Why can't I open one side of my mouth?

Inability to open one side of the mouth is generally due to temporomandibular joint (TMJ) disorders. Temporomandibular joint dysfunction is a major factor causing restricted mouth opening. Temporomandibular joint disorder is a chronic progressive condition; when muscle spasms, fatigue-induced inflammation, or irreversible anterior displacement of the articular disc occur, they can lead to movement restrictions in the joint and muscles, thereby limiting mouth opening. Infections in the deep facial spaces are usually caused by inflammation related to wisdom teeth, and when this inflammation affects the masticatory muscles, it can also result in trismus (inability to fully open the mouth).