Because most bruxism happens at night, most sufferers aren't even aware of it until a sleep partner mentions the noise (an extremely disturbing sound, like fingernails on a blackboard), or until a dentist notices that their teeth are damaged.

Nocturnal grinding can exert thousands of pounds of pressure per square inch on the surfaces of teeth. It can be rough not only on teeth but on the supporting bone, the gums and jaw joint. 

For many years, bruxism was attributed to the release of tension from emotional stress. However, many dental authorities today believe that the causes exist in the patient's mouth. Night grinding may be an unconscious effort to correct irregularities of the chewing surfaces of the teeth. Dentists term this a malocclusion. They grind away to eliminate a spot that is too high or to find a comfortable place to fit the upper and lower teeth together. 

If you have this nightly grind problem, your first stop should be your dentists office... before you do any serious damage to your teeth. 

Possible Complications:
-Without treatment, teeth, bones and gums may erode from the pressure of grinding. 
-May lead to temporomandibular joint syndrome. 

Bruxism in children
For children you may notice that they complain of sore jaw muscles. The exact cause of bruxism is unknown. Local, systemic, and/or psychological factors may play a role. Local factors may include an occlusal interference like premature contact between an upper and lower tooth, a high filling or crown, or some other irritating dental condition. Systemic factors may involve intestinal parasites such as pinworms, anal pruritis, nutritional deficiencies, allergies, or endocrine disorders. The psychological theory hypothesizes that bruxing can be a result of a personality disorder or increased stress. 

Treating bruxism in children should begin with simple measures. First, any occlusal interferences should be identified and removed. If no interferences are noted, it might be prudent for the pediatrician to examine the child to rule out any systemic conditions. If these steps are not successful, a splint or mouthguard-type appliance can be fabricated to help protect the teeth. The wearing of this guard should be carefully monitored to ensure it is actually helpful and to make adjustments as oral changes and growth occur. In cases where psychological factors appear to play a role, referral to a child counselor or child development expert may be helpful. 

You should first take your son/daughter to the dentist for an evaluation of his/her occlusion. An exam by your pediatrician may also be warranted. It is possible a mouthguard may be needed at some point, but some children outgrow bruxism. Be sure your son/daughter is drinking plenty of water during the day, especially during the hot summer months. 

How to Treat Bruxism:
There are several methods of treatment for bruxism.  Your dentist may prescribe a  nightguard for you.  This is simply a barrier worn between the top and  bottom teeth to stop them from grinding together.  Another method of treatment is biofeedback (relaxation exercises) or counseling  which teaches patients how to reduce muscle activity when the biting force becomes too great.  Once a more advanced stage of wear is present, however, treatment can become more complicated and more involved. In some cases, occlusal rehabilitation with certain restorations (usually crowns) is necessary for the best long-term results. The condition of the teeth, the condition of the occlusion, and the effect on the temperomandibular joint (TMJ) will aid in determining proper treatment. If the condition of the teeth is generally good, meaning that there are no cracks, no large restorations, or extreme wear, careful placement of composite resin can be done to restore some shape to the teeth. If the teeth exhibit cracks, large restorations, and extreme wear, crowns will need to be fabricated to replace missing tooth structure, restore proper occlusion, and decrease further wear. 

Prices for Treatments:
Prices for the simple procedures are, of course, less expensive. An occlusal guard (nightguard) can vary from $200 to $1,000. Composite resin fillings might cost $100 to $300. Full mouth reconstruction will be expensive, but may give you the best return on your investment in the long-term. It is difficult to say how many of your teeth might need crowns, but these have a great variation in cost from about $500 and up for each tooth. For full mouth reconstruction, some dentists may charge by the tooth or may charge a flat fee. You will find price variation due to differences in the materials used, dentist expertise, and local economic factors

References: 
-Weideman et al., "The incidence of parasomnias in child bruxers versus nonbruxers" Pediatric Dentistry (1996) 18(7):456-460. 
-Pinkham et al., Pediatric Dentistry: Infancy Through Adolescence, W.B. Saunders Company (1999). 
-Braham et al., Textbook of Pediatric Dentistry, B.C. Decker Inc., (1988)