Why Can’t I Open My Mouth All the Way? Understanding Restricted Jaw Opening
Few things are as disconcerting as waking up or finishing a meal only to realize you cannot open your mouth to its normal width. This sensation, often described as a "locked jaw," can range from a mild annoyance to a significant barrier to eating, speaking, and maintaining oral hygiene. While the term "lockjaw" is historically associated with tetanus, in the modern clinical setting, restricted opening is usually a symptom of a temporomandibular disorder (TMD).
In a healthy state, the average adult can open their mouth between 40 and 55 millimetres—roughly the width of three fingers stacked vertically. When this range drops below 35 millimetres, or when the jaw seems to catch or get stuck at a certain point, it is considered a restricted opening. Understanding why this happens requires a closer look at the unique anatomy of the temporomandibular joint (TMJ) and the muscles that control it.
The Mechanics of Jaw Movement
The TMJ is one of the most complex joints in the body. It is a Ginglymoarthrodial joint, meaning it both hinges and slides. When you begin to open your mouth, the lower jaw (mandible) hinges against the skull (temporal bone). As you open wider, the condyle (the rounded end of the mandible) must slide forward along the articular eminence.
Crucial to this movement is a small, fibrocartilaginous articular disc that sits between the two bones. This disc acts as a cushion and a sliding surface. In many people, this disc can become displaced. While some may experience a simple click when the disc pops back into place—a topic explored in our article What causes jaw clicking and popping — TMJ explained simply—others may find the disc remains displaced, physically blocking the jaw from sliding forward. This is known as disc displacement without reduction, or a "closed lock."
What Current Evidence Says
Research into TMD has evolved significantly with the establishment of the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). According to Schiffman et al. (2014), restricted opening is categorized into two primary types: those involving the joint itself (arthrogenous) and those involving the muscles (myogenous).
- Disc Displacement Without Reduction (DDWoR): The disc is stuck in front of the condyle. Because the disc does not "reduce" (move back onto the condyle), the jaw cannot complete its sliding motion. This often results in a sudden onset of limited opening, usually to about 20-30mm, often with the jaw deviating toward the affected side when attempting to open.
- Myofascial Trigger Points and Guarding: Sometimes, the joint is fine, but the muscles of mastication—specifically the masseter and temporalis—are in a state of high tension or protective guarding. This is often linked to bruxism (teeth grinding) or prolonged stress. A systematic review by Armijo-Olivo et al. (2016) highlights that therapeutic exercise and manual therapy are effective interventions for these muscle-related restrictions.
Contributing Factors
Restricted opening rarely occurs in isolation. Several factors may contribute to the sudden or gradual loss of jaw mobility:
Acute Trauma: A direct blow to the jaw or a long dental procedure where the mouth is held open for an extended period can strain the ligaments and displace the disc. *
Chronic Bruxism: Habitual clenching or grinding can lead to muscle fatigue and inflammatory changes within the joint space, increasing the likelihood of the disc sticking or the muscles spasming. *
Internal Derangement: Over time, the ligaments that hold the disc in place can become elongated or lax, making it easier for the disc to slip out of its optimal position. *
Inflammatory Conditions: Systemic conditions like rheumatoid arthritis can affect the TMJ, leading to joint space narrowing and restricted movement.
What a TMJ-Focused Assessment May Include
When a patient visits a practitioner with a clinical interest in TMJ at Union Health Network, the goal is to determine the source of the restriction. The assessment is non-invasive and musculoskeletal in nature. It generally includes:
Range of Motion (ROM) Measurement: Using a specialized ruler to measure the exact millimetres of opening, lateral movement, and protrusion. *
Palpation: Gentle pressure applied to the masseter, temporalis, and lateral pterygoid muscles to check for tenderness or trigger points. *
Joint Sound Analysis: Listening for crepitus (grating) or the absence of a previously present click, which often indicates the disc has moved from a "reducing" state to a "non-reducing" state. *
Cervical Spine Screen: Since the neck and jaw are functionally linked, the assessment often includes checking the upper neck joints, as dysfunction here can refer pain to the jaw or influence its movement patterns.
