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Biomedical subjects

L V Christensen

Publications and source records attributed to L V Christensen.

At least 73 records · Page 4Linked to original sources
PubMed1985

Lateral preference in mastication: relation to pain.

Ten subjects performed deliberate right and left-sided chewing of gum, each exercise with a duration of 60 s, followed by maximum voluntary teeth clenching (MVC) until onset of pains in the masseter muscles (pain threshold). Contractile activities of the right and left masseter muscles were assessed by integrated and cumulative surface electromyography (EMG). When the right and left muscles functioned as chewing side muscles only, they generated practically identical levels of chewing force; the same applied when they functioned as non-chewing side muscles only. During identical functions, EMGs suggested identical motor unit recruitment and firing patterns in the two paired muscles; i.e., units producing relatively high tensions for chewing side activity, and other units producing relatively low tensions for non-chewing side activity. During isometric MVC activity, until onset of pains, the right and left muscles generated practically identical levels of bite force, but right and left motor unit activity patterns seemed to differ. Right and left motor units might have fired at different rates or begun to drop out at different times. In the latter case, rapidly before slowly fatigued units. There was a tendency for a low pain threshold with high chewing side activity in both masseter muscles. Motor units producing high levels of tension, but easily fatigued, might have caused early onset of muscle pains. No relationships could be established between preferred chewing side and side of initial muscle pains, nor between MVC activity and side of pain onset and preferred chewing side.

Adult↗
PubMed1985

Isometric endurance of the human masseter muscle during consecutive bouts of tooth clenching.

Three human subjects performed teeth clenching at maximum voluntary contraction strength (MVC) of the mandibular elevator muscles. At intervals of 10s, ten successive bouts of MVC clenching were exercised until total exhaustion of the contracting muscles (isometric endurance). Isometric endurance time decreased exponentially from 59 to 12s. The curve of the decrease showed a monotone power function (y = x-1). Electromyographic recordings from masseter muscles suggested that fatigable motor units, possibly fast glycolytic units, dropped out during the initial stages of maintained MVC isometric activity. The silent period of the monosynaptic jaw jerk reflex was increased by about 35% following exhaustion of the masseter muscle.

Adult↗
PubMed1985

Lateral preference in mastication: a feasibility study.

To study lateral bolus placement during mastication, referred to as masticatory lateral preference, fifteen males and ten females chewed sugarless gum for 15, 20 and 25 s, and visual inspections were done of either right or left side bolus placements. In each of three series of observations, there were no significant differences between right or left side bolus placements. Three consecutive spot checks, in single subjects, showed that lateral preference occurred at random. However, information on a favoured chewing side predicted fairly reliably the side of observed masticatory lateral preference. Observed lateral preference could not be predicted from hand laterality. Consistent and predominant right or left lateral preference was, presumably, an expression of mainly motivational chewing behaviour.

Adult↗
PubMed1985

Lateral preference in mastication: an electromyographic study.

To study concurrence of specific electromyographic chewing patterns and the side of mastication, twelve subjects chewed gum for 15, 20 and 25 s. Gum bolus placement on the right or left side of the dentition was estimated by three series of visual inspections. Contraction patterns of the chewing and non-chewing side masseter muscles were appraised by integrated and cumulative surface electromyography. Consistent and predominant gum bolus placement on the right side of the dentition could be predicted fairly reliably from comparative electromyographic observations. This was also the case in instances of consistent left-sided gum bolus placement, but not in predominant left-sided bolus placement. The latter phenomenon was explained by deviant observations made in two subjects only. Agreement between a presumed chewing side and a predictive contractility pattern was established in 78% of observations (P less than 0.001).

Adult↗
PubMed1984

Effects of topical cooling on isometric contractions of the human masseter muscle.

