Orthopedics · Part Three · The Spine as a System
Lesson 25 / 44
TMD and the Cervical Connection: Why Jaw Pain and Neck Pain Arrive Together
Jaw pain rarely lives alone. The temporomandibular joint shares a spinal cord segment with the upper neck, and a skilled clinician reads them together as one pattern.
Temporomandibular disorder, or TMD, is pain and restricted movement in the jaw joint and the muscles that chew, often with a click or a limit on opening. Temporomandibular joint disorders reach 31 percent of adults. Jaw and neck symptoms travel together because sensory fibers from both regions end on the same cells in the upper cervical cord. The Unified Model of Tone reads the pair as one regulatory pattern surfacing wherever a given body has least reserve.
Jaw pain reported in a United States national survey
4.6 percent of adults
Cervical neurons carrying tooth-pulp input that also answered the masseter
84 percent
Median maximum mouth opening, women against men
40 millimeters against 44 millimeters
Neck disability against jaw disability across observational studies
standardized mean difference 0.72
Temporomandibular disorder
An umbrella term for pain and dysfunction in the jaw joint and the muscles that move it. The muscular form centers on the masseter, the temporalis and the pterygoids. The articular form centers on the joint itself, on its small fibrous disc, and on the relationship that disc must keep with the mandibular condyle through both rotation and glide.
Where jaw and neck signals meet
Sensory fibers from the jaw joint, the teeth and the dura run in the trigeminal system. That system’s lowest relay is continuous with the dorsal horn of the upper cervical spinal cord, so single second-order neurons answer to input from the face and from the neck. A brain reading one of those cells cannot always tell which region sent the signal.
01One joint, two regions
Jaw pain and neck pain usually arrive as one problem
The question most people carry is simple: why does treating my neck ease my jaw. Temporomandibular disorder, or TMD, describes aching in the muscles of mastication, sometimes with brief sharp pain on chewing, often paired with restricted jaw movement and a click or pop.
It is common. Pooling 21 studies that applied published diagnostic criteria, temporomandibular joint disorders reached 31.1 percent of adults and 11.3 percent of children and adolescents (Valesan 2021). Disc displacements accounted for 19.1 percent and degenerative joint disease for 9.8 percent.
How common jaw pain actually is
Pain is a narrower category than diagnosis. In the 2002 National Health Interview Survey, 4.6 percent of 30,978 respondents reported temporomandibular joint and muscle pain, 6.3 percent of women and 2.8 percent of men (Isong 2008). Prevalence among white women up to age 50 ran near 7 to 8 percent and fell after age 55.
That gap between findings and complaints is exactly why a clinician learns to see TMD as a pattern rather than an isolated hinge. The categories in routine use describe muscle and joint disorders, not dangerous disease. A clinician therefore has room to reason carefully, map the mechanism, and work with function rather than chase a single structure.
02Findings
What the research shows
From two prevalence studies, a diagnostic criteria validation, two human experimental pain studies, two meta-analyses and a kinematic study.
03Muscle, joint, or both
The first fork is whether the trouble is muscular or articular
Muscular TMD centers on the muscles that move the jaw, and myofascial irritation of the masseter, the temporalis and the pterygoids drives that presentation. Articular TMD centers on the joint itself and its small fibrous disc, which must keep a normal relationship to the mandibular condyle through both rotation and glide.
When the condyle slips off the disc and then slips back on later in the movement, that is disc displacement with reduction, or DDR. It is the classic cause of a brief jaw click with a clear beginning and end. It is also the single most frequent joint diagnosis, at 25.9 percent of adults and 7.4 percent of children (Valesan 2021).
What a click and a grind point to
When the disc does not return to its normal position, that is disc displacement without reduction, or DDNR, and a click is less likely. The published criteria separate that pattern further by whether mouth opening is limited. A continuous grating sound over a long arc of movement, called crepitation, points instead toward degenerative joint change, which the same pooled analysis put at 9.8 percent in adults and 0.4 percent in children.
Other recognized categories include arthralgia, intermittent locking, osteoarthritis, osteoarthrosis and subluxation. The full classification runs wider still, and the diagnostic criteria set out both the common and the uncommon forms in one system (Schiffman 2014). Muscle and joint problems also coexist in the same jaw, which is why the fork is a starting question rather than a verdict.
