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Biomedical subjects

L V Christensen

Publications and source records attributed to L V Christensen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Experimental occlusal interferences. Part V. Mandibular rotations versus hemimandibular translations.

Frontal plane mandibular rotations and corresponding hemimandibular translations were studied in vitro by using direct observations of a human cadaver mandible and in vivo by using the indirect observations of rotational electrognathography. A comparison between the two methods showed that rotational electrognathography erred in measuring the clinically relevant hemimandibular translations resulting from mandibular rotations having a unilateral molar point (simulated occlusal interference) as the pivot of frontal plane torque. In vitro frontal plane rotations about a unilateral mandibular molar tooth (simulated occlusal interference) suggested that the resulting hemimandibular upward translations of the lateral portion of the mandibular condyle, contralateral to the molar tooth, would cause considerable compressive loading of the temporomandibular joint disc.

Adult↗
PubMed1995

Experimental occlusal interferences. Part I. A review.

This review shows that experimental occlusal interferences (prematurities) may cause changes in the myoelectric contraction patterns of the human jaw muscles, and changes in the translatory motion patterns of the human mandible. However, it has not been unequivocally established that the observed changes have specific long-term detrimental effects. On the other hand, it is apparent that experimental occlusal interferences are associated with short-term clinical symptoms and signs, such as jaw muscle fatigue and pains, headaches, pains and clickings in the temporomandibular joints. This review suggests that new paradigms involving experimental occlusal interferences should be introduced.

Dental Occlusion, Traumatic↗
PubMed1995

Experimental occlusal interferences. Part II. Masseteric EMG responses to an intercuspal interference.

In 12 subjects, a rigid unilateral intercuspal interference (minimum mean height of 0.24 mm) was placed on either the right or left mandibular second premolar and first molar (sagittal physiological equilibrium point of the hemimandibular dental arch). During brisk and forceful clenching on the interference, bipolar surface electromyograms were obtained from the right and left masseter muscles. On the side opposite the interference, myoelectric clenching activity was significantly reduced. Correlation analyses showed that the interference elicited a non-linear (complex) co-ordination of the amplitude, but not the duration, of bilateral masseteric clenching activity, i.e. frequently there was significant motor facilitation on the side of the interference, and significant motor inhibition on the side opposite the interference. Theoretical considerations predicted that brief clenching on the interference would easily lead to frontal plane rotatory motions of the mandible which, indeed, occurred clinically.

Acrylic Resins↗
PubMed1995

Effects of electrode movements on masseteric electromyograms of teeth clenching in humans.

In six healthy subjects, the integrated electromyographic (IEMG) activity of the right masseter muscle was recorded during 10 s of maximum voluntary teeth clenching, without and with manual movements (at a rate of 1.6 Hz, with a force of approximately 3N) of the bipolar surface electrodes affixed to the cheek. All IEMG recordings were undertaken at discrimination thresholds of 1 microV and 30 microV. Electrode movements were the likely source of some distortion (artefact) of the IEMG readings. An increase in the discrimination threshold (30 microV vs. 1 microV) seemed to decrease the artefactual effects of electrode movements, possibly because the movements exerted their major distorting effects on the smaller (low voltages) masseteric motor units.

Adult↗
PubMed1993

Pressurized infusion of sodium hyaluronate for closed lock of the temporomandibular joint. Part I: A case study.

Patients with temporomandibular joint disorders (TMD) report a myriad of problems including headaches, facial pain, limited mouth opening capacity, and clicking and/or grating sounds from the temporomandibular joints. Although conservative therapy with an occlusal splint can bring relief for many of these patients, a small number of subjects must be treated by means of surgical procedures. Direct injections of either air or fluids (saline, local anesthetic, corticosteroid, hyaluronate) into the superior and/or inferior temporomandibular joint (TMJ) cavities have gained popularity. The injection of a local anesthetic and hyaluronic acid can provide relief for patients with persistent, painful nontranslatory closed-lock conditions of the TMJs. As documented through objective electronic and computer-enhanced measurements, this case report describes the effect of sodium hyaluronate on a closed lock condition of the TMJ. This case report explains the methodology employed for a larger group of closed lock patients treated and monitored for over one year. The results of that larger group will be reported at a later time after long-term efficacy is confirmed.

Adult↗
PubMed1992

Temporomandibular joint vibration analysis in a sample of non-patients.

