The Demystification of Sleep Bruxism – Is what's measured necessarily fact?

“If it is measured it is a fact, otherwise it is an opinion.” Barney Jankelson

But how it is measured is as important!

Dentistry is fast changing and we all struggle to keep up. What I was taught about bruxism as a student in dental school in the late seventies and what I taught when I was faculty had expiry dates. Recently, I had the privilege to be involved in the setting up of the NUS Edmund Tay Mai Hiong (ETMH) endowed fund which I hope will serve as a useful platform to introduce sleep medicine and airway-focused prosthodontics to the local dental profession.

As part of the forward planning for the endowment, a questionnaire survey (n=74) was conducted to assess the current knowledge and attitudes of local dentists regarding sleep and airway issues in dentistry (SAID). Alarmingly, 44.6% of responders were unaware that most sleep bruxism (SB) episodes occurred as a consequence to sleep micro-arousals and, worse, 39.2% still believed erroneously that ‘SB is an occlusal disorder’. Only 35.1% (not necessarily those who answered the 2 previous questions correctly) volunteered that they ‘felt confident’ in managing patients with SB!

Consensus in the definition & diagnosis of bruxism

The existing literature surrounding bruxism is often difficult to interpret. This is probably the result of continued disagreement about the definition and diagnosis of this complex trigeminal oromotor condition. Bruxism was recently re-defined by an international expert group [1] as “a repetitive jaw-muscle activity characterized by clenching or grinding of teeth and/or by bracing or thrusting of the mandible.  It has two distinct circadian manifestations: it can occur during sleep i.e. Sleep Bruxism, or during wakefulness i.e. Awake Bruxism.”

Undeniably, many of the cases referred to me for full-mouth prosthodontic reconstruction were deleterious consequences of bruxism. However, today when I see any patient referred to me for the management of ‘abnormal’ tooth wear, I would never fail to ask the following questions:

Is this wear functional or parafunctional?
Is it historic or ongoing?
If ongoing, is it occuring when the patient is awake, asleep or both?
If during sleep, does it occur in NREM sleep only, REM sleep only or both?
Are we dealing with a primary (idiopathic) sleep bruxism, secondary sleep bruxism, or a combination of the above? 

Fig. 1

Fig. 1

By consensus, a new diagnostic grading system was proposed whereby bruxism was categorized as possible, probable or definite [1]. (Fig. 2) It was implied that a ‘definite’ diagnosis of bruxism can be made only if we had polysomnographic (PSG) evidence, in addition to self-report (usually collected via questionaires and/or patient history), and physical examination.

Fig. 2

Fig. 2

Everyone acknowledges that historic tooth wear and self-reports are notoriously unreliable but is the full-night attended level I PSG with concomitant audio-video recording [2] really the gold standard? As far as research is concerned I do totally agree and would be extremely cautious interpreting any study on SB without PSG. However, the use of PSG for diagnosing bruxism in clinical dental practice has definite limitations.

Disadvantages of PSG in the diagnosis of SB in daily practice

In diagnosing SB, there needs to be a well-defined exclusion criteria that separates it from other involuntary orofacial activity (eg. swallowing, coughing) and other sleep disorders e.g. REM behavior disorder (RBD), epilepsy, tooth tapping. A very specific electromyographic (EMG) surrogate called rhythmic masticatory muscle activity (RMMA) is studied. RMMA is defined as 3 masseter muscle bursts or contractions (phasic, tonic or mixed) within an episode in the absence of teeth grinding. In other words, SB refers to the sleep movement disorder, whereas RMMA is the characteristic EMG pattern that is scored during sleep to make a PSG diagnosis of SB as a ‘Sleep-related movement disorder’ (Category 6: International classification of sleep disorders 3rd Edition, AASM 2014) [3]. The quantification of RMMA episodes in subjects with SB can be categorized into:

i. low frequency RMMA (≥2 and <4 RMMA episodes/hr of sleep)
high frequency RMMA (≥4 RMMA episodes/hr of sleep) and/or ≥ 25 EMG bursts per hour.

