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Biomedical subjects

G Hellsing

Publications and source records attributed to G Hellsing.

At least 37 records · Page 2Linked to original sources
PubMed1985

Arthroscopy of the temporomandibular joint. An autopsy study.

Arthroscopy of the temporomandibular joint (TMJ) is evaluated on an autopsy material. 2 different types of arthroscope--one with a rod-lens system and one with a so-called Selfoc system--were used and compared regarding diagnostic accuracy. On 54 cadavers, it was found that the upper joint compartment may be punctured with accuracy and without damage to vital tissues. Landmarks on the skin facilitating clinical arthroscopy were defined in relation to a guideline from tragus to lateral canthus. A further 49 TMJ specimens were investigated with arthroscopy. The findings are in good agreement with subsequent observations made during dissection. Regarding arthrotic changes, 100% diagnostic accuracy was achieved with both types of arthroscope. Regarding remodelling changes, the diagnostic accuracy was approximately 57%. No significant difference was noticed between the 2 arthroscopes. Photographic documentation with the rod-lens arthroscope was found to be of superior quality.

Adult↗
PubMed1985

Repeatability of the mandibular retruded position.

Repeatability of the centric jaw relation recorded with the one-handed push-back technique was tested on six subjects. Condylar positions were radiographically recorded using cold cure acrylic indices to lock the jaws in centric. This was done on two occasions with an interval of 1 week between recordings. Utilizing the subtraction technique, the radiographs of these condylar positions were compared. Intra-individual differences were not found to be significant and it may be concluded that centric relation registered with the push-back technique results in accurate and consistent repositioning of the condyles in the glenoid fossa.

Acrylic Resins↗
PubMed1984

Short and long-latency responses in human masseter muscle evoked by chin taps.

Ten healthy subjects received downward, backward and upward chin taps with standardized force and direction. Taps in all three directions elicited short (M1) and long (M2 and M3)-latency excitatory EMG responses in the masseter muscle. M1 (mean latency 8.9 ms, amplitude 150 microV) occurred more frequently and with shorter latency during clenching than during relaxation or opening. Downward taps were more efficient in evoking jaw-jerks (25 per cent) than upward (14 per cent) and backward ones (16 per cent). M2 was a weak biphasic deflection occurring during the silent period (mean latency 42 ms, amplitude 87 microV) and M3 was an EMG burst following the silent period (mean latency 69.3 ms, amplitude 169 microV). No long-latency evoked responses were obtained from the relaxed masseter. Thus, muscle stretch increases M1 response frequency but is not a necessary prerequisite. The hypothesis that vibratory transmission plays an important role was confirmed. Voluntary activation of the stimulated muscle (clenching) increases M1-response frequency and shortens response latency.

Adult↗
PubMed1984

Functional adaptation to changes in vertical dimension.

The traditional concept of PP stability defies neurophysiologic explanation. Conversely, the hypothesis presented to explain the rapid adaptation of jaw elevator postural tonus to sudden change of vertical dimension is in accordance with research of automotized motor behavior. Furthermore, there is no logical reason to believe that maladaptive reactions develop after prolonged procedures that increase the vertical dimension of occlusion. Rather, Goldspink reports that within a few weeks complete normalization probably occurs. Jaw muscle motor behavior is more dynamic and adaptable to environmental changes than has been believed.

Adaptation, Physiological↗
PubMed1984

Arthroscopy of the temporomandibular joint. Examination of 2 patients with suspected disk derangement.

2 patients with a history of reciprocal temporomandibular joint (TMJ) clicking were visually examined with arthroscopy of their right side TMJs. Clinical and radiographic examination revealed no signs of arthrosis deformans. One patient with significantly reduced opening ability combined with occasional disappearance of TMJ clicks showed advanced arthrotic changes of cartilage which were not visible radiographically. The other patient with unimpaired function also had a severe arthrotic lesion in the clicking joint. In neither case did the disk appear to be displaced. It is concluded that arthroscopy yields additional information for TMJ diagnosis which cannot be achieved by clinical and radiographic examination alone.

Adult↗
PubMed1983

Masseter muscle fatigue in man objectively quantified by analysis of myoelectric signals.

Localized muscle fatigue in the masseter muscle was studied with a method based on power spectrum analysis of myoelectric signals. Under the influence of fatiguing contractions, a gradual shift of the spectral curve occurred; the rate of change was taken as a measure of the development of fatigue. The fatigue was dependent on the bite force. The existence of a threshold value of force, below which significant myoelectric fatigue changes do not develop, was shown.

Adult↗
PubMed1983

The masseter muscle: the silent period and its clinical implications.

Standardized solenoid chin taps were delivered downward and upward as parallel as possible to the fibers of the superficial part of the masseter muscle and backward at a right angle to this direction. Each one of the 10 healthy subjects received 10 taps in each direction during isometric masseter muscle activity (clenching the teeth). Taps in all three directions evoked the classic jaw jerk response, M1, a short latency (mean, 8.3 msec) excitation followed by an SP (mean latency, 15.9 msec; mean duration, 42.6 msec). The SP duration varied considerably not only between subjects but also within individuals. Forty-nine percent of the SPs were divided into two parts by an EMG peak, M2, with mean latency 42 msec and mean amplitude 78 microV. Sometimes this peak marked the end of the SP. The SP duration has been claimed to be of diagnostic significance because it is longer in patients with mandibular dysfunction. It is concluded that the large variations of the parameter found in this as well as in other studies make it impossible to establish criteria for a healthy or pathologic SP duration. A carefully obtained history and thorough clinical examination are probably more reliable means to establish a correct diagnosis.

Adult↗
PubMed1983

Rotation of synergistic activity during isometric jaw closing muscle contraction in man.

5 healthy subjects were studied during 10-15 min of isometric jaw elevator contraction above fatigue threshold level. Bite force was measured between upper and lower front teeth and electromyographic (EMG) activity recorded from the right temporal and masseter muscles. Of the two muscles only the masseter was active at the start of the test and usually during the whole test. When the test was repeated, however, great relief from the pain in the fatigued masseter was sometimes experienced and the temporalis took over the load. All subjects experienced this "switch" phenomenon after a varying number of tests, one of them already during his first test. The mechanism seemed to be completely out of voluntary control and showed facilitation at repeated tests.

Electromyography↗
PubMed1982

Reflex responses to taps in various directions from the human digastric muscle.

Reflex responses to standardized solenoid chin taps were studied on 21 subjects with electromyographic (EMG) recordings from two jaw muscle antagonists, the masseter and the digastric. Taps were delivered downward and upward as parallel as possible to the masseter fibre direction and also backwards at right angles to these directions. Taps were delivered during isometric masseter and digastric activity as well as during relaxed postural position. Reflex excitation of the digastric muscle with a latency of 25-35 ms was recorded during all three situations after taps in all three directions. When this response was superimposed on ongoing digastric isometric activity after downward and upward taps, it was followed by a period of inhibition (mean duration 31 ms) and directly followed by a second EMG burst (mean latencies 73 and 75 ms, respectively). Responses were significantly (p less than 0.001) more often obtained during digastric background activity than during postural position and clench. Upward and downward taps were equally efficient in evoking the responses, significantly (p less than 0.001) more so than backward taps. The concurrent recordings of the masseter EMG imply the possibility of a reciprocal interplay between the two antagonists. The results accord with reports of the capability of the digastric muscle to produce reflex responses despite lack of anatomically-defined muscle spindles.

Adult↗