Search PubMed⌕ Search

Biomedical subjects

G T Clark

Publications and source records attributed to G T Clark.

At least 73 records · Page 4Linked to original sources
PubMed1993

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels.

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

Adult↗
PubMed1993

Use of sodium hyaluronate in treating temporomandibular joint disorders: a randomized, double-blind, placebo-controlled clinical trial.

This study assessed the efficacy of high-molecular-weight sodium hyaluronate as a treatment for certain intracapsular temporomandibular joint (TMJ) disorders. One hundred twenty-one patients were studied at three test sites using a randomized, double-blind, placebo-controlled experimental design. Patients were selected on the basis of 1) confirmed diagnosis of either degenerative joint disease (DJD), reducing displaced disc (DDR), or nonreducing displaced disc (DDN); 2) nonresponsiveness to nonsurgical therapies; and 3) severe dysfunction as established by the Helkimo indices (HI), visual analog scales (VASs), and physical measurements of joint movement and joint noise (arthrophonometry [APM]). Subjects received a unilateral upper joint space injection of either 1) 1% sodium hyaluronate in physiologic saline (MedChem Products, Woburn, MA) or 2) USP physiologic saline. Clinical evaluations were performed using HI, VAS, and APM at weekly intervals for the first month and then at monthly intervals up to 6 months postinjection. Statistical analyses for both categorical and continuous variables were performed for each diagnostic category at each examination interval. For DJD, no difference in outcome was seen between treatment groups. For DDN, significant between-group differences were seen through 1 month; however, beyond this time point, the number of DDN patients was insufficient to draw meaningful conclusions concerning efficacy. For DDR, statistically significant within-group and between-group improvement in all three measures (HI, VAS, APM) was seen for the hyaluronate group compared to the saline group throughout the 6-month test period. At the month-2 and month-3 examination intervals, twice as many patients treated with hyaluronate (90%) showed improvement compared to patients given placebo. Further, only 3% of patients with DDR who were treated with hyaluronate relapsed compared with 31% of patients with DDR given placebo.

Adult↗
PubMed1993

Reproducibility of examiner performance for muscle and joint palpation in the temporomandibular system following training and calibration.

The purpose of this investigation was to assess examiner ability to consistently perform specific tasks related to muscle and joint palpation. Four trained and calibrated examiners were asked 1) to deliver index finger pressures within a high (1.5-2.1 kg) and low (0.5-1.1 kg) target pressure range and 2) to precisely locate one joint palpation and four muscle sites. After passing a calibration test, the performance of the examiners was monitored during the course of a replicability study assessing the consistency of clinical findings during repeated exams for TM disorders. (1) Index finger pressure was regularly tested over a 3-month period with a hand held pressure algometer, and the reading of each trial was recorded. Data analysis showed a high proportion of trials within the pressure range (overall 89.5%). Examiner performance across target range of pressures was statistically different for success rate and mean pressure delivered. The differences in the mean finger pressure delivered by each examiner (intraexaminer variation) was low and varied from 0.12 to 0.22 kg/cm2 for the desired range of pressures. (2) Paired examiners were asked to independently and sequentially mark palpation sites over the forehead, superficial and deep masseter, anterior temporalis, and lateral capsule of the temporomandibular joint. Replicability of site locations was assessed by measuring, with a boley gauge, the distance between sites selected by the paired examiners. Except for the superficial masseter and the anterior temporalis, the paired examiners selected palpation sites within a distance of 7 mm more than 85% of the time.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Effect of anterior mandibular positioning on obstructive sleep apnea.