Six adult males performed tooth clenching for 10 and 80 s at maximum voluntary contraction strength (MVC). Motor activity in the right and left masseter muscles was monitored by surface electromyography. Local temperatures of both cheeks were monitored by a thermocouple. MVC activity for 80 s induced pain and fatigue in both muscles; 10 s of clenching caused no muscle discomfort. Ice, subsequently applied to the right cheek for 30 min, lowered the temperature of the cheek and masseter muscle. The isometric MVC exercises were then repeated. During 10 s of isometric contraction, MVC motor activity in the cooled masseter muscle was significantly increased by 29 per cent; that of the non-cooled contralateral muscle was insignificantly reduced by 12 per cent. During 80 s of clenching, MVC motor activity in the cooled muscle was significantly increased by 30 per cent; that of the non-cooled muscle was insignificantly reduced by 4 per cent. MVC activity for 80 s by the cooled muscle caused no pain and fatigue, but the discomforts continued in the non-cooled muscle. Increased MVC alpha motor activity in the cooled masseter muscle might have resulted from motor facilitation that was mediated by cutaneous, muscular or mucosal cold receptors, or it might have been due to the absence of pain and fatigue.

Adult↗
PubMed1984

Contractile activity of the masseter muscle in experimental clenching and grinding of the teeth in man.

Six human subjects exercised maximum voluntary tooth clenching and right-sided tooth grinding to determine the onset of fatigue in the right and left masseter muscle. Static and dynamic contractile activity of the two muscles was determined by surface electromyography. Muscle fatigue appeared after about 30 s of isometric contractions (clenching), while 30 s of combined concentric and eccentric contractions (grinding) induced no fatigue. In the right muscle the contractile activity of negative work (eccentric contractions of mandibular laterotrusion) was about 50% of that of positive work (concentric contractions of mandibular mediotrusion). During clenching an increased number of contacting teeth might have facilitated the contractile activity of the two muscles. During grinding the height of the cusps of the working side teeth might have contributed to a decrease of tension production by the right masseter muscle. Non-working side tooth contacts and peripheral receptors might have facilitated the contractile activity of the left masseter muscle during tooth grinding. Static contractile activity of the mandibular elevator muscles produced high levels of isometric tension and led to masseter muscle fatigue in about 30 s. The same duration of dynamic contractile activity, resulting in low levels of tension during positive and negative work, did not induce fatigue.

Adult↗
PubMed1984

Cumulative electromyography of the human masseter muscle during fatiguing isometric contractions.

Six adult males performed maximum voluntary tooth clenching (MVC) for 10, 20, 30, 40 s and, after 15 min, for 40, 30, 20, 10 s. During the isometric exercises the electrical currents of the masseter muscle were sampled by integrated and cumulative surface electromyography. Subjective masseter fatigue was present after 30 and 40 s of MVC clenching, accompanied by changes in myoelectrical activity. Strength testing of the masseter muscle, before and after endurance testing, showed that the strength increased by a significant 16% following two endurance tests. This observation was explained by a post-tetanic potentiation and/or a differentiated use of motor units in the fatigued muscle. It is concluded that brief MVC isometric activity, or strength testing, is not a reliable measure of fatigue in the masseter muscle when cumulative electromyography is used. Prolonged MVC isometric activity, or progressive endurance testing, monitors reliably the onset and progression of masseter fatigue.

Adult↗
PubMed1983

Tooth contact patterns and contractile activity of the elevator jaw muscles during mastication of two different types of food.

The pattern of molar and canine contacts and the contractile activity of the masseter and anterior temporal muscle were studied, through integrated electromyography, during right-sided mastication of banana and apple in ten healthy male subjects. Tooth contacts occurred on both the chewing and the non-chewing side. This study does not support the clinical concept that non-chewing side contacts are necessarily detrimental to the jaw muscles and the temporomandibular joints. The activity of the elevator jaw muscles and the tooth contact patterns suggest that the mandible tilted around a sagittal axis, and rotated around a vertical axis, during the phase of elevation of a masticatory cycle.

Adult↗
PubMed1983

The possible activity of large and small jaw muscle units in experimental tooth clenching in man.

Eight human subjects exercised maximum voluntary tooth clenching until there was complete exhaustion of the contracting jaw muscles (isometric endurance time). During the isometric muscle contractions the myoelectrical currents of the masseter and anterior temporalis muscle were sampled by bipolar surface electrodes, integrated, and cumulatively stored. The myoelectrical activity was studied at recording thresholds of 1 microV and 40 microV, i.e. all action potentials below threshold level were ignored. The observations suggested that the number of fast glycolytic and fast oxidative glycolytic motor units in the masseter muscle might have exceeded that in the anterior temporalis muscle; and/or the size of the masseter muscle units might have been larger than that of the anterior temporalis muscle units.

