Temporomandibular joint (TMJ) ankylosis is a joint disorder characterized by the fibrotic or bony adhesion of anatomical joint components, leading to severe limitation or loss of joint mobility. TMJ ankylosis affects mastication, digestion, speech, and oral hygiene. Onset during childhood results in secondary micrognathia, leading to a reduction in the oropharyngeal airway and psychological problems. We present the case of a 39-year-old female patient with bilateral TMJ ankylosis and micrognathia that developed during childhood. The patient had a history of a traffic accident at the age of 5 years and presented with trismus. Computed tomography revealed bony ankylosis of the right TMJ and fibrotic ankylosis of the left TMJ. Bilateral interpositional gap arthroplasty was performed using an intraoral approach, followed by mandibular distraction osteogenesis (DO). Following DO, oral rehabilitation with dental implants was performed. The patient’s facial profile and mastication significantly improved and were maintained for 10 years after treatment.