We Haven’t Connected All the Dots Between Bruxism and Sleep Apnea

Many people who grind their teeth during sleep also experience obstructive sleep apnea, and vice versa. But sleep professionals are divided on whether this relationship has clinical significance.

By C.A. Wolski

Is bruxism a symptom of obstructive sleep apnea (OSA) or is OSA a symptom of bruxism? Are they comorbid or just coincidental?

A growing body of evidence points to a relation between the two conditions. But while research and experience suggest a connection—it isn’t a clear-cut one.

“The main risk factors for sleep-related bruxism (SB) are comorbid sleep disorders, particularly obstructive sleep apnea, snoring, and parasomnias; anxiety and other psychiatric and neurologic disorders can also be risk factors,” explains Kannan Ramar, MBBS, MD, president of the American Academy of Sleep Medicine. “The exact etiology of why or how OSA can contribute to SB is unknown. The theory is that SB is most likely related to micro-arousals from sleep resulting in activation of the autonomic nervous system, and OSA can contribute to the latter.”

Complicating the connection is the nature of OSA patients. Often, they already have underlying comorbidities, such as obesity or diabetes, so the bruxism may be more coincidental than indicative of a sleep-related pathology.

Gilles Lavigne, DMD, MSc, PhD, says about 55% of OSA patients have a bruxism develop after their sleep apnea diagnosis and only about 25% have sleep-related bruxism rhythmic masticatory muscle activity (RMMA) evident prior to an OSA diagnosis.
There is “very low support for a cause and effect—it’s not a consistent sequence,” says Lavigne, who is professor, dean, and Canada Research Chair in Pain-Sleep-Trauma at the University of Montreal and a member of the American Academy of Dental Sleep Medicine. “Some more recent data suggest less rhythmic masticatory muscle activity—the EMG [electromyography] muscle biomarker on [polysomnography] for SB—in OSA patients. The why? It’s unknown and open to research.”

It could be due to the patient’s age, body mass index change, skeletal shape, genetic obesity risk, or other factors that need more research, he says.

Finally, not every case of bruxism is an indication of obstructive sleep apnea. Sleep-related bruxism and awake bruxism are “very different in etiology as well as symptomology. The type of bruxism that we are considering is the sleep-related type. There are all too often referred as one and the same; however, this is far from what the research has shown,” says Ken Luco, DDS, CEO of Luco Hybrid OSA Appliance Inc.

Sleep bruxism is characterized by three activities, Luco says: 1) phasic or rhythmic movements (grinding), 2) tonic or sustained contractions (clenching), and 3) mixed, having characteristics of both phasic and tonic.

This doesn’t mean that a patient with sleep bruxism will have obstructive sleep apnea. Luco notes about 10% to 12% of the population has sleep bruxism without OSA symptoms.

However, there is good evidence, according to Luco, that sleep bruxism and obstructive sleep apnea have a direct link.

“What is unique about SRB [sleep-related bruxism]/OSA is that the SRB events synchronize with the OSA events, occurring just before or just after the OSA event,” Luco says. “A study in 2019 of 147 patients found 1/3 of the OSA patients tested also demonstrated SRB and that these patients also demonstrated more respiratory-related sleep arousals and oxygen desaturations than the controls.¹ They noted that the SRB was predominantly phasic. In these cases, it was felt SRB offered a protective role with the associated micro-arousals stimulating respiration. There are other studies that claim SRB is only a reaction to OSA however they do not explain the vast number of cases of SRB that occur without stoppages in respiration.”

William Ondo, MD, director of the Movement Disorder Clinic at Houston Methodist Stanley H. Appel Department of Neurology, doesn’t see as clear of a connection. “There’s no doubt that there’s a jerk of the jaw when a patient is coming out of an apneic event, but it’s not what I would call bruxism,” he says.

But, perhaps, the best way to accept a connection between bruxism and OSA is as a complex, multifactorial relationship.