Joint effusion is an imaging finding rather than an examination finding
Joint effusion is fluid gathering inside the temporomandibular joint, and magnetic resonance imaging is what identifies it. Westesson and Brooks imaged 379 patients carrying symptoms alongside 11 asymptomatic volunteers. Effusion appeared in 7 percent of joints holding a normally positioned disc, 40 percent of those with DDR, 50 percent of those with DDNR and 27 percent of those with arthrosis (Westesson 1992).
No control subject showed effusion at all. That same series tied it to pain, at 46 percent of joints on the more painful side against 13 percent on the less painful side. A later cohort applying the DC/TMD guidelines to 158 participants and 312 joints found no association between effusion and arthralgia (Khawaja 2017). Effusion tracked disc position instead, at P = .001, with DDR carrying an odds ratio of 2.5.
Clinical teaching has long read pain on posterior and lateral palpation, together with pain during unassisted movement, as the signature of an effused joint. The accuracy of that reading has not been measured. What is measured is where effusion sits, which is in joints whose discs have moved, in half of those that do not reduce, and in none of the asymptomatic controls. Our model reads those palpation findings as a report on how hard the joint is guarding rather than on how much fluid it holds.
04Reading the jaw exam
A jaw examination provokes and relieves on purpose to find the mechanism
A good jaw exam provokes and relieves symptoms on purpose to find the mechanism. The clinician listens for joint sounds, palpates just anterior to the auricular canal and posterior to the condyle, and measures movement. Mouth opening under 40 millimeters is the conventional threshold for calling opening limited.
That threshold is a population number applied to an individual jaw. Across 1,045 patients, median maximum opening was 40 millimeters in women and 44 millimeters in men. Complaints of limitation appeared at 35 millimeters or less in women and 38 millimeters or less in men (Angelo 2025). Between those figures sits a band where the same measurement means different things in different people.
What the diagnostic criteria settled, and what they did not
Formal criteria fixed the reliability problem for painful TMD. The Diagnostic Criteria for Temporomandibular Disorders reach a sensitivity of at least 0.86 and a specificity of at least 0.98 for the common pain-related disorders. Inter-examiner agreement runs at kappa 0.85 or better (Schiffman 2014). One intra-articular disorder reaches 0.80 and 0.97.
The criteria for the other common intra-articular disorders do not reach that standard, and the same document restricts them to screening. Individual clinical tests are weaker still. A systematic review narrowed 131 candidate articles to seven, judged three of them high quality, and found no study that compared TMD against a competing non-TMD condition (Reneker 2011).
That review concluded the data were insufficient to support or reject the individual tests. No single test is definitive on its own, so a clinician reads the cluster of signs as a signature rather than leaning on any one result. The jaw and the upper neck share the same spinal cord segments, so work aimed at the neck moves jaw pain measurably (Bednarczyk 2024). That is not a coincidence. It is anatomy.
05Where nerves converge
Jaw and neck input reach the same second-order neurons
The neck and the jaw are wired together, and this is the heart of the lesson. Sensory input from craniofacial structures such as the temporomandibular joint, the teeth and the dura converges with cervical input at the trigeminal relay. The lowest portion of that relay is continuous with the cervical dorsal horn.
Direct recording shows the convergence at cell level. Of 61 neurons in the first cervical segment that fired to tooth-pulp stimulation, 84 percent also fired to stimulation of the masseter on the same side (Takeda 2005). Of those, 61 percent were driven through A-delta fibers and 39 percent through C fibers.
In effect the trigeminal relay is a rostral extension of the cervical dorsal horn, giving the head and neck one continuous, overlapping sensory map. This is trigeminocervical convergence, and it means a pain source anywhere in the upper cervical spine can excite the same relay neurons that receive input from the jaw. Three Headaches, One Neck works the same anatomy through the headache differential.
Why a receptive field grows
The link runs past referred pain. In the same recordings, a noxious chemical injected into the masseter enhanced the response of those cervical neurons to both touch and pinch, and significantly expanded their receptive fields (Takeda 2005). The changes reversed within 15 to 20 minutes.
A cell whose receptive field has grown reports a larger patch of the head and neck as one territory. Sustained input from an irritated cervical joint can hold trigeminal neurons in that state, which is what a nervous system tipped toward protection looks like at the first relay. When Pain Spreads carries convergence into widespread pain, and Central Sensitization sets out the mechanism in full.
06Reflex rather than resting tone
The neck to jaw link shows in reflex responses, not in resting muscle activity
The obvious version of the neck and jaw story is that a tense neck makes the jaw muscles tense. Direct measurement says otherwise. Investigators injected glutamate into the right masseter or into a neck muscle in 19 men and recorded activity from both masseters, the sternocleidomastoid and the splenius.
