Sleep bruxism is characterised by rhythmic masticatory muscle activity occurring during sleep, typically in the form of tooth grinding or jaw clenching. It is classified as a sleep-related movement disorder and is associated with sleep arousals, tooth wear, jaw pain, temporomandibular joint dysfunction, and morning headaches. The popular explanation that stress causes bruxism is partly correct but incomplete; the condition is more accurately understood as arising from the interaction of multiple neurological, mechanical, and psychological factors.
The Sleep Architecture Context
Sleep bruxism episodes predominantly occur in NREM sleep stages 1 and 2, typically during micro-arousals that interrupt sleep. Each episode represents a burst of rhythmic jaw muscle activity lasting approximately 8 seconds, occurring at a frequency of approximately one per hour in mild bruxism and more frequently in severe cases. The micro-arousals suggest that bruxism is partly a response to sleep instability rather than purely a psychological response to stress.
The Upper Airway Connection
Research by Guilleminault et al. has demonstrated a significant association between sleep bruxism and upper airway obstruction, including both obstructive sleep apnea and the milder upper airway resistance syndrome. The proposed mechanism is that jaw protrusion and rhythmic chewing movements during sleep represent a reflex response to upper airway narrowing, as these movements increase upper airway patency. This means that addressing sleep-disordered breathing may resolve or improve bruxism in a subset of patients.
Stress and Bruxism
Psychological stress, anxiety, and emotional suppression are consistently identified risk factors for sleep bruxism. A 2010 case-control study found that evening psychological stress scores were significantly higher on nights preceding bruxism events compared to bruxism-free nights. The catecholamine surge associated with stress appears to lower the arousal threshold during sleep, increasing the frequency of micro-arousals that trigger bruxism episodes.
Management Approaches
- Occlusal splints (night guards): the most widely prescribed treatment; protects teeth from wear but does not reduce the underlying bruxism activity
- Botulinum toxin (Botox) into masseter and temporalis: well-evidenced for reducing bruxism severity and jaw pain; requires repeat injection every 3 to 6 months
- Biofeedback therapy: devices that detect masseteric muscle activity and produce an auditory or tactile stimulus show modest but significant reduction in bruxism events
- Sleep apnea treatment: CPAP therapy has been shown to reduce bruxism frequency in patients with comorbid OSA
- Stress management: CBT, relaxation techniques, and exercise; evidence for modest but consistent improvement in bruxism frequency
Sources
- Lavigne GJ, et al. (2008). Sleep bruxism: overview of an oromandibular sleep movement disorder. Sleep Medicine Reviews, 12(2), 149-165.
- Lobbezoo F, et al. (2018). Bruxism defined and graded: an international consensus. Journal of Oral Rehabilitation, 45(7), 525-533.
- Saito M, et al. (2014). Comparison of effect of CPAP on bruxism activity in patients with and without sleep apnea. Journal of Dental Research, 93(9), 887-893.