Conservative Management Options
The good news is that many cases of restricted jaw opening respond well to conservative care without the need for surgery. A systematic review and meta-analysis by de Melo et al. (2020) found that manual therapy significantly improves jaw opening and reduces pain in individuals with TMD. Treatment at our Richmond Hill clinic may include:
Intra-oral Manual Therapy: Gentle stretching and mobilization of the jaw muscles and joint capsule from inside the mouth (using gloves). *
Soft Tissue Release: Addressing tension in the masseter and temporalis muscles to reduce protective guarding. *
Mobilization with Movement: Techniques that help "guide" the jaw through its proper track while the patient actively opens. *
Neuro-functional Acupuncture: Using thin needles to modulate the nervous system’s response to pain and relax hypertonic muscles.
Self-Management and Activity Advice
If you are currently experiencing a flare-up of jaw locking, evidence suggests several strategies may help manage the symptoms at home:
- The "Soft Food" Diet: Temporarily avoid hard, crunchy, or chewy foods (like bagels or steak) to give the joint and muscles a rest.
- Avoid Extreme Opening: Do not try to force your mouth open or "test" it by opening as wide as possible. Support your chin when you yawn to prevent the jaw from overextending.
- Heat or Cold: Applying a warm compress to the side of the face can help relax muscles, while a cold pack may help if there is acute inflammation.
- Gentle Range of Motion Exercises: Controlled, pain-free movements, such as the Rocabado 6x6 exercises, may help maintain mobility without aggravating the joint disc.
When to Seek Further Referral
While most jaw restrictions are musculoskeletal, there are times when a referral to a dentist or physician is necessary. You should seek a consultation if you experience:
Sudden, severe pain accompanied by a fever or facial swelling (possible infection). *
A complete inability to close the mouth (open lock). *
A recent history of major facial trauma. *
Persistent dental pain that feels like a toothache.
In many cases, a collaborative approach involving a chiropractor focused on musculoskeletal function and a dentist focused on dental occlusion or night guards provides the most comprehensive care.
FAQ
Q: How many fingers should I be able to fit in my mouth? A: A functional opening is typically three fingers width. If you can only fit one or two, your jaw mobility is restricted and should be assessed.
Q: Can a locked jaw fix itself? A: In some cases, a disc may spontaneously "reduce" or the muscles may relax on their own. However, if the restriction persists for more than a few days, conservative management is recommended to prevent chronic changes to the joint.
Q: Is jaw locking always painful? A: No. Some people experience a "painless lock" where the jaw simply won't open all the way, but there is no sharp pain. This is still a sign of joint dysfunction that warrants an assessment.
References
- Schiffman E, et al. "Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) for Clinical and Research Applications: recommendations of the International RDC/TMD Consortium Network* and Orofacial Pain Special Interest Group†." Journal of Oral & Facial Pain and Headache, 2014. [https://pubmed.ncbi.nlm.nih.gov/24397395/]
- Armijo-Olivo S, et al. "Effectiveness of Manual Therapy and Therapeutic Exercise for Temporomandibular Disorders: Systematic Review and Meta-Analysis." Physical Therapy, 2016. [https://pubmed.ncbi.nlm.nih.gov/26760572/]
- de Melo LA, et al. "Effect of manual therapy on jaw opening and pain in individuals with temporomandibular disorder: A systematic review and meta-analysis." Complementary Therapies in Medicine, 2020. [https://pubmed.ncbi.nlm.nih.gov/32470703/]
If jaw, back or joint symptoms are affecting your daily activities, a clinical assessment may help clarify the possible contributing factors and appropriate care options. Union Health Network is accepting new patients in Richmond Hill.
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