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Biomedical subjects

G T Clark

Publications and source records attributed to G T Clark.

At least 37 records · Page 2Linked to original sources
PubMed2000

Treating obstructive sleep apnea and snoring: assessment of an anterior mandibular positioning device.

BACKGROUND: Dental devices have been used to help manage snoring and obstructive sleep apnea, or OSA. This article reports on patients' compliance with and complications of long-term use of an anterior mandibular positioning, or AMP, device. METHODS: The device used was a custom-made, two-piece, full-coverage, adjustable acrylic appliance, connected with Herbst attachments. The appliance was used nightly and advanced the mandible by 75 percent of the patient's maximum protrusive distance. Patients were telephoned to determine whether they were still using the AMP device. If not, they were asked when and why they stopped using it. The study sample included 65 consecutive patients with mild-to-moderate obstructive sleep apnea and snoring. RESULTS: Long-term use (three years or more) of the AMP device in these patients was 51 percent (27 of 53 patients). Of the 53 responding patients, 40 percent reported jaw/facial muscle pain, 40 percent had occlusal changes, 38 percent reported tooth pain, 30 percent reported jaw joint pain and 30 percent experienced xerostomia. Of the 27 long-term AMP users, 22 rated themselves as being very satisfied and four as somewhat satisfied; one was neither satisfied nor dissatisfied with the appliance. CONCLUSIONS: It was determined that with use of the AMP device, 40 percent of patients will develop some minor complications of jaw, mouth and/or tooth pain, and approximately 26 percent of long-term users might experience a painless but irreversible change in their occlusion. Annual follow-up office visits with the dentist appear necessary for early detection of these changes. CLINICAL IMPLICATIONS: Patients with mild-to-moderate OSA who receive a two-piece, adjustable AMP device should be informed that 50 percent of patients quit using the device in a three-year period and some will experience shifts in their occlusion.

Adult↗
PubMed2000

Teledentistry: what is it now, and what will it be tomorrow?

A few years ago, teledentistry involved calling an expert on the telephone for advice. Now it involves consulting experts using the Internet. This article explains the basic ideas underlying teledentistry. It involves the local dentist digitizing and electronically transmitting drawings, diagrams, photographs, and X-rays to a specialist. Along with these data, the dentist will most likely need to fill out a standard consult form from the specialist's Web site. In return, the specialist will develop and return a confidential consultation report to the dentist or physician requesting help. For this service, a time-based fee will be paid to the expert. Unfortunately, it is likely that some doctors will use the Internet to set up and seek direct patient contact, thus becoming "cyberdentists." In most cases, cyberdentistry will not be in the best interests of the public. However, teledentistry should not only be a practice builder for the local dentist, but also has the potential for helping dentists better serve their patients while increasing their own knowledge.

Clinical Competence↗
PubMed1999

Effect of intravenous infusion of an alpha-adrenergic blocking agent on the haemodynamic changes in human masseter muscle induced by cold pressor stimulation.

This study evaluated the effect of intravenous infusion of a non-selective alpha-adrenergic blocking agent on masseter muscle haemodynamics induced by 4 degrees C cold pressor stimulation (CPS) of the right foot and ankle, which reportedly evokes a rapidly increasing sympathetic nerve activity in human skeletal muscle. Nine healthy non-smoking males (mean age 23.7+/-2.1 year) with no history of chronic muscle pain or migraine participated. The haemoglobin (Hb) concentration in the right masseter was continuously recorded by non-invasive, near-infrared spectroscopy. Heart rate and blood pressure were also recorded. The experiment involved the following sequence: (1) a placebo (physiological saline) with a CPS trial; (2) a 30-sec maximal voluntary clenching (MVC)-only trial; and (3) an alpha-adrenergic blocking agent with a CPS trial. The saline and drug trials each involved continuous recording for 1 min before, 2 min during and 5 min after the CPS. Physiological saline (20 ml) or phentolamine mesylate (20 ml) were infused at the rate of 2 ml/min. This infusion was begun 15 min before baseline recording and participants were not aware which solution (saline or phentolamine) was being infused. For the MVC trial, each participant performed a 30-sec MVC of his jaw-closing muscles followed by a 15-min rest between each trial. The individual Hb data were adjusted so that the baseline at the beginning of the experiment was equal to zero and all data were normalized as a percentage of the individual's highest absolute Hb change seen after the MVC. The mean baseline Hb concentrations 1 min before CPS were significantly higher in the alpha-blocker trial (83.6%) than in the placebo saline trial (P < 0.001). The change in mean Hb concentration from baseline during CPS in the alpha-blocker trial was significantly less than in the placebo trial (P = 0.006). Mean heart rate before CPS was also significantly higher in the alpha-blocker trial (85.2 beats/min) than in the placebo trial (69.6 beats/min) (P < 0.001). There were no significant differences in the mean systolic and diastolic blood pressures between the placebo and alpha-blocker trials in any time period. The results suggest that non-selective alpha-adrenoceptor blockade increases the blood volume in the masseter muscle. This change might be due to a combination of peripheral vasodilation and an increase in cardiac output.

