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In the author's experience, TMJ is rarely evaluated objectively in dentistry, yet it is the most important factor in occlusal stability as reviewed in this article.
In most dental practices, hygienists are the lead providers in assessing patients' ongoing dental health. A hygienist's responsibilities are broad and include oral health screening and updating records in addition to providing periodontal treatment. Hygiene visits consist of much more than just cleaning teeth. Screening the stability of the temporomandibular joint (TMJ) is important for all patients, especially those who are considering orthodontics, being prescribed any nighttime oral appliance, or undergoing significant dental treatment. It also plays a role in periodontal stability. The dental hygienist can play a crucial role in early detection of possible TMJ disorders as described in this article.
Indirectly, temporal mandibular joint disorders may affect periodontal health, contributing to tooth sensitivity, periodontal stability and may contribute to failed restorative care. TMJ damage or dysfunction often starts without symptoms. As symptoms develop, they can vary considerably. Consequently, the TMJ has been given the nickname "the great imposter" by many practitioners.1
A patient's habitual occlusion is directly related to TMJ alignment and function. The presenting habitual bite measurements (overbite, overjet, midline) along with the four measures of TMJ range of motion (ROM) become a reference of the condyle's position in the fossa, although this does not indicate whether the condyle's position is correct or incorrect. Checking the mobility of the joint can help identify TMJ internal damage/dysfunction.
Recording the lower dental midline in relation to the midline of teeth Nos. 8 and 9 at the patient's initial visit and at subsequent recare appointments is considered a "rapid screen" for change in the TMJ complex (Figure 1).
If patients have difficulty moving the mandible laterally, it is likely an indication of TMJ disc displacement or condyle/fossa misalignment, regardless of symptoms (Figure 2). The author has often noticed that patients with medially displaced discs may "wiggle" their mandible back and forth several times to enable the jaw to move left or right. This is a clinical sign of a potential disc displacement. While the medially displaced disc will not typically click or pop as a sign or symptom, it interferes with medial movement of the condyle, as occurs in lateral jaw movement away from the affected joint.
Measuring lateral jaw range of motion in these cases is accomplished more easily by having the patient lightly rest on the handle of a dental mirror placed between the canine and lateral incisor so they can slide on the handle. If the condyles are displaced posterior in the fossa due to growth imbalance or disc displacement, patients will need to protrude the mandible to an end to end or beyond in order to move their jaw laterally. In some cases of disc displacement, the patient will have to wiggle the jaw as well as protrude to overcome the disc displacement prior to a lateral jaw movement.
These can all be a sign of a pre-disposing TMJ misalignment or actual TMJ disc disorder. A posteriorly displaced condyle (Figure 1 and on the right in Figure 2) as can occur with growth imbalances or disc displacement cannot move posterior (as in a "working side" lateral jaw excursion) without first protruding.2,3,4
The four ranges of motion are:
1. Maximum unassisted mouth opening: 45 to 60 mm (Figure 3)
2. Left lateral mandibular movement: 8 to 12 mm
3. Right lateral mandibular movement: 8 to 12 mm (Figure 4)
4. Protrusion: At least 5 mm
Early, pre-symptomatic or progressing changes/damage in the TMJ can be recognized by comparing simple occlusal measurements such as overbite/overjet/dental midline taken at the patient's initial examination to subsequent recare appointments, as mentioned. Referencing the initial examination TMJ ROM and occlusal measurements at recare appointments can help the clinician have a quick, easy method to determine whether the TMJ is stable or if asymptomatic pathology may be occurring. The author has used these measurements in every patient's visit notes throughout his general dental/TMJ practice for 32 years; for 5 years, the practice was limited to TMJ and dental sleep therapy.
