Painless mandibular deviation on opening with limited range

Correct answer: C. The LEFT lateral pterygoid

• A. The medial pterygoid elevates the mandible and assists in medial excursion; it is not the primary protruder and does not drive opening.
• B. The right lateral pterygoid is the one working NORMALLY here. It is the unopposed translation on the right that produces the visible swing, but the muscle at fault is on the side the jaw moves toward.
• C. CORRECT. The mandible DEVIATES TOWARD THE AFFECTED SIDE. Opening is a combination of rotation and TRANSLATION, and the inferior head of the LATERAL PTERYGOID is what pulls the condyle and disc forward and medially down the articular eminence. If the LEFT side cannot translate fully — through muscle guarding, spasm, or a restriction within the joint — the right condyle translates normally, swings the midline across, and the chin ends up pointing LEFT. Deviation to the left therefore indicates the LEFT side is the restricted one.
• D. The masseter is an ELEVATOR, not a protruder. It closes the mandible and plays no part in the opening translation.

Note: This case is deliberately the OTHER pattern — no pain, no click, no crepitus, with muscle tenderness on palpation, which points to a MUSCULAR restriction rather than an intracapsular one. The rules to hold apart: persistent DEVIATION toward one side means restriction on that side; a DEFLECTION that corrects mid-opening with a click means disc displacement WITH reduction. Normal opening is 40–55 mm; under 40 mm is restricted.

Correct answer: D. Diagnostic local anaesthetic injection into the tender trigger point

• A. Electromyography is a research tool in this setting. It is not validated for routine clinical diagnosis of temporomandibular disorders and is not part of standard assessment.
• B. A panoramic film screens for gross bony change and for growth or fracture, but it images the condyles obliquely and superimposed. It tells you nothing about muscle, and nothing about the disc.
• C. Arthrocentesis is a therapeutic lavage for a joint that has already been identified as the problem. Performing it to establish the diagnosis is invasive and backwards.
• D. CORRECT. A DIAGNOSTIC TRIGGER POINT INJECTION of local anaesthetic is both a test and a treatment. If infiltrating the tender band abolishes the pain and improves the opening range, the source is MUSCULAR — the anaesthetic has interrupted the pain-spasm-pain cycle. If the restriction persists unchanged, the problem lies within the joint. It also confirms REFERRED pain patterns, since myofascial trigger points refer to predictable distant sites, masseter trigger points to the teeth and ear among them.

Note: The Diagnostic Criteria for TMD separate MYALGIA — local, myofascial, or myofascial with referral — from the INTRA-ARTICULAR disorders: disc displacement with or without reduction, degenerative joint disease, and subluxation. The clinical discriminator is whether palpation of the muscle REPRODUCES the patient's familiar pain.

Correct answer: B. Cyclobenzaprine at night

• A. There is no infection. Antibiotics have no role in temporomandibular disorders.
• B. CORRECT. CYCLOBENZAPRINE is a centrally acting MUSCLE RELAXANT, structurally a tricyclic, that acts on brainstem motor neurons to reduce tonic somatic motor activity. Low-dose nightly use is well established for masticatory myalgia and nocturnal parafunction, and its sedative effect is useful rather than incidental. It is a SHORT-TERM adjunct alongside the measures that actually matter: a soft diet, jaw rest, heat, stretching exercises, stress reduction and an occlusal splint.
• C. An NSAID is a reasonable adjunct where there is inflammatory pain, but this patient reports NO PAIN. Prescribing an anti-inflammatory for a painless muscular restriction treats the wrong target, and diclofenac carries the higher gastrointestinal and cardiovascular risk of the class.
• D. Systemic corticosteroids are not indicated for masticatory myalgia. They are reserved for inflammatory arthritides of the joint, and carry substantial risk for a self-limiting muscular condition.

Note: Sequence the management: reversible and conservative measures FIRST — patient education, jaw rest, soft diet, moist heat, gentle stretching, a stabilisation splint and physiotherapy. Pharmacotherapy is adjunctive and short-term. Irreversible treatment — occlusal adjustment, orthodontics, surgery — is not first-line, and most temporomandibular disorders improve without it.