The Temporomandibular Joint

The Temporomandibular Joint

1. TMJ Intro

   • named after bones forming the joint - termporal and mandible
   • allows gliding and small rotation, elevation and depression
   • Lined with fibrocartilage and contains fibrous disc/ meniscus
   • fibrous joint capsule surrounds joint completly enclosing it
   • Forms part of a link between CNS, tongue, and teeth during mastication

2. Movements of TMJ

   • Normal Pattern
     • chin goes inferiorly and posteriorly
       • mandibular condyle first pivots and then translates forwards
         • using articular disc as a cushion from mandibular fossa
   • No other joint has such a large amount of rotation and translation
     • first 35-50% of mouth opening involves mandible rotation

3. The Disc

   • divides TMJ into 2 compartments
     • upper and lower synovial cavity
   • Attaches to the mandible
     • not to the temporal bone except through joint capsule
   • During translation phase of mouth opening
     • disc is pulled anteriorly
     • forward translation is limited by RETRODISCAL LAMINA
     • intermediate portion of disc translates forwards while remaining between sup. part of mandibular condyle and articular process
       • allows for maximum joint congruency
   • During closing the mouth, process is reversed
     • tension of retrodiscal lamina starts to retract disc
       • initiating translation phase
         • later phase
           • rotation of condyle within disc concavity until upper and lower teeth meet

4. Injury to TMJ

   • With age, disc and fibrocartilage can degenerate
     • becoming pitted and perforated
   • Fibrocartilage = poor blood and nerve supply
     • repair is compromised
   • TEMPOROMANDIBULAR DISORDER (TMD)
     • group of musculoskeletal conditions involving tmj joint/ mastication muscle
     • 2:1 women
       • claimed it affects 12% of pop
     • massive structural change can occur and feels no pain
     • joint sounds or deviation of the mouth when opening occurs in 50%
       • limitations of mouth opening 5%
     • 2x likely to have pain in other joints and conditions
       • fibromyalgia 18%, vulvar vestibulitis syndrome, IBS 64%
       • jaw pain linked with inc Cx and trunk muscle activation
         • could be source of neck pain
         • could be a way of enhancing sport performance

5. Muscles and Movements

   • Primary Muscles of Mastication
     • ELEVATION
       • Masseter XXX
       • Medial Pterygoid XXX
       • Temporalis (XXX)
     • Minimal - X Moderate - XX Maximum - XXX
     • DEPRESSION
       • Lateral Pterygoid (inf. head) (XXX)
       • Suprahyoid muscle group (XXX)
     • LATERAL EXCRUSION
       • Masseter (X)
       • Medial Pterygoid (XXX)
       • Lateral Pterygoid (sup + inf head) (XXX)
       • Temporlais (X)
     • PROTRUSION
       • Masseter (X)
       • Med Pterygoid (X)
       • Lateral Pterygoid (sup + inf) (XXX)
     • RETRACTION
       • Temporalis (XXX)
       • Suprahyoid Muscle Group (X)