“Bruxism is a heterogeneous condition related to various underlying mechanisms, including the presence of OSA,” says Mayoor Patel DDS, MS, director of clinical education at Nierman Practice Management. “It appears that bruxism may be associated with micro-arousal occurring during sleep—this leading go jaw-closing muscles activation, which is then seen as bruxism. The causes of bruxism are multifactorial and are mostly of central origin. Both SB and OSA are probably genetically complex conditions that are likely to result from multiple interactions between genetic and environmental factors.² Recently, sleep bruxism has started to be regarded as a physiological phenomenon occurring in some parts of the population, rather than a pathological one.”

While additional research may be needed to better understand the relationship between bruxism and OSA, what is clear is there are patients who exhibit both.

Screening for Which?

While there is a seeming relationship between sleep bruxism and obstructive sleep apnea, should screening protocols be in place to determine if a patient with one has the other? The short answer is yes.

But as with the causal relationship between the two, it’s a bit more complex in practice.

Ondo notes that if a patient presents with bruxism and exhibits OSA risk factors—they have a thick neck, they’re overweight, they’re male, and their bed partner indicates they snore—then screening for OSA would be warranted.

“If there’s no other risk factors then I don’t recommend it,” he says, but adds that if a patient is undergoing a sleep study and would like more information about their condition, then adding a few more electrodes would be appropriate.

The AASM’s Ramar is more definitive on the screening: “Screening for OSA is reasonable for patients presenting with [sleep bruxism]. There is a population-based study that shows the odds ratio of OSA is 1.8 in patients with SB.³ This is particularly important in patients who might use a mouth splint/guard to prevent teeth wear from grinding, as this can potentially worsen OSA. Similarly, asking about SB is also reasonable in patients with OSA. Not addressing SB could result in jaw pain, morning headaches, and teeth wear.”

In many cases, bruxism is diagnosed by dentists. Every bruxism patient should be screened for OSA, according to Luco.

Sleep technology company SleepScore Labs may be helping to simplify the screening of sleep-related bruxism with its Do I Snore or Grind app, according to Nate Watson, MD, co-director of the University of Washington Medicine Sleep Center and SleepScore Labs advisor.

The snore/grind app “can be used in a home sleeping environment to help people understand if tooth grinding is an issue they need to get looked into by their dentist,” he says.

Making the Diagnosis/Diagnoses

For a diagnosis, jaw muscle movement during sleep must be recorded and analyzed.

Ramar says, “An in-lab sleep study provides objective evidence for [sleep bruxism] by looking at the electrodes on the scalp and chin, ie, looking at muscle activity from the masseter muscle.”

Luco says, “Home sleep studies can only detect this if equipped with a real time EMG and pulse oximeter recording in real time.” One example, Luco says, is the Medibyte from Braebon. “It has an EMG module you can plug in that gives real time data on the muscle activity of both the masseter and temporalis muscles,” he says.

Treating the Connection

There are a veritable menu of treatment options—both well established and emerging—that are available to treat sleep bruxism and obstructive sleep apnea. Among the most common are night guards and CPAP.

But common doesn’t mean it’s the right treatment. In fact, night guards for bruxism can make OSA more severe.

“This can happen in a large number of patients where if they have sleep apnea, the guard can make the situation much worse,” Patel says. “In a few cases the mouthguard for bruxism may have no effect on sleep apnea or rarely improve the number events associated with sleep apnea.”

On the flipside, CPAP may be an effective treatment for sleep bruxism whether the patient has OSA. “I suppose if there is a significant correlation that the unstable airway is causing the bruxism—via arousal of the central nervous system—then it should have a positive effect,” says Patel. “Do remember bruxism is multifactorial and other conditions can also cause bruxism. Successful treatment of sleep-related respiratory effort may lead to improved or resolution of bruxism in cases where such a causal relationship does exist.”⁴

There may be cases where both a night guard and CPAP together would be an effective treatment, Patel adds, particularly if the patient has a severe OSA case and is still bruxing while sleeping.

There are several newer and emerging therapies that show efficacy in treating sleep-related bruxism and OSA.

