Gross anatomy 017: TMJ & Mastication

sphenomandibular ligament -define -2 attachments (from ___ to ___) -strength compared to lateral (temporomandibular) ligament -described as ______ -function (2)

-a thin, flattened band -extends from spine of sphenoid bone inferolaterally to lingula of mandible. -considerably weaker & less protective -a "rope swing" function: -limiting mandible enlargement (inferiorly) -protect inferior alveolar nerve & vasculature passing through mandibular foramen from tensile stress that occurs during jaw movements

LATERAL PTERYGOID MUSCLE action (bilaterally vs. unilaterally)

-acting bilaterally: mandible depression & protrusion -acting unilaterally: contralateral deviation of mandible to contralateral side (pulling mandible towards midline)

Elevation (TMJ movement) -action to mouth -full mouth action of this movement requires what?

-closing of mouth -requires complex rotational & gliding actions by both mandibular condyles acting in unison

slight opening of the mouth (approx.~20mm) -what happens? (2)

-condylar process acts strictly like a hinge -rotation occurs in inferior synovial compartment b/w condyle head & articular disc

accessory muscles of mastication (5)

-digastric (anterior and posterior bellies) -mylohyoid -geniohyoid -infrahyoid

TEMPORALIS MUSCLE action (2)

-elevates mandible -posterior/horizontal fibers = retrude mandible

an anesthetic injection into the pterygomandibular space/raphe would affect what nerve? (3)

-inferior alveolar n. (V3) -mental n. (V3) -lingual n. (V3)

muscles associated with depression of mandible ("2")

-lateral pterygoid m. (+ gravity)

muscles associated with protrusion of mandible 1 main & assisted by 2

-lateral pterygoid m. -assisted by masseter & superficial head medial pterygoid m.

anterior dislocation of TMJ -define -what causes it? examples (3) -results in? -solution? -how common is it? -importance to dentistry?

-mandibular condyle = displaced anterior to articular eminence -results from excessive & prolonged opening of mouth (yawning, during dental procedures, taking a bite of a huge sandwich) -results in: joint = fixed in an open position -solution: manual reduction of anterior dislocation -most common type of TMJ dislocation -in clinical: make sure to tell your patients to relax their jaw rather than force open the mouth —> could cause anterior dislocation

what mediate the movements of TMJ? -function (4)

-mastication muscles -motion for biting, chewing, swallowing food & speaking

MUSCLES of MASTICATION -function -4 muscles of mastication

-mediate movements at TMJ -temporalis, masseter, lateral pterygoid & medial pterygoid muscles

Inferior alveolar nerve block would also affect what nerves? (2)

-mental n. (branch of inferior alv.) -lingual n. (medial to it)

is sphenoid bone part of the joint? what is it considered? function

-not actually part of joint -an accessory bone of joint -point of attachment for sphenomandibular ligament

Posterior dislocation of TMJ -cause -what happens? -in extreme cases, what can happen?

-occurs secondary to a direct blow to chin. -mandibular condyle = pushed posteriorly toward mastoid process -extreme cases: lead to damage to external auditory meatus

Depression (TMJ movement) -action to mouth -full mouth action of this movement requires what?

-open mouth -requires complex rotational & gliding actions by both mandibular condyles acting in unison

mental n. passes through ______ to access face; provide _______ innervation to (4)

-passes through mental foramen -sensory to: 1-2. skin of chin & lower lip 3. mucous membrane of lower lip 4. labial gingiva near mandibular incisors, canines & premolars

movements mediated by the TMJ (4) muscles tend to move _______ (a coordinated manner) what happens if they don't move in a coordinated manner?

-protrusion -retrusion -elevation -depression -bilaterally (coordinated manner) -unilateral action: produces lateral deviation of mandible (side-to-side & grinding jaw movements)

stylomandibular ligament -define -strength compared to other TMJ ligaments -attachments (from ___ to _____) -functions (2)

-reinforced band of cervical fascia -weakest & least protective of TMJ ligaments extends -from: styloid process of temporal bone -to: posterior aspect of angle of mandible. -serves as boundary b/w parotid & submandibular salivary glands -limiting excessive opening (inferior distension & protrusion) of mandible.

Superior dislocation of TMJ -cause -what happens? -result in (2)

-result of a direct blow to a partially opened mouth -upward migration of condylar head -result in: 1. facial nerve palsy 2. cerebral contusion or deafness

Lateral dislocations of TMJ -cause (2) -what happens?

