Anatomy of Temporomandibular Joint (TMJ)

"Temporomandibular joint forms the craniomandibular articulation"

·  Two synovial joints (right and left) connected with a single bone “the Mandible” makes the joint unique. Further coordinated movements of both joints facilitates the mandibular movements.

·         Boney components

1.      Contyle of mandible

2.      Squamous temporal bone of the skull

·         TMJ is a Complex joint – by function and by structure

·         Also it is a “Ginglymoarthoridal” jt

                                    Hinging movement – Ginglymoid movement

                                    Gliding movement – Arthroidal movement

·         Another classification of joints classify TMJ as a Compound Jt

-          By definition compound jt is joint composed of 3 or more bones

-    TMJ is composed of 2 bones , but considered compound jt  because articular discis is considered functionally non ossified bone

-         TMJ differs from other diarthoidal joints of the body

  I.  TMJ forms bilateral diarthrosis – functioning both Lt  Rt joints together

 II.Articular surfaces are covered by fibrocartilage instend of hyaline cartilage

III.TMJ is the only joint which has argitend point of closure, because when the mouth is closed the teeth come into occlusal contact

The Disc

·         Dense fibrous tissue

·         Devoid of blood vessels and nerves. Therefore it does not manifest marked inflammation in trauma.

·         Four Regions

1.       Anterior

2.       Intermediated – sits along articular eminence

3.       Posterior – Thickest – 12 ‘o clock on contyle

4.       Bilaminar region (Contains Blood vessels)

Collagen type I – Mainly

1.       Superficial layers – Parallel to anterior-posterior direction

2.       Central – Oriented random fashion

This arrangement provide ability with stand forces

 

Structure of Temporomandibluar joint

Anteriorly Disc divides into two lamellae

1.       Superior Lamella – Fuse with capsule  the periosteum of the anterior slope of articular eminence

2.       Inferior Lamella – anterior surface of the neck of the condyle

3.       Mid – with fibers of lateral pterygoid muscle

Muscles of Mastication

Although they are called muscles of mastication, they always function with other groups of the face, tongue, soft palate & hyoid bone

Masseter                                        

Superficial Part

Arises from lower border of Zygomatic arch                                                                           

Fibers directed downward back wards

Insert along the angle of the mandible

Insertion-  Lower 1/3 of the posterior border of the ramus and along lower boarder of the mandible to the 8 tooth

Deep Part                                                    

           Inserts above superficial masseter along the ramus of the mandible                              -

Function

1.       Elevation of the mandible

Nerve Supple

                      V Nerve      >    Mandibular branch          >       Masseteric Nerve

                                              

Temporalis

-                                                        Fan shaped muscle

-                                                        Attachment of large muscle extend to 

                                 I.                     Small portion of parietal bon- extends above

                               II.                    Greater Portion of the savamous portion of the temporal bone

                             III.                    Temporal surface of the frontal bove

                             IV.                    Temporal surface of greater wing of the sphenoid bove

                                                                      

·         Temporal Fascia attaches to supra temporal in border of the zygomatic arch.

·         Temporal Fascia

o   Thickens When passing downwards.

o   Splits in to two layers.

o   Superficial layer blends periosteum of the lateral Surface of the Zygomatic arch.

o   Deep Portion blunts T medial Surface.

o   Many of the muscle fibers original from the medial surface of the temporal fascia.

·         Insertion of temporalis.

o   Coronoid   Process

o   Antero medial Surface of the ramus of the mandible.

·         Function

o   Elevates the mandible.

·         Innervation

o   Deep temporal branches arising from the mandibular division of   V

Medial Pterygoid

                2. Heads 

• Superficial Head
• Deep head

Deep head- Originates from medial Surface of lateral Pterygoid plate a Pyarmydal Process of the Palatine bone.

Inserted in to Roughened medial  Surface of the mandible near the angle of the mandible.

Superficial Head-Originals from Tuberosity of the maxilla adjacent Pyramidal process of the Palatine bone.

Joins with deep head to in sear in to mandible.

Runs-  Downwards

         -  Backwards

         -  Laterally

Innervated by – Nerve to medial Pterygoid.

                       _ Branch of the mandibular.

                       _ Division of the Trigeminal Nerve.

Lateral Pterygoid

Two heads

·         Superior head

·         Inferior head

v  Superior head – Originals from infra temporal Surface of the grater wing of sphenoid.

Runs backwards, laterally, almost horizontally and insert to the disk capsule of the TMJ the condyle.

Function – Stabilizer the mandibular condyle against the reticular eminence during mastication.

v  Inferior head - Originals from lateral Surface of lateral Pterygoid plate.

Fibers extend Back wads, Upwads Out wads to insert in to neck of the condyle.

Function

Protrusion

Lateral excursion

Innervation

Branch of buccal nerve- From mandible division of  V

Other muscles

1.       Digastrics

2.       Mylohyoid

3.       Geniohyoid

4.       Platysma