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Trang 2 Learning objectives: At the end of this presentation students should be able to:1- describe the skeletal components and articular surfaces of the temporomandibular joint2- descri
§TEMPOROMANDIBULAR JOINT People’s Teacher Prof Hoàng Tử Hùng, DDS, PhD E: tuhung.hoang@gmail.com W: hoangtuhung.com Learning objectives: At the end of this presentation students should be able to: 1- describe the skeletal components and articular surfaces of the temporomandibular joint 2- describe the articular disc and related structures 3- describe the joint capsule and synovial membranes 4- describe the mechanics of the assembly of condylar-disc movement www.hoangtuhung.com INTRODUCTION The temporomandibular joint (TMJ(s)) is one of the most complex joint(s) in the body TMJ provides for both hinging and sliding movements classified as a ginglymo-arthrodial joint Five components of TMJ: Articular surfaces: • • Mandibular condyle Cranial articular surface Articular disc Joint capsule Synovial membranes Ligaments The mandible functionally operates as www.hoangtuhung.com a third-order lever ARTICULAR SURFACES Mandibular condyle Dimensions: - mediolateral: 15 - 20 mm - anteroposterior: - 10 mm Two poles: lateral pole and medial pole The medial pole is more prominent than the lateral anterosuperior aspect is working surface of the condyle A line drawn through the two poles will extend medially and posteriorly toward the anterior border of foramen magnum where it meets the corresponding line from the other side at an angle ≈ 145 - 160º www.hoangtuhung.com The cranial articular surface (temporal surface) The temporal articular surface is situated on the inferior part of the squamous portion of temporal bone, just anterior to the tympanic bone and posterior to the root of the zygomatic process Consists of: - An anterior eminence: the glenoid (articular) eminence - A posterior depression: the mandibular, or glenoid, or articular fossa The articular surfaces (condyle and temporal) are covered by nonvascularized noninnervated dense fibrous connective tissue (not by hyaline cartilage as in the case of other load-bearing joints) www.hoangtuhung.com TB ARTICULAR DISC A biconcave oval structure interposes between condyle and articular fossa It is a firm but flexible structure and composed of dense fibrous avascular connective tissue, In the sagittal plane, it can be divided into three regions: The posterior part ( ̴ band) is thicker than anterior part ( ̴ band) [≈ vs mm], the central part is thinnest (intermediate zone) ≈ mm Vessels and nerve have only in peripheral area www.hoangtuhung.com ARTICULAR DISC (cont’d 1) Retrodiscal tissue or Bilaminar zone The posterior border of the disc is attached by retrodiscal tissue Consists of: - The body of retrodiscal tissue, and - Two laminae of connective tissue Body of retrodiscal tissue Composed of loose connective tissue rich in vascular and nerve supply (“neurovascular tissue”)* Shunting system: A network of blood vessels with elastic walls allow blood to rush in to fill the space between the disk and posterior wall of articular capsule when the condyle moves forward When the condyle moves back, the blood shunted out the vessels (the system “vascular knee”) *The anterior tympanic artery supplies thewww.hoangtuhung.com retrodiscal tissue ARTICULAR DISC (cont’d 2) Superior retrodiscal lamina A lamina of connective tissue which contains highly elastic fibers covers the superior retrodiscal tissue and attaches the disc posteriorly to the tympanic plate Superior retrodiscal lamina helps to prevent the retrodiscal tissue from being trapped between the disc and the eminence as the disc slides back on mandibular closure Inferior retrodiscal lamina An inelastic band of collagen from the posteroinferior border of the disc attaches to the back of condyle (posterior ligament or inferior retrodiscal lamina) It acts to stabilize the disc on top of condyle and prevents the disc from rotating too far forward and from being displaced anteriorly www.hoangtuhung.com ARTICULAR DISC (cont’d 3) Collateral (discal) ligaments In the frontal plane, medial part is thicker than lateral part The collateral (discal) ligaments extend medially and laterally, bend downward and attach to the condyle below corresponding condyle poles Discal ligaments are true ligament, composed of collagenous connective tissue (inelastic) They permit the disc to be rotated antero-posteriorly on the condyle and form the condyle-disc complex or condyle-disc assembly Articular upper and lower compartments The disc is continuous with the articular capsule anteriorly and distally The discal ligaments and articular ligament divide articular space into two compartments: upper ̴ and lower ̴ www.hoangtuhung.com Borders of compartments: upper: the articular fossa and the superior surface of the disc Lower: the inferior surface of the disc and the condyle ARTICULAR CAPSULE The joint capsule surrounds the articular surfaces and defines the anatomical and functional boundary Wide at the temporal surface and tapering toward the condyle neck Articular capsule consists of three layers: the capsule: an acellular with thick bands of collagen forms the outer boundary of the joint the subsynovial tissue: a connective tissue rich in vascular