Neck muscle pain produced no tonic increase in jaw muscle activity. Jaw muscle pain did raise neck activity at rest, and isotonic saline injections produced neither pain nor any electrical change (Svensson 2004). Resting drive is a poor place to look for the connection.
Where the connection does show up
The reflex tells a different story. In 19 healthy men, pain evoked in either the masseter or the neck significantly increased jaw stretch reflex amplitude recorded in both the masseter and the sternocleidomastoid (Wang 2004). Onset, offset and duration of the reflex did not change, and saline again changed nothing.
Amplitude rose while timing held. That is a gain change in a shared circuit, not a change in how much the muscles are being told to contract. The pairing of these two experiments is the sharpest available statement of what the neck to jaw link actually is.
What the posture studies found
The clinical literature agrees. Across observational studies, neck disability tracked jaw disability at a standardized mean difference of 0.72, with an interval from 0.56 to 0.82 (Cuenca-Martinez 2020). Cervical alignment gave 0.02, with an interval running from 0.31 below zero to 0.36 above it, and craniocervical position gave 0.09 below zero.
The same analysis graded the evidence for lower pressure pain thresholds and reduced cervical range of motion as moderate, found cervical strength equal to controls, and called the electromyographic and motor control findings conflicting. Disability, sensitivity and available movement travel together in TMD. Head posture and cervical curve do not.
07The jaw as the loudest tissue
Neck problems change jaw mechanics before the jaw complains
Twenty adults with chronic non-specific neck pain and no jaw symptoms were compared with 19 healthy controls. The neck pain group showed reduced upper cervical rotation, longer condylar path length, and greater condylar translation on both opening and closing (Siu 2022). None of them had TMD.
Greater condylar translation correlated with reduced upper cervical mobility, with correlation coefficients from 0.322 to 0.397 below zero. Mechanical sensitivity of the upper trapezius was raised as well. The jaw was already travelling further to do the same work in people whose only complaint was the neck. The Neck as a Sensory Organ sets out what that region contributes to the rest of the body.
Overlap is the rule, and it is graded
Jaw pain also keeps company with pain elsewhere. Among 655 adults followed in a long-running cohort, overlap between chronic pain conditions was the norm. Fifty-one percent of people with headache carried at least one other overlapping condition, rising to 90 percent for those with fibromyalgia (Slade 2020).
The overlap was strongest between fibromyalgia and either TMD or low back pain. Headache and irritable bowel syndrome did not fit a single functional syndrome, and some pairings lost their association once the other conditions were accounted for. Overlap is real and it is uneven. When Pain Spreads owns the argument that these separately named illnesses are one regulatory problem.
08Treating the system
Care aimed at the neck moves jaw pain in the short term
Because the jaw and neck work as a system, the trials that treat the system are the ones worth reading. A meta-analysis screened 2,647 studies and found seven randomized trials of cervical interventions in adults with muscular TMD, judged at low risk of bias or with some concerns (Bednarczyk 2024).
Pain intensity favored the cervical arms at a standardized mean difference of 0.98, across five trials and 223 patients, with an interval from 0.28 to 1.67. Pressure pain threshold at the masseter gave 0.64 across six trials and 395 patients, and the temporalis gave 0.76. Cervical manual therapy alone or with neck exercise gave 1.52 across four trials and 203 patients.
Heterogeneity ran from 79 to 90 percent, and every effect was measured in the short term. The authors leave the long-term picture open. What the trials establish is a mechanism claim rather than a cure: input delivered to the neck reaches the jaw, and it does so through the shared cells described above.
Where the dentist owns the decision
The bite, the teeth and any occlusal appliance belong with a dentist, who assesses the dentition directly and holds the training to change it. Reading the jaw and neck together works alongside that judgment. Two clinicians looking at one joint from different access points is how a shared structure should be handled.
Clinicians increasingly pair a movement description with the structural label, asking what functional limitation a jaw shows and what reduces it. Repeated end-range jaw movement is used that way, as a way of finding a direction that eases symptoms. A clinician examines the neck whenever the jaw complains, and the reasoning above is why.
