What is proven to cause any restriction to the opening of the mouth?

Trismus is a condition that specifically involves a limited range of motion of the jaw, leading to difficulty or inability to open the mouth fully. This restriction can arise from various causes, such as muscle spasms, inflammation, or other underlying conditions affecting the jaw muscles or joints. The hallmark of trismus is the significant decrease in the ability to open the mouth, which can impact eating, speaking, and dental care.

The other options relate to different conditions: hemiplegia refers to paralysis of one side of the body and does not directly lead to mouth opening restrictions. Bruxism is the involuntary grinding or clenching of teeth, which can contribute to jaw pain but does not directly cause an inability to open the mouth. Temporomandibular Joint Disorder (TMJ) can involve symptoms that affect jaw movement, but the term encompasses a broader range of issues related to the jaw joint, not specifically limiting mouth opening as trismus does.