TMJ- BIomechanics

Disc displacement with reduction

"Pops" or "clicks" heard on opening and closing. - results in inflammation, joint pain, muscle guarding from excessive load on retrodiscal tissue - treatment not necessary if there is no pain - can just educate on reducing parafunctional activities, stress

key objective signs in TMJ

- active/passive max mouth opening - palpation of TMJ/masticatory muscles - TMJ compression response

hard crepitus (foot-step on gravel)

- arthritic changes in joint - uncoordinated muscle action of lateral pterygoid in the disc or OA

unique features of the TMJ

- biconcave intraarticular disk into an upper and lower joint space - articular surfaces of TMJ consist of fibrocartilage, not hyaline cartilage * fibrocartilage is more resistant to wear and tear

Cervical spine

- check cervical AROM - repeated motions - sustained positions - mandibular motion during cervical motion

joint dysfunction

- crepitus or grating feeling throughout ROM, palpable or audible - mobility impairments (hypermobility possible) - chief complaint in preauricular area (in front of ear) -pain over palpation of joint line

posterior disc displacement stages

- disc is ALWAYS in an anterior position with the mouth closed 2 clicks: 1. when the condyle moves over the posterior rim of the disc 2. when it moves over the anterior rim of the disc 2 clicks on closing

key subjective components in Dx of TMJ

- joint sounds - ROM limitations - tenderness - bruxism - sensitive teeth

muscles that open mouth

- lateral pterygoid - suprahyoids (stylohyoid, myohyoid, digastric, geniohyoid) - digastrics

soft/popping clicks

- ligament moving - articular surface separation - sucking of loose tissue behind condyle as it moves forward (from incoordination)

hard or cracking clicks

- likely due to joint pathology or joint surface defects

muscles that protrude mouth

- masseter - medial/lateral pterygoid

masticatory muscle disorder Dx

- pain with palpation of: masseter, temporalis, pterygoids - reproduction of chief complaint with unassisted maximum opening

muscles that close mouth

- temporalis - masseter - medial pterygoid

posterior disc displacement

- very rare - happens when lateral pterygoid muscle is over stretched - may result in an open-lock or inability to close mouth

muscles that retract the mouth

-temporalis - suprahyoids

masticatory muscle disorder

2 categories: with normal opening and with limited opening

disc displacements

3 types: - with reduction - without reduction, limited opening - without reduction, normal opening

disc displacement without reduction

NO pop or clicking due to the anteriorly dislocated disk all the time leads to -> excessive joint loading, tissue inflammation mouth usually opens less than 40mm

arthrokinematics: retraction

bilateral posterior and slight superior slide ROM: 3 mm

Rotation arthrokinematics

convex on concave- posterior roll

late phase of opening

discotemporal motion: in the upper cavity (translation) - condyle and disk slid together in an anterior and inferior direction

common pain referral- pterygoids

ear preauricular area lateral face/cheek (lateral) cervical region (medial)

mouth opening arthrokinematics

early phase: discomandubular motion in lower cavity (rotation) late phase: discotemporal motion in upper cavity (gliding/translation)'

lateral deviation arthrokinematics

ipsilateral condyle: lateral rotation/spinning contralateral condyle: anterior translation/medial rotation

common pain referral- masseter

lower teeth lateral face, cheek orbital area

What causes disk displacements?

macrotrauma - mouth opening during dental procedure repeated microtrauma - grinding, gritting, bruxing - anything causing excessive force on the disk

what bones make up the TMJ

mandibular condyle glenoid fossa of the temporalis bone

arthrokinematics: protrusion

mandibular condyles and disc slide together bilateral anterior and slight inferior slide ROM: 6-9 mm

lateral excursion muscles

masseter (ipsilateral) temporalis (ipsilateral) med/lat pterygoids (contralateral) ex: left excursion = - R med/lat pterygoids - L masseter/ temporalis

temporomandibular dysfunction

multifactorial condition affecting the temporomandibular joint, muscles of mastication, and other surrounding structures

indirect masticatory muscle disorder

muscle guarding: stress/anxiety, cervical dysfxn central sensitization can result in referred pain

Direct masticatory muscle disorder

overuse: nail biting, chewing gum, clenching/ grinding, bruxism muscle guarding: in response to such as inflammation, sinusitis overstretching: pain after dental procedures, blows to the mandible or other macrotrauma

what type of joint is the TMJ joint

ovoid and hinge joint

disk displacement without reduction stages

resting: disc rests anterior to condyle head open/close: disc PERMANENTLY stays anterior to the condyle head no reduction = no clicking

anterior disc displacement with reduction

resting: disc sits anterior to condyle opening: disk will reduce back on top of the condyle (1st click) closing: disk initially begins to translate posterior, but due to excessive contraction of lateral pterygoid, disk will displace anterior again (2nd click)

Biconcave intraarticular disc

upper cavity (discotemporal)- gliding or translation lower cavity (discomandibular)- rotation

common pain referral - temporalis

upper teeth temporal area orbital area maxilla