The effects of wide pulse neuromuscular electrical stimulation on elbow flexion torque in individuals with chronic hemiparetic stroke.

OBJECTIVE: Neuromuscular electrical stimulation that incorporates wide pulse widths (1ms) and high frequencies (100Hz; wide pulse-NMES (WP-NMES)) augments contractions through an increased reflexive recruitment of motoneurons in individuals without neurological impairments and those with spinal cord injury. The current study was designed to investigate whether WP-NMES also augments contractions after stroke. We hypothesized that WP-NMES would generate larger contractions in the paretic arm compared to the non-paretic arm due to increased reflex excitability for paretic muscles after stroke. METHODS: The biceps brachii muscles were stimulated bilaterally in 10 individuals with chronic hemiparetic stroke. Four stimulation patterns were delivered to explore the effects of pulse width and frequency on contraction amplitude: 20-100-20Hz (4s each phase, 1ms pulse width); 20-100-20Hz (4s each phase, 0.1ms); 20Hz for 12s (1ms); and 100Hz for 12s (1ms). Elbow flexion torque and electromyography were recorded. RESULTS: Stimulation that incorporated 1ms pulses evoked more torque in the paretic arm than the non-paretic arm. When 0.1ms pulses were used there was no difference in torque between arms. For both arms, torque declined significantly during the constant frequency 100Hz stimulation and did not change during the constant frequency 20Hz stimulation. CONCLUSIONS: The larger contractions generated by WP-NMES are likely due to increased reflexive recruitment of motoneurons, resulting from increased reflex excitability on the paretic side. SIGNIFICANCE: NMES that elicits larger contractions may allow for development of more effective stroke rehabilitation paradigms and functional neural prostheses.

Muscular torque generation during imposed joint rotation: torque-angle relationships when subjects' only goal is to make a constant effort.

It is a reasonable expectation that voluntarily activated spinal motoneurons will be further excited by increases in spindle afferent activity produced by muscle stretch. Human motor behavior attributed to tonic stretch reflexes and to reflexes recruited by relatively slow joint rotation has been reported from several laboratories. We reinvestigated this issue by rotating the elbow joint over the central portion of its range while subjects focused on keeping their elbow flexion effort constant at one of three different levels and made no attempt to control the position, speed or direction of movement of their forearm. There is evidence that subjects' voluntary motor status is constant under these conditions so that any change in torque would be of involuntary origin. On average, torques rose somewhat and then fell as the elbow was flexed through a range of 80 degrees at 10, 20 and 60 degrees/s and a similar pattern occurred during elbow extension; i.e., both concentric and eccentric torque-angle profiles had roughly similar shapes and neither produced consistent stabilizing cross-range stiffness. The negative stiffness (rising torque) during the early part of a concentric movement and the negative stiffness (falling torque) during the later part of an eccentric movement would not have occurred if a stabilizing stretch reflex had been present. Positive stiffness rarely gave rise to torque changes greater than 20% in either individual or cross-subject averaged data. When angular regions of negative stiffness are combined with regions of low positive stiffness (torque change 10% or less), much of the range of motion was not well stabilized, especially during eccentric movements. The sum of the EMGs from biceps brachii, brachioradialis and brachialis showed a pattern opposite to that expected for a stretch reflex; there was an upward trend in the EMG as the elbow was flexed and a downward trend as the elbow was extended. There was little change in the shape of this EMG-angle relationship with either direction or velocity. The individual EMG-angle relationships were distinctive for each of these three elbow flexor muscles in four of the six subjects; in the remaining two, biceps was distinctive, but brachioradialis and brachialis appeared to be coupled. Although the EMGs of individual muscles were modulated over the angular range, no consistent stretch reflexes could be seen in the individual records. Thus, we could find no clear evidence for stretch reflex stabilization of human subjects maintaining a constant effort. Rather, muscle torque appears to be reflexly modulated across a much used portion of the elbow's angular range so that any appreciable stabilizing stiffness that is sustained for more than fractions of a second is associated with a change in effort.

Career retention in the dental hygiene workforce in Texas.

