TMD and Bruxism as Expressions of Central Regulatory State

A Question That Has Followed Me for 35 Years

Picture two patients sitting in my chair on the same afternoon. Both have jaw pain. Both grind their teeth. Both show signs of temporomandibular disorder — the clinical umbrella for pain and dysfunction in the jaw joints and the muscles that move them. On paper, their x-rays and bite analyses look remarkably similar.

I treat them with the same approach. One gets better. The other doesn’t.

Over three and a half decades of practicing dentistry in Toronto and here in Vancouver, I have sat with this puzzle more times than I can count. It is not a niche observation. It is, in fact, the central unresolved problem in how our profession thinks about jaw disorders — and it is the question that drove me to develop the framework I am publishing today in the Journal of Clinical Medicine.

What We’re Talking About: TMD and Bruxism

Temporomandibular disorders (TMD) affect roughly one in ten adults, with women experiencing symptoms at a higher rate than men. Bruxism — the unconscious grinding or clenching of teeth, most often during sleep — is even more common, though exact numbers vary depending on how it is measured.

If you have ever woken up with a sore jaw, headaches concentrated at the temples, clicking or popping in the jaw joint, or been told by a partner that you grind your teeth in the night, you will recognize what these conditions feel like from the inside. They are disruptive to sleep, to eating, and to quality of life — and they have a frustrating tendency to come and go in ways that seem to have nothing to do with any dental change.

That last observation — that symptoms flare during stress even when nothing in the mouth has changed — is actually one of the most important clues we have, and for a long time, our profession’s most popular theories about these conditions couldn’t fully explain it.

Two Schools of Thought, Two Incomplete Stories

The history of how dentists have thought about jaw disorders can be summarized in two broad traditions.

The first holds that the structure of the bite is the primary driver. If your teeth don’t meet correctly, the reasoning goes, that misalignment creates strain in the muscles and joints. Fix the bite — with a night guard, an adjustment, a restoration — and the symptoms should resolve. This tradition produced real and lasting clinical insights about how the jaw works as a mechanical system. It also produced a generation of dentists, myself among them, who were trained to look first and hardest at the structure of the teeth and joints.

The second tradition, which grew out of pain science and behavioral medicine over the past few decades, takes a more expansive view. It argues that jaw pain is a centrally mediated experience — meaning it is shaped heavily by how the brain is processing signals, not just by what is happening in the joint. Psychological stress, anxiety, and sleep quality all turn out to matter enormously. This tradition correctly identified that fixing the bite alone does not help many patients — and it cautioned, rightly, against irreversible dental procedures as a first response.

Both traditions are right about something important. Neither one tells the whole story.

Two Patients. Same Outcome. Completely Different Treatments.

The two clinical cases that crystallized this framework for me illustrate the gap perfectly.

Two patients. The same clinical endpoint. Entirely different levels of intervention. No existing framework in our field offered a unified explanation for both outcomes — which told me that a new framework was needed.

Introducing FORM: A Three-Tier View of Jaw Function

The framework I am proposing — the Functional Occlusion Regulated Model, or FORM — reorganizes how we think about the jaw by placing it in its proper biological context: as a system that is continuously regulated by the brain and the autonomic nervous system, not just a set of mechanical parts that either fit together or don’t.

FORM is organized as a three-tier hierarchy. Each tier shapes the one above it.

This hierarchy inverts the assumption that most dentists — including me, for much of my career — brought to the treatment table. Structure is not the cause. It is the stage. And what happens on that stage depends enormously on the state of the nervous system directing the performance.

The Surprising Role of Breathing in Jaw Pain

One of the findings I find most compelling — and most practically useful — concerns breathing.

Most of us assume we breathe correctly, because breathing is automatic. But the pattern of how we breathe turns out to matter deeply to the regulation of the nervous system. Breathing that is too fast, too shallow, or too effortful reduces the level of carbon dioxide in the blood below its optimal range. This shift — called hypocapnia — activates brainstem alarm circuits that increase sympathetic tone (the “fight-or-flight” branch of the nervous system), elevate muscle tension throughout the body, and reduce the nervous system’s ability to adapt smoothly.

