An inability to open or close the mouth is known as locked jaw syndrome. It results from conditions affecting the temperomandibular joint and masticatory muscles and may lead to severe mastication dysfunction.
Among 37 cases recorded, 31 were in dogs and six in cats, with all but one canine case in an adult. Temperomandibular joint ankylosis due to fracture was the most common cause of locked jaw syndrome, with other causes including masticatory muscle myositis, neoplasia, trigeminal nerve paralysis and CNS lesions.
Journal of Veterinary Dentistry 25 (1):16-22.
Abstract reproduced by kind permission of Veterinary Practice magazine.