According to the cause, bruxism can be differentiated as follows:
- primary bruxism
- Idiopathic (with no apparent cause).
- Secondary bruxism – due to a variety of factors (see, below “Etiology – Pathogenesis”/”Causes”).
Another possibility of differentiation arises from the type of rhythmic masticatory muscle activity (RMMA):
- Phasic (rhythmic) bruxism – short, repetitive contractions of the masticatory muscles (> 3 muscle activities in the electromyogram of 0.25-2 seconds duration).
- Tonic (non-rhythmic) bruxism – muscle contractions > 2 seconds.
- A combination of both
Bruxism can be graduated as follows:
| Degree of bruxism | Episodes* of bruxism per hour |
| Mild bruxism | > 1 and ≤ 2 |
| Moderate bruxism | > 2 and ≤ 4 |
| sStrong bruxism | > 4 |
* Bruxism episode = at least six consecutive peaks of activity.
