1i - TMJ anatomy Flashcards
what is the most common complaint of someone w TMJ disorder
ear pain
what are examples of parafunctional habits
nail biting
clenching
grinding
lip biting
object biting
chewing gum
bruxism
what is bruxism
unconscious grinding, clenching teeth
- at night
what is a relevant characteristic of the TMJ capsule
thicker on outside
OIA of temporalis
O: entire temporal fossa
I: coronoid process & medial border of mandibular ramus
A: elevation, retrusion/retraction, ipsilateral lateral excursion (unilateral)
what is the main biting ms
temporalis
what are characteristics of the temporalis
thin but very large
dives behind zygomatic arch so can’t get to ms tendon junction
OI of masseter
superficial head
O: ant 2/3 of zygomatic arch
I: lat border of mandib angle
deep head
O: post 1/3 of zygomatic arch
I: superior border of mandibular ramus
actions of the masseter ms
elevation
ipsilateral lateral excursion (unilateral)
deep: retrusion/retraction
superficiala: protrusion
OI of medial pterygoid
O: lateral pterygoid plate of sphenoid bone and maxilla
I: medial surface of mandibular angle
what are the actions of the medial pterygoid
elevation
protrusion
contralateral lateral excursion (unilateral)
tonic contraction acts as a functional sling around angle of mandible
what holds the mandible in position
sphenomandibular lig needs a tonic contraction from the masseter, otherwise would just hang in fossa
- creates a functional sling
OI of lateral pterygoid
superior head
O: greater wing of sphenoid
I: disc
Inferior head
O: lateral border of sphenoid
I: condylar neck
what are the actions of the lateral pterygoid
protrusion (bilateral)
contralateral lateral excursion (unilateral)
superior: elevation
inferior: depression
what is the lateral pterygoid’s role in elevation
helps to eccentrically control disc tension and its position w closing
what is the lateral pterygoid’s role in depression
initiates open
what is the role of infrahyoid ms
stabilize the hyoid
what are the 4 infrahyoid ms
omohyoid
sternohyoid
sternothyroid
thyrohyoid
what are secondary ms to the TMJ and what is their role
infra and supra hyoids
aren’t directly acting on TMJ, but impact posture and way TMJ sits
what is the role of the suprahyoids
assist w mandibular depression
what are the 4 suprahyoid ms
digastric
geniohyoid
mylohyoid
stylohyoid
what are the primary ms innervated by and what are those ms
trigeminal (CN V) mandibular branch
masseter
temporalis
medial and lateral ptery
mylohyoid
what nerves innervate the secondary ms
hypoglossal n. (CN XII)
facial n. (CN VII)
ventral rami C1 via CN XII
ventral rami C1-3
what are the dermatomes relevant to the TMJ
C2-3: mandibular angle
mandibular branch of trigem (CN V) covers remainder of jaw
what are the mandible’s functional sling ms
masseter and medial pterygoid
what cervical ms impact the TMJ
suboccipital ms
SCM
scap ms
- UT, levator scap
what cervical joints impact the TMJ
AO joint
cervical facet joints
what ms are involved in elevation
masseter
temporalis
medial pterygoid
lateral pterygoid (superior fibers)
what ms are involved with depression
lateral pterygoid (inferior fibers)
suprahyoids
infrahyoids
what ms are involved with protrusion
masseter (superficial fibers)
medial pterygoid
lateral pterygoid
what ms are involved w retrusion/retraction
masseter (deep fibers)
temporalis
suprahyoids (digastric)
what ms are involved in lateral excursion
ipsi temporalis (uni contxn)
ipsi masseter (uni contxn)
contra med pterygoid (uni)
contra lat pterygoid (uni)
what is the osseous articulation of the TMJ
superior aspect of mandibular condyle on mandibular fossa of the temporal bone
what is the signficance of the coronoid process
important landmark for attachment poitns
how is the fibrocartilage structured and what is the importance of this
high density collagen content which allows for repetitive forces thru jaw to be withstood
moving it constantly w talking, eating, swallowing
- have to withstand repetition and force of eating
where is the fibrous capsule in relationship to the disc
fibrous capsule attaches to entire periphery of disc
anterior articulations of the TMJ disc
temporal bone (articular eminence)
mandibular condyle
superior head of lat ptery
posterior articulation of TMJ disc
retrodiscal lamina
what is the main function of the fibrocartilage surrounding the TMJ disc
dissipate and endure loads and stresses
why does the TMJ disc have such a high water content
dissipate forces
mobile when loaded
- if load front part of disc, water contents move post
how does the thickness of the disc change and why
thin intermediate region
- accommodates convexity of condyle
thicker anteriorly and posteriorly
- maximize congruency to dec pressure
biconclave shape that accommodates the convexity of the joint and inc the surface area
how does the vascularity and innervation change throughout the disc
thin intermediate region is avascular and not innervated
- can’t have pain which is good bc that is what contacts the fossa
thicker ant and post is vascular and innervated -> source of pain
how does the elasticity change throughout the disc and how does this impact the functioning
superior portion elastic
- stretches w opening
inferior portion less elastic
- stabilizes joint
what motions compose mastication
elevation and depression w lateral excursion and protrusion
- random and asymmetrical combo
what does mastication cause at the jiont
joint compression
what is mastication
tearing, chewing, and grinding motions via coordination of all ms
what are the arthrokinematics of depression
early phase - post rotation
late phase
- rotation
- ant and inf translation of condyle and disc together
when is there the greatest ligamentous tension in the TMJ joint
maximal opening
how much motion is there in the early phase of depression
0-26mm
how much motion is there in the late phase of depression
26-50mm
what functions are possible with <10mm of depression
can only drink
what functions are possible with 10-20mm of depression
push food in mouth
what functions are possible with 20-30mm of depression
can eat food using fingers
what functions are possible with 30-38mm of depression
can use fork and small pieces
what functions are possible with >38mm of depression
can eat normally
what initiates the arthrokinematics of elevation
tension in retrodiscal ligament
what are the arthrokinematics of elevation
condylar head and disc translate post and superiorly
condylar body rotates ant
slight ant rotation of disc d/t eccentric contraction of superior head of lateral ptery (helps to sit back into place)
what is the closed pack position of the TMJ
teeth clenched
- greatest joint congruency
arthrokinematics of lateral excursion
ipsilateral condyle
- rotation/spine
contralateral condyle
- translation
arthrokinematics of protrusion
ant translation
arthrokinematics of retrusion
post translation
what are protrusion and retrusion important components of respectively
protrusion - max opening
retrusion - max closing
what ROM is necessary for protrusion and why
26mm
at the end range of opening
