**Core Concept**
The temporomandibular joint (TMJ) is a complex synovial joint that facilitates jaw movement, including opening, closing, and lateral excursions. Normal TMJ function is characterized by smooth, pain-free movement, and certain palpable and audible signs.

**Why the Correct Answer is Right**
Pain while opening the mouth is not a normal feature of the temporomandibular joint. In fact, TMJ pain is a common symptom of various disorders, including temporomandibular joint dysfunction (TMD) and temporomandibular joint disorders (TMDs). These conditions can be caused by factors such as misalignment of the teeth, bruxism, or trauma to the jaw. Pain in the TMJ can manifest as tenderness to the touch, clicking or popping sounds, or limited range of motion. The presence of pain is a significant departure from normal TMJ function.

**Why Each Wrong Option is Incorrect**
**Option A:** Joint sound, such as clicking or popping, is a common feature of the TMJ, especially during movement. This is due to the presence of the articular disc and the associated ligaments that can cause a palpable or audible click as they move.

**Option C:** Deviation of the mouth in the opposite direction during eccentric movements is a normal finding in the TMJ. This occurs due to the natural movement of the articular disc and the condyle as the jaw moves.

**Option D:** None of the above is incorrect because option B, pain while opening the mouth, is indeed not a normal feature of the TMJ.

**Clinical Pearl / High-Yield Fact**
When assessing the TMJ, it's essential to note that clicking or popping sounds are not necessarily a sign of pathology. A thorough examination, including palpation and radiographic evaluation, is required to determine the underlying cause of any symptoms.

**Correct Answer:** **✓ Correct Answer: B. Pain while opening the mouth**