**Core Concept**
Trismus refers to a reduction in the range of motion of the jaw, characterized by difficulty opening the mouth, often resulting from muscle spasms, pain, or inflammation. This condition can be caused by various factors, including infections, trauma, or inflammation of the temporomandibular joint (TMJ) and surrounding tissues.

**Why the Correct Answer is Right**
Trismus is commonly seen in cases of **infectious mononucleosis** (also known as glandular fever), particularly due to the involvement of the TMJ and surrounding muscles. The Epstein-Barr virus (EBV) causes infectious mononucleosis, leading to inflammation and swelling of the TMJ, which in turn results in trismus. This condition is often accompanied by fever, sore throat, and lymphadenopathy.

**Why Each Wrong Option is Incorrect**
**Option A:** Temporomandibular joint (TMJ) disorders can cause trismus, but they are not the most common cause.
**Option B:** Bell's palsy is a condition that affects the facial nerve, leading to weakness or paralysis of the facial muscles, but it is not commonly associated with trismus.
**Option C:** Dental abscesses can cause pain and swelling in the jaw, but they are not the primary cause of trismus.

**Clinical Pearl / High-Yield Fact**
It's essential to consider infectious mononucleosis as a potential cause of trismus, especially in patients presenting with fever, sore throat, and lymphadenopathy.

**Correct Answer: C.**