III. Fibrillation and denervation hypersensitivity

The denervation of a skeletal muscle (lower motor neuron lesion) causes fibrillation with flaccid paralysis and denervation hypersensitivity.

Fibrillation

Fibrillation means fine irregular contractions of individual muscle fibers.

Denervation Hypersensitivity

After denervation, the muscle becomes highly sensitive to acetylcholine released from neuro-muscular junction. This is called denervation hypersensitivity.

IV. Myasthenia gravis

In this disease, grave weakness of the muscle occurs. This is due to the inability of neuro-muscular junction to transmit impulses from nerve to the muscle. It is a serious and sometimes a fatal disease.

Cause of Myasthenia Gravis

Myasthenia gravis is an autoimmune disease. The body develops antibodies against its own acetylcholine receptors. These antibodies destroy the acetylcholine receptors. So, though the acetylcholine release is normal, it cannot act because of the destruction of the receptors.

Symptoms of Myasthenia Gravis

Because of the defective neuro-muscular activity, the muscular contraction is very slow and weak. Fatigue occurs quickly when the patient attempts repeated muscular contractions.

In severe conditions, there is paralysis of muscles. The patient dies mostly due to the paralysis of respiratory muscles.

Emg application in dentistry different branches

Local electromyography is used in surgical dentistry at masticatory (chewing) muscles dystrophies and hypertrophies; in stomatoneurology – at traumatic and infectious injuries of nerves of maxillo-facial region; in dentistry of children – for determining the soft palate muscles bioelectrical activity in children under norma and congenital developmental anomalies.

Stimulatory electromyography is used in stomatoneurology and surgical dentistry at face nerve injuries for its conduction and impulses spreading velocity through the nerve determining as well as for the assessment of expression muscles paresis degree.

Interferential electromyography has the biggest spreading in various dentistry branches. For example, it is used in therapeutical dentistry for the registration of masticatory muscles contraction force regulation at parodontites because there are functional-dynamic disturbances of masticatory apparatus at this disease. It is usually performed in parallel with gnatodynamometry for the assessment of mandibular (lower jaw) force during chewing. In surgical dentistry interferential EMG is used at:

• jaws fractures;

• maxillar-facial region inflammatory diseases (phlegmones, abscesses, osteomyelitis);

• during myoplastic operations at expression muscles pareses.

In orthopedic dentistry this method is applied for study of bioelectrical activity of chewing muscles under the condition of complete teeth absence in course of adaptation to the new demountable (removable) dentures. In dentistry of childhood interferential EMG is used for zygomatic and masticatory muscles coordinating correlations reorganization control while bite anomalies treatment.