My oldest would grind so loud she'd wake me up over the baby monitor at night! Dentist said she'd grow out of it, but to watch MY stress levels. Well, after the birth of my second child, we decided I'd stay home for awhile. She stopped grinding almost immediately.
My youngest, now almost 2, has Downs Syndrome and grinds constantly. Her speech and occupational therapiest say it is sending messages to her brain about the strength and location of the new teeth, part of the process of learning to chew solids for some kids. I've tried teething rings of all types, and she's not interested. They've suggested allowing her to chew on my finger (carefully avoiding teeth if possible) or providing gentle pressure on the jaw joint, rubbing and pulling it forward slightly. Saying things like, "No grinding" repeatedly as I'm doing these things.
I asked our pediatric specialist from Riley if she had any advice or ways to stop it. She laughed and said if I discovered something to stop it, I could make lots of money.
Well, I'm not rich, but she is doing it less. She also now does respond to me just saying, "No grinding" without doing anything else...SOMETIMES. :)
Good luck.