What is Trismus (Lock Jaw)? And How Best is it Treated?

What is Lockjaw?

Trismus (or lockjaw) is a condition where mouth opening is severely restricted. It’s commonly encountered by dental practitioners and responds well to treatment from a trained physical therapist.

Causes range from minor issues to potentially life-threatening conditions. Normal mouth opening varies from 40–60 mm (about two to three finger widths). Trismus is often defined as less than 20 mm opening.

• >30 mm but <40 mm: mild trismus
• 15–30 mm: moderate trismus
• <15 mm: severe trismus

Limited mouth opening can interfere with:

• Dental examination and treatment
• Oral hygiene (can lead to cavities, infection, or bad breath)
• Eating, chewing, swallowing, and speaking
• Kissing
• Emergency medical procedures (e.g. inserting a breathing tube)

Lockjaw Causes

1. Infection
   • Odontogenic (tooth-related): pulpal, periodontal
   • Non-odontogenic: tonsillitis, tetanus, meningitis, parotid or brain abscess
2. Trauma
   • Surgical extraction of mandibular molars
   • Post-anesthetic injections (especially medial pterygoid trauma)
   • Facial or mandibular fractures
3. Dental treatment
4. Temporomandibular Joint (TMJ) disorders
5. Tumors (benign or malignant)
6. Drug-induced (e.g. phenothiazines, tricyclic antidepressants, metoclopramide)
7. Radiotherapy or chemotherapy (fibrosis/scarring)
8. Congenital disorders
9. Psychogenic causes (e.g. hysteria, lupus)
10. Post-surgical fibrosis

How to Diagnose Lockjaw / Trismus

The spatula test helps diagnose trismus. Touching the posterior pharyngeal wall with a spatula triggers a reflexive masseter spasm (positive) instead of a gag reflex (negative).

Because trismus is difficult to treat once established, early recognition and intervention are crucial. A physical therapist specializing in Temporomandibular Dysfunction (TMD) can perform manual therapy and teach exercises to restore motion and prevent TMJ disc disorders.

Lockjaw Treatment – Physical Therapy Examples

1. 1. Sustained stretching with tongue depressors (with or without heat modalities)

1. 1. Manual soft tissue mobilization to affected muscles and self-massage instruction

1. 1. Finger Spread technique for home stretching

1. 1. Gentle joint mobilizations if capsular tightness develops

Physical therapy aims to reduce swelling, soften and stretch fibrous tissue, restore circulation, and regain full motion. The sooner treatment begins, the faster recovery occurs. Post-radiation and long-undiagnosed cases may take several months.

Do you have lockjaw? Have questions about symptoms or treatment? Contact Us: info@treatingtmj.com