Action Potentials↗
PubMed1982

Delayed onset of masseter muscle pain in experimental tooth clenching.

At 100% and about 50% of maximum voluntary isometric contraction strength of the masseter muscle, six healthy human subjects exercised tooth clenching until there was onset of muscle pain in 42 and 146 sec, respectively. Onset of pain, at maximum contraction strength, might have been due to the cumulative amount of activity in relatively large motor units. The delayed onset of pain might have been associated with a decline in the quantity and quality of contracting large motor units. The Clinical implications of this study suggest that an increase of the vertical dimension of the face will delay the onset of muscle pain in patients suffering from tooth clenching.

Adult↗
PubMed1981

Jaw muscle fatigue and pains induced by experimental tooth clenching: a review.

Maximal voluntary isometric contractions of the elevator jaw muscles, with the mandible in the position of maximal intercuspation of the natural teeth, can induce fatigue and weak as well as severe pains in the jaw muscles of children and adults. A subjective sensation of muscle fatigue appears after about 0.5 min of clenching, and it seems as if the psychological parameter of fatigue onset to a large, but unknown, extent is determined by the physiological parameter of the amount of isometric contractile activity, and perhaps also the original strength of the muscle; however, also individual psychological factors seem to play a role. Pains in the elevator jaw muscles appear after about 1 min of clenching. Although isometric contractions are necessary to cause onset of jaw muscle pains, it is conceivable that perception of the moment of onset of pains to a large, but unknown, extent depends on psychological factors, perhaps the intensity of pains; however, also physiological factors may play a role. The severe muscle pains and gradually increasing subjective exhaustion of the elevator jaw muscles can be endured for about 2 min of maximal voluntary tooth clenching. It is suggested that the psychological parameter of muscle endurance to a large, but unknown, extent depends on the physiological parameter of isometric contractile activity but also individual psychological factors seem to play a role.

Bruxism↗
PubMed1981

An electromyographic and cephalometric study on facial pains and facial morphology in children.

Twelve children, five girls and seven boys with a mean age of 12 years, exercised maximal voluntary tooth clenching until intolerable pains and total subjective exhaustion of at least the right masseter muscle forced the children to stop the isometric muscle exercise; that is, the pain tolerance, or the isometric endurance time, of at least the right masseter muscle was determined in seconds, and it amounted to an average of 100 s. Concomitantly, the electrical activity in the right masseter muscle was recorded by bipolar surface electrodes and integrated, and it showed a significant decrease of 32% during the endurance test, probably as an expression of progressive physiological muscle fatigue. A large ANB angle was associated with relatively little decline of the contractile activity and a trend not to endure pains, possibly because isometric tension was generated predominantly by muscle fibres with a high anaerobic capacity.

Cephalometry↗
PubMed1981

Progressive jaw muscle fatigue of experimental tooth clenching in man.

To determine the onset of subjective fatigue and the subjective endurance of fatigue and pains in the masseter muscle, ten adult male subjects exercised maximal voluntary tooth clenching. Concomitantly, the electrical activity in the masseter muscle was recorded by bipolar surface electrodes and integrated. Onset of subjective fatigue occurred on average 21 s after onset of muscle hyperactivity and the isometric endurance time of the masseter muscle, during which period severe muscle pains were present, was on average 82 s. The electrical muscle activity of the threshold and endurance tests showed a curvilinear configuration (y =a + b log x), and it is suggested that progressive physiological, or peripheral, muscle fatigue accompanied the psychological, or central, endurance of tooth clenching.

Adult↗
PubMed1980

Some electromyographic parameters of experimental tooth clenching in adult human subjects.

Eight adult human subjects exercised maximal voluntary tooth clenching until fatigue and pains were experienced, and could no longer be endured, in the right masseter muscle. The integrated electrical activity in the right masseter muscle was determined as a ratio of the different isometric exercises, and it showed a consistent decrease from onset of fatigue, via onset of pains, to the endurance of pains, possibly because of progressive muscle fatigue. The relative muscle activity might have determined the perception of the moment of onset of fatigue in the masseter muscle, and the perception of the moment of muscle exhaustion, but not the perception of the moment of onset of muscle pains.

Adult↗