N.H.
I tried a mouth guard and it did help. I've learned that a magnesium deficiency can cause teeth grinding. I tried magnesium (calcium) citrate with great success (no morning headaches!). I just make sure I stay within the RDA (Children: 150-200 mg).
Here are two websites that were helpful to me: www.vitaminsdiary.com/minerals/magnesium.htm
www.health911.com/remedies/rem_teethg.htm
Hope this helps in some way. :)