Epidemiological studies, which evaluated the prevalence of temporomandibular disorders (TMD) in given populations, reported a prevalence between 40% and 60% in the general population with any type of TMD, e.g. myofacial dysfunction, internal derangement or degenerative joint disease. Many papers underline the need for a standardized classification for TMD signs and symptoms. There are a number of classification schemes used in studies of TMD that incorporate clinical signs, which are the Helkimo Index, the Craniomandibular Index and the Research Diagnostic Criteria for TMD.