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Biomedical subjects

L V Christensen

Publications and source records attributed to L V Christensen.

At least 19 recordsLinked to original sources
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↗
PubMed1991

An electrognathographic study of aspects of 'deprogramming' of human jaw muscles.

Three-dimensional electrognathography of an incisor point was used to detect peripheral correlates of deprogramming of the jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 10-15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied mandibular displacements were those that occurred during voluntary elevation of the mandible from the postural to the intercuspal position. Use of the leaf gauge did not affect the displacement patterns. Within a freeway space of about 0.2 mm3, the incisor point moved about 2 mm vertically, about 1 mm sagittally, and about 0.2 mm laterally.

Adult↗
PubMed1991

Postural contractile activities of human jaw muscles following use of an occlusal splint.

As induced by an occlusal splint over a period of 1 week, this study monitored surface electromyographic changes in the postural contractile activities of jaw elevator and depressor muscles in six healthy adults. The immediate effect of the occlusal splint was to increase the postural contractile activities of the suprahyoid muscles. All postural muscle activities showed wide-ranging biological variation, but the activities induced by the splint tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles.

Adult↗
PubMed1991

Activity index and isometric contraction velocity of human jaw muscles.

To determine the relative contribution of the masseter and anterior temporalis muscles to global isometric bite force, activity indices were constructed on the basis of the peak mean voltage (microV) and the integrated voltage (microV.s) of bipolar surface electromyograms obtained during brief maximum voluntary teeth clenching (MVC). The index that was based on integrated myoelectrical activity showed that the masseter muscle contributed the major part of the isometric MVC force. The index that was based on instantaneous peak myoelectrical activity also showed that activity in the masseter muscle predominated over that in the anterior temporalis muscle. In addition, the latter index showed a negative linear association with the initial (0-50% MVC) isometric contraction velocities of the masseter and anterior temporalis muscles. Both indices appear to be promising clinical diagnostic tools.

Action Potentials↗
PubMed1990

Observations in the time and frequency domains of surface electromyograms of experimental brief teeth clenching in man.

Maximum voluntary teeth clenching was performed for about 1 s to study the interactions between subjective sensory-motor events and changes in the time and frequency domains of surface electromyograms of the masseter and anterior temporalis muscle. Isometric jaw muscle contractions were examined for their speeds of contraction, the total energy content and median frequency of their power density spectra, and for the specific rate of change and the efficiency of their voluntary and involuntary activation efforts. The observations suggested that, in general, brief maximum isometric contractions were not preprogrammed, but rather were regulated by a subconscious proprioceptive feedback mechanism; the mechanism, possibly a transcortical loop, appeared to have a low gain and to be based on recruitment/decruitment of motor units.

Bite Force↗
PubMed1990

An electromyographic study of aspects of 'deprogramming' of human jaw muscles.

Surface electromyograms from the right and left masseter and anterior temporalis muscles were used to detect peripheral correlates of deprogramming, also known as programming and reprogramming, of jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied contractile activities were those of postural activity (subconscious, semi-isometric, minimal activity) and intercuspal teeth clenching (conscious, isometric, maximal activity). Use of the leaf gauge did not affect normalized postural activity (about 4%), the duration (about 900 ms) and static work efforts of clenching (about 1200 microV.s), the time to peak mean voltage of clenching (about 400 ms), and the peak mean voltage of clenching (about 300 microV). Activity and asymmetry indices showed that the studied motor innervation patterns were not changed by the leaf gauge.

Adult↗
PubMed1989

Relationship of the maxillary canines to the incisive papilla.

The positioning of denture teeth in a completely edentulous patient is dependent on many factors. Anatomic landmarks are frequently valuable in complete denture fabrication. The topography of the palatal soft tissue in relationship to tooth position in dentate patients may be an aid in the placement of denture teeth. By using casts formed from irreversible hydrocolloid impressions, 50 subjects were examined to determine the orthographic distance from the posterior of the incisive papilla to a line intersecting the distal contact points of the maxillary canines. In 92% of subjects the posterior point of the incisive papilla was approximately 3 mm anterior to the line between the distal points of the canines. Neither gender, age, nor maxillary tooth arch form affected this distance.

Adolescent↗