Contracture of the masticatory muscles

Prolonged tension and contraction of the muscles that provide movement of the lower jaw during chewing (musculi masticatorii) is diagnosed as a contracture of the masticatory muscles.

Epidemiology

Clinical statistics on cases of contracture of the masticatory muscles are not available, but it is known that, for example, temporomandibular joint syndrome (TMJ) is detected in approximately 10-15% of adults who have consulted a doctor about craniofacial pain.

Causes of the chewing muscle contractures

In the movements of the  lower jaw  when chewing solid food, the superficial and deep  chewing muscles  (musculus masseter) are involved, which are connected to the lower jawbone and the zygomatic arch; temporal muscles (musculus temporalis) - anterior, middle and posterior; medial and inferior lateral pterygoid muscles (musculus ptererygoideus). All of these muscles are bilateral and are innervated by the mandibular nerve, which is a branch of the trigeminal nerve. [1]

There are such main reasons leading to musculi masticatorii contracture as:

• fracture, dislocation and  subluxation of the lower jaw  (including habitual);
• problems with the dental system - a violation of the occlusion (closure) of the teeth, that is,  malocclusion  (maxillary or mandibular prognathism);
• temporomandibular joint disorders - temporomandibular joint  syndrome (TMJ), the movement of which is provided by chewing muscles;
• myositis - inflammation of muscle tissue;
• tendinitis of the temporal muscle - inflammation of its tendons, which may be associated with hyperactivity of this muscle;
• mandibular defects , for example, hyperplasia of the coronoid process and the angle of the mandible;
• facial hyperkinesia , in particular, abnormal movements of the lower jaw (oral hyperkinesis) - bruxism, "lower" Bruegel's syndrome, tardive orofacial dyskinesia, oral masticatory syndrome (hemimastikatory spasm) of the elderly;
• spastic paralysis  of the muscles of the face (facial hemispasm);
• paralysis of the soft palate;
• mandibular nerve injury.

Types of contracture of masticatory muscles

There are such types or types of  contracture ,  [2]such as:

• post-traumatic contracture of masticatory muscles,
• inflammatory contracture of the masticatory muscles (with fever, diffuse swelling of the face and craniofacial pain);
• post-paralytic contracture of masticatory (and mimic) muscles in case of cerebrovascular accident as a result of a stroke - with damage to the upper motor neurons and the development of spastic muscle hypertonicity and facial hemispasm;
• neurogenic contracture of masticatory muscles , for example, in patients with epilepsy or pseudobulbar palsy, which is the result of damage to the central motor neurons and cortical-nuclear pathways of the brain.

Risk factors

Determining the risk factors for the development of masticatory muscle contracture, first of all, experts emphasize the role of maxillofacial injuries, dental / orthodontic manipulations and local infectious processes (periostitis, pericoronitis, infection at the site of the third molar eruption, other inflammatory foci in the oral cavity and nasopharynx), which can lead to inflammation of the masticatory muscles, as well as muscular dystrophy / dystonia and diseases of the muscle tissue of autoimmune origin (polymyositis).

The risk of musculi masticatorii contracture with dysfunction of the masticatory system is increased in epilepsy, pseudobulbar palsy and chronic stress. Thus, stress-induced tension in many people is accompanied by involuntary motor activity of the jaw muscles with clenching or grinding of teeth - bruxism (from the Greek brykein - to bite or grind teeth). [3]

But it should be borne in mind that long-term use of antipsychotic drugs can lead to a side effect in the form  of neuroleptic syndrome , which is characterized by a tonic spasm of the masticatory muscles - lockjaw (from the Greek trismos - creak). [4]

By the way, it is trismus that can cause shortening of the immobile muscle fibers of the pterygoid, temporal and masticatory muscles and chronic limitation of their mobility.

Pathogenesis

In case of fractures of the lower jaw or facial bones, to which the chewing muscles are fixed, in cases of dislocations of the neck of the condyle of the lower jaw, the pathogenesis of contracture may be due to the formation of a hematoma, focal rupture of muscle fibers, sustained muscle spasm (trismus), as well as structural changes in muscle tissues - with the formation adhesions and scars, that is, fibrosis (fibrodysplasia), and even ossifying traumatic myositis.