Adrenergic alpha-Antagonists↗
PubMed1999

Effect of intravenous infusion of a beta-adrenergic blocking agent on the haemodynamic changes in human masseter muscle induced by cold-pressor stimulation.

Eight healthy non-smoking males (mean age: 24.1 +/- 1.1 years) without any history of chronic muscle pain and migraine participated in this study. Haemoglobin (Hb) and oxygen (O2) saturation in the right masseter muscle were continuously recorded with a non-invasive near-infrared spectroscopic device. Heart rate and blood pressure were also recorded. The experiment had three phases: a placebo drug (physiological saline) with cold-pressor trial, a 30-sec maximal voluntary clenching (MVC) trial, and a propranolol with cold-pressor trial. The saline and drug trials each involved continuous recording for 1 min before, 2 min during and 5 min after the cold-pressor stimulation (4 degrees C). Physiological saline (20 ml) or propranolol hydrochloride (20 ml) were infused at the rate of 2 ml/min. This infusion was begun 20 min before the baseline recording and participants did not know which solution (saline or propranolol) was being infused. For the MVC trial, each participant was asked to perform a 30-sec clench of their jaw-closing muscles. There was a rest period of 15 min between each trial. The individual Hb and O2 data were normalized so that the baseline at the beginning of the experiment was equal to zero, and the Hb and O2 data were normalized as a percentage of the individual's own highest absolute Hb and O2 after and during the MVC, respectively. The results showed that the mean baseline Hb 1 min before cold-pressor stimulation was significantly lower in the beta-blocker trial than in the placebo trial (p = 0.035). The mean change in Hb from baseline during cold-pressor stimulation in the beta-blocker trial was also significantly less than in the placebo trial (p = 0.035). The mean Hb rebound change after the cold-pressor stimulation in the beta-blocker trial was significantly higher than in the placebo trial, and no significant heart-rate differences were observed in the period after cold-pressor stimulation. Overall, the mean heart rate before and during that stimulation was significantly lower in the beta-blocker trial than the placebo trial (p < 0.001). There was no significant mean blood-pressure difference between placebo and beta-blocker trials at any time. These results suggest that beta-adrenoceptor blocking decreases the blood volume in the resting masseter, suppresses the incremental blood-volume change during cold-pressor stimulation, and discloses a hidden vasoconstrictive effect after that stimulation.

Adrenergic beta-Antagonists↗
PubMed1999

Haemodynamic changes in human masseter and temporalis muscles induced by different levels of isometric contraction.

This study evaluated the influence of low contraction forces on intramuscular haemodynamics in human masseter and temporalis using near-infrared tissue spectroscopy. This method allowed the intramuscular haemoglobin (Hb) to be assessed dynamically before, during and after a 5, 15, 25 and 100% maximum voluntary contraction (MVC). Twenty volunteers, 10 males and 10 females, without pain or dysfunction in the masticatory system were included in this study. Data were recorded for 30 s before, 30 s during and 5 min after the four sustained contraction tasks. The results showed that all four levels of voluntary contraction produced a clear haemodynamic response (during and after contraction) in both muscles. For analytical purposes, the maximum Hb achieved after 100% MVC was set equal to 1.00. In the masseter the mean peak Hb during the 5, 15, 25 and 100% MVC was 0.49, 0.92, 1.30 and 1.73 while after the contractions it was 0.50, 0.65, 0.78 and 1.00, respectively. In the temporalis the peak Hb during the contractions was 0.23, 0.36, 0.48 and 0.66 and after the contractions 0.32, 0.45, 0.56 and 1.00, respectively. Repeated-measures analysis of variance revealed a significant main effect for the different contraction levels both in the masseter (during contraction, p = 0.001; after contraction, p<0.001) and the temporalis (during contraction, p = 0.002; after contraction, p<0.001). These data suggest that low levels of contraction induce a clear haemodynamic response, even at 5% effort. When compared, the masseter and anterior temporalis showed clearly different patterns for the Hb signal during the contraction (p<0.001) as well as after it (p = 0.007). Specifically, the Hb during the contractions in the masseter appeared more stable than in the temporalis, which showed a strong return to baseline. Obviously the contracting masseter had a stronger and more sustained venous occlusion than the contracting temporalis. It is speculated that variation in architecture between the two muscles contributes to these differences in blood flow.