PURPOSE: The purpose of this study was to determine the factors that influence the retention and attrition of dental hygienists within the workforce in Texas. Respondents' perception of the role of employee benefits and practice of dental hygiene on career retention were explored. Demographic descriptors, including educational level, marital status, age, employment setting, and practice statuses, were also examined. METHODS: A questionnaire modified from the American Dental Hygienists' Association Extension Study: Retention of Dental Hygienists in the Workforce Final Report, April 1992, was mailed to a systematic sample of licensed Texas dental hygienists in March 1999. Descriptive statistics were computed for dental hygienists currently in practice in Texas and those not in practice at the time of the survey. Differences in demographics, benefits, and attitudes between dental hygienists currently in practice in Texas and dental hygienists not in practice at the time of the survey were tested using independent t-tests for interval data and chi-squared tests for categorical data. All statistical analyses were conducted using the Statistical Package for Social Scientists (SPSS v. 9, Chicago, Illinois). RESULTS: A response rate of 68.1% was obtained. Results revealed the primary reasons for remaining in the practice of dental hygiene were salary, family responsibility, professional collaboration, and variety of work. The primary reasons for leaving dental hygiene practice were family responsibility, boredom, salary, and lack of benefits. Secondary and tertiary reasons stated for staying in clinical practice revealed additional factors including benefits, participation in decision-making, and a safe environment. Dental hygienists in clinical practice were more likely to be employed by a dentist in a single practice and see more patients per day, have a certificate or associate's degree, be unmarried, have fewer children, and be younger than dental hygienists not in practice. CONCLUSION: The findings suggest that dental hygienists in Texas who remain in the workforce are positively influenced primarily by salary. Dental hygienists in Texas who had left the workforce were primarily influenced to leave practice because of family responsibility. Boredom and lack of benefits were also important factors in deciding to leave clinical practice. Employers of dental hygienists need to be aware of these factors in the hiring process. In addition, dental hygiene educators should prepare students in interviewing techniques for better communication regarding retention factors.

Abnormal joint torque patterns in the paretic upper limb of subjects with hemiparesis.

This study presents the results of a novel paradigm for characterizing abnormal coordination in subjects with hemiparesis. Subjects generated maximum voluntary torques (MVTs) isometrically in four randomly ordered blocks consisting of elbow flexion/extension, shoulder flexion/extension, shoulder abduction/adduction, and shoulder external/internal rotation. A 6-degree-of-freedom (DOF) load cell was used to measure torques in secondary DOFs at the elbow and shoulder, as well as in the torque direction the subject was attempting to maximize. This allowed characterization of the multijoint torque patterns associated with the generation of MVTs in the eight directions examined. Significant differences were found between the torque patterns exhibited by the paretic limb of the hemiparetic group (n = 8) and those observed for the nonparetic limb and control group (n = 4). Potential neural and biomechanical mechanisms underlying these abnormal torque patterns are discussed along with implications for the functional use of the paretic limb.

Upper-limb discoordination in hemiparetic stroke: implications for neurorehabilitation.

Clinically, upper-limb discoordination after stroke is evident in the form of stereotypic movement patterns that reflect a loss of independent joint control. These movement abnormalities, in conjunction with our recent quantitative findings under isometric conditions, provide evidence for an impaired capacity to generate certain muscle coactivation patterns in the impaired limb. In this article, we examine the parallels that exist between coordination disturbances observed under isometric and movement conditions. Our results suggest that discoordination in stroke may largely represent a manifestation of additional neural constraints on motor outflow. The neurotherapeutic implications of our findings are discussed.

Deficits in the coordination of multijoint arm movements in patients with hemiparesis: evidence for disturbed control of limb dynamics.

This study provides a detailed analysis of disturbances in the kinematics and dynamics of the acceleration phase of multijoint arm movements in six patients with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in three control subjects. Subjects performed rapid movements from a central starting point to 16 targets located equidistantly around the circumference of a circle. Support of the upper limb was provided by an air-bearing apparatus, which allowed very low friction movements in the horizontal plane. We found that patients retained the capacity to modulate, in response to target direction, the initial direction of movements performed with the paretic limb. However, in comparison to the nonparetic limb or control subjects, movements of the paretic limb were misdirected systematically. An inverse dynamics analysis revealed an abnormal spatial tuning of the muscle torque at the elbow used to initiate movements of the paretic limb. Based on electromyographic recordings, similar spatial abnormalities were also apparent in the initial activations of elbow muscles. We argue that these spatial abnormalities result from a systematic disturbance in the control signal to limb muscles that cannot be attributed to previously identified mechanisms such as weakness, spasticity mediated restraint, or stereotypic muscle activation patterns (muscle synergies). Instead, our analysis of movement dynamics and simulation studies demonstrate that the spatial abnormalities are consistent with an impaired feedforward control of the passive interaction torques which arise during multijoint movements. This impaired control is hypothesized to reflect a degradation of the internal representation of limb dynamics that occurs either as a primary consequence of brain injury or secondary to disuse.