In a sample of 20 non-patients, 60% of the subjects had an absence of subjective temporomandibular joint (TMJ) complaints (noises/sounds) that agreed with objective joint vibration analyses (electrovibratography). Among the remaining 40% of subjects, only 50% of the examined joints showed agreement between subjective and objective findings. Subjects appeared to be unable to reliably detect "weak" (early) symptoms of TMJ dysfunction but were able to reliably detect "strong" (late) symptoms of TMJ dysfunction and possibly disease. As measured through active protrusion and laterotrusion of the mandible, the guidance angles of the anterior teeth could not explain the absence and presence of TMJ vibrations.

Adult↗
PubMed1992

Surface electromyographic estimates of recruitment/rate coding of masseteric motor units.

Surface electromyographic (EMG) recordings were obtained from the masseter muscles in healthy subjects performing brisk maximum voluntary teeth clenching (MVC) for about 1 s. During the onset (0-600 ms) of ballistic MVC activity, the peak amplitude of the EMG interference patterns showed a consistent and significant increase, on examination for 0-200 ms, 200-400 ms, and 400-600 ms of MVC activity. The peak (maximum) and median (centroid) frequencies of power spectrum density functions of the raw surface EMGs (interference patterns) showed an absence of consistent and significant changes during 0-600 ms of ballistic MVC activity. However, the estimated total energy contents (peak amplitude x peak frequency) of the surface interference patterns showed a consistent and significant increase from 0 to 600 ms of ballistic MVC activity, and this was interpreted as global recruitment/rate coding of masseteric motor units.

Adult↗
PubMed1992

Reproducibility of temporomandibular joint vibrations (electrovibratography).

Surface electrovibratographic (EVG) recordings were obtained from the temporomandibular joints (TMJ) of clinically normal subjects (absence of TMJ sounds) and clinically abnormal subjects (presence of TMJ sounds). As examined through single factor analyses of variance and coefficients of intraclass correlation, the EVG recordings showed excellent reproducibility. The analyses showed also that, in comparison with clinically normal TMJs, the vibrations of clinically abnormal TMJs had higher median (+79%) and peak (+137%) frequencies, higher peak amplitudes (+740%), and higher intensities as expressed through the estimated total energy contents (+1843%) and the integrals (+1215%) of power spectrum density functions.

Adult↗
PubMed1992

Physics and the sounds produced by the temporomandibular joints. Part I.

In clinical dentistry, the sounds (clicking) and noises (grating) produced by the temporomandibular joints (TMJ) usually signify dysfunction or disease of the mandibular locomotor system. In an attempt to provide guidance to the general practitioner, this article discusses some pertinent parameters defining the physics of airborne and solid-borne vibrations.

Biophysical Phenomena↗
PubMed1992

Physics and the sounds produced by the temporomandibular joints. Part II.

In clinical dentistry, the solidborne vibrations (tissue pressure waves) produced by the temporomandibular joints (TMJ) may signify dysfunction or disease of the mandibular locomotor system. This article discusses aspects of the applied mathematics and electronic recording of solidborne vibrations of the TMJ (electrovibratography).

Adult↗
PubMed1992

Methodological observations on positive and negative work (teeth grinding) by human jaw muscles.

Through electrognathography and surface electromyography of the right and left masseter muscle (MM), this methodologic study examined the excentric (lengthening) and concentric (shortening) contractions of brief (2000 ms) voluntary teeth grinding performed through canine as well as group function of the opposing teeth. We inferred that the most anterior and superior portions of the right and left MM were lengthened and shortened by at least 4.23 mm (right MM) and 4.82 mm (left MM). For the negative work efforts (excentric contractions) of canine function, the tensions of the ipsilateral MM ranged from 10 to 20% MVC and those of the contralateral MM from 4 to 14% MVC. For the positive work efforts (concentric contractions) of canine function, the tensions of the ipsilateral MM ranged from 11 to 44% MVC and those of the contralateral MM from 20 to 41% MVC. A comparison between canine and group function showed that the negative as well as positive work efforts of group function exceeded those of canine function.

Adult↗
PubMed1992

Preliminary observations on oral blood flow.