Palpation over the TMJ during opening and closing of a patient's mouth provides basic clinical information about disc/condyle status. Noises such as clicking and crepitus (grating sounds), along with pain or discomfort, should never be considered normal. If a patient is asymptomatic but experiences joint noises or restricted mobility in any of the four ROM, it is probable that the patient has a TMJ disorder/disc displacement that is still within their adaptive capacity. The disorder may flare up or cause occlusal imbalances at some point.4
Published TMJ ROM measurements have been reported as 40 to 50 mm in the open position and 8 to 12 mm laterally, with 8 mm protrusion.2 In the author's experience, most dentists specializing in TMJ disorder consider 48 to 52 mm to be a normal opening. The author has found a 40-mm opening to suggest an internal disc disorder. If identified, informed consent would be medically/legally appropriate if a TMJ disorder is suggested by examination and signs/symptoms such as pain, limited motion, sudden occlusal irregularities, etc. (Documenting that the dentist/hygienist has noticed signs/symptoms that may indicate a TMJ disorder and prompt a discussion that further diagnostics or treatment are indicated. If the patient refuses and it flares up during a dental or hygiene visit, will help protect the office from patients saying that the practitioners were responsible for "causing" the TMJ issues; this is similar to documenting periodontal disease and the risks/benefits of treatment vs no treatment.) Abnormal TMJ ROM can also warrant a referral to a dentist specializing in TMJ disorders for assessment and/or treatment if your office does not treat these disorders.
Causes and Precipitation of TMJ Disorder
Patients who are predisposed to a TMJ disorder due to condyle malpositioning but are asymptomatic may become symptomatic unexpectedly, such as by yawning or by waking with acute disc pain resulting from parafunction during sleep.
Direct trauma to the jaw may also cause a TMJ disorder; however, this was seen rarely in the author's practice. If no previous TMJ ROM or occlusal measurements were recorded and if the patient is asymptomatic, the clinician will not know whether the TMJ is already damaged. Similarly, periodontal disease is not always obvious unless measurements are taken. That is the rationale for the objective dental screening of TMJ mobility at each visit (Figure 1).5,6
When a dental procedure triggers TMJ symptoms, the patient is likely to assume that the procedure caused the TMJ problem. Typically, the procedure was the final provocation of a silent, progressive condition. Having records of basic occlusal parameters and TMJ ROM measurements can help uncover this predisposition and avoidany misunderstanding about the dentist "causing" a TMJ problem.
The author explains to incoming patients whose TMJ onset was associated with a dental visit as being analogous to someone turning their neck or bending over and hearing a pop or sharp pain as a disc "slips" in the neck or back. Typically, the individual would be unaware of the progressing problem until the time the disc slipped. The movement would be simply be the "straw that broke the camel's back," not the root cause.
As in any orthopedic disorder, repetitive injury in relation to the TMJ eventually leads to an acute or sudden onset of symptoms. In the author's 35 years of practice, it was rare that a patient with a TMJ condition did not have an underlying orthopedic joint misalignment.
Screening, Informing, and Offering Further Evaluation or Referral
A thorough clinical history and examination7 allows the dentist to identify an asymptomatic TMJ condition due to a patient's underlying predisposition. The patient can be informed of the risk of precipitating a TMJ disorder over time with normal functional habits or during a routine dental procedure that may precipitate a flare-up. It can also become symptomatic under normal function.
With cone-beam computed tomography (CBCT), joint space and condylar position(s) can be measured based on international norms8 to assess underlying predisposition or arthritic changes. Panoramic dental images are considered inadequate in assessing anatomic factors in comparison with CBCT.9
At follow-up visits, changes of more than 2 to 3 mm in the left or right lateral movement as well as 3 to 4 mm in maximal interincisal opening should be noted. If either of these changes are present, the dentist should review them with the patient and offer additional screening or referral to a dentist with specific training in TMJ dysfunction. Changes in occlusal measurements, such as a midline shift; changes in overbite/overjet; signs or symptoms like joint noise; or the onset of parafunction should alert the dental team to consider a more detailed evaluation and/or referral.10
The traditional dental literature focuses on stress and other psychosocial factors as the cause of TMJ disorder, as well as bruxing and clenching. The muscular pain of TMJD is often attributed to overuse, secondary to presumed stress and parafunction. Short-term, intense life events do contribute to muscle tension or disturbed sleep and may, in a predisposed patient, trigger an underlying, asymptomatic TMJ disorder. Nonetheless, the stress was not the cause but an aggravating or precipitating factor in a predisposed joint.
