I started taking magnesium when I was having my TMJ treated. It really helped when I first had to wear a plate and then I continued taking it after that because I find I sleep really well and fall asleep quickly as I take it 20 mins before bed.
When I was having TMJ issues I was taking it morning and night. I stopped a while ago but I got some more when I started exercising again and was getting back pain.
I use Ultra Muscleze by BioCeuticals
but it's an Aussie company. It also contains calcium and lots of other nutrients but not zinc.
The serving is 5g but I tend to just put 1/2t in water.