To Read More on: Neuromuscular Instrumentation – CMS (Jaw Tracking), EMG, ESG and TENS
Safety of TENS devices has been scrutinized by the medical community over the past 40 years. The scientific literature is unanimous in validating the safety of TENS devices.
The following excerpt from the FDA publication titled: “An Introduction to Electrical Nerve Stimulation: TENS” ( August 1986, published by the Center for Devices and Radiologic Health branch of the FDA) stated:
“The approximately one hundred publications from the most recent years are vitually unanimous in TENS safety. The notable exception is a necessary awareness of potential fetal stimulation during labor pain. In all other aspects, TENS risk is limited to minor and easily remedied skin irriatations from electrodes and electrode gels in a rather small number of reported cases.”
- The U.S. Food and Drug Administration has very specific guidelines for all manufacturers in listing of FDA’s Indications. Contraindications, Warnings, Adverse Effects and Precautions (pls see pages 1-3 of J4, J5/BNS-40 Operating Guide). “ Shorting out” or injuring the nervous system is not a listed adverse effect or precaution of TENS devices and can not be attributed to TENS therapy.
- One other issue, J4/J5/BNS-40 are one of only few TENS devices that are equipped with a “Patient Fail-Safe Circuit”. The delivery of current to the patient will be automatically interrupted if the Fail-Safe circuitry is activated.
The Myo-monitor TENS (Transcutaneous Electro Neural Stimulation): Its use and abuse paper published in Quntessence International, volume 9, February/March 1978, report 1601; page 1 – 11 references the effective stimulus of ALL of the muscles of mastication via the motor nerve branchs V & VII by the Myo-monitor.
- Specifically, Fuji and Mitani have shown neural mediation of the stimuli – which is why the specific Myotrode placement protocol has been scientifically established over the coronoid notch, as this provides direct access to the nerve branches.
FDA has granted Myotronics TENS 510K approval status from the Center for Devices and Radiological Health (a branch of the FDA). Myotrode placement guidelines for the use of low frequency TENS is specifically approved for both the V and VII cranial nerve stimulation.
- To date, no published studies have been demonstrating superior efficacy for other Myotrode electrode stimulation placement sites.
- To date no other Myotrode electrode stimulation placement sites have been tested scientifically and approved for use by the United States CDRH and the FDA.
- Other Myotrode placement sites, e.g. XI accessory have not been cleared for FDA approval with published studies demonstrating efficacy.
- The FDA had already tightened up on claims in the early 1980′s when the manufacturer (Myotronics-Noromed, Inc.), filed for the J4 Myomonitor TENS and required submission of published studies supporting its indications and after reviewing these articles, cleared the device for its intended use. The clearance requires that the device be used according to instruction for use which specifically sites electrode placement. Deviations from specific electrode placement requires new application with the FDA. Based on the established published studies, the FDA’s clearance requires that the electrodes be placed over the mandibular notch, as sited in the User’s Guide, facilitating 5th and 7th nerve stimulation as documented in the articles that were filed with the FDA.
MYO-MONITOR NEURAL MEDIATION of the 5th and 7th CRANIAL NERVES VS. MUSCLE STIMULATION
INTRODUCTION
The following articles are controlled studies supporting the thesis that Myo-monitor induced contraction of muscles is neurally mediated via the 5th (Trigeminal) and 7th (Facial) nerve branches.
Jankelson, B., Spark, S. and Crane, P. Neural conduction of the Myo-monitor stimulus: A quantitative analysis. J. Prosthetic Dentistry. Vol 34 No. 3, pp 245- 253 September 1975.
PURPOSE AND SCOPE OF THE INVESTIGATION
The purpose of this investigation was to examine the response of muscles to external stimulation in order to determine whether the resulting contraction was mediated by direct depolarization of the muscle membrane or whether it resulted from an induced neural action potential which stimulated the muscle via the neuromuscular junction. The scope of this investigation was limited to the specific question of whether contractions that follow transcutaneous stimulation with the Myo-Monitor result from direct muscle fiber stimulation (De Boever, J., and McCall W.D. 1972; Bessette, R.W. and Quinlivan J.T. 1973) or whether the contractions are a response to stimuli transmitted through the motor nerves (Choi, B., and Mitani H., 1973).
METHOD OF INTENSITY-DURATION CURVES
Intensity-duration testing was selected as the core method for the experiments, because it is well established and reliable: “. . . the technique that has proved most satisfactory and is in widest use is the recording of the intensity- duration relationship of applied electrical stimuli. It is a straightforward and reliable investigation. The relationship between the strength of the stimulus and its duration in time for a constant response of an excitable tissue gives an accurate measure of the excitability of that tissue.” (Lenman, J., and Ritchie, A.E. 1973).
