The Whole Truth About the Diagnosis of Bruxism
The debate and research surrounding the phenomenon of bruxism remain very active today, particularly within the academic community.
In this article, we present different perspectives on bruxism and its diagnosis.
We asked ourselves what is actually known about bruxism, how it has been studied to date, and questions such as:
- Who is and who is not a bruxer?
- Do only some people grind or clench their teeth, or does everyone?
- Can tooth wear be explained by bruxism? To what extent?
- Does bruxism explain my jaw pain or headache?
Before continuing, you may wish to read our previous article on the physiology of bruxism, where we explain how and why bruxism occurs. In this article, we focus on how it is diagnosed—if indeed it can be.
HOW IS BRUXISM DIAGNOSED?
The FisioCraneo team led a study on this topic, published at the end of 2023, which identified as many as 73 different methods for diagnosing bruxism (1). However, not all methods are equally valid, nor do they assess the same aspects. We explain this below.
By definition, bruxism is “an involuntary activity of the masticatory muscles and is neither a movement disorder nor a sleep disorder in otherwise healthy individuals.” In other words, it is not considered a disease, and therefore does not necessarily require treatment. We will explain why later. Based on this definition, the first obvious question is:
Do all people have involuntary activity of the masticatory muscles, or only some?
The answer is yes. Everyone can naturally experience involuntary activity of the masticatory muscles during both sleep and wakefulness. Therefore, bruxism is a natural phenomenon of the human condition (see the previous article).
Despite this conclusion, it is still reasonable to ask whether excessive masticatory muscle activity could indicate an underlying problem or contribute to other conditions. This naturally led researchers to ask how bruxism should be measured.
Professor Gilles J. Lavigne and a team of researchers evaluated 36 participants (18 with bruxism and 18 controls) over several nights using polysomnography to estimate the differences between the two groups (2).
Who Were the Participants?
The participants were volunteers who received financial compensation for taking part in the study and met the following criteria:
- Between 20 and 45 years of age.
- Produced tooth grinding sounds at least five nights per week for six months.
- The grinding sounds had been confirmed by a bed partner or roommate.
- Met at least one of the following three criteria:
- Tooth wear or shiny spots on dental restorations according to Johansson et al. 1993 (3).
- Reported morning pain or fatigue in the masticatory muscles.
- Masseter hypertrophy assessed by palpation, with the muscle increasing to three times its resting volume during contraction.
These criteria are now considered highly debatable and introduce considerable bias, especially since participants received financial compensation for what was essentially a subjective diagnosis. However, in fairness, better diagnostic criteria were not available at that time. As we will see, the problem was that these findings were embraced with excessive enthusiasm.
All participants underwent two consecutive nights of assessment. The first night was considered an adaptation night, while the second was used for evaluation. This point is also highly relevant, as later studies have shown that sleep architecture varies considerably from one night to another, even in the same individual.
Masseter muscle contractions were classified into three categories depending on whether they were:
A) Rhythmic (phasic); B) Sustained (tonic); C) Mixed.
Bruxism episodes were defined as follows:
- One phasic episode: At least three bursts lasting between 0.25 and 2 seconds, separated by intervals without bursts.
- One tonic episode: A sustained burst lasting at least 2 seconds.
- In both cases, electromyographic activity had to exceed 20% of the maximum voluntary contraction, based on another study conducted in 1991 that is no longer publicly available (4).
Prior to the evaluation, electromyography (EMG), which measures muscle activity, was calibrated. The participants performed five tasks: coughing, swallowing, rhythmic contractions (teeth tapping), lateral jaw movements, jaw protrusion, and finally a maximum voluntary clench, obtaining values corresponding to 100%, 50%, and 20% of their maximum voluntary contraction.
Once all participants had completed the overnight recordings, the following results were obtained and are presented below in graphs created by the authors:
The bruxism group showed the following findings:
- There were more episodes per hour across all sleep stages.
- The number of bursts per episode was slightly higher.
- The total number of bursts per hour was also higher.
One particularly interesting finding was that there were no differences between the bruxism group and the control group in the amount of time spent in each sleep stage, the total sleep time, the time taken to fall asleep, or the number of nighttime awakenings. Therefore, sleep architecture and bruxism were not associated. It is possible that sleep quality, metabolism, and other factors during sleep may better explain bruxism.
With these results,
Can we conclude that bruxism is the cause of pain and tooth wear?
Absolutely not. The only conclusion we can draw is that the researchers were able to distinguish participants classified as bruxists from those classified as non-bruxists. If we recall the study’s inclusion criteria, only 6 of the 18 participants in the bruxism group reported morning pain or fatigue in the masticatory muscles, and in fact, none reported pain—only fatigue.
The study reported that most episodes were phasic (52.5%) or mixed (36.1%), while only 11.4% were tonic. Based on the definition of a bruxism episode and the reported averages, the participants in the bruxism group experienced, at most, 108 bursts per hour.
Let’s do some calculations:
Applying these percentages, the episodes are distributed into 56.7 phasic bursts, 39 mixed bursts, and 12.3 tonic bursts. We know that phasic bursts last less than 2 seconds, so if we accept a duration of 2 seconds, they account for a total of 113.4 seconds (56.7 × 2 seconds).
