TMJ Mechanics

Question 1

how many joints are there in the TMJ articulation

Answer 1

4
-disc makes additional 2 joints. the disc is concave inferiorly and convex superiorly, making for 2 different joint arthrokinematics within the TMJ joint itself

Question 2

each TMJ consists of..

Answer 2

• mandibular condyle
• articular eminence of temporal bone
• articular disc

Question 3

types of joints of TMJ

Answer 3

1. hinge joint
   - -mandbibular condyle and inferior surface of disc
2. plane/gliding joint
   - -articular eminence and superior surface of disk
   - TMJ is a synovial joint but without hyaline cartilage, rather, fibrocartilage is present
   - -leads to improved healing properties b/c vascularized
   - lots of wear+tear in joint, hyaline cartilage would disappear too quick

Question 4

retrodiscal bilaminar tissue

Answer 4

-attaches disc posteriorly to surface. viscoelastic properties that prevent the disc from being pulled forward by the lat. pterygoid, the stretch pulls the disc back into place

Question 5

3 regions of disc

Answer 5

anterior, middle, posterior

• anterior and posterior are both thick regions with high vascularity
• middle region is thin with low vascularity

Question 6

joint arthrology: mandible

Answer 6

• body and rami, angle=intersection of the two

- mandibular condyles

Question 7

mandibular condyles

Answer 7

• medial protrusion 15-20mm from rami
• palpate lateral pole ant. to ext. auditory meatus
• unable to palpate medial pole

Question 8

joint arthrology: coronoid process

Answer 8

• ant to mandibular condyle
• closed mouth=present under zygomatic arch
• palpable with mouth open
• temporalis muscle attachment

Question 9

joint arthrology: temporalis bone

Answer 9

• condyle at glenoid fossa
• -thin, translucent: not a lot of stress on bone
• articular eminence: where articular occus with condule. greatest fibrocartilage, densest bone. compression forces occur
• -trabecular bone
• -primary articular surface
• -convex on convex

Question 10

joint arthrology: articular eminence and condyle

Answer 10

• dense, avascular collagenous tissue covering with some cartilage cells=fibrocartilage
• most found at articular eminence and anterosuperior condyle
• -evidence for compression
• deep fibers aligned perpendicular
• superficial fibers aligned parallel
• fibro vs hyaline cartilage repair process?

Question 11

articular disc

Answer 11

• biconcave
• is TMJ congruent?-yes (matching up.fitting together
• -convex condyle on concave inferior disc, concave superior disc on convex articular eminence

Question 12

articular disc attachments

Answer 12

• firm attachment with medial and lateral poles of condyle
• not firmly attached to capsule medial and lateral
• -allows for free rotation (disc allowed to freely rotate with condyle)
• anteriorly attached to joint capsule and lateral pterygoid muscle
• -restricts posterior translation

Question 13

-articular disc attachments

Answer 13

• posteriorly attached to the bilaminar retrodiskal pad
• complex structure
• allows for anterior disk translation with mouth opening and repositioning of disk with mouth closed
• neither lamina (superior and inferior) under tension with TM joint at rest

Question 14

articular disk morphology

Answer 14

• thickness varies between 2 mm anteriorly to 3 mm posteriorly to 1 mm in the middle
• -variation aids in congruency
• anterior and posterior portions are vascular and neural
• middle portion avascular and aneural
• -force accepting portion of disk avascular and aneural
• -middle portion subtly shifts anterior and posterior when the tmj is at rest to repair

Question 15

articular disc function

Answer 15

• 3 functions
  1. provides increased congruence of joint surfaces (biconcave)
  2. shape allows for greater flexibility of disc to conform to bony surfaces with rotation and translation arthrokinematics
  3. thick/thin/thick arrangement provides a self-centering mechanism for disc on condyle
• increase pressure=disc rotation so thinnest portion is btwn articulating surfaces
• decreased pressure=joint disarticulation=rotation of a disc to a wider portion (may be ant. or post.)