09Claims removed from this page
Six claims from the earlier version were removed
The earlier text put TMD signs in 50 to 70 percent of the general population and a persistent symptom in about 33 percent, with no source attached to either. The published figures are 31.1 percent for temporomandibular joint disorders by diagnostic criteria (Valesan 2021) and 4.6 percent for reported jaw pain in a national survey (Isong 2008). Both replacements are lower and both are anchored.
Three exam claims came off. The statement that the trigeminal nucleus extends to the C3 level was dropped because the level could not be verified. The sourced version is direct recording of trigeminal input in first cervical segment neurons (Takeda 2005). The 5 millimeter protrusion threshold had no source. The claim that systematic review work tied exam findings to subtypes with useful reliability reverses what the review reported (Reneker 2011).
Two treatment claims came off. Improving spinal alignment was said to raise the success rate, and the pooled observational data put cervical alignment at 0.02 with an interval crossing zero (Cuenca-Martinez 2020). The claim that patients with TMD have weak, low-endurance cervical flexors was regraded: the same analysis found maximal cervical strength equal to controls and rated reduced endurance as limited evidence.
10The model on jaw and neck pain
What the Unified Model of Tone claims about TMD
Everything above is established science, including the findings that cut against the postural account. What follows is our model’s reading, stated as ours rather than drawn from the papers cited.
Our model names temporomandibular disorder in a short list of illnesses that medicine treats as unrelated. Fibromyalgia, irritable bowel syndrome, temporomandibular disorder and chronic pelvic pain are classified as four separate illnesses, assigned to four specialties and four organs. We read them as one regulatory problem appearing at four addresses. When Pain Spreads carries that argument in full.
The cohort data show the shape our reading predicts. Overlap was the norm and it was graded, reaching 90 percent for fibromyalgia while headache and irritable bowel syndrome refused to collapse into one syndrome (Slade 2020). Each body has a different pattern of reserve, and a disturbance surfaces wherever that particular body can least absorb it.
Site is not source
Convergence supplies the anatomy. Eighty-four percent of the recorded cervical neurons answered to both jaw and muscle input (Takeda 2005), which means the nervous system holds jaw and upper neck as one territory before any interpretation happens.
From that we draw a claim about location. The most symptomatic site is frequently a compensation splinting a distortion elsewhere, so the loudest tissue is the weakest link rather than the origin. A jaw that clicks and aches may be the tissue with the least remaining capacity to absorb a pattern held further down. Twenty people with neck pain and no jaw symptoms were already moving their condyles further to open (Siu 2022).
The prediction
An input interacting with a tone creates an outcome, and there is no such thing as an input acting on an empty body. This is why seven cervical trials returned effects with heterogeneity of 79 to 90 percent (Bednarczyk 2024). The same neck technique met different jaws, and the samples were never stratified by the pattern each person was holding.
Our model predicts that four measures recorded together in the same people will share one underlying factor rather than varying independently. The four are jaw stretch reflex amplitude, pressure pain threshold at the masseter, upper cervical rotation range, and time to return to baseline mouth opening after a standardized chewing load.
Our model further predicts the direction of change under an input that restores regulation. People who begin with high reflex amplitude and people who begin with low amplitude both move toward the middle, and the spread narrows. This is a claim about how jaw and neck pain are organized rather than a claim about what treatment does.
If jaw stretch reflex amplitude, masseter pressure pain threshold, upper cervical rotation range and time to return to baseline mouth opening after a chewing load are shown to move together, the unification claim is confirmed.
11The tone reading
How jaw and neck pain express tone
Every topic in this library expresses all of tone. In TMD three aspects carry the signature, because pain induced in a neck muscle changed the jaw reflex while leaving resting jaw activity untouched.
Coupling
Jaw and neck run as one circuit. Pain in either muscle raised jaw stretch reflex amplitude in the masseter and the sternocleidomastoid together, in 19 healthy men.
Gain
Sensitivity climbs before tissue fails. Pressure pain thresholds fall in the neck muscles of people whose presenting complaint is the jaw, and cervical movement narrows with them.
Constraint
Protective narrowing shows in millimeters. Median maximum opening sits near 40 in women and 44 in men, and condyles travel further when upper cervical rotation is reduced.
The remaining foundations run through TMD as well. Set point: the resting level of jaw guarding decides how much chewing it takes to provoke pain. Input quality: a joint whose mechanoreceptors report poorly gives the brain a blurred estimate of where the mandible is. Prediction: a jaw braced against an expected click moves differently from one that is not. Load: clenching, chewing and sustained posture accumulate demand that the same joint tolerates on one day and not the next. Time course: expanded receptive fields in cervical neurons reversed within 15 to 20 minutes, which sets the timescale the system works on. Oscillation: jaw pain that follows a daily rhythm is reporting the regulator rather than the joint surface. These are readings of one organization rather than separate systems, which is the core claim of the Unified Model of Tone.
