The Role of Nocturnal Bruxism

For decades dentists believed that the primary cause of TMJ disorders is nocturnal bruxism (clenching or grinding).  They tried to change the bite in a way that would prevent the activity.  However, eventually they learned that nocturnal bruxism is not affected by the bite.  It is a product of normal sleep, usually occurring during transitions from a deeper to a shallower sleep stage.  It is more frequent and intense during times of stress, but it affects everybody to some extent.

Now we know that nocturnal bruxism cannot be considered an important cause of TMJ disorders.  In some people, a drug or a period of extreme stress can cause severe nocturnal bruxism that damages the teeth or the TMJs.  However, it occurs no more frequently in TMJ disorder patients than in other people.  

Nocturnal bruxism can exert huge forces on teeth, because it occurs when our jaw protective reflexes are absent.  These jaw protective reflexes were all designed for chewing.  They were not needed during sleep.  When our ancestors went to sleep, their jaw muscles were tired and needed rest.  Today, we work our jaw muscles so vigorously during sleep that many people even exceed their maximal voluntary bite force.  For example, if you put a little scale between your teeth and you bite as hard as you can, you might produce 100 lbs of force, but during sleep you might produce 120 lbs.  Thus nocturnal bruxism can cause various forms of damage to teeth.

ROOT CANALS are required if sustained clenching strangles teeth.  Holding a tooth forcefully down in its socket can compress its only source of circulation - the little umbilical cord that supplies the tooth through a hole at the end of its root.  The resulting loss of circulation initially causes inflammation of the pulp that makes a tooth temperature sensitive.  Eventually it can cause the tooth to die.  After a tooth dies, it needs a root canal to clelan out and fill the empty space left where the pulp used to live.

GUM DISEASE can be exacerbated by grinding, because the forceful wiggling of teeth can loosen them by widening their sockets like loosening a fencepost.  It also creates gumline defects by slightly bending the teeth at the gumline, causing some of the brittle enamel in that area of maximal flexure to break off or pop out - leaving V-shaped gumline defects (called abfractions) on the outermost (buccal) aspects of primarily the canines and premolars.   These defects can cause plaque accumulation at the gumline and lead to decay.  Before we understood their cause, these defects were blamed on aggressive tooth brushing - a misconception that created the market for soft tooth brushes, which still persists today.

TMJ DAMAGE can be caused by nocturnal bruxism, especially when there is a dislocated disk.  The disk forms the cushion in the joint.  When it is no longer in place between the bones, those bone surfaces are especially susceptible to damage from the large forces used in nocturnal bruxism.  While there are no oral appliances that are able to prevent bruxism, nightguards and stabilization appliances protect the teeth from its effects, joint protective appliances protect the TMJs from its effect, front flat bite plates reduce its force, and functional orthodontic appliances can redirect it to perform orthodontic benefits.