friends like old friends.

Provision of replacement complete dentures for an increasingly elderly population presents problems for the dentist. Reduced adaptability in the older person leads to difficulty in learning to use new appliances unless existing skills can be employed. It is therefore helpful to reproduce familiar features of a patient's old appliances, especially if these have been used for some years. This paper describes a method of treatment that provides both clinician and laboratory with the ability to achieve this objective, while retaining freedom to eliminate clinically-identified faults in the old appliances in the process of provision of the new. The technique depends on the substitution of conventional wax-rimmed record blocks with wax replicas of the old appliances. These replica record blocks lend themselves to any - major or minor - alteration during occlusion recording. They also incorporate a rigid baseplate and function as special trays.

Adaptation, Physiological↗
PubMed1988

Study of age changes in the motor units of the first dorsal interosseous muscle in man.

The effect of ageing on the threshold firing rate of motor units from the first dorsal interosseous muscle was investigated. Two groups of 9 healthy male subjects between the ages of 20-29 and 60-69 years took part in the study. The threshold firing rate of motor units in young subjects showed close agreement with previous observations. However, a significant decrease was found in the older age group and, in addition, these units showed a prolongation of their contraction times, confirming our previous findings from this muscle. These results are discussed in relation to changes previously reported in human skeletal muscle and may indicate a functional change of the muscle with age.

Adult↗
PubMed1987

The use of computed tomography in the detection of radiolucent denture base material in the chest.

With the introduction of acrylic resin denture base materials to the dental profession, radiolucency was recognized as a significant deficiency at an early stage. Continuous research into the production of a radiopaque material has been directed at including radiopaque glasses, salts or metals powders in an otherwise radiolucent polymer. However, the majority of new dentures are still made in radiolucent material which is notoriously difficult to locate by conventional radiography and reports continue to appear relating to the inhalation or ingestion of dentures (or fragments of them), occasionally leading to the death of the patient. Advances in radiographic techniques and equipment have seen the development of computed tomography (CT). This has proved invaluable as a diagnostic aid for disease and therapy but little attention appears to have been given to the use of this sophisticated technique in the detection of foreign bodies, in particular those of dental origin. This study investigates the use of CT in the detection of radiolucent denture base material. The results suggest that CT has substantial advantages over conventional radiography in the detection of this material and should be considered as a valuable diagnostic aid in those patients thought to have inhaled dentures or fragments of dentures.

Acrylic Resins↗
PubMed1986

Changes in the contractile properties of the human first dorsal interosseous muscle with age.

The effect of ageing on the contractile properties of the first dorsal interosseous muscle was investigated. A group of 42 healthy male subjects between the ages of 10 and 80 years took part in the study. The time to peak tension was significantly prolonged with increasing age but no evidence was found of an extension of the half relaxation time. When left and right hands were compared no significant differences were found. The results are discussed in relation to the changes previously observed in ageing muscle and may indicate a general age change of the muscle or the loss of faster twitch fibres.

Adolescent↗
PubMed1985

An alternative method for recording the occlusion of the edentulous patient during the construction of replacement dentures.

An alternative method of recording the occlusion for the edentulous patient is described. The method is applicable to situations where replacement dentures are to be prescribed. In place of conventional record blocks, shellac-based wax replicas of the existing dentures are used. Such record blocks facilitate both retention of satisfactory features of the existing dentures and also the incorporation of specific modifications.

Dental Impression Technique↗