Question 16

muscular control of the TM joint

Answer 16

• ant. and post. digastrics
• medial and lateral pterygoids
• temporalis
• masseter

Question 17

mandibular elevation/mouth closure

Answer 17

• temporalis: fan shaped with extensive attachments inserting at coronoid process for elevation
• masseter: quadrilateral shaped mm
• superior portion of lateral pterygoid
• -rotates disc anteriorly on condyle with mouth closing (holds it steady as jaw comes back. maintaining ant. position

Question 18

mandibular depression/mouth opening

Answer 18

• lower portion of lateral pterygoid=depression
• digastrics: primary mandibular depression
• accounts for 40-55 mm normal opening
• concentric contraction of both digastrics may cause choking
• usually ant. is a concentric contraction, isometric contraction post

Question 19

mandibular osteokinematics: protrusion

Answer 19

-bilateral masseter, medial pterygoids and lateral pterygoids

Question 20

retrusion

Answer 20

-bilateral posterior fibers of temporalis and assist by anterior portion of digastrics

Question 21

-lateral deviation

Answer 21

• contralateral medial and ipsilateral lateral pterygoids
• ex: R LD by R lat pterygoid and L med pterygoid
• temporalis deviates to ipsilateral side

Question 22

force couple during deviation

Answer 22

• temporalis and lateral pterygoid work together to rotate
• mandible slides contralateral and rotates ipsilateral to direction of deviation
• fibers of lateral pterygoid and temporalis are on opposite side of mandible, pull in opposite but parallel directions. make the ipsilateral side rotate

Question 23

TM joint arthrokinematics: mouth opening

Answer 23

• initial anterior roll of condyle followed by anterior and inferior translation of disc and condyle nearing full opening
• instantaneous center of rotation shifts anterior during opening
• 40-55 mm normal mouth opening
• -condyle rotates 11-25 mm anteriorly
• -disk and condyle translates remainder

Question 24

abnormal muscle mechanics

Answer 24

• muscle adaptively tightened, limits antagonist direction

- muscle organically weak, limits agonist direction

Question 25

joint is a compression or tension loaded structure

Answer 25

-tension loaded, compression only in pathology

Question 26

TM joint arthrokinematics: mouth closing

Answer 26

- reverse of opening - initial posterior and superior translation of disc and condyle followed by posterior roll of condyle on the disc - instantaneous center of rotation shifts posterior during closing - C shaped curve if dysfunction/derangement, deviate towards tight side

Question 27

TMJ arthrokinematics: protrusion/retrusion

Answer 27

- bilateral condyle translation anterior and inferior or posterior and superior respectively along articular eminence (likely just post. if retrusion from neutral position) - protrusion: 6-9mm - retrusion: 3 mm - ant inf for protrusion, from the protruded position will have post and sup, but from neutral will most likely just be posterior

Question 28

TMJ arthrokinematics: mandibular lateral deviation

Answer 28

Ex left - left condylar and disk spin about a vertical axis combined with right condylar anterior translation or gliding - lateral deviation= 8mm

Question 29

dentition

Answer 29

- intimate involvement of teeth in the function of the TMJ - 1.5-5 mm freeway space b/w upper and lower teeth=resting position of mandible - -space btwn upper and lower central incisors - -firm approximation=occlusal position (bruxism. bad position) - resting position allows for decreased intra-articular pressure, decreased stress on articular structures allowing tissue rest and repair - resting position allows for healing of disc

Question 30

pathomechanics

Answer 30

- insult secondary to direct trauma such as MVA, fall, fight - poor posture or oral habits (bruxism-grinding/clenching) - reciprocal click (intracapsular dysfunction, joint out of place) - locking - osteoarthritis

Question 31

reciprocal click

Answer 31

=anteromedial displacement of the disk-anterior part is most problematic - noted on opening and a second click upon closing - condyle 1st in contact with retrodiskal tissue - click noted with disk contact upon opening - upon closing, late clikc as condyle leaves the anteromedially displaced disk - late vs early click? - -late=further displaced disc, worse condition - -early=less pathology, less anteromedially displaced

Question 32

locking

Answer 32

- only roll occurs, with not anterior or posterior translation of condule - anteriorly displaced disk acts as a buttress (prevents further motion) - inability to close vs decreased ability to open

Question 33

closed lock

Answer 33

- cannot open fully - disc is sig anteromedial to condyle disallowing anterior and inf glide - cannot open fully secondary to mechanical buttress

Question 34

open lock

Answer 34

- cannot close - disk is post to condyle disallowing post and sup glide - cannot close fully secondary to mechanical buttress

Question 35

osteoarthritis

Answer 35

- due to increased and/or altered compressive and shear loading of TMJ surfaces - most often unilateral - loss of posterior teeth may lead to OA due to simple occlusion of remaining teeth creates impact b/w TMJ surfacess - teeth extracted, limites force per unit area. erosion of bone where teeth removed b/c wolffs law