Stretch reflex adaptation in elbow flexors during repeated passive movements in unilateral brain-injured patients.

OBJECTIVE: To evaluate the effects of repeated, externally imposed, flexion-extension movements of the elbow on the resulting stretch reflex response in hemiparetic spastic brain-injured patients. These effects were compared within a recording session and across sessions for the same subject to determine the impact of movement history on the quantification of spastic hypertonia using the stretch reflex response. DESIGN: Twenty to 30 sequential, constant velocity flexion-extension movements were applied to the impaired elbow of our cohort, with a 10-second hold interposed between flexion and extension. Movements were applied regularly at 1-minute intervals. Changes in stretch reflex responses were monitored during the applied movements. PARTICIPANTS: We examined a convenience sample of seven hemiparetic brain-injured subjects between the ages of 26 and 60 yrs, with moderate-to-severe spastic hypertonia of elbow muscles (Ashworth score 2-4/4). Subjects participated in 2 to 9 sessions. MEASURES: Elbow torque, position, velocity, and electromyograms of the biceps, brachioradialis, and triceps muscles were recorded for each flexion and extension movement. Stretch reflex torque was calculated by subtracting passive torque from total elbow torque, recorded over large amplitude movements. A linear regression analysis quantified both the initial torque response of the stretch reflex and the ensuing adaptation of the stretch reflex during sequential movements. Intersession variability was characterized both for spastic hypertonia measures and for stretch reflex adaptation. RESULTS: Repeated, externally imposed, sequential flexion-extension movements of the elbow decreased the elbow flexor stretch reflex in six of seven subjects. The mean reduction in reflex torque after 30 movements was 50% of the initial torque values (p = .001, t test vs. 0% change). Intersession stretch reflex responses for each subject were found to vary greatly (SDs of reflex torque ranged from 0.1 to 4.0 Nm), and there were also significant variations in the degree of adaptation between subjects. CONCLUSIONS: Stretch reflex adaptation must be taken into consideration when spastic hypertonia is quantified using repeated joint motion, as is often the case. The magnitude of intersession variation in spastic hypertonia measures suggests that ideally, such measurements should be made across multiple sessions before conclusions are made regarding the efficacy of spastic hypertonia interventions. This study provides quantitative evidence that repeated joint movements may have a significant short-term beneficial effect on spastic hypertonia.

Developing a competency-based curriculum for a dental hygiene program.

A three-step process was used that involved developing a competency document, an evaluation plan, and a curriculum inventory. The competency document, Competencies for the Dental Hygienist, included three domains, nine major competencies, and fifty-four supporting competencies. These became the department's educational goals. The evaluation plan included multiple methods for assessing each of the nine major competencies. The faculty initially identified evaluation methods that were currently in place and then added strategies for the various gaps in the plan. The curriculum inventory defined the entire curriculum in terms of the competencies. For each supporting competency, there was a list of major and foundation topics, each linked to specific courses. The strategy used to identify both the evaluation methods and curriculum topics was to survey the faculty. Information from assessments and the curriculum inventory directed the modification of the curriculum for alignment with the competencies. This process has resulted in improvements in teaching, evaluation, and student learning. The strengths and weaknesses of this competency-based curriculum development are presented, with specific recommendations for other-programs undergoing similar curriculum development.

Reorganization of flexion reflexes in the upper extremity of hemiparetic subjects.

We examined spatiotemporal abnormalities in the flexor reflex response in the impaired upper extremity of hemiparetic subjects. Electrical stimulation was used to elicit flexion reflexes in both upper extremities of 8 hemiparetic brain-injured and 6 control subjects. Electromyograms (EMGs) were recorded from 12 arm muscles, and reflex forces and moments were recorded at the wrist with a load cell, and converted to shoulder and elbow torques. We found that the onset of reflex torque and EMG was delayed in the impaired arm and delays were greater at the shoulder than at the elbow. The normal reflex torque response consisted of elbow flexion, shoulder extension, and shoulder adduction. In contrast, in the impaired limb shoulder, flexion torque was observed in 7 subjects and shoulder abduction in 3. The delays in reflex onset and altered torque patterns in the impaired arm may be related to the abnormal movement synergies observed following stroke. © 1999 John Wiley & Sons, Inc.