Using laser Doppler flowmetry (LDF), the blood microcirculation of the masseter muscle was studied in one healthy male subject performing clenching and grinding of the teeth. LDF suggested that blood flow was increased during clenching, and that it did not change appreciably during grinding. In one female patient (acute pain from myofibrostic lesion in masseter muscle), LDF suggested that flow within the lesion was increased during rest (postural position). In three healthy adults, subjected to simulated traumatic occlusion of the incisors, LDF suggested an absence of consistent changes in pulpal blood flow.

Adult↗
PubMed1992

A transcranial radiographic examination of the temporal portion of the temporomandibular joint.

The temporomandibular joints of 20 human cadaver heads were examined by means of photography (gross anatomic images) and radiography (lateral oblique transcranial images), using the angle created by a line parallel to the Frankfurt horizontal and a line coinciding with the posterior slope of the most lateral (outermost) portion of the articular tubercle. This lateral eminence angle, made visible through an attached metal wire and a straight stick pin and pertaining to the outermost (zygomatic) portion of the eminentia, was about 45 degrees on both enlarged photographs and enlarged radiographs. There were no significant differences between the photographic and radiographic lateral eminence angles on the right and left sides. A more medially placed angle, yet pertaining to the lateral - and supposedly functional (protrusion) - portion of the glenoid fossa, was about 56 degrees on the right side and 51 degrees on the left side of the radiographic images. There were significant differences between the ipsilateral radiographic lateral and medial eminence angles. A separate decision-making analysis concluded that lateral oblique transcranial radiography is an effective, reliable, and inexpensive method for detection of bony changes in the lateral portions of the temporomandibular joints.

Cartilage, Articular↗
PubMed1991

An evaluation of temporomandibular joints and jaw muscles after orthodontic treatment involving premolar extractions.

Experimental subjects (n = 29) were patients who had undergone orthodontic treatment in combination with extraction of maxillary or mandibular premolar teeth, or both. Control subjects (n = 29) were healthy dental students with no orthodontic or extraction experience. Sagittal (corrected axis) tomograms of the TMJs were used to determine the narrowest linear distances between the anterior and posterior outlines of the TMJ condyle and the TMJ fossa, expressed as the joint space ratio. There were no significant (p greater than 0.05) differences between the control and experimental ratios. Bipolar surface electromyograms of the masseter and anterior temporalis muscles were used to determine the isometric contraction velocities of these muscles until 50% and 100% voluntary isometric contraction effort (teeth clenching) was achieved. There were no significant (p greater than 0.05) differences between the control and experimental subjects. Electromyograms were also used to determine the relative contribution of the masseter and anterior temporalis muscles to the bite force developed during brief maximum voluntary tooth clenching, expressed as the activity index. There were no significant (p greater than 0.05) differences between the control and experimental subjects.

Adolescent↗
PubMed1991

Observations on the motor control of brief teeth clenching in man.

Without artificial feedback control, maximum voluntary isometric contractions were performed for about 1 s by six subjects. Randomly selected surface electromyograms of the anterior temporalis and masseter muscles suggested that, in some cases, the motor control of the entire isometric contraction might have been preprogrammed through the phenomenon of anticipation. In the majority of cases, the control of the initial contraction phase might have been preprogrammed, followed by a phase of servo-controlled motor activity. As a functional basis for the servo-control of isometric force generation, it was suggested that compartmentalized 'extrafusal and intrafusal motor units' were recruited and decruited in an orderly manner, and periods of alpha-motor inhibition were interpreted as signs of switching from one control scheme to another, possibly via a transcortical loop.

Adult↗
PubMed1991

Stimulus-response latencies of two instruments delivering transcutaneous electrical neuromuscular stimulation (TENS).

Stimulus-response latencies of low-frequency transcutaneous electrical neuromuscular stimulation (TENS) were studied in 15 healthy subjects, applying the two different pulse configurations delivered by the Biotens and the Myomonitor instruments. Latencies, in milliseconds, were determined on bipolar raw surface electromyograms (EMG) of the suprahyoid muscles, using the skin surface over the sigmoid notches of the mandible as the site of stimulation. Stimulus-response times were measured from the onset of the stimulus artefact to the first response peak on EMG, and their mean values showed ranges of 3.79-4.49 ms for Biotens and 5.10-5.34 ms for Myomonitor. It was concluded that low-frequency TENS caused direct stimulation of motor nerves, and that the timing of the contraction response was not affected by altered electrode placement, lead-wire reversal or unbalanced (right/left) stimulation.

Adult↗