Bruxism when the parafunctional activity occurs – during sleep ("sleep bruxism"), or while awake ("awake bruxism"). This is the most widely used classification since sleep bruxism generally has different causes to awake bruxism, although the effects on the condition on the teeth may be the same. The treatment is also often dependent upon whether the bruxism happens during sleep or while awake, e.g., an occlusal splint worn during sleep in a person who only bruxes when awake will probably have no benefit. Some have even suggested that sleep bruxism is an entirely different disorder and is not associated with awake bruxism.
Bruxism often initially deny clenching and grinding because they are unaware of the habit. Often, the person may re-attend soon after the first visit and report that they have now become aware of such a habit. Several devices have been developed that aim to objectively measure bruxism activity, either in terms of muscular activity or bite forces. They have been criticized for introducing a possible change in the bruxing habit, whether increasing or decreasing it, and are therefore poorly representative to the native bruxing activity. These are mostly of relevance to research, and are rarely used in the routine clinical diagnosis