My son does this, he grinds so hard it makes me cringe. I did as well, prior to getting on adrenal support. My jaws would be so inflamed I couldn't close my mouth all the way-I'd have as much as a 1/2" 'gap' between my molars until the swelling went down. Broke my two wisdom teeth as well (the only ones I had) grinding.
DS does it much, much worse when he's under stress-any kind, good or bad (good stress = birthday party the next day, something exciting planned, etc.)
Magnesium was a joke for bruxism (tinnitus is ringing ears ) for us; Pantethine 500mg and Pyrodoxine 250 mg (B5 & B6) plus 100 mgs Bcomplex are the only things that even remotely help for DS...but depending on the situation, even they aren't a fix.
Chief cook & bottle washer for one kid, a dog, 6 hens, 2 surprise! roosters, two horses, and a random 'herd' of quail.
~The ultimate ignorance is the rejection of something one knows nothing about and refuses to investigate~