Mouthguards or biteguards are a very useful tool in preventing excessive teeth wear due to bruxism or clenching at night. Simply put, when you grind, the bit of plastic between your teeth prevents your teeth from touching. It also acts as a cushion sometimes providing relief to an aching TMJ joint. Mouthgaurds are available both over the counter at drugstores and can be made in a dental lab by a dentist. The over the counter kind are fine for most people but if you require a better fitting or thinner material then the dentist can get you a better appliance.
Some mouthguards are made to prevent snoring or sleep apnea. They function by repositioning the lower jaw forward to lift the tissue at the back of the throat. This type should be fabricated by a dentist because it can cause problems with the bite if made incorrectly.