Biomechanics TMJ

TMJ Temporomandibular Joint TMJ is not the name of the disorder it is the name of the joint; the name of the disorder is Temporomandibular Dysfunction or Disorder (TMD) Anatomy Review Osseous Muscular Articular Biconcave disc allows for stability Anterior half - convex condyle Below space/disc - inferior compartment Above space - superior compartment 2 movements that occur in TMJ Translation Superior compartment Rotation Inferior compartment Downloaded by Vegeta Ouji ([email protected]) lOMoARcPSD|5612835
Condyle has to go down slope for jaw to open Condyle of mandible is convex Going from convex convex articulation, so need biconcave disc as open jaw further → keep TMJ stability Dentists and PTs Dentists starting to realize the craniocervical part of TMD Physical therapists can assist dentists with their patients because of our knowledge of the TMJ and concurrent effects with the cervical spine Basic features Compound synovial joint between the mandible and cranium Articulating surfaces are covered by avascular fibrocartilage which can withstand large amounts of compressive and shearing forces The active joint surface is from the superior part of the fossa to the anterior / inferior slope of the eminence all the way to the apex of the eminence The articular disc divides the TMJ into an upper and lower compartment Innervated by the mandibular division of the trigeminal nerve In the sagittal plane, The convex condyle does not articulate with the concave temporal or mandibular fossa but against the convex slope and apex (convex with convex) In the Horizontal Plane, the direction of the temporal joint is in an oblique and sagittal direction This orientation causes the condyles to translate laterally as we open our mouths as the condyles slide forward Palpation of this movement Articular Disc Plays a central role in the stability of the TMJ by making up for the congruency problem between the two joint surfaces The disc is biconcave and oval in shape This orientation presents the disc to be thinner in the central portion and thicker in the peripheral portions; self seating capacity of the disc Excellent shock absorber Laterally and medially the disc is stabilized by collateral ligaments The disc divides the joint into two compartments Rotation takes place in the inferior compartment Translation takes place in the superior compartment Muscles of Mastication Temporalis: Muscle fibers in antero and postero inferior directions Origin: entire temporal fossa Insertion: coronoid process and anterior border of the ramus and some fibers to the skeletal orbit of the eye Downloaded by Vegeta Ouji ([email protected]) lOMoARcPSD|5612835
Function: Bilateral contraction closes the mandible Unilaterally deviates the mandible to same side Posterior fibers minimally retract the mandible from rest position All fibers retract mandible if it is fully protruded; helped by suprahyoid Guides biting motion Lateral pterygoid Prime mover of TMJ and guides disc both during eccentric and concentric contractions Medial pterygoid Similar to the masseter but smaller Function: elevates the mandible; unilaterally deviates mandible toward opposite side; participates in chewing motion Biomechanics of the TMJ Functional unit Cranio-cervical joint posteriorly Cranio-mandibular joint anteriorly TMJ problem, check the cervical spine and vice versa Complex synovial joint: moves in three planes 4:1:1 ratio between opening, lateral excursion, and protrusion For 40 mm if opening, there is 10 mm of lateral excursion and 10 mm of protrusion When we measure left lateral excursion, we are measuring the function of the right TMJ Joint surfaces and the articular disc Stability based upon on the shape and relationship of the joint surfaces TMJ is unstable The anterior slope of the temporal surface is convex and the condyle is convex: so convex on convex relationship: not stable Not a problem with rolling but a problem with sliding: grinding and instability Disc solves this problem by being biconcave and creates two compartments The 2 departments of the TMJ Disc-condylar (inferior) and disc-temporal/eminence (superior) joints Inferior department: rotation Superior department: translation Disc will follow the condyle as long as there is apposition of the two joint surfaces and there is no subluxation Centric relation: term that refers to the most congruent contact between disc/eminence and disc/condyle with the disc interposed TMJ movements Downloaded by Vegeta Ouji ([email protected]) lOMoARcPSD|5612835
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