Adult↗
PubMed1999

Haemodynamic responses in chronically painful, human trapezius muscle to cold pressor stimulation.

The aim was to compare haemodynamic responses in trapezius muscles to cold pressor stimulation in individuals with localized trapezius myalgia and asymptomatic controls. Nine males with chronic localized pain in the trapezius (mean age, 23.2 years) and nine male controls (mean age, 24.6 years) who had no medical history of migraine, hypertension or sustained pain in the trapezius region were investigated. Two experimental (cold pressor and mock) trials were performed in a randomly assigned sequence. In the cold pressor trial the participant's left foot and ankle were immersed in 4 degrees C cold water for 2 min; the mock trial was done without that stimulus. Blood volume was continuously recorded 1 min before, 2 min during, and 5 min after cold pressor stimulation using near-infrared spectroscopy. Each participant's blood-volume data were baseline-corrected and submitted to statistical analysis. Results showed that the individuals with muscle pain exhibited a significantly lower mean blood volume than the controls during cold pressor stimulation (p = 0.0367). Upon withdrawal of that stimulation, the mean blood volume in both groups fell below the baseline. These results suggest that individuals with chronic regional trapezius myalgia have less capacity to vasodilate this muscle during cold pressor stimulation than those without such myalgia. It is not yet known if this difference in the haemodynamic response is a cause or an effect of the myalgia.

Adult↗
PubMed1999

Effect of cold pressor stimulation (4 degrees C) on human masseter muscle haemodynamics during and after sustained isometric contraction.

The effect of cold pressor (CP) stimulation and sustained isometric contraction on the blood volume of the right masseter muscle was examined in seven healthy males, who performed 1 min of isometric jaw clenching at 50% of their maximum voluntary contraction without, with and again without a 4 degrees C CP stimulation. Total haemoglobin was measured in the masseter before, during and after the contraction task using near-infrared spectroscopy. CP stimulation during the isometric contraction diminished the magnitude of the contraction-induced decrease of blood volume when compared to the trials without CP stimulation. However, in the immediate post-contraction period (while the CP stimulation was still in place), no increase in blood volume above the usual post-contraction hyperaemia was evident. Once the CP stimulation had been removed, there was a clear decrease (faster return to baseline) in the vasodilation occurring in the post-contraction period. This diminished period of vasodilation occurred in spite of the fact that the vascular resistance (blood pressure) and heart rate were still substantially elevated by the CP effect during this same period. These data suggest that the strong CP stimulation produced a biphasic response. First, there was an early-onset strong vasodilation (during CP), which was followed by a period of diminished vasodilation, suggesting that an active, but delayed, vasoconstrictive drive may be induced by the CP stimulus.

Adult↗
PubMed1999

Sixty-eight years of experimental occlusal interference studies: what have we learned?

STATEMENT OF PROBLEM: Understanding is needed regarding the effect that occlusal interferences have on the teeth, periodontium, and especially on jaw function. PURPOSE: This article summarizes research in which experimental occlusal interferences have been placed on the teeth of animals and human volunteers. MATERIAL AND METHODS: Data from 18 human and 10 animals studies were reviewed. Experimental occlusal interferences were grouped into those that alter intercuspal position and those contacting on lateral jaw movement only. The outcome of these interferences were analyzed according to their local pulpal-periodontal, jaw function, or bruxism effects. RESULTS: Experimental occlusal interferences in maximum intercuspation had a deleterious effect on periodontal and pulpal tissues of the affected tooth; sometimes this produces a disruption of smooth jaw function and occasionally jaw muscle pain and clicking. Experimental occlusal interferences that contact only in a lateral jaw movement are infrequently harmful to jaw function. Furthermore, no reliable evidence demonstrates that occlusal interferences can cause nocturnal bruxism, or stop it. CONCLUSION: Transient local tooth pain, loosening of the tooth, a slight change in postural muscle tension levels, chewing stroke patterns, and sometimes a clicking joint can be induced by an experimental occlusal interference. Because such findings are present in relatively asymptomatic patients, these data do not prove that occlusal interferences are causally related to a chronic jaw muscle pain or temporomandibular joint dysfunction problems.

Animals↗
PubMed1999

Cold pressor stimulation effect on hemodynamic changes following sustained isometric contraction in human jaw-closure muscles.