This type of attended sleep study requires sophisticated instrumentation, high levels of technical competence, is time-consuming and very expensive especially if performed in a hospital setting. In the Singapore experience, most PSG technicians and reporting sleep physicians are either unfamiliar with the 1996 Research Diagnostic Criteria (RDC) proposed by Lavigne et al[4] for scoring SB, not keen and/or would charge a disproportionately higher fee for the service as there is no automated scoring system available. Realistically, there simply is no market right now, at least in Singapore!

Patients are made to sleep and are studied in a very unnatural setting with 2 belts around their chest and abdomen, and many recording electrodes on their face and body. They are coerced to sleep supine even though it might not be their habitual sleeping posture, and we already know from the literature that more SB-RMMA episodes will be elicited when subjects are lying on their backs. Patients with Upper Airway Resistance (UARS) [5] usually adopt positional strategies (e.g. prone or side sleeping) and partly because of their anxious personalities and/or inherent low arousal thresholds, they, unlike their obstructive sleep apnea (OSA) counterparts, have great difficulty adjusting to this environment. Many returned sleep data which the reporting sleep physician often dismissed for ‘first night syndrome’ requiring expensive re-tests. Ironically, UARS patients because of inspiratory flow limitations and respiratory effort-related arousals (RERAs) report the most SB and are the ones who are more likely to have comorbid TMD rather than their OSA counterparts [6].

Realize also the PSG report is but a snapshot of a single night’s RMMA activity whilst the night–to-night variability of SB is but well documented. Another more alarming revelation for the interested dental clinician is RMMA index (i.e. number of RMMA episodes per hr. of sleep) that is being scored has been shown to have poor correlation with waking symptomology (transient morning headaches and masticatory muscle myalgia) and pain related to TMD. In fact, patients with SB with low frequency RMMA have higher risks for orofacial pain and headache than patients with a high frequency of RMMA [7].

The continual search for pragmatic clinical tools in the diagnosis of bruxism: Quo vadis?

So other than the PSG, what is the wet-fingered dentist to do?  The general concensus of an panel of experts was 'until widely available, cost-effective, reliable and valid diagnostic tools are developed, it is suggested that clinicians and researchers apply the proposed grading system using the best available evidence."[1]

In line with the above recommendations, I will introduce and discuss the advantages of a novel 6-week clinical protocol in establishing a putative diagnosis of awake and sleep bruxism, in a subsequent blog.



  1. Lobbezoo F, et al. Bruxism defined and graded: an international consensus. J Oral Rehabil, 2013. 40(1): p. 2-4.

  2. Carra MC, Huynh N, Lavigne G. Sleep bruxism: a comprehensive overview for the dental clinician interested in sleep medicine. Dent Clin N Am, 2012. 56(2): p. 387-413.

  3. American Academy of Sleep Medicine. International classification of sleep disorders–third edition (ICSD-3). Darien, IL: American Academy of Sleep Medicine, 2014.

  4. Lavigne GJ, Rompré PH, Montplaisir JY. Sleep bruxism: validity of clinical research diagnostic criteria in a controlled polysomnographic study. J Dent Res, 1996. 75(1): p. 546-552.

  5. Guilleminault C, Chowdhuri S. Upper airway resistance syndrome is a distinct syndrome. Am J Respir Crit Care Med, 2000. 161(5): p. 1412-3.

  6. Tay DKL and Pang KP. Clinical phenotype of South–East Asian temporomandibular disorder patients with upper airway resistance syndrome. J Oral Rehabil, 2018. 45(1): p. 25-33.

  7. Rompré PH, Daigle-Landry D, Guitard F, Montplaisir JY, Lavigne GJ. Identification of a sleep bruxism subgroup with a higher risk of pain. J Dent Res, 2007. 86(9): p. 837-842.

The views and opinions expressed in this article are those of the author's alone.