TMJ Biomechanics

Question 1

TMJ

Answer 1

Most frequently used joint in the body
Consists of mandible suspended from temporal bone via ligaments and mm
True synovial joint capable of gliding, hinging, sliding and slight rotation

Question 2

TMJ articular surfaces are

Answer 2

fibrocartilage - ability to regenerate

Question 3

Mandible and temporal bone are separated by

Answer 3

a meniscus

Sup and inf cavities with disc between

Question 4

Upper joint space

Answer 4

Temporal bone to disc
Flat articular surfaces in horizontal plane
Joint surface motion = gliding

Question 5

Lower joint space

Answer 5

disc to condyle of mandible
Uniaxia hinge joint - axis mediolateral
Joint surface motion = angular

Question 6

articular surfaces - mandibular condyles

Answer 6

ant surface = convex

Trabecular bone underneath, covered with fibrocartilage

Question 7

articular surfaces - mandibular glenoid fossa of temporal bone

Answer 7

articular eminence = concave

Trabecular bone underneath, covered with fibrocartilage

Question 8

articular surfaces - Intraarticular disc

Answer 8

vascular/innverted biconcave middle portion avascular allows congruency
Middle is not vascularized

Question 9

Intrarticular disc - disc attachments

Answer 9

Mandibular condyle (firm) - attached to medial and lateral poles
Joint capsule (A/P) not ML- disc is attached to capsule AP
Lateral pterygoid mm (ant)
Bilaminar retrodiscal pad (post)

Question 10

Intrarticular disc - disc attachments - bilaminar retrodiscal pad

Answer 10

Sup strata/lamina (elastic, stretches disk repositioning)

Inf (inelastic, attach neck of condyle and limits forward translation, anchors disc from condyle)

Question 11

Joint capsule - inf is attached to

Answer 11

neck of mandibular condyle

Question 12

Joint capsule - sup is attached to

Answer 12

articular tubercle (on ant surface)
squamotympanic fissure
circumference of glenoid fossa –> medial and lateral

Question 13

Joint capsule - ant and post attached to

Answer 13

attachment to the disc allows for translation of the disc within the capsule

Question 14

Rest position

Answer 14

Joint in loose packed position when jaw closed with 2-5mm space btw teeth
Connective tissue at rest and upper and lower pterygoid at rest too

Question 15

Movement - DF

Answer 15

3 DF

Question 16

Movement - Mandibular depression

Answer 16

Open mouth
Disc and condyle experience short translation ant (glide)
Upper/lower head of lat pterygoid contract to guide the disc and condyle forward
Post connective tissue tightens

Question 17

Movement - Mandibular elevation

Answer 17

Condyles glide back post/sup
Disc glides ant relative to condyle
Upper head of lateral pterygoid contracts to guide disc
Lower head relaxes
Post connective tissue returns to function rest position

Question 18

Movement - Protrusion and Retrusion

Answer 18

Protrusion - 6-9mm
Retrusion - 3mm
Teeth are separated
Condyle and disc translate AP together
Post disc attachments stretch/relax
Post disc structures (soft tissue in retrodiscal area) and TM ligament limit post movement

Question 19

Movement - lateral deviation of mandible

Answer 19

Happens with chewing with molar on one side
In ipsilateral direction = axial rotation
Contralateral side = ant translation

Question 20

Ligaments - Temperomandibular Ligament - oblique

Answer 20

Oblique (outer portion)
attach at neck of condyle, articular tubercle
Resists downward, post movement
Resists rotation of condyle with opening mouth

Question 21

Ligaments - Temporomandibular Ligament - horizontal

Answer 21

Horizontal (inner portion)
Lateral pole of condyle, post disc, articular tubercle
Resists post motion of condyle
Protects retrodiscal tissue

Question 22

Ligaments - Stylomandibular ligament

Answer 22

Styloid process of temporal bone, post border ramus mandible
Limits protrusion of jaw

Question 23

Ligaments - Sphenomandibular ligament

Answer 23

Spine of sphenoid, middle surface of ramus of mandible
Suspends mandible - prevents dropping
Prevents excessive forward translation too
MAjor suspensory ligament

Question 24

Mouth opening

Answer 24

First half - early phase = spin at lower joint space, limited translation
Second half - later phase = gliding at upper joint space, angular motion, translation along a slope

Question 25

Muscles - Masseter O and I

Answer 25

Zygomatic arch and process to the Angle and lateral ramus of mandible

Question 26

Muscles - Temporalis O and I

Answer 26

Temporal fossa to the coronoid process and medial ramus of the mandible

Question 27

Muscles - Med Pterygoid O and I

Answer 27

Sphenoid bone to the angle and med ramus of mandible

Question 28

Muscles - Lat Pterygoid O and I

Answer 28

Wing of sphenoid to the condyle of the mandible

Question 29

Muscles that elevate

Answer 29

Masseter
Temporalis
Med Pterygoid

Question 30

Muscles that Protrude

Answer 30

Lateral Pterygoid
Masseter (sup part)
Medial Pterygoid

Question 31

Muscles that do lateral deviation

Answer 31

Temporalis (ipsilater)
Masseter (ipsilater)
Pterygoids (contral)

Question 32

Muscles that do retrusion

Answer 32

Temporalis (post fibers)
Digastric
Stylohyoid

Question 33

Mandible and chewing

Answer 33

Chewing stroke - depression, lateral deviation towards working side, elevation
Compress and shift food up and medial
Shear action

Question 34

Loads/Molar Bite vs. Loads/Incisor Bite

Answer 34

Motion predominantly sagittal for both
to develop same force on molars and incisors you have to develop more force with muscles (incisors) to get the same force
Teeth alignment has impact on force mm have to produce and the forces that the joint experiences