Etiology of Bruxing Events

Over the years, a great deal of controversy has surrounded the etiology of

bruxism and

clenching. Early on, the profession was quite convinced that bruxism was

directly related to occlusal interferences.Therefore treatments were directed

toward correction of the occlusion condition. Later studies did not support

the concept that occlusal contacts cause bruxing events. Although it is clear

that occlusal contacts influence function of the masticatory system, they are

not likely to contribute to bruxism. One factor that seems to influence

bruxing activity is emotional stress. Early studies that monitored levels of

nocturnal bruxing activity demonstrated a strong temporal pattern

associated with stressful events (Fig. 7-3). This pattern can be seen clearly in

Fig.7-4 when a single subject is monitored over a long period of time. As the

subject encountered a stressful event, the nocturnal masseter activity

increased. Associated with this activity was a period of increased pain. Of

note is that more recent studies found this relationship to be true in only a

small percentage of the patients studied. At the writing of the first edition of

this textbook (1983), a common and well-accepted concept was that

parafunctional activity was a significant etiologic factor in TMDs. In fact, it

was thought that if parafunctional activity could be controlled, TMD

symptoms would be controlled thought that if parafunctional activity could

be controlled, TMD symptoms would be controlled. As the field has matured,

new information has shed new light on the etiology of TMD. Presently it is

still believed that parafunctional activity can be an etiologic factor, but it is

far more complex than that. Clinicians also recognize that bruxing and

clenching are common, almost normal findings in the general population.

Most individuals have some type of parafunctional activity that never results

in any major consequence. However, on occasion parafunctional activity

does precipitate problems, and therapy needs to be directed toward

controlling it. In other instances it may not be the primary cause of the TMD

symptoms but a perpetuating factor that maintains or accentuates

symptoms. In this case both the major etiology and the parafunctional

activity need to be addressed for complete resolution of symptoms. The

effective clinician must be able to differentiate when parafunctional activity

is important to the patient's symptoms and when it is only an accompanying

condition. This is accomplished by carefully scrutinizing the patient's history

and examination findings.

Rugh demonstrated that daily stress is reflected in nocturnal masseter

muscle activity. (From Rugh JD, Solberg WK: In Zarb GA, Carlsson GE,

editors: Temporomandibular joint: function and dysfunction, St Louis, 1979,

Mosby.)

Long-term relationship of stress, muscle activity, and pain. These three

measurements have been obtained from a single subject for a 140-day

period. Shortly after a stressful experience, the nocturnal muscle activity

increases. Not long thereafter, the subject reports pain. (From Rugh JD,

Lemke RL:Significance of oral habits. In Matarazzo JD Herd AJ, Weiss SM,

editors: Behavioral health: a handbook of health enhancement and

disease prevention, New York, 1984, John Wiley & Sons.)