TMJ Biomechanics PDF

TMJ Biomechanics Prof. Olga Hoyos López MSc PT The Temporomandibular joint (TMJ) Bilateral action One of the most continuously used joints in the body Mastication, talking, swallowing Synchrony and synergy essential for correct jaw function. Mastication process: to...

TMJ Biomechanics Prof. Olga Hoyos López MSc PT The Temporomandibular joint (TMJ) Bilateral action One of the most continuously used joints in the body Mastication, talking, swallowing Synchrony and synergy essential for correct jaw function. Mastication process: together with tongue and teeth. Bicondylar synovial joint between condyle in lower jaw (mandible) and the the mandibular fossa of the temporal bone 2 Anatomy of the TMJ 3 Anatomy of the TMJ 4  Arthrology of the TMJ The TMJ is a synovial joint that permits a wide range of rotation as well as translation. An articular disc cushions the potentially large and repetitive forces inherent to mastication. The disc separates the joint into two synovial joint cavities -The inferior joint cavity is between the inferior aspect of the disc and the mandibular condyle. -The larger superior joint cavity is between the superior surface of the disc and the segment of bone formed by the mandibular fossa 5 Anatomy of the TMJ Mandibular Condyle Convex Shape. It possesses short projections known as medial and lateral poles. The medial pole is more prominent than the lateral Covered by a thin layer of fibrocartilage. 6 Anatomy of the TMJ Mandibular Fossa 7  Anatomy of the TMJ Articular disc Dense fibrocartilage. Lacks blood supply and sensory innervation (except the periphery) Main function: generate greater congruence. The thickness of the disc varies between its anterior and posterior regions The disc position protects the condyle as it slides forward across the articular eminence during the later phase of opening the mouth widely. The articular disc maximizes the congruency within the TMJ to reduce contact pressure. The disc also adds stability to the joint and helps guide the condyle of the mandible during movement. In the healthy TMJ, the disc slides with the translating condyle 8  Anatomy of the TMJ Articular Disc 9  Stability of the TMJ Passive stability -Fibrous capsule (firm medial & laterally, looser anterior and posteriorly. It provides more stability with lateral movements. TMJ can dislocate anteriorly without damaging the capsule ) -Articular disc -Lateral temporomandibular ligament (provides lateral stability to the capsule and it assists guiding the movement of the condyle during opening of the mouth) -Retrodiscal tissue (contains both elastic and collagenous fibers) Active stability: musculature 10 Osteokinematics of the TMJ PROTRUSION-RETRUSION LATERAL EXCURSION DEPRESSION-ELEVATION *All of these movements occur during different phases of mastication 11  Osteokinematics of the TMJ PROTRUSION AND RETRUSION – Anterior translation without significant rotation – Essential component for maximum opening of the mouth. – Retrusion: opposite movement. Important component of closing the widely opened and protruded mouth 12  Osteokinematics of the TMJ ▪ LATERAL EXCURSION Side-to-side translation of the mandible Average of 11mm translation is considered normal movement Usually combined with rotations and other type of translations. Line of movement guided by mandibular fossa and articular disc. 13  Osteokinematics of the TMJ DEPRESSION AND ELEVATION – Depression causes the mouth to open Maximum opening occurs during yawning or singing. 50 mm average opening from frontal area (aprox. 3 knuckles) Mastication requests about 18 mm of opening (around 36% maximum opening) – Elevation of the mandible closes the mouth – action used to grind food during mastication 14  TMJ arthrokinematics -Movement of the mandible typically involves bilateral action of the TMJs. -Abnormal function in one joint naturally interferes with the function of the other. -In general, during rotational movement the mandibular condyle rolls relative to the inferior surface of the disc, and during translational movement the mandibular condyle and disc slide essentially together. The disc usually moves in the direction of the translating condyle. 15 TMJ Arthrokinematics-Protrusion and Retrusion PROTRUSION: Mandibular Condyle and disc translate anteriorly and slightly downwards, relative to the fossa. RETRUSION: Mandibular Condyle and disc translate posteriorly and slightly upwards, relative to the fossa. 16  TMJ Arthrokinematics-Lateral excursion/deviation Primary: side-to-side translation of the condyle and disc within the fossa Secondary: Slight rotational components. During Left Lateral excursión, the left condyle forms a pivot point within the fossa as the right condyle rotates slightly anteriorly and medially. 17 TMJ Arthrokinematics: Depression and Elevation Combination of rotation and translation among the mandibular condyle, articular disc, and fossa. No other joint experiences so much translation and rotation proportionally. Rotation and translation occur simultaneously; hence the axis is constantly moving. The arthrokinematics of opening the mouth are depicted for an early and a late phase: -The early phase: first 35% to 50% of the ROM. Primarily rotation of the mandible relative to the temporal. The condyle rolls posteriorly within the concave inferior surface of the disc. (The direction of the roll is described relative to the rotation of a point on the ramus of the mandible) The rolling motion swings the body of the mandible inferiorly and posteriorly 18 TMJ Arthrokinematics: Depression and Elevation -The late phase: consists of the final 50% to 65% of the total ROM. This phase is marked by a gradual transition from primary rotation to primary translation. During the translation the condyle and disc slide together in a forward and inferior direction against the slope of the articular eminence At the end of opening, the axis of rotation shifts inferiorly. The exact point of the axis is difficult to define, but during the later phase of opening, the axis is usually below the neck of the mandible. 19 KINETICS OF THE TMJ 20  KINETICS OF THE TMJ MASSETERUS – Deep and Superficial Heads. Similar function – Bilateral contraction: Elevates the mandible to bring teeth into contact. Also BL contraction also protrudes mandible slightly. – Unilateral contraction – slight ipsilateral excursion. 21 KINETICS OF THE TMJ TEMPORALIS -Bilateral contraction elevate the mandible, and slightly retrude it. -Unilateral contraction of the temporalis, therefore, as when chewing in a side-to-side manner, causes slight ipsilateral excursion of the mandible 22  KINETICS OF THE TMJ MEDIAL PTERYGOID – Two heads, same function – Bilaterally: mandible elevation and slight protrusion. – Unilateral contraction: contralateral lateral excursion 23  KINETICS OF THE TMJ LATERAL PTERYGOID Difficult to be clear about the actions of the Lateral Pterygoid due to depth, but mostly accepted: -Unilateral contraction produces: depression (esp. Inferior head during resisted opening), contralateral excursión & rotates the ipsilateral condyle anterior-medially within the horizontal plane -BL contraction: strong protrusion of the mandible Special Role of the Superior Head of the Lateral Pterygoid in Adjusting Disc Position 24  KINETICS OF THE TMJ SECONDARY MUSCLES OF MASTICATION: The suprahyoid and infrahyoid muscles. Main function: depression of the mandible 25