DentAI – Bruxism: Disorder or Behavior? The 2018 International Consensus on Assessing Bruxism

About This Study

This article is a commentary, not new laboratory research — it summarizes the consensus reached by a group of leading bruxism researchers from around the world, who were cautious enough to title it itself "a work in progress." In other words, this isn't the final word; it's a midpoint agreement that says, for now, this is as far as we've gotten.

The story begins in 2013, when this same group proposed a simple definition of bruxism that became well established in the literature, but it had two loose ends: the terms bracing and thrusting remained ambiguous within the definition, and a grading system was disputed. To resolve these two issues, an international meeting was held in San Francisco in 2017, and this paper is the output of that meeting.

Four Core Terms

According to this consensus, bruxism takes four forms. The first two are familiar and require tooth contact:

Clenching: pressing the teeth together.
Grinding: rubbing the teeth against each other.

The next two are the very terms that remained ambiguous in the 2013 definition, and their key feature is that they do not require tooth contact:

Bracing: holding the jaw rigidly in a fixed position under tension — the muscles are contracted and the jaw is locked, without the teeth necessarily meeting.
Thrusting: pushing the jaw forward or sideways under tension — again without any need for tooth contact.

The main message of these four terms together: bruxism is fundamentally a muscle activity, not merely an event occurring at the tooth surface. A muscle can be under excessive tension and activity even without the teeth ever touching — consistent with the view that bruxism is centrally driven (by the brain), not peripherally driven (by tooth arrangement/occlusion).

Two Definitions Instead of One

The single 2013 definition was retired, replaced by two separate definitions:

Sleep bruxism: masticatory muscle activity during sleep, which can be rhythmic or non-rhythmic.
Awake bruxism: masticatory muscle activity during wakefulness, manifesting as repeated or sustained tooth contact, or as bracing and thrusting.

Two features of these definitions are deliberate. Both begin with "muscle activity" to emphasize that the origin of the problem is muscular, not dental. And both end with "in healthy individuals," because in most people bruxism is not a disorder — but in some, it signals a genuine underlying problem, such as sleep apnea or epilepsy, which must be taken seriously.

Disorder or Behavior?

This is the article's most important conceptual point.

There is a difference between something that is inherently harmful by itself (a disorder) and something that merely raises the probability of harm without guaranteeing it (a risk factor). The group's conclusion was: in a healthy individual, bruxism is not a disorder; it is either a risk factor, or simply a multi-causal motor behavior.

Bruxism can raise the risk of things like muscle pain, temporomandibular joint pain (TMD), severe tooth wear, and premature failure of prosthetic work. But a point that is often overlooked is this: sometimes bruxism is even protective — for example, in sleep apnea it can help keep the airway open, or in gastroesophageal reflux (GERD) it can increase saliva flow and help buffer chemical tooth erosion.

So bruxism has three possible states: neutral (a harmless behavior), a risk factor (associated with a negative outcome), or a protective factor (associated with a positive outcome) — and these can occur simultaneously. For example, a patient could have sleep bruxism that causes tooth wear while also keeping their airway open at the same time.

How Do We Assess Bruxism?

There are two general approaches to assessment: non-instrumental and instrumental.

Non-instrumental: includes patient self-report and clinical examination. Self-report is the primary tool, but it has a subtle weakness: bruxism's relationship with stress and anxiety can lead patients to over-report — meaning self-report sometimes reflects psychological distress rather than actual muscle activity.

For awake bruxism, the recommended approach is to first explain to the patient exactly what clenching and bracing are, and then have the patient monitor themselves for one to two weeks using a diary. For sleep bruxism, a partner — or, in children, a parent — can help, since the patient is asleep and cannot be their own observer.

Clinical signs common to both types include hypertrophy of the masticatory muscles, indentations of the teeth on the tongue or lips, and a white line on the buccal mucosa (linea alba). Tooth damage, repeated restoration failure, and tooth wear (attrition) are also signs — but with an important caveat: tooth wear can be a sign of past bruxism and is not necessarily evidence of current activity; wear is a historical record, not a real-time diagnosis.

Instrumental: for awake bruxism, electromyography (EMG) during wakefulness and momentary ecological-sampling apps are used. For sleep bruxism, EMG during sleep and polysomnography are used, supplemented by audio and video recording.

The Cut-off Point

The paper explicitly states that using a single fixed cut-off point for everyone — "this number means bruxism is present, that number means it isn't" — is not appropriate in healthy individuals. The reason is that these cut-off points were developed for research purposes, not for everyday clinical use; moreover, the point at which bruxism actually becomes dangerous varies depending on which clinical outcome is being discussed.

The paper offers a clear example: prolonged tooth clenching can overload the muscle and joint, but as soon as fatigue or pain sets in, the body itself reduces muscle activity — meaning there is a built-in protective mechanism that makes a fixed cut-off point essentially unworkable. The final recommendation is that bruxism should be assessed as a continuous spectrum, rather than by a rigid count of events.

A New Grading System

The 2013 version had three tiers but came with a flaw. The revised version is as follows:

Possible: based solely on a positive patient self-report.
Probable: based on a positive clinical examination, with or without self-report.
Definite: based on a positive instrumental assessment (such as EMG), with or without the other two criteria.

The paper itself emphasizes that this system, too, is only a proposal and needs to be validated by future research.

Roadmap and Conclusions

The paper states that we are still some distance from an ideal assessment, and it proposes a principle for future research: the A4 principle — accurate, applicable, affordable, and accessible.

The paper's four final conclusions: first, sleep and awake bruxism are both masticatory muscle activities occurring during sleep and wakefulness, respectively. Second, in healthy individuals bruxism is not a disorder; it is a behavior that can simultaneously be a risk factor and/or a protective factor. Third, both non-instrumental and instrumental methods are usable, but both need further research. Fourth, a fixed cut-off point should not be used in healthy individuals; bruxism should be viewed as a continuous spectrum.

Frequently Asked Questions

Is bruxism a disorder?
Not in healthy individuals. The 2018 international consensus explicitly considers bruxism, in these individuals, to be a behavior rather than a disorder — one that, depending on circumstances, can be a risk factor, a protective factor, or entirely neutral.

What is the difference between sleep bruxism and awake bruxism?
Sleep bruxism is rhythmic or non-rhythmic muscle activity during sleep; awake bruxism is repeated or sustained tooth contact, or bracing/thrusting, during wakefulness. Both are fundamentally muscle activities, not phenomena that originate at the tooth surface.

Is there a fixed number for diagnosing bruxism?
No. The paper explicitly argues against a fixed cut-off point for healthy individuals and recommends that bruxism be assessed as a continuous spectrum rather than by a single cutoff number.

Does tooth wear mean a person is currently bruxing?
Not necessarily. Tooth wear is a historical record of past activity and is not, by itself, evidence of current muscle activity.