-result of mandibular fractures or a sideways blow to jaw/chin when mouth = opened -condylar head migrates laterally/superiorly & can be palpated in temporal space

prior to entering mandibular canal, inferior alveolar n. gives rise to what nerve? -this nerve provides ____ innervation to 2 muscles

-rise to mylohyoid n. -supplies motor innervation to: 1. mylohyoid m. 2. anterior belly of digastric m.

muscles associated with retrusion of mandible -1 & assisted by 1

-temporalis m. -assisted by masseter (deep head)

muscles associated with elevation of mandible (3)

-temporalis m. -masseter m. -medial pterygoid m.

an INFERIOR ALVEOLAR NERVE BLOCK produces temporary anesthesia of: (4)

1. 8 mandibular teeth & mandible's body/inferior ramus 2. vestibular gingiva & mucosa adjacent to the incisors, canines & premolars 3. lingual gingiva adjacent to incisors, canines, premolars & molars 4. anterior 2/3rd of tongue & floor of oral cavity proper

TMJ dislocation/displacement can potentially damage structures that surround it including (8)

1. facial n. 2. auriculotemporal n. 3. maxillary a. 4. mandibular division of CN V3 5. otic ganglion 6. external auditory meatus 7. ear (petrous temporal bone) 8. middle cranial fossa contents

Mandibular landmarks associated w/ TMJ & their attached supportive ligaments (6) slide 11

1. head of mandible: articular surface for TMJ (on mandible side) 2. lingula: attachment pt. for sphenomandibular ligament 3. angle: attachment pt. for stylomandibular ligament, masseter m., medial pterygoid m. 4. coronoid process: temporalis & (few fibers) from masseter muscle 5. pterygoid fovea: lateral pterygoid muscle 6. ramus: masseter & medial pterygoid muscle

Temporal bone landmarks associated w/ TMJ & their attached supportive ligaments (4) slide 12

1. mandibular fossa (aka glenoid fossa) & articular eminence (tubercle) = temporal bone articular surfaces for the TMJ 2. styloid process = point of attachment for stylomandibular ligament 3. postglenoid tubercle = structure situated posterior to mandibular fossa helps prevent posterior dislocation of TMJ

motor deficits associated w/ damage/dysfunction of MANDIBULAR DIVISION of TRIGEMINAL NERVE include (3)

1. mastication muscles' paralysis & atrophy on lesion side 2. TMJ laxity: decreased bite strength 3. jaw deviation TOWARDS lesion side

arterial supply to TMJ (3)

1. superficial temporal a. 2-3. deep auricular/anterior tympanic arteries (maxillary a.) -these are also the first 2 branches of maxillary

LATERAL PTERYGOID m. - spatial relationships in the infratemporal fossa (6)

Lateral pterygoid (inferior): b/w 2 heads of medial pterygoid Maxillary artery: -can go superficial or deep to lateral pterygoid -leave through superior/inferior heads of lateral pterygoid Long buccal n.: coming out of superior/inferior heads Inferior alveolar n./a.: coming as a pair under inferior head of lateral pterygoid Neck of mandible/articular disc

does the central portion of articular disc receive any vascular supply or sensory innervation? If not, what does?

No. Retrodiscal tissue does (posterior of disc)

open the mouth > 20mm -_____ of TMJ must occur -what must happen? -what must both engage to execute this?

TRANSLATION of TMJ must occur in superior synovial compartment -condylar head & articular disc both glide anteriorly in mandibular fossa & down articular eminence (of temporal bone) both superior & inferior synovial compartments must be engaged to execute rotational & gliding movements to fully open mouth https://youtu.be/4Wu0w8mGvUI

practice question

answer = D lingual lingual n. = more medial inferior alveolar n. = more lateral

Protrusion (protraction) (TMJ movement) -action to mouth

anterior gliding movement of both mandibular condyles --> chin

fibrous joint capsule of TMJ attaches to _____ of temporal bone along ______ & around ____ of mandible to ______ joint cavity. -texture of capsule & why?

attaches to: -squamous portion (of temporal bone) along outer margins of articular area -around neck (of mandible) to encapsulate joint cavity. capsule = thin & loose allowing for a wide range of movements within TMJ

maxillary artery passes b/w what 2 structures before entering infratemporal fossa?

b/w neck of mandible & sphenomandibular ligament

sensory innervation of the TMJ (2) apart of which CN

branches of the auriculotemporal & masseteric nerves Trigeminal V3

function of superior synovial

gliding motion articular disc glides against mandibular fossa of temporal bone

benefit of having 2 synovial compartments rather than 1

greater range of jaw movements

location of head of mandible when mouth opens

head of mandible slides anteriorly to articular eminence

post-glenoid tubercle -location -function

helps to prevent posterior dislocation of TMJ

temporomandibular joint -define -formed by what? (3)

highly modified hinge-type synovial joint formed by articulation b/w: 1. head on condyle (mandible) 2-3. mandibular fossa & articular eminence (squamous of temporal bone)

nerve branches mediate sensation from mandibular teeth & adjacent gingiva (4) -what they innervate -which branch give rise to other nerve branches & list the names of these branches

inferior alveolar n.: -mandibular teeth -gives rise to n. to mylohyoid & mental n. mental n.: -skin of chin -vestibular gingiva adjacent to mandibular incisors, canines and premolars lingual n.: -anterior 2/3rd of tongue -lingual gingiva long buccal n.: -vestibular gingiva adjacent to mandibular molars

location of head of mandible when mouth closes

into mandibular fossa

what can be observed in temporal region regarding to TMJ/mastication? (2)

lateral aspect of joint capsule & temporomandibular ligament

what is the main muscle that opens mouth?