Tonic bursts last at least 2 seconds. If we arbitrarily assign them an average duration of 10 seconds, we obtain 513 seconds. Added to the duration of the phasic bursts, this gives a total of 626.4 seconds, equivalent to 10 minutes and 30 seconds of bruxism-related muscle activity above 20% of the maximum voluntary contraction over an average night’s sleep of 7.5 hours.
Furthermore, since 65% of these movements were associated with whole-body movements, we can assume that not all contractions were true bruxism events, but rather spontaneous muscle activity associated with changes in sleeping position. Even so, we will not adjust our calculations to account for this percentage, and will therefore accept an average of 10 minutes and 30 seconds of bruxism-related activity during sleep.
Finally, the study established four levels of bruxism severity based on the number of bruxism events—also known as rhythmic masticatory muscle activities (RMMA)—per hour of sleep. These categories were defined as follows:
Severe bruxism: ≥ 9 RMMA events per hour.
Moderate bruxism: ≥ 4 and < 9 RMMA events per hour.
Mild or low-frequency bruxism: Between 1 and 2.2 RMMA events per hour.
Controls or non-bruxist subjects: Fewer than 1 RMMA event per hour.
At this point, two obvious questions arise:
- How much does bruxism activity vary within the same individual over multiple nights?
- Are 10 minutes of muscle activity above 20% of maximum voluntary contraction enough to cause tooth wear, muscle fatigue, or masseter hypertrophy?
Regarding the first question, Gilles Lavigne himself designed another study in which nine participants with moderate or severe bruxism, according to the categories established in the previous study, were evaluated (5). The authors also reviewed the literature and found that bruxism activity varies moderately over the course of months and even from one night to another within the same week. Therefore, in patients who report daily jaw heaviness or muscle tension, morning jaw fatigue, or restricted mouth opening upon waking, bruxism cannot be assumed to be the sole cause of all these symptoms.
As for the second question, what becomes clear is that 10 minutes of intermittent muscle activity, rather than continuous contraction, seems to be too little to justify these symptoms. Other mechanisms must therefore be responsible for the self-reported symptoms, and these will be discussed in the next article on bruxism.
Tooth wear cannot be explained by bruxism alone either. Tooth wear is a multifactorial process and may result from a variety of causes, including biochemical and metabolic factors that are beyond the scope of this article. In short, reduced dental tissue quality can lead to tooth wear regardless of bruxism activity. Moreover, these signs often reflect past events rather than the patient’s current level of bruxism activity.
Given such poor diagnostic reliability, the FisioCraneo research team conducted a comprehensive review of the literature to identify all the different ways in which patients with bruxism had been included in research studies. We identified 73 different diagnostic methods, which we classified into ten categories, each further divided into subcategories. For example, when polysomnography was used, it could be performed either in a sleep laboratory or at the patient’s home, over one to four nights, with or without an adaptation night.
If there is such considerable variability in the diagnosis of bruxism even when using the same diagnostic method, it is evident that changing or modifying the method only increases that variability. Moreover, if there are as many as 73 different methods for diagnosing bruxism, then the variability becomes overwhelming, and the validity of the diagnosis becomes highly questionable (see the tables and discussion in the published study).
DISCUSSION AND FINAL THOUGHTS
The diagnosis of bruxism is currently made using arbitrary criteria and methods with very limited validity. To date, symptoms such as jaw fatigue, restricted mouth opening, and mandibular discomfort cannot be adequately explained by bruxism alone. Likewise, tooth wear, dental sensitivity, and other physical signs affecting the tissues of the oral cavity may not reflect a person’s current level of bruxism activity. These signs and symptoms are therefore more likely to be explained by mechanisms other than bruxism itself.
This discussion would be of little importance if patients presenting with symptoms such as jaw fatigue, pain, limited mouth opening, and disability—who are subsequently diagnosed with bruxism—were not routinely subjected to expensive and ineffective treatments that fail to address the underlying problem, while placing a significant financial burden on the patients themselves.
For this reason, treatment decisions should always be based on informed consent. Patients deserve to understand what they can realistically expect from the treatment being offered. The signs and symptoms commonly attributed to bruxism are, in reality, better explained by other mechanisms, which we will discuss in a future article. Their management is often simpler, more effective, and less costly than the approaches commonly used in everyday clinical practice.
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REFERENCES
- Padros-Auge, J., Nouhaila, Z., Miquel, C., Morales-Vigo, A., Sebastién, C., & Laurine, P. (2023). Diagnostic criteria for bruxism: A Scoping Review. Journal of Oral Health and Oral Epidemiology, 12(3), 98-104.
- Lavigne, G. J., Khoury, S., Abe, S., Yamaguchi, T., & Raphael, K. (2008). Bruxism physiology and pathology: an overview for clinicians. Journal of oral rehabilitation, 35(7), 476–494
- Johansson, A., Haraldson, T., Omar, R., Kiliaridis, S., & Carlsson, G. E. (1993). A system for assessing the severity and progression of occlusal tooth wear. Journal of oral rehabilitation, 20(2), 125–131.
- Kondo, K., & Clark, GT. (1991). A method for detecting a bruxism event. J Dent Res 70, 1969.
- Lavigne, G. J., Guitard, F., Rompré, P. H., & Montplaisir, J. Y. (2001). Variability in sleep bruxism activity over time. Journal of sleep research, 10(3), 237–244.