Oral appliances for sleep apnea are sometimes used off-label for bruxism therapy. The Luco Hybrid OSA Appliance, a two-part mandibular advancement dorsal type device, has actually been FDA cleared for both indications: OSA (mild to moderate) and bruxism.

Luco says, “The device contacts only on the cuspid and first bicuspid. This patented ‘forward bite’ is critical. It provides a very even stress distribution when biting compared to a conventional full bite. The forward bite also activates a protective reflex, the periodontal masseter reflex that inhibits contraction of the masseter and temporalis muscles. This reduces the force of the SRB event to normal ranges. The third is that the forward bite activates a parasympathetic TCR [trigeminal cardiac reflex] response of lower heart rate, lower blood pressure, and slowing breathing. This negates the sympathetic SRB stimulation of the TCR and on post sleep studies of SRB patients wearing the device, the SRB events are reduced to normal ranges within weeks. The initial symptoms of headaches and tooth sensitivity are usually eliminated within 10 days.”

Ondo has done significant studies on the investigational use of Botox (onabotulinumtoxinA injection) to control bruxism.⁵ “Botox is a muscle relaxer and is an elegant treatment that relaxes the muscle but doesn’t impede any of the [other anatomy],” he says.

While it has been shown to be effective—and indeed noted as an emerging therapy by other interviewees for this article—Ondo says treatment can be difficult because there’s yet to be any standardization. He frequently refers patients for night guards additionally—which he says has helped to stop teeth wear.

Other treatments, Watson says, include “conservative measures [such as] implementing proper sleep hygiene and cognitive behavioral therapy with biofeedback can be helpful. Assessment of the presence of medications, eg, antidepressants and antipsychotics, with bruxism as a side effect is also important….Pharmacotherapy with clonazepam or clonidine can also be considered.”

Ramar says treatment should be collaborative between a sleep physician and a dentist.

Boyoun Kuang, a PhD candidate at dentistry school Academisch Centrum Tandheelkunde Amsterdam (ACTA), who won an award for research about sleep bruxism and sleep apnea,⁶ says the continuum is evolving in a way that follows the diagnosis. “Although the diagnosis and treatment of sleep-related disorders fall under medicine, some sleep disorders touch on dentistry (viz, sleep-related breathing disorders—snoring, obstructive sleep apnea) as well as sleep-related orofacial pain, xerostomia, hypersalivation, gastroesophageal reflux disease, and bruxism,” he says. “The dentist may, for example, be able to identify risk factors or consequences of certain sleep disorders in the mouth or masticatory system and thus contribute to the diagnostic process….[And] some sleep disorder treatments have consequences for the mouth and masticatory system.”

In a bit of journalistic serendipity, as he was researching this article Los Angeles-based freelancer C.A. Wolski, who has bruxism, was fitted with a new night guard.

References

1. Tan MWY, Yap AUJ, Chua AP, et al. Prevalence of sleep bruxism and its association with obstructive sleep apnea in adult patients: a retrospective polysomnographic investigation. J Oral Facial Pain Headache. Summer 2019;33(3):269–77.
2. Palmer L J, Redline, S. Genomic approaches to understanding obstructive sleep apnea. Respir Physiol Neurobiol. 2003;135:187–205.
3. Balasubramaniam R, Klasser GD, Cistulli PA, Lavigne GJ. The link between sleep bruxism, sleep disordered breathing and temporomandibular disorders: an evidence-based review. JDSM. 2014:1(1):27-37.
4. Martinot JB, Borel JC, Le-Dong NN. et al. Bruxism relieved under CPAP treatment in a patient with OSA syndrome. Chest. 2020;157.3: e59-62.
5. Ondo WG, Simmons JH, Shahid MH, et al. Onabotulinum toxin-A injections for sleep bruxism: A double-blind, placebo-controlled study. Neurology. 2018 Feb 13;90(7):e559-64.
6. Kuang B, Li D, Lobbezoo F, et al. A large-scale polysomnographic study on the associations between masticatory muscle activity and arousals in OSA patients. JDSM. 10 Apr 2020;7.2: Abstract #003.

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