TMJ Biomechanics Flashcards
How many joints comprise the TMJ
4
What are the 4 joints of the TMJ
2 rolling glide joints and 2 planar joints
What are the 2 rolling glide joints
Lower joints
What are the 2 planar joints
Upper joints
What does each TMJ consist of (3)
- Mandibular condyle
- Articular eminence of temporal bone
- Articular disc
What forms the hinge joint of the TMJ
Mandibular condyle and the inferior surface of the disc
What forms the plane/gliding joint of the TMJ
Articular eminence and superior surface of disc
What type of joint is the TMJ
Synovial joint
What type of cartilage does the TMJ have
Fibrocartilage
What does fibrocartilage allow for
Healing properties
True or False:
The TMJ is capable of being very strong and powerful, but very delicate and precise at the same time
True
True or False:
You will see lots of TMJ problems in the clinic
False
Is the articular disc of the TMJ free floating
Nope
What holds the disc in place
Anterior side: Lateral pterygoid superior head
Posterior side: Retrodiscal bilaminar tissue
How many layers of laminar rings does the retrodiscal tissue have
2
What is the thickness of the disc in the TMJ
Thick, thin, thick
Where is the thinnest portion always located
The middle of the disc
How do you palpate the coronoid process and temporalis
With the mouth open
Where is the coronoid process located when the mouth is closed
Under zygomatic arch
Is the mandibular fossa thin and translucent or thick and opague
Thin and translucent
Why is the mandibular fossa thin and translucent
Because no compression occurs there (Wolff’s Law)
What type of bone is the articular eminence
Trabecular
What orientation does the mandible and articular eminence have
Convex on convex
Where is the most fibrocartilage found in the TMJ disc
Articular eminence and anterosuperior condyle
How are the deep fibers aligned in the disc
Perpendicular
How are the superficial fibers if the disc aligned
Parallel
What is the shape of the articular disc of the TMJ
Biconcave
What is the configuration of the TMJ joint
Convex condyle on concave inferior disk and concave superior disc on convex articular eminence
Is the disc firmly attached to the capsule medial and lateral
No
What does the disc not being attached firmly to the capsule allow
Free rotation of disc with condyle
What does the lateral pterygoid restrict
Posterior translation
What does the bilaminar retrodiscal tissue restrict
Too much anterior translation of the disc
Are the bilaminar retrodiscal tissues or lateral pterygoids tense when the TMJ is at rest
Negative
What happens to the disc when you close your mouth
It shifts ever so subtly anteriorly or posteriorly
Why does the disc shift at rest
For repair
What is the thickness of the disc anteriorly, posteriorly, and middle
Anterior: 2mm
Posterior: 3mm
Middle: 1mm
True or False:
The anterior and posterior portions are vascular and neural
True
True or False:
The middle portion is avascular and aneural
True
What are the 3 functions of the articular disc
- Increased congruency of joint surfaces
- Shape allows for greater flexibility of disc
- Thick, thin, thick provides self centering mechanism
What does greater flexibility of the disc allow for
To conform to the bony surfaces with rotation and translation arthrokinematics
If you increase pressure how does the disc rotate
So the thin portion is between the articulating surfaces
If you decrease the pressure how does the disc rotate
To either wider portion
What are the muscles that act on the TMJ (6)
- Anterior digastric
- Posterior digastric
- Medial pterygoid
- Lateral pterygoid
- Temporalis
- Masseter
What are the muscles that cause mandibular depression (3)
- Inferior head of lateral pterygoid
- Anterior digastric
- Posterior digastric
What is the norm for mandibular depression
40-55mm
What happens to the superior head of the lateral pterygoid during depression
Goes on slack
How do the anterior and posterior digastrics cause mandibular depression
Posterior digastric contracts isometrically and anterior digastric contracts concentrically
What muscles cause mandibular protrusion (3)
- Massester
- Medial pterygoids
- Lateral pterygoids
What muscles cause mandibular retrusion (2)
- Posterior temporalis
2. Anterior digastric
What muscles cause mandibular lateral deviation (3)
- Ipsilateral temporalis
- Ipsilateral lateral pterygoid
- Contralateral medial pterygoid
What is the axis of rotation during lateral deviation
Ipsilateral condylar process
What is a force couple
Parallel and opposite direction of forces that cause rotation
What are the arthrokinematics of mandibular depression
Initial anterior roll followed by anterior inferior translation of the disc and condyle
During mandibular depression when does the anterior ad inferior translation occur
Near full opening
How does the ICR shift during mandibular depression
Anteriorly
How much of the mandibular depression comes from the condyle rotation
11-25mm
Where does the rest of the mandibular depression come from
Disc and condyle translating
What does the muscle being adaptively shortened limit
Agonist direction
What does the muscle being organically weak limit
Antagonist direction
True or False:
You should have compression loading of tissues
False
What do we as PTs enhance the roll or the translation
The translation
What are the arthrokinematics of mandibular elevation
Initial posterior and superior translation of disc and condyle followed by posterior roll of condyle
How does the ICR shift during mandibular elevation
Posteriorly
What are the arthrokinematics of mandibular protrusion
Bilateral condyle translation anterior and inferior
What are the arthrokinematics of mandibular retrusion
Bilateral condyle translation posterior and superior
What is the norm for mandibular protrusion
6-9mm
What is the norm for mandibular retrusion
3mm
What are the arthrokinematics of mandibular retrusion from neutral
Posterior translation
What is the norm for mandibular lateral deviation
8mm
What is the normal “freeway” when the mandible is in the resting position
1.5-5mm
What does firm approximation of the upper and lower teeth equal
Occlusal position
What is another name for an occlusal position
Bruxated position
What does the resting position allow for
Decreased intra-articular pressure and stress on articular structures
What happens with forward head overtime
Mandible will depress and retrude
What is bruxism
Grinding teeth
What are 5 ways to injure the TMJ
- Direct trauma
- Poor posture or oral habits
- Reciprocal click
- Locking
- Osteoarthritis
What causes a reciprocal click
Anteromedial displacement of the disc
When do the clicks occur
First during opening and second during closing
What causes the 1st click
Condyle contacting the anteromedially displace disc
What causes the 2nd click
The condyle leaving the anteromedially displaced disc during closing
What does an early click signify
Less anteromedially displaced disc
What does a late click signify
More anteromedially displaced disc
What happens during locking
Only roll occurs
Does anterior or posterior translation occur with locking
Not at all
Which way is the disc displaced during locking
anteriorly
What causes close locking
Disc is anteriomedial to the condyle
What are the symptoms of closed locking
Cannot open mouth fully
What causes open locking
Disc is posterior to the condyle
What are the symptoms of open locking
Cannot close mouth fully
Is OA of the TMJ usually bilateral or unilateral
Unilateral
Motivation
Just keep swimming. Just keep swimming. Just keep swimming swimming swimming
