Functional Disorders of the Orofacial System
The orofacial system includes the maxilla and the mandible with the sets of teeth, the masticatory muscles, the temporomandibular joints (TMJs), and the neuronal control with motor end plates. Functional diseases of this system develop as a result of multifactorial mechanisms. A functionally impaired masticatory system will display monotonous movement sequences, for instance, whereas variable movement patterns are seen in a healthy system (Fig 11-1).
Under certain circumstances, functional disorders may not cause any distinct symptoms in a patient and can only be identified by thorough investigation. If symptoms do occur, they frequently affect the muscles of mastication and the TMJs and are evident as tension, muscle and joint pains, jaw clicking, migraine-type headaches, and ringing in the ears (tinnitus). They can be divided into myopathies (muscular diseases) and arthropathies (joint diseases).
The purely muscular diseases range from dull muscle pain during mandibular movements to genuine tissue inflammation, muscle spasms through to changes in the muscle tissue (Fig 11-2). As well as physical illnesses, psychologic problems are a possible cause of muscular disorders.
The physical causes include occlusal discrepancies due to missing or displaced teeth, joint deformations and similar conditions, head or neck injuries, extremely wide mouth opening, or pathologic muscle tension due to postural abnormalities. Wrongly shaped chewing surfaces, wear facets in fillings, or prosthetic teeth indicate occlusal disorders that may induce muscular hyperactivity or parafunctional mandibular movements.
Psychologic problems caused by chronic stress lead to hyperactivity of the masticatory muscles and abnormal, enforced movement patterns (parafunctional habits). Such parafunctional activities always produce muscular problems, eg, grinding the teeth while asleep (bruxism). With bruxism, the force and duration of tooth contacts are prolonged; the muscles and periodontal tissues are overloaded; and tension headaches, joint pains, and muscle tension in the neck area can develop.
Physiologic tooth contacts (approximately 40 minutes a day) take place during chewing and swallowing, and the mean force level is 20 to 30 N, with peaks of up to 600 N. Periodontal tissues and masticatory muscles have long recovery periods in between. Loads of up to 950 N can arise from parafunctional masticatory movements such as grinding and gnashing of teeth.
Teeth grinding (bruxism or bruxing) refers to unconscious, rhythmic, compulsive, nonfunctional gnashing or clenching of the teeth by intermittent or persistent contractions of the masseter and temporal muscles, which is associated with grinding sounds.
Teeth grinding mostly happens at night during REM (rapid eye movement) sleep, but it can sometimes occur during the day, especially in stressful situations. A distinction is made between waking or daytime bruxism and sleep bruxism.
Disorders in the neurotransmitter system of the brain are considered to be causes of teeth grinding, which means bruxism is a centrally controlled and not a peripherally controlled disorder. Smoking, alcohol, illness, trauma, drug misuse, psychiatric disorders, and malocclusions favor this parafunctional activity. Stress or abnormally suppressed aggression as well as other psychologic factors have less influence than was previously thought to be the case.
Clenching as an apparently milder form of grinding, in which the teeth are only pressed onto each other and not rubbed against each other, is nearly as harmful. The abnormal masticatory forces during clenching and the transverse stresses during grinding lead to severe periodontal damage, considerable abrasion of the occlusal surfaces with wedge-shaped defects, and TMJ diseases and myopathies, muscle pains, or restricted movement of the masticatory muscles. Insomnia, sporadic headaches, and pains in the nape, back, neck, or shoulders arise.
These parafunctional movements can be treated and muscle tone normalized with what are known as bruxism splints or muscle relaxation splints in the form of occlusal guards. Splint therapy is intended to prevent damage to teeth, reduce grinding and clenching activities, and prevent sleep disturbances.