This method is based on the observation made in 1883 by Erb (Erb, W. 1883) that has since been firmly established. That is, a long-lasting stimulus will excite both nerve and muscle, whereas a short stimulus will excite only the nerve. Hence, if a stimulus, known to be too short in duration to directly cause muscle depolarization, is applied and muscle contraction results, it can be confidently concluded that the stimulus responsible for the contraction arrived via the motor nerve.
DESCRIPTION OF THE EXPERIMENT
Subjects: The subject sample consisted of six women and four men, ranging from 20 to 60 years of age. One of the subjects was completely edentulous, and none reported clinical symptoms of T.M.J. disorders, occlusal problems, or serious muscle spasm.
Recording curves: The technique of intensity-duration recording requires that one detect the occurrence of a consistent minimal response. While detection of threshold contraction by careful palpation and inspection has been considered adequate and is the means most commonly used in intensity-duration testing, a graphic form of recording has long been sought to lend further objectivity and accuracy to the method.(Lenman, J., and Ritchie A.E., 1973) In these experiments, the mandibular kinesiograph, (Jankelson, B. et al., 1975) an instrument which electronically senses and records mandibular movement, was used to precisely measure and record a consistent amount of mandibular rise (closure). Since the amount of mandibular closure is directly correlated to the degree of muscle contraction, precise graphic recording of the amount of closure assured that a consistent contraction was elicited for each of the various stimulus duration. Throughout the investigation, for each subject and at each stimulus duration being used, the intensity of the stimulus was monitored and adjusted to produce the uniform. 0.2 mm. mandibular closure. Kinesiometric recording of consistent contraction proved to be a useful refinement in intensity-duration testing.
INVESTIGATION TO PROVE APPLICABILITY OF MYO-MONITOR
Following the same protocol as outlined earlier, a subject was sequentially stimulated through the same electrodes with a constant-voltage source, the MyoMonitor, and a constant-current source. In this manner, comparative peak currents could be measured without disturbing the electrode positions, thereby making it possible to assess the relative effect of the Myo-Monitor pulse. The peak current was adjusted for each subject to produce a consistent 0.2 mm. mandibular closure. Page 100 Myo-monitor – Neural Mediation
A mathematical routine employing a least-squares curve-fitting program was used to match the standard intensity-duration curve to the data. As was done earlier, the data was expressed as a ratio relative to the peak current at 3 msec.
Further examination of the data leads to the conclusion that Myo-Monitor is indeed adequate for use in our investigation. Also, because even the constantcurrent stimulator did not result in a chronaxy of greater than 0.26 msec., these data alone are strong evidence for neural mediation of the current stimulus.
RESULTS
Data on current recordings. Peak current records from the 10 subjects are presented in Table 1. The spread in peak current values for any given pulse duration reflects the variability in anatomic configuration that is to be expected in a population. Fig. 4 expresses these data in terms of the relative stimulus intensity, which is defined as the ratio of the peak current required at a duration of 3.0 msec. (rheobase). Data displayed in this manner tend to normalize the anatomic variability without distorting the critical parameters of the experiment. The mean ratio of the population is plotted in Fig.4.
Chronaxy. The use of transcutaneous stimulation as a diagnostic aid in the determination of muscular innervation hinges on the clear-cut distinction between the excitability curves for nerve and muscle. Among the indices used to quantify intensity-duration curves is the chronaxy, which is defined as the time required for a stimulus of twice the threshold intensity (rheobase) to elicit a consistent response. A mathematical analysis (formula follows) of the data shown in Fig. 4 yields a chronaxy of approximately 0.158 msec. at a relative stimulus intensity of 2.0. Individual chronaxies for the 10 subjects ranged from 0.125 to 0.180 msec. Myo-monitor – Neural Mediation
In all 10 subjects, individual curves followed the same general hyperbolic shape with no significant discontinuities. The data were fitted with a curve of the form:
I = Io 1
1-e -t/k
where: I = stimulation current (Ma.); Io = rheobase current (Ma.); t = duration of current pulse (msec.); and k = characteristic of data (time constant, msec.).
Chronaxy values for normal muscles of the face being stimulated through their motor nerve range from 0.02 to 0.3 msec., depending primarily on the stimulator impedance. If the muscle fibers were being stimulated directly, without the transmission of the signal across the neuromuscular junction, the chronaxy value would be from 50 to 100 times greater (Fig. 5). (Watkins, A.L. 1968; Harris, R., 1971)
DISCUSSION
The intensity-duration curves reported for this study support the findings of a previous electromyographic study (Choi, B.B., and Mitani, H., 1973), that is, the muscle contraction resulting from Myo-Monitor stimulation is generated through a neurally mediated sequence. In that investigation of 15 subjects in which tiny wire electrodes were used, it was reported that, “The evoked E.M.G. was recorded from anterior portion of the temporal, the masseter, anterior ventral of the digastric, the obicularis oris and the buccinator muscles….The Myo-monitor pulse stimulates the nerve trunks of the fifth and seventh cranial nerves at the superior mandibular notch percutaneously and it appeared to have afferent and efferent effects. (Choi, B.B., and Mitani, H., 1973).