It is postulated that an altered adrenergic response pattern may be associated with chronic muscle pain states. To evaluate this hypothesis, one must fully understand the effect of an adrenergic activation on masticatory muscle blood flow under various conditions. This study evaluated the effect of a 12 degrees C cold pressor stimulation (a mild adrenergic activator), applied to the hand-forearm area, on intramuscular hemodynamics in the human masseter and temporalis muscles following a sustained isometric contraction. We assessed hemodynamics by measuring intramuscular hemoglobin concentration repeatedly, using a non-invasive near-infrared spectroscopy device. Measurements were taken before, during, and after a 30-second sustained 50% maximum voluntary contraction task. Fourteen healthy subjects, seven males and seven females, with no history of muscle pain in the masticatory system participated in this study. This protocol was repeated three times, but in the second trial, the cold pressor stimulation was applied to the subject during and for 5 min after the sustained contraction task. Repeated-measure analysis of variance performed on these data revealed that the peak hemoglobin concentration levels in the post-contraction recovery period were significantly reduced (between 13 and 14%) with cold pressor stimulation, both in the masseter (p < 0.001) and in the temporalis (p < 0.001) muscles. The results suggest that cold pressor stimulation produced a reduced intramuscular vasodilative response in these muscles during the immediate post-contraction period. One explanation for these results is that altering the local chemical environment of the muscle affects the adrenergic response pattern typically induced by a cold pressor stimulation.

Adult↗
PubMed1999

Effect of occlusal appliances and clenching on the internally deranged TMJ space.

AIMS: Stabilization appliances and mandibular anterior repositioning appliances have been used to treat patients with internal derangement of the temporomandibular joint (TMJ) based on the assumption that these appliances work by decompressing the TMJ. The purpose of this study was to indirectly test this assumption. METHODS: Bilateral TMJ tomograms of 7 subjects with unilateral anterior disc displacement without reduction (ADDwor) were taken during comfortable closure and during maximum clenching in maximum intercuspation; tomograms were also taken with the 2 types of occlusal appliances in use. Outlines of the condyle and the temporal fossa were automatically determined by an edge-detection protocol, and the minimum joint space dimension of the joints with and without ADDwor was automatically measured for each experimental condition as the outcome variable. RESULTS: Upon comfortable closure and maximum clenching, the minimum joint space dimensions of the ipsilateral and contralateral joints with the use of stabilization appliances and mandibular anterior repositioning appliances were not significantly different from those seen in maximum intercuspation. CONCLUSION: These findings do not indicate that these appliances induce an increase in joint space during closing and clenching in joints with ADDwor.

Adult↗
PubMed1999

Pressure pain threshold with and without iontophoretic anesthesia of the masseter muscle in asymptomatic males.

AIMS: The pressure pain threshold (PPT) in the superficial masseter muscle was measured with and without cutaneous anesthesia to determine whether there would be a difference in PPT scores. METHODS: In 14 healthy male subjects, cutaneous tissues in the target areas were anesthetized with lidocaine with the help of an iontophoretic device. As a control, physiologic saline solution was applied iontophoretically to the contralateral masseter site. The subject and the PPT examiner did not know which side contained anesthesia, and the selection of which side to anesthetize was done in a random fashion. Multiple PPT measurements were made in the target sites before and immediately after the iontophoretic anesthesia. RESULTS: The PPT level on the lidocaine side was not statistically different from the PPT level recorded on the control side (339.0 +/- 87.6 kPa and 337.5 +/- 77.7 kPa, respectively). CONCLUSION: Pressure pain sensation in the human masseter is not derived predominantly from the cutaneous tissues, but from the muscle itself.

Adult↗
PubMed1998

Cold pressor stimulus temperature and resting masseter muscle haemodynamics in normal humans.

Cold pressor stimulation reportedly increases sympathetic nerve activity in human skeletal muscles. This study examined the effect of cold pressor stimulation on the resting haemodynamics of the right masseter muscle in normal individuals, using near-infrared spectroscopy. Nine healthy non-smoking males with no history of chronic muscle pain or vascular headaches participated. Their right hand was immersed in a water bath (4, 10, 15 degrees C) for exactly 1 min. Each trial lasted 7 min (1 min before, 1 min during, 5 min after stimulation) and a strictly random order was utilized for the three test temperatures and the mock trial. Masseter muscle haemoglobin concentration and oxygen saturation, as well as heart rate and blood pressure, were continuously recorded in each trial. After completing the four trials, each participant produced and sustained a 30-s maximum voluntary clench in the intercuspal position. Data across the four trials were baseline-corrected and then magnitude-normalized to the individual's highest absolute haemoglobin and oxygen signal during the 30-s maximal clenching effort. Haemoglobin and oxygen saturation increased progressively during cold pressor stimulation as the water temperature decreased (Hb, p < 0.0001; O2, p = 0.0327); very little effect was seen during the mock trial. Heart rate and blood pressure also increased progressively during the stimulation as the temperature decreased (heart rate, p = 0.0013; systolic blood pressure, p = 0.0042; diastolic blood pressure, p = 0.0156). These data suggest that cold pressor, stimulation induces a strong increase in intramuscular blood volume which appears to be due to both a local vasodilative response and increased cardiac output.

