EMG application in orthopedical dentistry.
Interferential EMG is applied for masticatory muscles bioelectrical activity assessment at teeth complete absence during adaptation to complete temporary dentures. Denturing with complete temporary dentures leads to masticatory muscles bioelectrical activity increasing during mastication with dentures and after their removal. During adaptation to complete temporary dentures all mastication time is reduced due to masticatory movements quantity decreasing and one masticatory movement time shortage. Masticatory muscles adaptation to new conditions on EMG indexes takes place during first 6 months of dentures usage. At bite height increasing after orthopedic treatment of teeth pathological wiping off with EMG bite hightening admitted boarders are under control. Central occlusion height increasing in admitted limits (8-10 mm) leads to temporal muscles resting bioelectrical activity. Such activity appearance in proper masticatory muscles is a symptom of excessive (more than 10 mm) bite increasing. EMG investigation allows to assess objectively the effectiveness of occlusion straightening out and to control symmetrical muscles activity co-ordination.
EMG application in children dentistry and orthodonthia.
Interferential EMG is applied for control of temporal and masticatory muscles functions co-ordinational correlations reorganization during bite anomalies treatment. Local one – for soft palate muscles bioelectrical activity study in children under norm and at congenital developmental anomalies. After soft palate fissures operative removal EMG is applied for operative determining the possibility of speech restoration prognosis as well as for control during muscles special trainings with myogymnastic exercises special complex.
2. Study aims:
To know: excitement conductance mechanisms and regularities through nervous and muscular fibers; main factors determining conductance velocity; nervous fibers action potential forming and features; electromyogram formation mechanism.
To be able to: draw schematically excitement conductance mechanism through non-myelinated and myelinated nervous fibers.
3. Pre-auditory self-work materials.
3.1. Basic knowledge, skills, experiences, necessary for study the topic:
| Subject | To know | To be able to |
| Medical biophysics | Skeletal muscles electrical features peculiarities | Use electrical devices |
| Histology | Skeletal muscle histological structure | Differentiate skeletal muscle preparation |
| Neurology | Mechanism of nervous impulse distribution through nerves and muscles, excitable tissues general features and laws of work | Determine muscles tone and force |
| Sportive medicine | Laws of excitement wave distribution through nervous and muscular fibers, excitable tissues general features | Determine muscles tone and force |
| Dentistry (all branches) | Mechanism of nervous impulse distribution through nerves and muscles, excitable tissues general features and laws of work, possibilities of EMG usage | Interpret masticatory muscles EMG. |
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Topic content.
Electromyography is a functional method that allows to registrate graphically electrical muscular activity while its excitement. With other words, it is registration method of skeletal muscles electrical potential oscillations occurrence under rest, at tonic tension and arbitrary movements. At muscular contractions visual observation under muscle or nerve irritation one tells about electrical excitability investigation.
EMG allows to study structure and function of neuro-motor apparatus consisting of functional elements named as motor units (MU). MU is an integrity of motoneuron and muscular fibers group innervated by it. On EMG potentials oscillations in neuro-muscular endings (motor plates) occurring under impulses action from medulla oblongata and spine motors are fixated. EMG-record is performed at paper and tape movement velocity equal to 4-5 cm/sec and 20 cm/sec for oscillations quantity estimation.
The curve receiving at this method usage is named electromyogram. It is the result of interference of multiply action potential that appear asynchronically in different muscular fibers and is registrated by means of intracellular electrodes.
There are 3 main electromyogram kinds:
1. interferential – muscular biopotentials are taken off from large surface while applying the electrodes on skin;
2. local – separate motor units activity is registrated by means of needle electrodes;
3. stimulatory – the registration of electrical muscle answer to the stimulation of nerve innervating it.
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At EMG with needle electrodes it is necessary to make EMG record under rest and at the investigated muscles weak tension. At necessity one can investigate muscles reaction to nerve electrical irritation or doctor can apply dosated muscular loading, reaction to fatigue and different pharmacological substances (for example, proserin, at myasthenia).
Muscular potentials bringing out is performed by means of electrodes:
– needle – they are involved in the muscle and bioelectric potentials of separate muscular fibers are registrated;
– surface – they registrate summary muscles activity from many muscular fibers.
At EMG analysis one should takes into account:
– altitudes level;
– potentials oscillations frequency;
– common oscillograms structure (osclillations monotony or division into volleys, volleys form, duration and frequency).
Parameters of motor units are different because non-equal amount of muscular fibers are included in motor unit. That is why for taking information about state of motor unit of a given muscle it is essential to registrate not less than 20 action potentials. Action potential duration is 5-13 msec. Under norma in a resting state (at local bringing out with needle electrodes) the bioelectrical potentials oscillations don’t increase (at summary EMG one can see low-altituded weak oscillations up to 10-15 mcV). Reflectory tonus increasing is accompanied by insignificant rising up of electrical activity (up to 50-100 mcV). At arbitrary tension frequent high oscillations (1000-2000 mcV) are occured. In healthy people summary EMG dependently on muscular force has altitude up to 400 mcV and frequency up to 400 fluctuations per 1 second.
EMG have different picture at movement disorders that are connected with anomalies of central and perypheral nervous system and muscular apparatus as itself. The muscular bioelectrical activity changes are delt with pathological process topics, severity and course stages. EMG helps at diagnostics of central, segmentary, neurithic and myopathic motor disturbances, it helps to determine typical disorders at early disease stage under conditions of low-expressed symptoms. It also gives the opportunity to observe process dynamics and treatment effectiveness. Sometimes in neurological practice tthey use electroneuromyography – complex investigation method including in it:
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§ registration and analysis of muscles and nerves stimulated potentials parameters (stimulated potentials parameters latent period, form, altitude and duration);
§ functionning motor units determining;
§ impulses transmission velocity through peripheral nerves motor and sensor fibers et al.
§ At interpherential EMG one should determine such parameters as:
§ altitude;
§ duration and
§ temporary course of bioelectrical activity during functional probes;
§ symmetrical muscles activity correlation;
§ activity distribution in muscles of one and different groups.
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