The dental profession has long been aware that clenching and bruxing the teeth can be a cause of pain from the masticatory muscles. Parafunctional activity refers to any activity, not just clenching and grinding, that is not considered functional, such as chewing, speaking, and swallowing. It can also include certain oral habits.

It is useful to think of clenching and bruxing as two separate phenomena, those that occur during the day (diurnal) when there is the potential for some conscious control, and those that occur during sleep (nocturnal) when conscious control is not possible. There has been extensive research done on clenching and bruxism. It is beyond the scope of this discussion to address it thoroughly. However, several outstanding articles by some of the most published authors on this subject are available in the CORE LITERATURE collection [BRUXISM]. We will summarize some of the key points of this research here.

In addition to the possibility that the patient may clench or grind their teeth, other oral habits can be present and often the individual will not be aware of them. These may include cheek and tongue biting, finger and thumb sucking, unusual postural habits, occupation-related activities, and holding objects such as a telephone or violin under their chin. Not uncommonly a person may clench their teeth when concentrating on a task or performing strenuous physical chores. Similarly, this can also occur when a person is driving a car, reading, writing, or typing. It can also occur during the playing of certain musical instruments or when a diver bites for periods of time on a mouthpiece.

Many of these parafunctional activities occur at a subconscious level. For this reason, since the patient is not likely to be aware of doing them, they may deny such activity on a questionnaire or when asked. However, not uncommonly, once they have been asked, they may begin to notice that they do exhibit these behaviors and may later report that they have “caught” themselves doing them. This awareness may be the first step in overcoming activities of this kind that occur during the day and that can be controlled consciously with some focused attention during waking hours.

Nocturnal parafunctional behaviors have received a great deal of research attention and appear to be a much different and more complex problem than diurnal bruxism. In spite of the amount of research that has been done, there appear to be contradictory findings. It is thought that some degree of nocturnal bruxism is present in most normal subjects. There was a time when the dental profession was convinced that bruxism was related to occlusal interferences. Research has failed to demonstrate such a relationship. Another commonly held opinion is that bruxism is the result of emotional stress. Although some studies have been able to demonstrate in certain individuals that their bruxing events were closely correlated with stressful events in their lives and that these subsided during periods of decreased stress, this appears to be true of only a small percentage of patients studied.

It is known that certain medications can increase bruxing events.