For many years, occlusal splint therapy has been used for the diagnosis and treatment of various masticatory system and temporomandibular joint disorders. Oral parafunction, unstable occlusion, symptoms of stress-related pain, occlusal interferences and extensive restorative treatment are the most common conditions requiring occlusal splint therapy. The aim of this article is to introduce the basic physiology of occlusal splint therapy for the treatment of temporomandibular disorder (TMD), bruxism, and certain forms of headache.