TMJ and muscles of mastication Flashcards
TMJ
articulation between mandible and skull
modified hinge joint:
- articular eminence and tubercles of temporal bone
- mandibular fossa of temporal bone
- condyle of mandible
Mandibular fossa
- Receives mandibular condyle
- Articular surface covered with dense fibrous tissue
- Borders of mandibular fossa
Borders of mandibular fossa
Lateral
-Zygomatic process of temporal bone
Medial: spine of sphenoid bone
Anterior: articular eminence
Posterior: squamotympanic and petrotympanic fissures
Squamotympanic fissure
separates mandibular fossa of squamous portion of temporal bone from tympanic plate of temporal bone
Petrotympanic fissure
adj to small wedge of petrous temporal bone
*CHORDA TYMPANI PASSES THROUGH PETROTYMPANIC FISSURE
Mandibular condyle
Roller shaped w/ medial + lateral poles
- long axis of condyles angled posteriorly
- neck of condyle connects condyle to ramus of mandible
Articular surface of condyle
covered with dense fibrous tissue w/ isolated groups of chondrocytes + little surrounding matrix,
reflecting formation by intramembranous ossification
External oblique line
attachment for depressor anguli oris
Gonial angle
Junction of posterior border of ramus and inferior border of body of mandible
Antegonial notch
Junction of ramus and body of mandible
Digastric fossa
Anterior internal aspect, above inferior border.
Small depressions, anterior belly of digastric
Mental spine (genial tubercles)
Midline, superior to digastric fossae.
May be 4 or single fused spine
Genioglossus (upper aspect)
Geniohyoid (lower aspect)
Mylohyoid ridge (line)
Runs obliquely from lateral aspect of digastric fossae to below lingual alveolar crest of last mandibularmolar
– origin of mylohyoid muscle
Sublingual fossa
above mylohyoid line, accommodates sublingual gland
Submandibular fossa
below mylohyoid line, submandibular gland
Mandibular foramen
midpoint of ramus of mandible
Mandibular canal
continuation of mandibular foramen, deep into mandible
- runs inferiorly and anteriorly through ramus and body just below roots of mandibular teeth and ends at midline.
- carries inferior alveolar n and artery to mandibular teeth
- cutaneous branches pass to facial aspect of mandible via mandibular foramen
Lingula
guards superoanterior border of mandibular foramen
- sphenomandibular ligament attached
May interfere with anesthetic injections of inferior alveolar n at mouth of mandibular foramen
Mylohyoid sulcus (groove)
runs downward and forward from inferior border of mandibular foramen.
* n to mylohyoid muscle
Coronoid notch
Concavity on anterior border of ramus as it approaches body below
Internal oblique line (temporal crest)
buttressing ridge of bone on internal surface of ramus
- slopes downward and forward
- as it goes to last molar, divides to pass around last molar, divisions becoming continuous with buccal and lingual alveolar crests
- enclosed triangle: retromolar triangle
Retromolar fossa
depression between anterior border of ramus and temporal crest
Articular disc
Bi-concave
- allows flexibility in disc so it can conform during TMJ motion
- allows disc to be self-centered
Articular Disc Divisions
Divides joint into superior/inferior compartments
*disc attached to inner periphery of articular capsule by superior and inferior sheets or lamellae that continue superiorly and inferiorly to blend with walls of capsular ligament
superior lamella: elastic, inferior = collagen
TMJ
like all synovial joints possesses fibrous capsule that encloses joint surface
Capsular ligament, lateral/temperomandibular ligament
reinforcements of joint/intrinsic ligaments capsule region
- prevent excessive lateral movement and posterior dislocation
Stylomandibular ligament
extrinsic ligament
- runs from styloid process to angle of mandible
limits protrusion
Sphenomandibular ligament
Runs from spine of sphenoid to lingula of mandible
- Supports weight of mandible
- Prevents excessive lateral movements of mandible
Movements of mandible
- Elevation/depression
- fulcrum located approximately at mandibular foramen - Protrusion/retrusion
- Lateral excursion (deviation)
Hinging and Gliding at TMJ
Most mandibular movement
- Hinge movement takes place in LOWER joint compartment
- Gliding (translation) in upper joint compartment
- Upon opening, both condyle and disc translate forward to sit on articular eminence
Muscles of mastication
- Temporalis
- Masseter
- Lateral pterygoid muscle
- Medial pterygoid muscle
Temporalis muscle
Attachments:
- temporal fossa
- tip of coronoid process, ramus of mandible
Action: bilateral: elevation, REtrusion of mandible unilateral: ipsilateral deviation --holds resting position of mandible Inn: Deep temporal branches
Masseter muscle
Attachments:
- outer and inner surfaces of zygomatic bone and arch
- angle and lateral surface of ramus of mandible
Action:
Bilat: elevation, PROtrusion of mandible
Unilat: ipsilateral deviaion
Inn: masseteric n
Lateral ptyergotd muscle
Attachments:
Superior head: greater wing of sphenoid
Inferior head: lateral pterygoid plate
Both: capsule, disc, condyle
Action:
Bilateral: depresses, protracts mandible
Unilateral: contralateral deviation
Inn: lateral pterygoid nerves
Medial Pterygoid Muscle
Attachments:
- Lateral pterygoid plate, tuberosity of maxilla
- Medial ramus of mandible, inferior to mandibular foramen
Action:
Bilat: Elevation, PROtrusion
Unilat; CONTRAlateral devision
Inn: medial pterygoid nerve
Nerve supply
Most of the TMJ supplied by sensory articular branches of auriculotemporal nerve
- small anterior portion supplied by sensory fibers arising from masseteric branches of V3
-posterior and posterolateral regions of joint capsule contain free nerve endings - pain impulses from joint
(protection against excessive mandibular movement)
-retrodiscal inferior lamella has proprioceptive mechanoreceptors -detect condylar movement and position
Blood supply
- Articular branches from superficial temporal a to supply most of the joint
- A from muscular branches of maxillary artery that supply anterior aspect of joint
Examination of TMJ
Palate area
Muscles: temporalis and masseter
TMJ movement:
anterior: lateral aspect of TMJ palpated just anterior to ear. Pt opens/close while palpating bilaterally
Posterior: finger inside ears and press gently anteriorly.
Pt open/close several times, check for pain and equal motion bilaterally
-Auscultation may assist in evaluation
