How to slim jaw muscles from grinding?

Night appliance: Use of a properly made night time appliance is effective. Also, Botox has been shown to help.

Many causes: Someone may grind their teeth for a number of reasons. Often, the problem occurs because the muscles of the face and jaw are trying to get the teeth in a comfortable position. The muscles may be in spasm, you may have a tmj/tmd problem, stress, infection. Best to see a dentist asap. Often the cause is difficult to determine, so may have to treat the symptoms with a mouthpiece.

Botox: One very successful treatment is Botox injection of masseter and temporalis muscles. Has to be repeated every 3-6 months.