and nerve supply the synovial membrane: (presented separately) Afferent nerve fibers for proprioception and nociception are branches of the auriculotemporal, masseteric, and posterior deep temporal nerves www.hoangtuhung.com ARTICULAR CAPSULE (cont’d 1) On the temporal surface of TMJ, joint capsule runs along: ‒ Anteriorly: eminence crest ‒ Laterally: outside of the root of zygomatic process, lateral edge of the eminence and articular fossa ‒ Posteriorly: squamotympanic fissure ‒ Medially: sphenosquamosal suture ‒ Anteromedially: not discrete tructure* *since the superior head of the lateral pterygoid www.hoangtuhung.com muscle attach to the fused capsule and disc ARTICULAR CAPSULE (cont’d 2) Anteriorly, the capsule is attached to the disc and to the superior head of lateral pterygoid muscle by tendinous fibers Posteriorly, some fibers of the capsule blend with the bilamina zone, Elastic bundles also extend from squamotympanic fissure ( ̴ Glasser) to the posterior of the condyle neck www.hoangtuhung.com SYNOVIAL MEMBRANES TMJ possesses two synovial membranes for each compartment Synovial membrane is the inner most layer of articular capsule Composed of a thin layer specialized vascularized connective tissue lines the inner surfaces of the joint capsule The synovial membrane form folds over the retrodiscal tissue when the condyle and disc are retruded Small projections (synovial villi) may also extend into the superior and inferior joint compartments anteriorly The two synovial spaces only intercommunicate when the disc is pathologically perforated www.hoangtuhung.com SYNOVIAL MEMBRANES (cont’d 1) Synovial membranes produce synovial fluid, a proteoglycan-hyaluronic acid complex The volume of the TMJ compartments and synovial fluid are not defined, the joint spaces are normally collapsed but can be inflated by injecting fluid The synovial fluid act: as a medium for nutritional and metabolic interchange of the articular surfaces which are nonvascular as a lubricant between articular surfaces during function the synovial tissue may possess immunologic capacity Macrophages are also present in articular spaces, they probably eliminate cellular debris and toxic products www.hoangtuhung.com LIGAMENTS Collateral and posterior discal ligaments (above) Capsular and Temporomandibular ligaments The TMJ capsule is a ligamentous capsule The capsule is reinforced laterally by the TM ligament TM ligament is a strong, tight fibers that consists of an outer oblique portion and an inner horizontal portion Ligaments are innervated by both proprioceptors and nociceptors Ligaments play an important role in protecting structures They are collagenous connective tissue and have a particular length; they not stretch If extensive forces applied to a ligament, whether suddenly or over a prolonged period of time, the ligament can be elongated www.hoangtuhung.com LIGAMENTS (cont’d 1) capsule The outer portion extends from the base of process of the temporal bone downward and oblique to the neck of the condyle Outer oblique portion The inner portion extends from the outer surface of the articular eminence posteriorly and horizontally to the lateral pole of the condyle and posterior part of the disc www.hoangtuhung.com Inner horizontal portion Zygomatic process (temporal bone) LIGAMENTS (cont’d 2) Accessory ligaments Sphenomandibular ligament: from the sphenoid bone extends downward to the mandibular lingula Stylomandibular ligament: from styloid process extends downward and forward to the angle of the mandible It limits excessive protrusive movements Pterygomandibular ligament: from hamulus to the retromolar area of mandible These are not true articular ligaments - they have no direct relationship with the joint - they may help to limit the mandibular movements www.hoangtuhung.com MECHANICS OF CONDYLAR MOVEMENT Nature of condyle-disc assembly in mandibular movements The structure of two synovial compartments facilitates rotational and translational movements of the condyle disc assemblies The disc can slide forwards and backwards over the condyle and generally moves together with the condyle During movements the plastic nature of the disc allow continuous adaptation between the opposing convex articulating surfaces The loose retrodiscal tissue is seated posteriorly to the disc, filled the temporal fossa and moved forwards and backwards toghether with the disc www.hoangtuhung.com MECHANICS OF CONDYLAR MOVEMENT (cont’d, 1) Condyle-disc assembly in centric relation In centric relation, the disc is positioned on top of the condyle at the most forward position that posterior ligament allows “The condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences” (GPT* 2017) *The Glossary of Prosthodontic Terms www.hoangtuhung.com MECHANICS OF CONDYLAR MOVEMENT (cont’d 2) Opening: As the inferior belly of lateral pterygoid muscle (LPm.) starts to pull the condyle forward, the superior belly of LPm releases contraction to allow the elastic fibers to start pulling the disc more to the top of the condyle Maximum opening: When the condyle reaches the eminence crest, the disc should be directly on top of the condyle The elastic fibers have rotated the disc back The superior belly of LPm is in realease Posterior ligament becomes more lax as the disc moves back www.hoangtuhung.com