Task-dependent weakness at the elbow in patients with hemiparesis.

OBJECTIVE: To investigate the task dependence of elbow weakness in patients with hemiparesis. DESIGN: Descriptive study based on interlimb comparisons of maximum voluntary torques (MVTs) generated isometrically in elbow flexion and extension under four task conditions: without explicit control of the torques at adjacent joints and in combination with each of three submaximal shoulder abduction/adduction torque levels. SETTING: Rehabilitation center research laboratory. PATIENTS: Volunteer samples of six patients with chronic hemiparesis and four controls. MAIN OUTCOME MEASURE: Residual strength (RS), defined as the ratio of MVTs for the paretic and nonparetic limbs of patients and nondominant and dominant limbs of controls. RESULTS: For the patient group a significant effect of task condition on RS was found (analysis of variance, p = .0003 and p = .002 for elbow flexion and extension, respectively). With increasing shoulder abduction torque level, elbow flexion RS increased and elbow extension RS decreased. In contrast, for the control group, the effect of task condition on RS was not significant. CONCLUSION: In hemiparetic patients, weakness of the paretic elbow musculature shows a strong task dependence. This task dependence likely reflects the existence of abnormal synergies between elbow and shoulder muscles of the paretic limb and has important implications for the rehabilitation of motor function following hemiparesis.

Guidance-based quantification of arm impairment following brain injury: a pilot study.

This paper reports the design and preliminary testing of a device for evaluating arm impairment after brain injury. The assisted rehabilitation and measurement (ARM) Guide is capable of mechanically guiding reaching and retrieval movements across the workspace and of measuring constraint forces and range of motion during guidance. We tested the device on four hemiplegic brain-injured individuals and four unimpaired control subjects. During guided movement, the brain-injured subjects generated distinct spatial patterns of constraint force with their impaired arms that were consistent with the standard flexion and extension "synergies" described in the clinical literature. In addition, the impaired arms exhibited well-defined workspace deficits as measured by the ARM Guide. These results suggest that constraint force and range of motion measurements during mechanically guided movement may prove useful for precise monitoring of arm impairment and of the effects of treatment techniques targeted at abnormal synergies and workspace deficits.

Reflex torque response to movement of the spastic elbow: theoretical analyses and implications for quantification of spasticity.

A parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51 degrees +/- 10 degrees s.d. (n = 98) after the initial rise. This torque "plateau" was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles.

The use of extracted teeth for in vitro bonding studies: a review of infection control considerations.

OBJECTIVE: Infection control concerns regarding the handling of teeth for research purposes have prompted investigators to evaluate the effects of disinfection/sterilization on extracted teeth. The objectives of this literature review were to assess the reported findings of the effect of disinfection or sterilization on teeth used for in vitro bonding studies and make recommendations on their use. METHODS: A search of the literature was performed to obtain background information on infection control guidelines and current findings regarding disinfection or sterilization of extracted teeth. Published articles addressing the effects of different disinfection and sterilizing procedures on the tooth, such as structural changes of dentin and dentin permeability or effect on bond strengths, were examined and compared for agreement or disagreement of findings. The review was organized by the type of disinfection or sterilization method utilized by the investigators. These methods were evaluated in an attempt to address whether disinfection/sterilization of extracted teeth can be recommended or if the procedure simply produces another variable. RESULTS: Formalin, chemical heat sterilization (Chemiclave), autoclave, ethylene oxide and gamma radiation methods of disinfection/sterilization have been investigated for their effects on extracted teeth. When the effect of formalin storage on dentin bond strengths was examined, investigator results were extremely varied. Autoclave and chemical sterilization were found to produce comparable dentin bond results when compared to controls. Gamma radiation did not produce structural changes in the dentin but it currently has not been investigated for its effect on dentin bond strength. And while ethylene oxide produced similar dentin bond strength results when compared to controls, its use as a sterilant was determined to be ineffective. SIGNIFICANCE: Investigators have found formalin storage to be effective for infection control purposes. It cannot, however, be recommended as a storage medium for dentin bonding studies due to the variability in dentin bond strengths resulting from its use. Ethylene oxide is also not recommended due to its inability to effectively sterilize teeth. Chemical heat and autoclave sterilization methods are recommended for preventing cross-contamination during in vitro dentin bonding research. This recommendation is based on current research findings which examined the effect of these sterilization methods on dentin and dentin bond strengths.

Dental and dental hygiene students' attitudes in a joint local anesthesia course.