Generally, focusing on stress or anxiety as an approach to TMJ problems allows the orthopedic problem to worsen. It did not seem productive or appropriate to this author to treat merely the symptoms for a patient presenting with an orthopedic dysfunction of the TMJ if there are objective clinical examination findings consistent with a TMJ disorder. Orthopedic dysfunctions/chronic pain, especially in the head and neck, can contribute to anxiety; however, the author does not ascribe to the belief that the TMJ pain is primarily a psychologically mediated disorder.
In the author's TMJ practice, newly referred patients reported that they did not have isssues until their dentist or dental treatment "caused" their TMJ problem, implying that it was the dental team's "fault." At that point, the author explained the pre-disposing factors and precipitating event with the following analogy. If a pebble were placed in your shoe for several days, your foot would begin to hurt. The arthrokinetic reflex would tense muscles in order to alter your gait to avoid irritation from the pebble. In a short time, it is reasonable to assume that the lower back, hips, and/or knees would become painful in response to the avoidance mechanism that altered the gait because of the pebble. A slipped disc in the TMJ is like the pebble. It goes unnoticed until the body can no longer compensate for the damaged joint. Muscles of the TMJ complex follow the arthrokinetic reflex, as other joints do.11 If a joint becomes injured, unstable, or inflamed, it signals the muscles to alter joint motion by contracting to protect the joint from further damage. This may alter functional demands on associated joints and muscles, contributing to additional muscle pain and tension.
In this scenario, the person with a pebble in their shoe cannot be counseled or medicated to help them accept the pain and dysfunction the rock is causing; the pebble must be removed from the shoe. In the TMJ, the joint and disc must be properly aligned. Such is this author's approach to orthopedic TMJ disorders. Complementary treatments may be prescribed, but only to aid the efficacy of the primary orthopedic treatment. The author's approach to treating TMJ disorders follows orthopedic principles. Dentists typically look at the teeth and occlusion and may check centric relation to manage a TMJ concern. The concept of a manually manipulated centric relation that compresses the condyles is an old paradigm that is incompatible with TMJ health.12
Clinical Screening of Occlusion to Determine TMJ Changes
Any change in the TMJ, whether disc displacement, arthritic changes (secondary to disc pathology), or reactive muscle spasm, will manifest as a change in occlusion. Sometimes patients report a sore tooth, myalgias (intraoral, masseter, or temporalis muscles), or that their jaw has started clicking. Early symptoms of a TMJ disorder can be vague but typically are described as a sense that the bite feels different.10
If the overbite, overjet, and dental midline were not recorded at the initial patient examination, subsequent measurements may not provide new information relating to TMJ changes unless the changes continue. The clinician should be looking for changes from baseline measurements, which help identify which joint has changed. Decreased overbite and increased overjet from the initial examination record (3 mm or more, per author's protocol) may suggest a TMJ disc displacement, even if symptoms or clicking/popping have not yet appeared (Figure 5 and Figure 6).
Unless initial-traced CBCT images in centric occlusion were taken in addition to the basic TMJ measurements recommended in this article, an uneven midline may be "normal" for that patient or could represent an asymptomatic internal TMJ condition. The point is to be aware of any change in these measurements at every visit.10
To determine which side may be involved, a third measurement is the midline in the habitual bite compared with the initial examination measurements. The measurement will determine whether the mandible has moved to the left or right due to shift of the TMJ. The "bite" should be measured using consistent landmarks. The author always measured overbite or overjet on the same anterior tooth or teeth. Whatever anterior measurement of OB/OJ/midline is easiest should be used to ensure consistency.
If the ROM and/or occlusal measurements (overbite/overjet/midline) were not recorded in a patient's initial examination, the clinician can begin noting them at follow-up appointments. If the clinician finds a change in the ROM measurements, the patient can be advised that a TMJ disorder may be progressing.
If one joint or disc develops pathology, the mandible/bite will typically show a change in the overbite (decreased 1 to 2 mm), overjet (may increase a millimeter or 2), and midline. The midline will typically shift to the dislocated side 1 to 2 mm and sometimes more, in my experience. The important factor is not whether the shift is 3 or 4 mm; it is the change from baseline (only assuming baseline TMJ alignment was normal) that presents a clue to a TMJ disorder. Clicking may not be present at this point.