In the jaw, this shows up as increased activity in the masseter muscle — the powerful chewing muscle you can feel on your cheek when you clench. In our clinical observation, when carbon dioxide levels dropped toward the lower edge of the normal range, masseter muscle activity increased and jaw pain returned. When breathing was retrained to maintain healthy CO₂ levels, the muscle activity settled back to baseline and the pain resolved — without any dental intervention whatsoever.

This is not a fringe observation. It converges with decades of research showing that the brainstem circuits that regulate breathing, jaw movement, arousal, and sleep all share the same neural real estate. The jaw is not separate from the autonomic system. It is embedded within it.

Why Bruxism Happens at Night (And What That Tells Us)

Sleep bruxism — the grinding and clenching that happens during sleep — has long been one of the more puzzling phenomena in dentistry. It does not correlate cleanly with bite problems. It waxes and wanes with life stress in ways no dental treatment reliably tracks. It can run for years and then stop, or begin suddenly after a period of illness or anxiety, seemingly from nowhere.

Polysomnographic sleep studies — where patients are monitored with sensors tracking brain activity, muscle activity, and breathing throughout the night — have offered a revealing picture. Bruxism episodes in sleep are not random jaw activity. They occur in tight association with brief cortical micro-arousals: tiny moments when the sleeping brain flickers toward wakefulness. And critically, those micro-arousals are almost always preceded by a surge in heart rate, sympathetic activity, and breathing disturbance.

In other words, the grinding is not the cause — it is one of the last events in a cascade that begins with central nervous system arousal. FORM frames bruxism not as a primary dental phenomenon, but as a downstream motor expression of a system that is operating under excess regulatory load. Treating only the teeth — protecting them with a night guard, for instance — addresses the consequences without touching the upstream driver. Night guards remain an important protective tool, but they are not, and have never been, a cure.

Where the Research Goes From Here

FORM is a theoretical framework, not a tested clinical protocol, and I want to be clear about that distinction. The paper proposes four specific, testable predictions — designed to be falsifiable with measurement tools that already exist in clinical research settings. These include validated chewing efficiency tests, short-term heart rate variability recordings, and standardized capnometry to measure end-tidal CO₂. The predictions are:

• Chewing efficiency will correlate more strongly with autonomic markers than with static bite measurements in patients with and without TMD symptoms.
• Interventions that improve regulatory state — breathing retraining, heart rate variability biofeedback — will measurably improve chewing efficiency, even without any occlusal modification.
• Patients with better autonomic regulation before treatment will show greater and more lasting benefits from structural dental intervention.
• Fluctuations in masticatory performance over time will track changes in autonomic state more closely than changes in occlusal morphology.

If these predictions hold, they would provide a roadmap for identifying, before treatment begins, which patients are most likely to respond to structural intervention and which ones need regulatory support first. That kind of precision has been missing from our field — and its absence has real costs, measured in treatments that don’t work and patients who go years without finding relief.

Dentistry at a Crossroads

The implications of FORM extend beyond TMD and bruxism. For patients considering dental implants, a nervous system under sustained regulatory load may generate parafunctional forces that accelerate mechanical complications — independent of how precisely the implant was placed. For orthodontic patients, regulatory capacity may influence how smoothly the system adapts to progressive changes in bite. For anyone undergoing comprehensive restorative treatment, the same logic applies: structural precision matters, but so does the patient’s capacity to function well within the structure we create.

None of this diminishes the importance of excellent structural dentistry. It contextualizes it. And in my experience, that context changes everything about how we listen to patients, how we investigate their symptoms, and how we design their care.

The mouth is not a mechanical system sitting in isolation. It is a regulated biological interface between an individual and their world. Treating it as anything less has always left some patients behind. FORM is my attempt, developed across 35 years of practice and grounded in the current scientific literature, to do better.