Thus, contracture develops when normally elastic tissues are replaced by non-elastic fibrous tissue that tightens the muscle.

Studies have shown that structural changes in muscle tissue are more rigid - due to increased passive mechanical stress. At the same time, the tension of muscle fibers is accompanied by stretching of sarcomeres (functional muscle units consisting of contractile proteins myosin and actin, combined into myofilaments), which leads to their functional inferiority, and the generation of active tension in the muscles decreases, causing rigidity (stiffness of movements).

Symptoms of the chewing muscle contractures

With contracture of the masticatory muscle, the first signs are manifested by a limited ability to open the mouth. There is acute  pain in the masticatory muscle  and the jaw is tilted towards the lesion (asymmetry of the lower face).

At a later stage, the pain (dull or aching) may also be at rest with a reflection in the ear and temple area.

Also, symptoms include a constant feeling of tightness and stiffness of the muscles (due to their hypertonicity); difficulty with eating (it is impossible to bite and chew); problems with brushing teeth, yawning, articulation; clicks are felt in the temporomandibular joint, muscle fasciculations are possible.

Complications and consequences

Complications and consequences of masticatory muscle contracture include painful muscle spasm and limitation of temporomandibular joint function and mandibular mobility, which can be defined as facial myofascial pain syndrome, masticatory myofascial syndrome, Kosten's syndrome, or painful dysfunctional facial syndrome.

Diagnostics of the chewing muscle contractures

The diagnosis of contracture begins with the examination of the patient and the collection of anamnesis.

Laboratory tests may be needed - blood tests for lactate, lactate dehydrogenase and creatine phosphokinase levels.

Instrumental diagnostics includes panoramic radiography of the lower jaw, CT of the maxillofacial region and temporomandibular joints, ultrasound of the muscles, electroneuromyography. [5]

Differential diagnosis

Differential diagnosis is carried out with arthrogenic  contracture of the lower jaw , arthrosis, neoplasms localized in the jaw region, trigeminal neuralgia, Bell's palsy (neuritis of the facial nerve), etc.

Treatment of the chewing muscle contractures

Treatment should be aimed at eliminating the underlying causes. A partially impacted tooth may require extraction; in case of malocclusion, orthodontic treatment is carried out; in case of infection, antibiotic therapy is prescribed; surgical treatment (by a dental or maxillofacial surgeon) is required for injuries and some anatomical defects of the lower jaw.

To relieve inflammation and pain, NSAIDs are recommended - non-steroidal anti-inflammatory drugs, for example,  Ibuprofen  (0.2-0.4 g three times a day), or other  tablets for muscle pain .

To reduce muscle tone in small doses, drugs from the muscle relaxant group are used, for example, Tizanidin (Sirdalud). Side effects of the drug can manifest as increased fatigue and drowsiness, dizziness and arterial hypotension, dry mouth, nausea.

Physiotherapy treatment is carried out by the method of drug phonophoresis (with NSAIDs). At home, you can do wet hot compresses (several times a day for 15-20 minutes). Heat helps relieve pain and stiffness by relaxing the muscles and increasing blood circulation.

Medical rehabilitation for contracture of the masticatory muscles after the removal of inflammation is aimed at restoring their normal function and includes, in addition to physiotherapy, therapeutic exercises and massage of the masticatory muscles.

Prevention

Timely treatment of inflammatory diseases of the oral cavity and nasopharynx, as well as prevention of occlusion disorders in children and, if possible, correction of malocclusion can be considered preventive measures.

Forecast

With contracture of the masticatory muscles, the prognosis depends entirely on the cause of its occurrence. When muscle fiber shortening is caused by overuse, overload, or physical stress and is within physiological limits, it is reversible. Contracts due to severe injuries, in which a significant part of the tissues of the muscle-tendon structures are destroyed, may be irreversible.