In 1995, the local anesthesia course was combined for dental and dental hygiene students. It was also the first time that dental hygiene students were instructed clinically in local anesthetic techniques. Faculty felt it important to evaluate student attitudes regarding these curriculum changes. This study assessed students' perceptions of the adequacy of background preparation courses, concerns about administering local anesthetics and attitudes about its administration by dental hygienists. A pre/post survey was completed by dental and dental hygiene students. T-tests were used to determine if differences in attitudes existed between groups and if changes in attitudes occurred within groups after taking the course. Results indicated that both groups believed they had adequate background preparation. Apprehensions about administering local anesthetics were similar, but the dental hygiene students felt significantly less anxiety (p < 0.01). Results also differed significantly on the issue of hygienists administering local anesthetics, with hygiene students in support of it and dental students opposed (p < 0.01). Results confirmed that no changes were needed in the existing prerequisite courses for both groups. A need to address student anxiety about local anesthetic administration has been identified. In addition, it may be beneficial to expand dental students' appreciation of dental hygiene education to foster mutually successful working relationships in the future.

Long-lasting reductions of spasticity induced by skin electrical stimulation.

We studied the effects of electrical stimulation of the skin on upper extremity spasticity in nine hemiparetic stroke subjects. The effects were quantified by comparing reflex torque responses elicited during ramp and hold angular perturbations of the elbow recorded before and after low-intensity skin stimulation. Electrical stimulation was applied to skin over the biceps muscle for a period of ten minutes at a 20 Hz frequency, pulse duration 0.1 ms, with an intensity level below motor threshold but above sensory threshold. In seven of the nine subjects, stimulation of skin over spastic muscle reduced peak torque responses in both flexors and extensors for at least 30 min. In these seven subjects there were significant increases in mean threshold angle for the onset of reflex torque so that a greater angular rotation was required to initiate the stretch reflex response. This shift occurred without change in reflex impedance. The origins of these long-term changes in reflex torque are unclear, but may reflect synaptic plasticity of spinal circuitry outside the stretch reflex loop.

Joint dependent passive stiffness in paretic and contralateral limbs of spastic patients with hemiparetic stroke.

Torque-angle relations at the elbow and ankle joints of relaxed normal controls and patients with hemiparetic stroke were compared. Low velocity flexion/hold/extension angular perturbations were applied to the joint under examination. The resulting torque-angle profiles described a hysteresis loop with similar slopes during the extension and flexion stages but separated by a vertical torque offset. Torque-angle responses obtained in the absence of significant muscle activation, as recorded by surface electromyographic activity, were designated as passive. Elbow passive stiffness estimates were calculated from the slope of the torque-angle response during the flexion stage of the perturbation. The elbow torque-angle plots exhibited linear passive stiffness with magnitude significantly lower than the passive stiffness of the ankle in both normal subjects and spastic patients. Changing ramp velocity had no significant effect on the passive torque-angle hysteresis loop at the elbow. A comparison of the torque-angle relations between hemiparetic spastic and normal control arms showed no significant differences in passive stiffness. Furthermore, no significant differences were found between paretic and contralateral upper limbs of a given hemiparetic subject. By contrast, significant differences in the torque-angle hysteresis loop were present between the paretic and contralateral ankles in all hemiparetic patients tested. These differences were more significant during dorsiflexion, and therefore seem to be related to preferential changes in mechanical properties of plantar flexor muscles. It is hypothesised that the differences in the torque-angle hysteresis loop between elbow and angle joints are related primarily to the larger amount of connective tissue in the calf muscles, as well as to a larger total physiological cross sectional area of calf muscles compared with elbow muscles. It is further hypothesized that the preferential increases in passive stiffness at the ankle in spastic legs result from immobilisation induced changes in muscle connective tissue, which are most prominent in muscles with predominantly slow-twitch fibres (such as soleus). Connective tissue surrounding such slow twitch muscle fibres have been shown to be more sensitive to immobilisation than those in fast twitch muscle. The functional, pathophysiological, and clinical implications of our findings are reviewed.

Abnormal muscle coactivation patterns during isometric torque generation at the elbow and shoulder in hemiparetic subjects.