If a single parameter changes, the patient should be asked several questions, such as:
1. Does it feel like your bite has changed or is uneven recently?
2. Do you have teeth that have become painful to chewing or sensitive to cold or heat?
3. Are you having problems chewing?
4. Do you have any clicking in your TMJ?
5. Have you had any trauma or injury to your head, jaws, or neck recently?
If two or more occlusal parameters have changed, the dentist should inform the patient that it may indicate a disorder of the TMJ complex and could progress to a symptomatic condition with or without treatment. If the patient reports or senses a change in occlusion, difficulty chewing, or reports pain in the head, jaws, or neck, they should be informed that something may be changing in their TMJ. The dentist should document their complaints and recommend further evaluation or a referral to a dentist specializing in TMJ as an "informed consent" as they would for other dental findings.
The clinician could provide the patient with an information sheet, which should suffice as an informed finding.13 The practice should decide whether the dentist(s) is comfortable making a diagnosis or ruling out an early TMJ condition; if not, then have a protocol for referral to a TMJ specialist.
Adjusting the bite, also called equilibration, for TMJ disorders or other TMJ/muscular pain removes vertical support from the TMJ complex, likely compressing the disc and joint further up and back (posterior) in the socket (fossa), contributing to additional damage. The posterior space between the condyle and "ear" has a vast complex of nutritional vessels that supply the joint and soft tissues. Continued compression of this area from a displaced condyle/disc or non-physiologic retrusive occlusal techniques that displace the condyle against these tissues can be damaging and painful.
Equilibration of the bite is almost always contraindicated in TMJ disorders. If performed, it simply aligns the occlusion to match a malposed condyle/disc assembly, especially if the change is manually manipulated or brought about by an oral device that displaces the condyle posterior and/or superior. Any change in the orthopedic alignment can temporarily decrease muscular symptoms due to the interruption of the arthrokinetic reflex however, if the joint is positioned posterior/superior (as in centric relation manipulation), it likely will accelerate the orthopedic damage.14,15
As the pressure in the TMJ increases, the disc will stick more during movement due to reduction of the weeping lubrication.Weeping lubrication is a small amount of synovial fluid releasing from joints that are under pressure to help reduce the friction. However, joints that are under prolonged compressive forces will exhaust their supply of synovial fluid, thus reducing weeping lubrication.16
TMJ receptors activate protective muscle contractions that cause headaches and other muscle symptoms as TMJ pressures become excessive. This may occur in some having had occlusal equilibration(s) can reduce posterior occlusal support to the joint or, distalize the mandible. This would objectively present as an increase in overjet and decreased overbite. Pre-post equilibration measures of OB/OJ/midline as well as ROM in subsequent follow up should be recorded.
A progressive, decompressive orthopedic-based orthotic, such as a pivot splint,17 is recommended as an initial daytime orthotic. Specific orthopedic night orthotics, such as an EMA or ON2 were used by the author to maintain a decompressed, "Gelb 4/7 condylar position" during sleep so as not to allow compressive damage to the TMJ complex as can occur with flat plane maxillary/mandibular appliances worn while sleeping. Other oral orthopedic appliances may be subsequently used to reposition the condyles into a physiologic position after the joint has been objectively and subjectively decompressed and mobility reestablished. These appliances can be used indefinitely to support the TMJ in a healthy, physiologic alignment.
Hygienists are the providers most often seen in many dental practices and develop rapport, personal relationships, and confidence with their patients. Their clinical observations and therapeutic recommendations for their patients are important to dental health and patient's have trust in the recommendations.
Temporomandibular joint disorders are significant contributors to head and neck musculoskeletal pain, occlusal trauma that may lead to periodontal breakdown in addition to chronic head and neck pain. Screening for TMJ disorders using occlusal measurements (using the periodontal probe for OB, OJ) and simple TMJ range-of-motion measures can be done in less than 2 minutes by someone who is familiar with the techniques. This can help the dental office offer treatment and/or referral should a potential symptomatic or asymptomatic change is found.
About the Author
Mark J. Barnes, DDS (retired)
Founder, TMJ SleepSolutions.com
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