Temporomandibular joint disorders – a lookback in time

The variety of terms used has contributed to a great amount of confusion that exists in this already complicated field of study. Lack of communication and coordination of research efforts often begins with differences in terminology. Therefore in an attempt to coordinate efforts, the American Dental Association began to use TMD to include all functional disturbances of the masticatory system. The article reviews the research work done by various authors pertaining to the disorders of the temporomandibular joint.


Introduction
Why the term temporomandibular disorder? The clinical signs and symptoms displayed by masticatory disorders are much too varied to be classified as a "syndrome." According to medical definition, a syndrome is a set of symptoms which occur together; a symptom complex. The term is meant to apply to symptoms as such. A disorder is a derangement or abnormality of function, a morbid physical or mental state. This term applies not to symptoms but to conditions. The general term temporomandibular disorders should designate the conditions that comprise complaints of the masticatory system involving the craniomandibular articulation and its musculature. This term does not suggest merely problems that are isolated to the joints but includes all disturbances associated with the function of the masticatory system. Over the years functional disturbances of the masticatory system have been identified by a variety of terms. In 1934 James Costen described a group of symptoms that centered on the ear and temporomandibular joint (TMJ). Because of his work the term Costen syndrome developed; later the term temporomandibular joint disturbances became popular. In 1959 Shore introduced the term temporomandibular joint dysfunction syndrome. Later came the term functional temporomandibular joint disturbances, coined by Ash and Ramfjord. Some terms described the suggested causes, such as occlusomandibular disturbance and myoarthropathy of the temporomandibular joint. Others stressed pain, such as pain dysfunction syndrome, myofascial pain dysfunction syndrome, and temporomandibular pain dysfunction syndrome. Because the symptoms are not always isolated to the TMJ, some authors believe that the foregoing terms are too limited and that a broader, collective term should be used, such as craniomandibular disorders. Bell suggested the term temporomandibular disorders (TMDs), which has gained popularity.

The Literature Review for the Temporomandibular Disorders
Saper [1] (1957) commented that temporomandibular joint pain was psychogenic; Copland observed neuromuscular tension in 74 his patient, which increased in association with examinations, emotional disturbances. Johan Ulrich [2] (1959) summarized the shape of the joint surfaces do not govern movements, but these are determined rather by the synergistic action of muscles. Schweitzer JM [3] (1961) conducted a study on masticatory function in man. The study gave a composite picture of the total envelop of motion and the functional envelop and demonstrated the difference between these two envelopes.
In an examination of 200 males in a Veterans administrative hospital, Loiselle [4] (1969) reported that despite many occlusal disharmonies none was considered to have temporomandibular dysfunction. Edentulous persons despite overclosure, rarely have myofacial pain and those who wear dentures with decreased vertical dimension, or other occlusal problems, rarely have temporomandibular joint disturbances. Laskin and Perry H.T. [5] (1969) introduced the term Myofacial pain dysfunction syndrome and re-emphasized that the disease entity is primarily in the muscle and only secondarily a joint problem. His concept is the Psycho physiologic theory. Gibbs [6]  They concluded that within the scope of the methods used in the study there appear to be no significant differences in occlusion between symptom and control groups. There was no significant relationship between anxiety level and dental malocclusion in the symptom group. Mongini F [8] (1977) evaluated an anatomic and clinical investigation of condylar remodeling, the position of the condyle in centric occlusion and the relationship of these two factors to each other and to the feature of the dentition. Jose Granados [9] (1979) evaluated whether changes in attrition and loss of teeth would correlate with a change in the articular eminence. Kopp and Rockier [10] (1979) found that patients with temporomandibular joint crepitation showed a higher frequency of radiologic abnormalities than patients without crepitation. Catherine D. Campbell [11] and her co-workers (1982) determined the relationship between the temporomandibular joint syndromes and a-history of referred pain patterns. DE Boevera JA and Adriaens PA [12] (1983) studied the occlusal relationship in patients with pain dysfunction symptoms in the temporomandibular joints. Williamson and Lundquist [13], (1983) studying the effect of various occlusal contact patterns on the temporal and masseter muscles, reported that when subjects with bilateral occlusal contacts during a laterotrusive excursion were asked to move in that direction, all four muscles remained active.  [24] in 1992 demonstrated that the articular disc of human TMJ appears to have a neural network extending from the precapsular connective tissue peripherally into the disc. Ai M. and Yamashita S [25] (1992) investigated the tenderness of the temporomandibular joint, muscles and their relation to occlusion in patients with temporomandibular joint dysfunction Cohen SG [26] (1994) studied "Internal derangements of the temporomandibular joint (TMJ) that can elicit symptoms of pain, clicking and noises described subjectively as popping, grinding or grating.
Greene CS [27] in 1994 studied the temporomandibular disorders in geriatric population and concluded that overall prevalence of TMD diminishes in the elderly population, but it is not as low as the treatment seeking numbers might suggest. Zaki [50] (2014) reviewed that the blood supply to the TMJ is circumferential. Every vessel within a radius of 3 cm contributes branches to the joint capsule and contributes one or two branches to it. Larissa Soares Reis Vilnova [51] (2014) Myofascial pain (MFP) is the most common temporomandibular disorder (TMD) and is characterized by muscle tenderness, local and referred pain on the temporomandibular joint (TMJ) and/or masticatory muscles, and a slightly limited range of jaw motion.

Conclusion
Temporomandibular joint is a ginglimo diarthrodial joint,consisting of two synovial joint cavities separated by an articular disc. Rotatory movement of the condyle takes place in the lower joint cavity between the disc and the head of the condyle, whereas translatory movement of the condyle occurs in the upper joint compartment between the articular disc and glenoid fossa. The presence of a dense avascular fibro cartilage disc between the condyle and articular fossa is another unique and characteristic feature of this joint, so the load and stress during mandibular function is taken up by the disc and not the fossa. The temporomandibular joint does not function independently, one joint is interdependent on the other. This interdependence makes simple opening movement of the mandible up to 2 cm, there is rotation of the head of the condyle beneath the inferior surface of the disc. Beyond this distance, there is bodily translation of the head of the condyle with the disc moving along with it as one unit. During protrusion the condyles travel forward, one condyle may take a longer translation than the other. During the lateral movement of the mandible while the condyle of one joint moves by inward, downward and forward, a compensating side shift of the opposite condyle takes place to accommodate the medial movement of the downward and forward moving condyle. This movement was described by Bennett, hence it is known as Bennett side shift or "Bennett movement". The temporomandibular joint are guided by the nature of the occlusal surface of the teeth. There exists an occluso articular harmony; any situation which interferes with this harmony may cause T.MJ. dysfunction. A combination of dental and medical therapy is most effective in the treatment of TMJ. Non-surgical treatments such as counselling, pharmacotherapy, and occlusal splint therapy continue to be the most effective way of managing over 80% of patients. Finally it should be emphasised that the movements of the joint is influenced by neuromuscuiar proprioceptive signals from the periodontal membrane of teeth, musculature and the joint itself. The proprioceptive receptors situated in the periodontal membrane perceive the character of occlusal surface and the nature of food between the teeth; transmits this information to the CNS, which in turn program the muscle function to activate the most physiological mandibular movement to compliment the prevailing occlusal condition. Thus, the final decision of mandibular movement will be programmed to a large extent from the proprioception of periodontal membrane and musculature to initiate a plan of action for the chewing cycle. When pathological occlusion or any form of occiusal disharmony exists the proprioceptive signals initiate a plan of inaction. This is seen in the form of inhibition and deviation of normal mandibuiar movements and spasm of the muscles.