This prospective case report series utilized an anterior mandibular positioning (AMP) device on obstructive sleep apnea (OSA) patients and evaluated the changes in the respiratory disturbance index (RDI) and subjective overall satisfaction with the treatment. The RDI was based on all-night polysomnographic studies performed before and after approximately 4 months of appliance use. Overall satisfaction with the treatment was rated using a Likert scale (0 to 10) after 6, 18, and 36 months of AMP device use. Although only 15 of the 24 subjects agreed to undergo post-appliance polysomnograms, 14 of the 15 subjects showed a clear decrease in the RDI. The effect on the other subjects is unknown, but even if the 9 subjects without polysomnograms had no change in the RDI from the AMP device, a minimum rate of 58% of the subjects (14 of 24) would have substantially improved the RDI at the 3-month time point. Of the 24 subjects, 2 subjects claimed no immediate benefit and stopped using the device, 4 subjects were lost to followup, 1 subject lost weight and stopped using the device, 1 subject had mandibular advancement surgery after using the appliance for a period of time, and 3 stopped using the appliance because of persistent temporomandibular pain problems. The remaining 12 of the 23 (52%) original subjects were still using the appliance successfully at 36 months. One subject died of non-apnea-related causes before the 18-month follow-up time point. The 16 subjects who responded at 36 months reported a mean overall satisfaction with treatment of 6.9 +/- 3.3 on a scale of 10.

Adult↗
PubMed1993

Co-activation of sternocleidomastoid muscles during maximum clenching.

In an attempt to determine the degree of co-activation present in selected cervical muscles during clenching, we instructed 12 male subjects to produce four brief maximum voluntary contraction (MVC) efforts (clenching) in a position of maximum intercuspation. Surface EMG activity was recorded bilaterally from the masseter and sternocleidomastoid (SCM) muscles. The contraction level for the SCM during clenching was reported as a percentage of the SCM's maximum activity achieved during maximum neck flexion against resistance. All EMG signals for the masseter and SCM were converted to a true RMS voltage signal and digitized at a 100-Hz sampling rate. Mean peak EMG voltage levels were determined for the activity recorded during each brief MVC task. All subjects demonstrated co-activation of the SCM during strong abrupt clenching efforts. The mean levels (+/- S.D.) of SCM activity were 11.8 +/- 9.6% (right) and 14.2 +/- 9.4% (left) of the MVC capacity. Fifty percent of masseter activity was required to achieve 5% activity of the SCM bilaterally, and there was a progressive development of the SCM co-activation which paralleled the masseter activation.

Adult↗
PubMed1993

Sternocleidomastoid muscle inhibition induced by trigeminal stimulation.

Among numerous reports of anatomical and functional coupling between the trigeminal and cervical systems is the demonstration that the sternocleidomastoid (SCM) muscles may become activated along with the masseter muscles during forceful abrupt biting maneuvers. Whether the co-activated SCM is also inhibited by stimuli that produce masseter inhibition is not known. This study evaluated the SCM for the presence of inhibition during mechanically-elicited (chin or forehead tap) and electrically-elicited (anterior maxillary gingiva stimulation) inhibition of the masseter muscle in ten healthy men. Surface EMG data were recorded bilaterally from the masseter and SCM muscles. The data for each muscle were converted to ratios of the pre-stimulus maximum voluntary contraction activity for each subject and averaged across subjects. Means of these percentages were determined at several defined pre- and post-stimulus intervals. The results indicate that masseter inhibition was clearly elicited by the electrical and both forms of mechanical stimulation. SCM co-inhibition could be evoked by electrical and chin tap stimulation but not by forehead tap. The responses to these stimuli varied among subjects, from trial to trial, and within subjects depending on the experimental condition. The fact that it was possible for this co-inhibition to be evoked is presented as further indication of the functional coupling of the trigeminal and cervical systems.

Adult↗
PubMed1993

Diagnosis of intracapsular pathology associated with temporomandibular joint disorders.

The clinical diagnosis of a Temporomandibular Disorder (TMD) has traditionally been based on data gathered by means of a medical history and physical examination. The most common signs and symptoms associated with TMD are reduced jaw opening, pain and elevated tenderness in the muscles of mastication, pain and elevated temporomandibular joint (TMJ) tenderness, and TMJ noises upon movement. These signs and symptoms are routinely detectable by a skilled clinician upon examination. Unfortunately, the clinical problem described globally as a TMD has several different and overlapping patho-physiologic disease processes, and a traditional clinical examination does not provide highly tissue-specific pathologic information. Were it readily available, such information would be greatly useful, since logical and accurate treatment planning requires that each disease process be correctly identified. One important challenge for researchers interested in TMD will be the careful definition and subsequent validation of diagnostic methods which identify the relevant ongoing pathological disease process. On such research area, which has great promise, is the establishment of a valid diagnostic technique for intracapsular pathologies unique to TMD patients. This paper provides a critical review and discussion of the diagnostic validity of TMJ arthroscopy and other related methods of identifying intracapsular pathologies associated with TMD.