However, Bessette and Quinlivan, (Bessette, R.W. and Quinlivan, J.T., 1973) in another electromyographic study using surface electrodes, reported that they were unable to record a consistent response from the anterior temporal muscle in five subjects, and in one of the five subjects, a wire electrode inserted into the medial pterygoid muscle failed to detect myographic evidence of contraction. These investigators also measured a single latency and used that measurement to calculate what they incorrectly defined as “conduction velocity.” From that calculation and their inability to record electromyographic signals from the temporal or the medial pterygoid muscles, they concluded that neural conduction was not involved and the contraction was the result of direct stimulation of only the masseter muscle fibers.
When confronted with differing conclusions, one must look to the conditions of the experiment and the analysis of the data. Myo-monitor – Neural Mediation Page 101
In the study by Bessette and Quinlivan (Bessette, R.W. and Quinlivan, J.T., 1973) which concluded that neural conduction was not involved, in all five subjects, the single latency was measured as the time from start of the stimulus to peak of the response. This departure from the conventional definition of latency (the time from start of the stimulus to the onset of response) produced a measurement of 3 msec., which then became the basis for their, “conduction- velocity” calculations.
To obtain accurate conduction-velocity measurements, stimulation must be done at two points along the nerve and the latency measured for each response. The distance between the two points of stimulation must then be divided by the difference between the two measurements of latency so that, in calculating the velocity, and allowance is made for the time it takes the impulse to cross the neuromuscular junction, (Watkins, A.L., 1968; Lenman, J., and Ritchie, A.E., 1973; Goodgold, J., and Eberstein, A., 1972; Johnson, E.W., 1971)
Conduction velocity = Distance
(Latency 2 – Latency 1)
A single latency, as used by Bessette and Quinlivan, (Bessette, R.W. and Quinlivan, J.T., 1973) does not give a true indication of conduction velocity along the nerve.
In contrast with peak measurement, the conventional measurement to onset of response would yield a latency of 2 msec. or less (See Bessette and Quinlivan, (Bessette, R.W. and Quinlivan, J.T., 1973) Fig. 2). The neurally mediated pathway would incur (1) a finite delay in charging dermal capacity of about 0.5 msec., (2) neural conduction time (assuming a conduction velocity of 69 M. per second over a distance of cm.) of 0.46 msec., (3) a delay of 0.3 to 1 msec. at the neuromuscular junction, and (4) an intermuscular delay dependent on electrode placement. A latency of 2 msec. (Oester, Y.T. and Light, S., 1971) is well within the expected range of a neurally mediated response.
Neither the methodology nor the analysis of the data of the investigation under discussion (Bessette, R.W. and Quinlivan, J.T., 1973) provided for recognition of neural stimulation that might have occurred. The conclusions that the nerve trunk is anatomically inaccessible to a stimulus and that only muscle fiber stimulation was involved are not warranted either by the method of the data analysis of the experiment.
SUMMARY
With the introduction of the Myo-Monitor to dentistry, the question has arisen whether the stimulus is neurally mediated (Choi, B.B. and Mitani, H., 1973) or results from direct depolarization of only the fibers of the masseter muscle. (Bessette, R.W. and Quinlivan, J.T., 1973) Intensity-duration curves recorded for 10 subjects quantified the relationship between stimulus intensity and the duration of the stimulus required to elicit a consistent contraction response to transcutaneous stimulation vie the Myo-Monitor. Individual chronaxies ranged from 0.125 to 0.180 msec., with a mean calculated at 0.158 msec. Stimulating the muscle fibers directly, without transmission of the signal across the neuromuscular junction, would have produced chronaxy values a least 50 to 100 times greater. The distinction is clear-cut. The chronaxy values unequivocally establish transmission of the stimulus across the neuromuscular junction.
In all 10 subjects, contraction of muscles remote from the site of stimulation was evident by inspection and palpation. These data lend support to the conclusion of Choi and Mitani (Choi, B.B. and Mitani, H., 1973) that the MyoMonitor stimulates the fifth and seventh cranial nerves.
The data derived here correlate with those of other investigations and clearly establish that the transmission of the Myo-monitor stimulus is accomplished by transcutaneous neural stimulation.
Neuromuscular Dentistry – Objective Measurements and Evaluation
