What do we need to know about TMJ disorders? TMJ helps in opening and closing your mouth, enabling you to eat and speak. TMJ disorders are conditions, which affect the TMJ joint and its muscles. TMJ disorders cause severe pain, loss of mobility, and tenderness in the joints and associated muscles. The TMJ is the joint that connects your mandible (lower jaw) to your skull. Learn about TMJ disorders. TMJ disorders affect the temporomandibular joint, causing pain and restricted movement in the jaw. The temporomandibular joint is complex and can be a hard area of the body to treat. This MNT ... Temporomandibular joint disorder, often referred to as TMJ disorder, affects the jaw joint and surrounding muscles. It can cause discomfort and impact jaw movement. The exact cause of TMJ disorder is not always clear, but several factors may contribute to its development.