Arthroscopy↗
PubMed1993

The utility and validity of current diagnostic procedures for defining temporomandibular disorder patients.

This paper describes the evolution of different concepts of classifying and defining Temporomandibular Disorders (TMD) for both clinical and research settings. The literature is reviewed with respect to the utility and validity of the different questionnaire and examination procedures that have been used to assess TMD patients. The presented view is that many of these procedures have not been validated, that there is a lack of standardization in the use of the procedures themselves, and that an ideal method of classifying this broad group of patients into better-defined subgroups has not yet been developed. More standardized and better-defined research by trained and calibrated researchers is needed worldwide to elucidate these subgroups so that a better and widely agreed upon research classification system can be developed for widespread use. It also seems clear that as research requirements for defining TMD patient subgroups become more stringent over time, it may not be practical for the clinician to implement them on a day-to-day basis in his or her practice. As such, a practical utilitarian definition of the common subtype of TMD patients is also needed which parallels any research grouping, so that data from research are valuable and generalizable to the practicing clinician.

Facial Pain↗
PubMed1993

Oral motor disorders in humans.

Motor disorders affecting the orofacial musculature include bruxism, chronic orofacial muscle pain affecting the jaw and neck muscles and the involuntary waking period disorders such as orofacial dyskinesia, oral mandibular dystonia, tremor and others. Research at UCLA has touched these and many other areas. Current results have indicated the usefulness of contingent afferent electrical stimulation of the lip to control bruxism; provided information regarding the fatigue, endurance and recovery faculties of the protrusive jaw muscles; explored the issue of chronic muscle hyperactivity inducing headache pain; and worked with botulin toxin as a method to treat orofacial dystonia and dyskinesia.

Bruxism↗
PubMed1993

Screening for psychological problems in temporomandibular disorder patients.

Research efforts have been directed to determine whether temporomandibular disorder (TMD) patients have psychological problems and whether these factors influence treatment outcome. Because there is no consensus about the best way to quickly assess psychological problems in TMD patients, this study was designed to evaluate a simple method for identifying psychological factors that may need to be addressed as part of a comprehensive treatment program. This method involved having TMD patients systematically rate themselves, using a brief screening questionnaire, for the presence or absence of psychological problems. These ratings were then compared to results from extensive psychological testing. Sensitivity, specificity, and ordinal rank-based association model analyses showed moderate to strong associations between patients' ratings and the corresponding psychometric measures. These results provide evidence that the brief self-ratings of psychological factors utilized in this study may be a useful first step to screening for psychological difficulties in TMD patients.

Adult↗
PubMed1992

Effect of altered occlusal guidance on lateral border movement of the mandible.

The purpose of this study was to evaluate the effects of a change in the lateral anterior guidance pathway on the lateral border movement pathway of mandible. The results showed that altered occlusal guidance reproducibly and reversibly changed (increased) the lateral border movement area in two subjects who had unilaterally restricted lateral border movements.

Adaptation, Physiological↗
PubMed1992

Accuracy testing of three-dimensional digitizing systems.

An accuracy test designed as a standard for digital occlusal wear measurement devices was applied to such a device designed by the authors. The test was used for quantitative determination of measurement error for a given angle of tangential contact with the inclined planes of the surface being measured. Using known dimensions of the digitizer contact tip and of a precision steel sphere, we determined trigonometrically the error in the Z-axis measurement due to the slope of any point on the surface of the sphere. These values were used for a point-by-point correction of data obtained from actual digitization of the sphere. The corrected values would equal zero if no mechanical source of error existed. These values, then, quantitatively indicated the accuracy (in microns) of the device as a function of the slope of the measurement point. The results indicated a linear relationship between surface slope angle and measurement error for the device tested.

Dental Occlusion↗
PubMed1992

Predicting response to treatment for temporomandibular disorders.

