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TMJ “Craniomandibular Joint”: or synovial lined joint TMJ • Mandibular fossa of temporal bone with condyle of mandible • Incongruent surfaces • Two joint cavities with articular disc interposed • Lower cavity = hinge joint • Upper joint = gliding TMJ TMJ Mandible Mandible TMJ • Capsule – Surrounds the joint – Encloses the disc – Attaches above the margins of the mandibular fossa – To the neck of the mandible – Inner aspect of capsule attaches to disc – Above disc – capsule loose – Below disc - taut TMJ Capsule TMJ Capsule TMJ • Ligaments • Lateral ligament – From zygomatic bone to run inferiorly and posteriorly to blend with the joint capsule to attach to lateral and posterior parts of the neck of the mandible • Sphenomandibular – Strong thin flat band lying on medial aspect of the joint – Passes inferiorly and forwards from the spine of the sphenoid to the lingula • Stylomandibular – Extends from the apex of the styloid process to the lower part of the posterior border of the ramus of the mandible, near the angle TMJ Capsule TMJ • Innervated by CN V, Mandibular branch • Movements – Elevation, depression, retraction, protraction, side to side • Elevation and depression involves the hinge like rotation of the condyle against the disc in the lower compartment • Protraction and retraction – actions whereby the condyle and disc move as one unit against the mandibular fossa. In protraction the condyle and disc glide forwards so that the condyle rides on the articular eminence – retraction = opposite CN V Trigeminal TMJ Motions TMJ Motions TMJ • Side to side – grinding movements – Mandible is alternately protracted and retracted with the two sides moving in opposite directions so that one side is protracted while the other is retracted – Actions combined with elevation and depression, rhythmically and alternately Muscles of Mastication • • • • • • Masseter Temporalis Lateral pterygoid Medial pterygoid All innervated by CNV Opening of jaw (depression) primarily passive or gravity assist Masseter Temporalis Pterygoids Pterygoids A. Temporal Bone Cranial component Mandibular fossa Articular eminence Articular surface from superior fossa to the anterior aspect of the eminence, thickest bone. • • • • B. Mandibular Component: Condyle • Condylar dimensions: A-P 8-10 mm M-L 15-20 mm • Articular surface: anterior superior aspect C. Articular Tissue • Origin: modified periosteum of intramembranous bone, NOT endochondral origin. A consequence of 2 embryonic tissue masses growing towards each other, NOT a single tissue mass cleft to form a joint articulation.
