Dental guards. People who grind their teeth at night can wear down their teeth. A dentist can fit a person with dental guards (like a retainer) to prevent the teeth from grinding during sleep. In some cities, there are dental specialists who customize dental "appliances". There are also generic over-the-counter guards to prevent grinding, but one should ask his dentist if the otc guard is fitting well.
Depends. Should see a dentist and possibly get to source of the grinding or have a custom mouthpiece constructed. If the teeth are worn down, this will change your bite, which in turn can cause muscle and TMJ problems.
Mouth Guard. If you are a persistent "grinder" you will need some help. I would see the dentist or orthodontist and get evaluated. They will more than likely fit you with a mouth guard to wear at night to prevent grinding of the teeth. This will wear away your teeth and cause you much problem and cost you "much dollars"! you may need to be treated for anxiety or other issues if they are present.