Adult↗
PubMed1998

Concurrent cervical and craniofacial pain. A review of empiric and basic science evidence.

Because many patients present themselves for treatment with both craniofacial and craniocervical pain, 2 questions arise: (1) What are the sensory and motor consequences of dysfunction in either of these areas on the other? (2) Do craniofacial and craniocervical pain have a similar cause? These questions formed the impetus for this review article. The phenomenon of concurrent pain in craniofacial and cervical structures is considered, and clinical reports and opinions are presented regarding theories of cervical-to-craniofacial and craniofacial-to-cervical pain referral. Because pain referral between these 2 areas requires anatomic and functional connectivity between trigeminally and cervically innervated structures, basic neurophysiologic and neuroanatomic literature is reviewed. The published data clearly demonstrate neurophysiologic and structural convergence of cervical sensory and muscle afferent inputs onto trigeminal subnucleus caudalis nociceptive and non-nociceptive neurons. Moreover, changes in metabolic activity and blood flow in the brainstem and cervical dorsal horn of the spinal cord in both monkeys and cats have been demonstrated after electric stimulation of the V1-innervated superior sagittal sinus. In conclusion, the animal experimental data support the findings of human empiric and experimental studies, which suggest that strong connectivity exists between trigeminal and cervical motor and sensory responses.

Animals↗
PubMed1998

Diagnostic value of 4 criteria to interpret temporomandibular joint normal disk position on magnetic resonance images.

OBJECTIVE: This study was undertaken to evaluate different criteria to establish normal disk position on magnetic resonance images. STUDY DESIGN: Magnetic resonance image findings of 137 consecutive patients with temporomandibular disorders and 23 asymptomatic volunteers were used in this study. Three calibrated observers interpreted the images individually. Four closed-mouth and 1 open-mouth criteria were tested for their ability to define normal and abnormal temporomandibular joint disk positions on magnetic resonance images. RESULTS: For the 46 joints in the asymptomatic volunteers, the criterion that yielded the highest percentage of normal disk position diagnoses was the disk's intermediate zone (93.5%). Clock face criteria produced the following declining percentages of normal disk position diagnoses: 10 o'clock, 82.6%; 11 o'clock, 63.0%; and 12 o'clock, 39.1%. Similar results were obtained for the patients with temporomandibular disorders. In both groups, as the number of normal disk position diagnoses declined, the percentage of joints with a diagnosis of disk displacement with reduction increased. Conversely, the percentage of joints with a diagnosis of disk displacement without reduction (in the group of patients with temporomandibular disorders) did not appear to be substantially affected by the 4 closed-mouth disk position criteria. CONCLUSIONS: These results suggest that the intermediate zone criterion for disk displacement is the more stringent criterion and the one that would yield the lowest number of false positives when the disk position is being judged in the closed-mouth sagittal view.

Chi-Square Distribution↗
PubMed1998

Mandibular advancement devices and sleep disordered breathing.

It has been nearly 90 years since a dentist first fabricated a dental appliance for a patient with snoring. Since then, mandibular advancement devices or MADs have become a common treatment for obstructive sleep apnea and are used to increase the caliber of the airway during sleep. Their primary use is for the patient who has snoring or mild to moderate, but not severe, OSA problems. Unfortunately, only a small amount of empirical data exists on the topics of long-term compliance, complications and contraindications for these devices. Nevertheless, it appears that only a small percentage of patients will quit using a MAD because of temporomandibular joint (TMJ) or masticatory muscle soreness. An even smaller percent of the long-term MAD users will get changes in their occlusion. Compliance reports suggest that only 50% of the patients will be using the device after 3 years. Overall, these data suggest that MADs should be carefully fabricated by dentists who work on a referral basis with sleep medicine physicians and patients using MADs must be monitored regularly for ongoing efficacy and for associated complications. The good news (with good data support for this conclusion) is that MAD's are a moderately effective treatment of snoring and mild to moderate OSA.

Journal Article↗