Seminar On

TemporoMandibular Joint and Its MovementsIndex 1. Introduction 2. Development of TMJ 3. Anatomy of TMJ 4. Blood supply 5. Nerve supply 6. Postures and movements 7. Applied anatomy of TMJ 8. Surgical anatomical consideration 9. Surgical approaches to mandibular condyle and TMJ

Presented byDr Madhu Verma Department of Oral and Maxillofacial Surgery, Pb.Govt.Dental College and Hospital Amritsar

IntroductionThe sites of junctions between bones are known as articulations or joints. It plays important role in bone growth phenomenon, initially during development and movement of body parts and their function during adult life. The joints can be divided functionally into 2 typesa. Movable joint (Diarthroses) b. Immovable joint (Synarthroses) Fibrous connective tissue-Syndesmosis Cartilage Bone -Synchondrosis -Synostosis

The TMJs are bilateral, diarthrodial, ginglymoid, and synovial and freely movable joints. TMJ is one of the most complex joints in the body and is the area in which the mandible articulates with the cranium. it provides for the hinge movement in one plane and therefore can be considered a ginglymoid joint. At the same time it also provides for the gliding movements, which classifies it as an arthroidal joint. Thus the TMJ has been technically considered a ginglymoarthroidal joint. The TMJ is also classified as a compound joint. By definition, a compound joint requires the presence of at least three bones, yet the TMJ is made up of only two bones. Functionally, the articular disc serves as a nonossified bone that permits the complex movements of the joint. Because the articular disc functions as a third bone, the craniomandibular articulation is considered a compound joint. The fundamental design of synovial joint is an adaption that promotes to free and forceful movement of the body parts. Consequently the bearing surfaces of the opposing bones are padded with smooth, slippery, highly resilient, hyaline cartilage. The articulating parts are connected by a flexible capsular sleeve, which completely encloses the joint cavity to contain its lubricating fluid. Development of TMJ The TMJ is secondary in development, both in its evolutionary and embryological history. The joint between the malleus and incus that develops

at the dorsal end of Meckels cartilage is phylogentically the primary jaw joint. With the development of middle ear chamber, this primary Meckels joint loses its association with mandible and reflects the adaptation of the bones of the primitive joint. The mammalian temporomandibular joint develops as an entirely new and separate jaw joint mechanism. It developes from widely separated temporal and condylar processes that grow towards each other. Between 10-12 weeks- secondary cartilages of condyle grows towards temporal bone. During 12th week i.u. 2 clefts develop in interposed vascular fibrous connective tissue and forming two joint cavities. After cavitation synovial membrane invasion occurs. At 22nd week i.u. - petrous and tympanic portions of the temporal bone fuse. At birth mandibular fossa is practically flat; there is no articular tubercle. Its only after eruption of deciduous dentition, articular tubercle begins and becomes prominent and does not complete its development until 12 th yr of life. Anatomy of temporomandibular joint The components of the TMJ are presented in the following sequenceMandibular component The articular part of mandible is ovoid condylar process seated atop narrower mandibular neck. The condyle is usually strongly convex anteroposteriorly and mildly convex mediolaterly, convexity increase towards the medial portion(58%). 25% of the condyles may be flat superiorly and approx. 12% are pointed or angular in shape and 3% are bulbous are rounded in shape. The condyle is broad laterally and narrower medially. Lateral pole- Roughened, bluntly pointed & projects only moderaly from plane of ramus. Medial pole-Often rounded, extend strongly inward from the plane of ramus. In lateral view condyle appears tilted forward on the mandibular neck.

The articular surface thus faces the posterior slope of articular eminence when jaw is held in complete occlusion. The articular surface continues medially down, faces entoglenoid process of temporal bone. The condyle is about 15 to 20mm from side to side & about 8 to 10mm from front to back. Its long axis lies at a right angle with the plane of the ramus & thus does not lies in frontal plane. Thus, if long axes of two condyles extended medially they meet approximately at basion at the anterior limit of foramen magnum, forming angle of 145-160 degree open towards front. Cranial component It is situated on the inferior surface of temporal squama. To elaborate this part, first we must understand distinction between articular tubercle and articular eminenceArticular tubercle Non-articulating, small, rough bony knob raised on outer end of anterior root of zygomatic process of temporal bone. It serves as attachment for collateral ligaments of the joint. Articular eminence: Its is entire transverse bony bar, forms anterior root of zygoma.It is strongly convex in anteroposterior direction & somewhat concave in transverse direction, the radius of curvature varies from 5-15mm. The preglenoid plane is slightly hollowed almost horizontal articular surface continuing anteriorly from the height of eminence. The pressure-bearing surface consists of three regions1. Posterior slope to height of convexity of articular eminence, just anterior to glenoid fossa. 2. Flattening preglenoid plane continuing anteriorly from height of eminence.

3. Enteglenoid process continuous with narrow medial glenoid plane on its inferior edge. The boundary between squama and temporal bone is formed byLaterally-by tympanosqamosal suture Medially-Tegmen tympani protrude between tympanic bone and temporal squama, dividing simple fissure into anterior petrosqamosal & posterior petrotympanic fissure. Posterior part of the joint fossa is elevated to form cone shaped prominence called postglenoid process. The roof of mandibular fossa separating it from the middle cranial fossa, is always thin & thus is not functionally stress bearing part of the craniomandibular joint. The function is normally between the condyle and disc on one hand, and disc and articular fossa on other side. In cross section, the fossa and the eminence form a lazy S Articular coverings It is the smooth, slippery, pressure bearing tissue carpenting the surface of bones. It is essentially a bed of tough collagen fibers bound by special glycoproteins. On condyle - thickest on anteroposterior convexity & Medial (0.8mm)> Lateral (0.37mm) On temporal component- thickest along slope & crest of eminence and preglenoid plane. Eminence Medial