By Gerard Meskill, M.D.
The occurrence of gnashing or grinding of teeth is not new. The Bible makes reference to this phenomenon both in the Old Testament, "His anger has torn me and hunted me down; he has gnashed at me with his teeth," (Job 16:9) and in the New Testament, "But the children of the kingdom shall be cast out into outer darkness: there shall be weeping and gnashing of teeth" (Matthew 8:12). While this problem is many centuries old, it is only recently that we have come to understand why this may occur, particularly at night while we are asleep.
Teeth clenching or grinding -- a behavior known as bruxism -- is a common problem that can lead to broken teeth, enamel damage, headaches, and temporomandibular joint (TMJ) disorders. The term "bruxism" comes from the Greek word "brychein," which means "to grind or gnash the opposing rows of upper and lower teeth." The American Academy of Orofacial Pain defines bruxism as "diurnal or nocturnal parafunctional activity which includes clenching, gnashing, gritting and grinding of teeth." Data on the prevalence of bruxism varies based upon research criteria, working definition, population samples, and clinical criteria. Indeed, almost everyone clenches or grinds their teeth at some point. However, this becomes pathologic (and thus clinically significant) when it leads to tooth damage or other symptoms, as described above. In 2004, Basić and Mehulić estimated that at least 10 percent of the adult population engages in clinically significant nocturnal bruxism.
For many years (centuries even), physicians and dentists alike have been perplexed as to the cause of this nocturnal behavior. However, we now understand that a significant cause of nocturnal bruxism is airway instability during sleep, such as what occurs in Upper Airway Resistance Syndrome (UARS) and Obstructive Sleep Apnea (OSA). Intuitively, this makes sense. As we fall asleep, muscle tone regulation changes, leading to relaxation of our muscles. The upper airway largely is comprised of muscles and soft tissue. As we fall asleep, the tongue becomes less tense, regressing toward the back of the airway. The mandible, which is held in place by facial muscles, also has a tendency to retrude as those muscles relax. Since the base of the tongue is anchored to the mandible, this leads to further regression of the tongue toward the back of the throat. In individuals with narrower craniofacial anatomy, this can lead to significant upper airway resistance or obstruction during sleep. One possible defense against this process is to clench the teeth, holding the mandible in place to combat this retrusion and keep the airway more patent.
In recent years, clinical research has shown that treatment of the obstructive respirations during sleep leads to improvement or resolution of nocturnal bruxism in many cases. Oksenberg and Arons demonstrated that treatment of OSA with positive airway pressure (e.g., CPAP) led in many cases to resolution of nocturnal bruxism previously observed in affected individuals.
This result was reproduced by Simmons and Prehn, who also demonstrated the same trend in patients with UARS. To distinguish this more subtle form of obstructive respirations during sleep, they used esophageal manometry to measure intra-thoracic pressure during sleep. As the upper airway becomes narrower, the body compensates by expanding the chest to create a more negative intra-thoracic pressure, thus increasing the driving force of air into the lungs. Unlike more severe OSA, in cases of UARS the increased effort to breathe may cause brief disruptions in the normal sleep pattern before the airway collapses, and therefore the measurement of intra-thoracic pressure serves to identify periods of time in which increased breathing effort is causing disruptions of normal sleep. Simmons and Prehn showed that patients with UARS who were treated with CPAP also had significant improvement in nocturnal bruxism, with more than half of the treated patients having complete resolution and most of the rest having at least partial resolution.
So if you grind or clench your teeth at night, wake up with temporal headaches or TMJ pain, or you have been told you're wearing down your teeth, you should consider seeing a sleep specialist, because you may have restricted airflow during sleep that could be causing cardiovascular problems as well. This issue may be as old as the Bible, but finally treatment is now available.
Basić, V., Mehulić, K. "Bruxism: an unsolved problem in dental medicine." Acta Stomatol Croat. 2004;38(1):93-6.
Oksenberg, A., Arons, E. "Sleep bruxism related to obstructive sleep apnea: the effect of continuous positive airway pressure." Sleep Med. 2002 Nov; 3(6):513-5.
Simmons, J. Prehn, R. "Nocturnal bruxism as a protective mechanism against obstructive breathing during sleep." Abstract: 2009 APSS conference.
Gerard Meskill, M.D., is a neurologist and sleep disorders specialist. He completed his sleep fellowship training at the Stanford Center for Sleep Sciences and Medicine. This Center is the birthplace of sleep medicine and includes research, clinical, and educational programs that have advanced the field and improved patient care for decades. He now practices sleep disorders medicine and neurology in the Greater Houston area at Comprehensive Sleep Medicine Associates, with offices in the Woodlands, the Houston Medical Center, and Sugar Land, Texas.
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