Trismus, from the Greek trismos, is defined as a prolonged tetanic spasm of the jaw muscles by which the normal opening of the mouth is restricted (Locked Jaw).
Trismus is an inability to open the mouth to a normal gape
- Associated with dental injections of local anesthetics
- Trauma to muscles or blood vessels in the infra-temporal fossa is the most common etiological factor in trismus associated with dental injections of local anesthetics.
- Local anesthetic solutions into which alcohol or cold sterilizing solutions have diffused, produce irritation of tissues (ex muscle), leading potentially to trismus.
- Local anesthetics have been demonstrated to have slight mycotoxic properties on skeletal muscles.
The injection of local anesthetic solution either intramuscularly or supra-muscularly leads to a rapidly progressive necrosis of the exposed muscle fibers.
- Hemorrhage is another cause of trismus.
Large volumes of extra-vascular blood can produce tissue irritation, leading to muscle dysfunction as the blood is slowly resorbed.
Severe & progressive trismus occasionally follows a few days after an IANB as the result of the development of the haematoma in the media pterygoid muscle.
The passage of the local anesthetic needle through this muscle may unavoidably pierce a small blood vessel and cause some bleeding between the muscle fibers. Fibrosis of the haematoma may result in prolonged limitation of mouth opening unless active stretching exercise are employed.
- A low grade infection after injection can also cause trismus.
- Every needle insertion produces some insult to the tissue through which it passes>>> multiple needle penetrations correlate with a greater incidence of post injection trismus.
- Excessive volumes of local anesthetic solution deposited into a restricted area produce distention of tissues, which may lead to post-injection trismus. (multiple missed IANBs)
- Associated with extractions
- Extraction of teeth may result in trismus, or limitation in mouth opening.
- Trismus commonly seen following extractions, particularly lower molars.
- Trismus results from inflammation involving the muscle of mastication.
- Inflammation and edema may spread from this region to affect the powerful jaw closing muscles, masseter and medial pterygoid, which are then painful when stretched.
- Surgical extraction of impacted mandibular third molars usually results in some degree of trismus because the inflammatory response to the surgical procedure is sufficiently widespread to involve several muscles of mastication.
Trismus is usually not sever and does not hamper the patient’s activity.
- Trismus due to edema normally resolve spontaneously with the inflammation but the patient can be made more comfortable meanwhile by the application of heat to the affected area.
- Associated with Fractures:
- Maxillary Fractures
- Mandibular Fractures (ex angle, subcondyle)
- Zygomatic (Malar) Fractures: Obstruction of coronoid process
- Textbook of General and Oral Surgery (Wray. Stenhouse. Lee. Clark)
- Handbook of Local Anesthesia 5th edition (Malamed)
- Contemporary Oral and Maxillofacial Surgery 5th edition (Hupp. Tucker. Ellis)
- Tooth Extraction, A Practical Guide (Robinson)