SSRIs can cause jaw clenching.
There are reports of people unconsciously gritting or grinding their teeth while taking Paxil, Lexapro, and other SSRIs. This bruxism can lead to headaches, jaw pain, and cracked fillings or other dental problems.
It's thought that SSRIs can cause bruxism by indirectly lowering dopamine levels. Dopamine inhibits certain movements including jaw clenching.
Treatment with other agents that affect dopaminergic neurotransmission such as antipsychotics, amphetamines, and levodopa are also associated with bruxism. There are also case reports with venlafaxine (Effexor) and bupropion (Wellbutrin).