What typically causes trismus?

Trismus, or "lockjaw," is primarily caused by muscle spasms of mastication, which are the muscles responsible for moving the jaw. These spasms can occur in response to several factors, including infections (such as tetanus or more commonly, dental infections), trauma, or other irritants affecting the muscles or surrounding tissues. The involuntary contractions lead to limited jaw movement, making it difficult for an individual to open their mouth fully.

While infections of the middle ear can lead to referred pain and tension in jaw muscles, they do not directly cause trismus. Injuries to the eye may cause discomfort affecting one's ability to chew or speak but are not associated with muscle spasms of mastication. Heat-related illnesses mainly affect thermoregulation and electrolyte balance, resulting in a variety of symptoms but are not linked to trismus. Therefore, muscle spasms of mastication remain the primary reason for this condition.