12Across the library
How this page relates to the rest of the library
The jaw is where several of this section’s arguments meet in one small joint.
The same convergence anatomy applied to headache, and the criteria that separate three look-alikes.
Why separately named illnesses behave as one regulatory problem, and what convergence has to do with it.
The spindle density and sensory role that make the upper neck a reporting organ rather than a hinge.
The same reasoning carried down the arm, where one nerve is compromised at two points along its length.
The relay that holds the trigeminal nuclei, and what else it decides on the way through.
How receptive fields, second-order neurons and body maps are built, which is what convergence rearranges.
Neck pain as a measurable regulatory state, with the instruments used to read it.
13Frequently asked
Questions patients ask about jaw pain and the neck
Can jaw pain be related to my neck?
Yes. Sensory fibers from the jaw joint, the teeth and the dura end on the same cells in the upper cervical spinal cord as fibers from the neck. In one recording study, 84 percent of first cervical segment neurons driven by tooth-pulp stimulation also fired to masseter stimulation on the same side. Because those cells carry both, a problem in the upper neck can excite the same relay that receives jaw input, and the two regions are read as one territory.
What are the signs of a temporomandibular disorder?
Common signs are aching in the chewing muscles, brief sharp pain on chewing, clicking or grating from the joint, and restricted opening. A clinician sorts muscular from articular causes. A brief click with a clear beginning and end suggests the disc slipping off the condyle and back on, which is the most frequent joint diagnosis at 25.9 percent of adults. A continuous grating sound over a long arc points toward degenerative joint change instead. Degenerative joint disease accounts for 9.8 percent of adults.
Does treating the neck help jaw pain?
The trials say it moves the measurements. A meta-analysis of seven randomized trials in adults with muscular TMD found pain intensity favored cervical treatment at a standardized mean difference of 0.98. Cervical manual therapy with or without neck exercise gave 1.52 across four trials and 203 patients. Masseter pressure pain threshold improved by 0.64. Every effect was short term, heterogeneity ran from 79 to 90 percent, and the long-term picture is open. Cervical treatment reaches the jaw because both regions report to the same relay.
How common is TMD?
Pooling 21 studies that used published diagnostic criteria, temporomandibular joint disorders reached 31.1 percent in adults and 11.3 percent in children and adolescents. Disc displacements accounted for 19.1 percent and degenerative joint disease for 9.8 percent. Reported pain is far less common than joint findings. In a national survey of 30,978 people, 4.6 percent reported jaw joint and muscle pain, 6.3 percent of women and 2.8 percent of men. Most jaws that show something on examination do not hurt. A joint finding does not explain a complaint.
Is limited mouth opening measured at a fixed number?
The conventional threshold is 40 millimeters, and it is a population figure rather than a personal one. Across 1,045 patients, median maximum opening was 40 millimeters in women and 44 millimeters in men. Complaints of limitation appeared at 35 millimeters or less in women and 38 millimeters or less in men. Between those values sits a band where the same reading carries different meaning depending on whose jaw is being measured. The number is read against the person rather than against the table.
Should jaw pain be seen by a dentist?
The bite, the teeth and any occlusal appliance belong with a dentist, who examines the dentition directly and holds the training to change it. Reading the jaw and the neck together as one mechanical and neurological unit works alongside that judgment rather than around it. One joint viewed from two access points is how a shared structure is properly handled. The cervical view adds upper cervical rotation, masseter pressure threshold and jaw reflex behavior to what the dental examination records. Both readings describe one joint.
What does the Unified Model of Tone say about TMD?
That the jaw is one address for a regulatory problem rather than an isolated hinge. Our model names temporomandibular disorder alongside fibromyalgia, irritable bowel syndrome and chronic pelvic pain, four labels assigned to four specialties. From convergence it draws a claim about location: the loudest tissue is the weakest link rather than the origin. It predicts that jaw reflex amplitude, masseter pressure threshold, upper cervical rotation and recovery of opening share one underlying factor. That prediction concerns how the jaw is organized rather than what treatment does.
14The sources
References
14 primary sources, each linked to its record. Figures quoted on this page were checked against the published abstract.
Related evidence