To study abnormal spatial patterns of muscle activation in hemiparetic stroke, we compared EMG activity in paretic and contralateral elbow and shoulder muscles of 10 hemiparetic subjects during 1.5-s voluntary isometric contractions, against five to eight different loads. Isometric forces were generated in eight directions, referenced to a plane orthogonal to the long axis of the forearm, and were recorded by a three degrees of freedom load cell, mounted at the wrist. Surface and intramuscular EMGs of six elbow and six shoulder muscles were recorded from both impaired and contralateral upper extremities of each subject. The spatial characteristics of EMG activation of individual muscles were summarized using two measures. The first, called the 'net resultant EMG vector' is a new measure which calculated the vector sum of EMG magnitudes for each of the eight directions, and the second, index of EMG focus, is a measure of the range of EMG activation recorded for each load level. Use of these measures permitted us to describe spatial EMG characteristics quantitatively, which has not been done previously. We observed consistent and statistically significant shifts in the resultant EMG vector directions in the impaired limb, especially in shoulder and other proximal muscles. Significant increases in the angular range of EMG activity were also identified and were most evident at the elbow. Correlation analysis techniques were used to assess the degree of coactivation of different muscle pairs. There were consistent EMG coactivation patterns observed across all subjects (both normal and hemiparetic). However, in spasticparetic limbs, additional novel coactivational relationships were also recorded, especially between elbow flexors/shoulder abductors and elbow extensors/shoulder adductors. These novel coactivation patterns represent a reduction in the number of possible muscle combinations, or in the number of possible 'synergies' in the paretic limb of the stroke subject. This reduction in number of 'synergies' could result from a loss of descending command options; from an increased reliance on residual, descending brainstem pathways (such as the reticulospinal and vestibulospinal projections); from changes in spinal interneuronal excitability; or from a combination of several of these factors. The relative merits of these hypotheses are addressed.

Bond strengths between elastomeric impression materials and disinfected preliminary impressions.

Bond strengths between disinfected putty impressions and subsequent wash applications were determined in specimens made to simulate clinically an interrupted two-step impression technique. The effect of a disinfectant on the bond strength between a disinfected wash impression and a subsequent wash application was also evaluated to simulate perfecting a disinfected final impression clinically. Vinyl polysiloxane (putty or wash) and polyether (wash only) impression materials were placed in perforated metal cylinders, allowed to set, and dipped in an iodine or glutaraldehyde disinfectant. Wash material was then applied to the disinfected material by use of another metal cylinder and allowed to set before the specimen was tested in tensile mode. Significant decreases in bond strengths were found in both clinical simulations but were limited to specific impression material and disinfectant combinations.

Estimation of muscle forces about the wrist joint during isometric tasks using an EMG coefficient method.

A technique for estimating isometric muscle forces based on EMGs and anatomical parameters is presented. In the present study, we record EMGs from five muscles acting at the wrist, during a series of isometric contractions in flexion, extension, ulnar deviation and radial deviation. The method then uses these EMG signals and the necessary anatomical data to estimate individual muscle forces. For one subject, complete anatomical parameters were estimated by MRI reconstruction of muscle moment arms and lines of muscle action. In all subjects, the errors associated with variability in the EMG signals were reduced through the use of signal processing techniques and intensive subject training. These EMG-based force estimates were then validated by evaluations at torque directions in which no mechanical redundancy existed. The stability of the solution space was examined using Monte Carlo simulations. The results of our study show that individual muscle forces at the wrist can be estimated with considerable accuracy, without assuming any control strategy (as is done with optimization theories). However, due to the limited mechanical redundancy of the wrist, it is uncertain whether the method can be used to estimate muscle forces in more highly redundant systems.

Wettability of impression materials treated with disinfectants.

The purpose of this investigation was to comprehensively compare various combinations of impression materials, die stones and disinfectants so as to provide clinical guidelines for selection of materials. The effect of immersion disinfection on the wettability of five types of impression materials, polyether, light-cured polyether urethane dimethacrylate, polysulfide, hydrophilic and hydrophobic polyvinyl siloxanes, was evaluated. This evaluation was determined by contact angle measurement of two die stones on the impression materials and also by bubble formation in casts made from the same materials after disinfection. The disinfectants utilized were 0.5% sodium hypochlorite and 0.13% glutaraldehyde-phenate. There were significant interactive effects (P less than 0.02) on contact angle between stone and disinfectant, impression and disinfectant, and impression and stone. The effect of disinfection was found to vary among impression materials. Although there was a significant correlation found between contact angle and bubble formation, contact angle was not found to be a strong predictor of bubble formation in this study. For these findings, it is recommended to evaluate each disinfectant and impression material combination individually.