lateral pterygoid muscle

4 parts of pterygoid muscles & label them

lateral pterygoid muscle: -superior -inferior medial pterygoid muscle: -superficial -deep

temporal bone articular surfaces (2)

mandibular fossa & articular eminence

what can be observed within infratemporal region regarding to TMJ/mastication? (1)

medial aspect of joint capsule

long buccal nerve mediates _____ from ________ & ______ -apart of what nerve branch?

mediates sensation from: 1. vestibular (buccal) gingiva next to mandibular molars 2. skin of cheek/mucosa lining it part of V3 trigeminal

MASSETER MUSCLE origin (superficial vs deep) insertion (2) innervation action: (general vs. superficial vs. deep)

origin: -superficial/deep = inferior border of zygomatic arch insertion: lateral surface of ramus & angle of mandible (anterolateral aspect of coronoid process) innervation: masseteric n. branch of mandibular division of trigeminal nerve (V3) action: -elevates mandible -superficial: assists in protrusion -deep: assists in retrusion

MEDIAL PTERYGOID MUSCLE origin: (superficial vs deep) insertion (2) innervation action (2)

origin: -superficial: maxillary tuberosity & pyramidal process of palatine bone -deep: medial surface of lateral pterygoid plate (of sphenoid) & pyramidal process (of palatine bone) insertion: -medial surface of ramus -angle of mandible posterior to mylohyoid groove innervation: -medial pterygoid n. (branch of the mandibular division of the trigeminal n. V3) action: -elevates the mandible -assists in protrusion

TEMPORALIS MUSCLE origin (2) insertion (2) innervation (2)

origin: -temporal lines -floor of temporal fossa insertion: -medial surface + apex + anterior border of coronoid process -anterior border of mandibular ramus innervation: -anterior & posterior deep temporal nn. (trigeminal n. V3)

LATERAL PTERYGOID MUSCLE origin (superior vs. inferior) insertion (2) innervation

origin: -upper/superior head: infratemporal ridge/surface (of sphenoid greater wing) -lower/inferior head: lateral surface of lateral pterygoid plate (of sphenoid bone) insertion: -pterygoid fovea (on neck of mandible) & articular disc of TMJ innervation: -lateral pterygoid n. (trigeminal nerve: mandibular V3)

shape of mandible's head -what is it? -function

ovoid (oval) provide more stability to joint

Retrusion (retraction) (TMJ movement) -action to mouth

posterior gliding movement of both mandibular condyles --> chin

function of inferior synovial

rotates against articular disc to create hinge/rotational movements

lateral/temporomandibular ligament -define -purpose (2)

thickening of TMJ articular capsule's lateral aspect -provide lateral strength to capsule -prevent TMJ posterior dislocation

Connective tissue structures that support articulation b/w mandible & temporal bones (4) purpose?

- articular disc - synovial membranes (line joint's articular surfaces) - joint capsule (surrounds joint cavity) - supportive ligaments (for structural support) allow mobility

temporalis & masseter muscle hypertrophy -bilateral hypertrophy of the temporalis and masseter muscles result in _______ -common causes (3)

- result in pseudomasses - comorbid anxiety, bruxism, chronic gum chewing

articular disc -define -function

-a fibrocartilaginous disc -separates temporomandibular joint cavity into 2 synovial compartments

TMJ = stabilized by ______ (4) serve to connect _____ to ______

-a fibrous joint capsule & 3 additional ligaments serve to connect mandible to cranium

Innervation: 1. vestibular gingiva (5) 2. lingual gingiva (2) 3. tooth (5) -distinguish b/w V2 & V3 and palate or mouth's floor -what does a "tooth innervation" include? (3) - Schematic summarizing the sensory innervation of the teeth and adjacent gingiva by branches of V2 and V3

tooth innervation = tooth pulp, periodontal ligament & alveolar processes note: -for tooth innervation: incisive branch of inferior alveolar is NOT apart of the dental branches of inferior alveolar -middle superior alveolar nerve: 1. tooth innervation: premolars + mesiobuccal root of 1st molar 2. vestibule gingiva: premolars only

Inferior alveolar nerve -part of what branch -passes b/w __(bone)___ & ___(ligament)___ and through ___2___ foramen to enter ____3___ canal -forming _______ -______ innervation to what structures (2) through ____ branch

trigeminal V3 1. passes b/w mandibular ramus & sphenomandibular ligament 2. through mandibular foramen 3. enter mandibular canal -forming inferior dental plexus sensory innervation to: 1. mandibular teeth 2. labial gingiva of mandibular incisors, canines and premolars through its mental branch

retrodiscal tissue -define -purpose

vascularized & innervated posterior portion of articular disc since central portion of articular disc has no vascular supply or sensory innervation

TMJ DISLOCATIONS (4)

Anterior dislocation Posterior dislocation Lateral dislocations Superior dislocation