Digital occlusal evaluation in patients with temporomandibular joint disorders

During the recent decades controversial opinions have dominated the literature on the etiology, diagnostics and treatment of temporomandibular joint disorders (TMD) [1]. According to the results of study carried out by Luther, from 7% to 84% of the world population (aged 3-74) suffer from these disorders [2]. In 2013 the TMJ Association in the USA came to the conclusion that approximately 35 million of the US population are affected by the disorders of temporomandibular joint and the masticatory muscles. Epidemiological study has shown that approximately 75% of adult population have at least one symptom related to TMD dysfunction, 30%-two or more symptoms [3]. Patients tend to indicate different clinical symptoms: pain during mouth opening, chewing, crepitation, clicking in the area of temporomandibular joint or ear, limited mandibular opening, morning stagnation and sleep disorders [4,5]. It is difficult to identify a single main reason for the symptoms in the area of this joint [6], thus the etiology of the disorders is polyetiological. However, the relationship between dental occlusion and TMDs is still a subject of debate by different researchers in the dental community. Back in 1993, there was a strong argument that the role of dental occlusion in the etiology of TMDs was not important [7]. According to the study results, in the cases of chronic pain in the temporomandibular joint area patients’ could be treated by physiotherapy (e.g., electromyographic biofeedback for muscle relaxation) rather than occlusal correction [8]. Still there is no evidence if repetitive or extensive occlusal therapy can have a significant impact on TMDs [9]. In addition, there is evidence that due to adaptation characteristics of human articulatory system, morphological disorders in temporomandibular joint are not an invariable consequence of occlusal disorders [10]. According to Chinese researchers, occlusal interferences are directly related to pain in masticatory muscles and instability of mandibular condyle, which influences TMDs [11]. The Glossary of Prosthodontic Terms states that occlusion should be balanced and muscle tension-free to the highest possible extent. To achieve static occlusion, posterior teeth should be in simultaneous contact, with equally distributed force on the dental arch [12]. The most stable central occlusion occurs when the mandibular condyle is located in the mandibular fossa, slightly (~0.5 mm) glided forward and downward, from the apex of its front position, at the base of articular tubercle of the temporal bone [13]. The occlusal forces are concentrated and distributed evenly on the dental arches, whereas temporomandibular joints are affected only by a minor load [14]. But adequate occlusal load depends on occlusal surfaces, tilting of each tooth and the degree of tilt [15].