This study examined whether pretreatment psychological characteristics of temporomandibular disorder (TMD) patients were related to the response to treatment in a TMD and facial pain clinic. The care provided to patients was either an evaluation only or an evaluation followed by a course of physical medicine/dental procedures (occlusal appliances, physical therapy, anti-inflammatory medications). Outcomes were assessed in terms of pain levels, jaw function difficulties, and satisfaction with care at 6 months posttreatment by phone and 16 months posttreatment by mail. There were no pretreatment differences between treated and evaluated patients except for higher pretreatment jaw function difficulty scores in the evaluated only patients. Factor analysis of pretreatment scores revealed distrust, pain, anxiety, and somatization. Somatization predicted follow-up pain levels at both follow-ups in the treated patients but only at the 16-month follow-up in the evaluated only patients. Pretreatment pain levels predicted posttreatment pain in both groups only at the 6-month follow-up. Posttreatment jaw function difficulties were related inconsistently to the pretreatment dimensions, while satisfaction was not predicted by pretreatment scores except for a possible connection between this outcome and distrust. It is concluded that an overconcern about bodily functioning appears to decrease the likelihood that patients obtain pain relief from physical medicine care.

Adult↗
PubMed1991

The relationship between lateral border movements of the mandible and the determinants of occlusion.

Border movements of the mandible were measured with a jaw movement analyzer in nine subjects. This instrument records movement with 6 degrees of freedom and has the ability to accurately and linearly record the full range of jaw movement. The result of this study showed a relationship between the presence of balancing-side molar contacts and restricted contralateral jaw border movements. This restriction is probably due to aberrant external pterygoid muscle activity.

Adult↗
PubMed1991

Arthroscopic treatment of temporomandibular joint locking resulting from disc derangement: two-year results.

This article reports 2-year postarthroscopic surgical treatment data for 18 subjects (17 female and 1 male) who had a diagnosis of restricted mandibular movement due to an internal derangement of the temporomandibular joint (TMJ). These subjects had been treated by an average of 2.1 +/- 1.1 doctors for their TMJ problem before seeing the surgeon for arthroscopic treatment. The subjects' mean pain score at the final time point (21 to 30 months after surgery) was decreased by 57% in usual pain intensity. Jaw function showed an average improvement of 67%. These subjects also showed a 13-mm mean increase in their maximum active opening ability at the 2-year postsurgical time point. Slight to definite clicking noises were present presurgically in 11 of 18 patients, and similar joint noises were reported in 14 of 18 patients postsurgically. The mean overall improvement was rated as 8.18 +/- 2.4, with 10 the highest possible rating. One subject rated her improvement as 0, two subjects rated their improvement as 6 out of 10. No significant morbidity was reported by the subjects as a result of their surgery.

Adolescent↗
PubMed1991

Etiologic theory and the prevention of temporomandibular disorders.

Over the last 75 years, a variety of etiologic factors has been suggested as the cause of pain and dysfunction in the temporomandibular system. The earliest and still-popular etiologic theory proposed that temporomandibular disorders are induced by abnormal structure, usually described as a malocclusion of the teeth or jaws. The fact that this theory was based on mechanical concepts, ignored biologic diversity, and had limited factual experimental evidence to support it as well as extensive evidence in opposition did not seem to matter to its proponents. In the late 1960's and early 1970's, the structural occlusal model for TM Disorders was challenged and has yielded ground to a more multifactorial model of TMD causation. Other etiologic factors for TM disorders--such as anatomical susceptibility of TM tissues to trauma, polyarthritic diseases, joint laxity, repetitive parafunctional behaviors, and stress-related muscle dysfunction--need to be recognized and quantified. Unfortunately, many practicing dentists demonstrate a very poor understanding of and often fail to recognize these etiologic factors as agents that produce TM disorders. This failure is largely due to the fact that the dental profession has spent the last 90 years dealing with a variety of misconceptions about the etiology of temporomandibular disorders. In the 1990's, one of the more formidable challenges we face is acquiring the ability to segregate and define validly the specific TM Disorder of concern and then correctly identify and measure the specific etiologic factors that produce it. Until these problems are solved, it is unlikely that we will be able to prevent disease of the TM apparatus.

Dental Occlusion, Traumatic↗