tmj :- temperomandibular joint
-tmj is one of the most frequently used and mobile joints in the body .
engaged during mastication ,swallowing and speaking.
tmj is a third class lever
-it is designed to maintains its structural inspite of significant forces acting on it. .
-articular suface are conered with pseudofibrocartiliage.
-ability to remodel and repair able to tolerate repeated high level stress.
mastication -tremendous power speaking fine motor control
osteokinematic motion:-
mandibular depresion ,elevation ,protrution ,retraction and left and right excursions.
arthrokinematic motion:-
rolling ,anterior glide distraction and lateral glide.
-fundamental components of masication
-to accomplish mandibular depression and elevation the mandibular condyle must role and glide.
-during rotation ,the mandibular condyles spins relative to the inferior surface of the disc in the lower joint.
-during translation,mandibular condyle and disc glide together as a condyle disc complex along articular eminence
-normal mandibular depression range 40-50 mm
-measured both incisal edges of upper and lower front teeth.
mastication 18 mm of mandibular depression
mandibular depression rolling occurs with 11 mm or 25mm resulting from rotation of condyle on the disc.
other motion:-
anterior translation of condyle disc complex along articular eminance.
degree of mandibular depression 2 knuckles placed both upper and lower incision functionally
-3 knuckles is normal
-gravity assist with mandibular depression mandibular elevation provide eccentric control of mandibular depression
-mandibular elevation :-
reverse mandibular depression
-mandibular condyles rotated posteriorly on the disc in teh lower joint and codyle disc complex translates posteriorly upper joint.
-control of disc during mandibular elevation and depression.
-active and passive control occurs is exerted on the articular disc during mandibular elevation and depression.
passive control occurs through the capsuloligamentous attachment of t he disc to the condyle
lateral pterygoid muscle isattached to anterior portion of the disc producing active control mandibular depression
-medial and lateral attachments of the disc to the condyle limit the motion between disc and condyle to rotation
-as condyle translates biconcave shape of disc cause it to track the condyle without additional active or passive assistance
-inferior retrodiscal lamina limits forward excursion of the disc
-superior portion of the lateral pterygoid muscle attaches to the disc and appearance to be positioned to assist with anterior translation.
-no activity during mandibular depression.
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