TMJ Mechanics Flashcards
1
Q
how many joints are there in the TMJ articulation
A
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
2
Q
each TMJ consists of..
A
- mandibular condyle
- articular eminence of temporal bone
- articular disc
3
Q
types of joints of TMJ
A
- hinge joint
- -mandbibular condyle and inferior surface of disc - 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
4
Q
retrodiscal bilaminar tissue
A
-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
5
Q
3 regions of disc
A
anterior, middle, posterior
- anterior and posterior are both thick regions with high vascularity
- middle region is thin with low vascularity
6
Q
joint arthrology: mandible
A
- body and rami, angle=intersection of the two
- mandibular condyles
7
Q
mandibular condyles
A
- medial protrusion 15-20mm from rami
- palpate lateral pole ant. to ext. auditory meatus
- unable to palpate medial pole
8
Q
joint arthrology: coronoid process
A
- ant to mandibular condyle
- closed mouth=present under zygomatic arch
- palpable with mouth open
- temporalis muscle attachment
9
Q
joint arthrology: temporalis bone
A
- 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
10
Q
joint arthrology: articular eminence and condyle
A
- 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?
11
Q
articular disc
A
- biconcave
- is TMJ congruent?-yes (matching up.fitting together
- -convex condyle on concave inferior disc, concave superior disc on convex articular eminence
12
Q
articular disc attachments
A
- 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
13
Q
-articular disc attachments
A
- 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
14
Q
articular disk morphology
A
- 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
15
Q
articular disc function
A
- 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.)
16
Q
muscular control of the TM joint
A
- ant. and post. digastrics
- medial and lateral pterygoids
- temporalis
- masseter
17
Q
mandibular elevation/mouth closure
A
- 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
18
Q
mandibular depression/mouth opening
A
- 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
19
Q
mandibular osteokinematics: protrusion
A
-bilateral masseter, medial pterygoids and lateral pterygoids
20
Q
retrusion
A
-bilateral posterior fibers of temporalis and assist by anterior portion of digastrics
21
Q
-lateral deviation
A
- contralateral medial and ipsilateral lateral pterygoids
- ex: R LD by R lat pterygoid and L med pterygoid
- temporalis deviates to ipsilateral side
22
Q
force couple during deviation
A
- 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
23
Q
TM joint arthrokinematics: mouth opening
A
- 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
24
Q
abnormal muscle mechanics
A
- muscle adaptively tightened, limits antagonist direction
- muscle organically weak, limits agonist direction
25
Q
joint is a compression or tension loaded structure
A
-tension loaded, compression only in pathology
26
Q
TM joint arthrokinematics: mouth closing
A
- 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
27
Q
TMJ arthrokinematics: protrusion/retrusion
A
- 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
28
Q
TMJ arthrokinematics: mandibular lateral deviation
A
Ex left
- left condylar and disk spin about a vertical axis combined with right condylar anterior translation or gliding
- lateral deviation= 8mm
29
Q
dentition
A
- 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
30
Q
pathomechanics
A
- 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
31
Q
reciprocal click
A
=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
32
Q
locking
A
- 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
33
Q
closed lock
A
- cannot open fully
- disc is sig anteromedial to condyle disallowing anterior and inf glide
- cannot open fully secondary to mechanical buttress
34
Q
open lock
A
- cannot close
- disk is post to condyle disallowing post and sup glide
- cannot close fully secondary to mechanical buttress
35
Q
osteoarthritis
A
- 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
