2/14: Mechanics of Mandibular Movement Flashcards
What are the 4 anatomic determinants of anatomic movement?
- Right TMJ
- Left TMJ
- Teeth/occlusion
- Neuromusculature
What are the two types of movements within the TMJ?
- Rotational movement
- Translation movement
Where does rotational movement occur?
In the inferior joint compartment
Where does translation movement occur?
In the superior joint compartment
What is rotation?
Process of turning about an axis
When does rotation occur?
When the mouth opens and closes around a fixed point or axis within the condyles
What compartment does rotation occur within?
The inferior joint compartment
How do the condyles move during rotation?
Condyle rotates on the inferior aspect of the articular disk
Rotation occurs for the first ________mm of opening
20-25
What occurs when it further opens?
Translation occurs
What planes can rotational movements occur?
In all three reference planes in the mandible
1. Rotation in the Sagittal plane around a horizontal axis
2. Rotation in the Horizontal plane around a vertical (frontal) axis
3. Rotation in the Frontal plane around a sagittal axis
What is the rotation like around a horizontal center with a sagittal plane?
What is the rotation like around a vertical center of rotation with a horizontal plane?
What is the rotation like around a sagittal center of rotation with a vertical plane?
What is the horizontal axis that passes through both R and L condyles called?
– Terminal hinge axis
– Transverse hinge axis
– Horizontal hinge axis
What movement is clinically identifiable and recordable?
Rotation in the sagittal plane around a horizontal axis
What is the only rotational movement that can be isolated clincially?
Rotation in the sagittal plane around a horizontal axis
When does Rotation in the sagittal plane around a horizontal axis only occur?
When the mandible is in CR
What is frontal axis of rotation?
Rotation in the horizontal plane around a frontal (vertical) axis
When does frontal axis of rotation occur?
- During lateral movement
- frontal axis is in the working side condyle
How does the non-worknig side condyle move in frontal axis of rotation?
Medially (and forward) in the horizontal plane orbiting around this frontal axis
What is sagittal axis of rotation?
Rotation in the vertical plane around a sagittal center of rotation
When does sagittal axis of rotation occur?
- During lateral movement
- sagittal axis is in the working side condyle
How does the non-working side condyle move in sagittal axis of rotation?
Inferiorly in the frontal plane around the sagittal axis
What is the rotational center of the condyle?
Where all three axes (horizontal, vertical, and sagittal) meet
What is translation?
Every point in an object (mandible) simultaneously moving in the same direction with the same velocity
When does translation occur?
- Depression of the mandible (beyond 25 mm), and
in Protrusion (both condyles translate) - In lateral movement:
non-working condyle: moves Downwards,
Forwards, and Medially - In lateral movement (Lateral Translation of the
mandible): working side condyle may shift
laterally
What is bodily lateral movement of the working side condyle called?
Bennett movement
What is the working side condyle?
During a lateral movement, this is the condyle on the side towards which the mandible moves
What is the working side condyle AKA?
Rotating condyle
What is the non-working condyle?
condyle on the side opposite to which the mandible moves
What is the non-working condyle AKA?
Orbital condyle
Where does the working side condyle rotate in lateral movement of the mandible?
Around a vertical axis
Where does the non-working side condyle rotate in lateral movement of the mandible?
Downwards, forwards, and medially through a series of rotations
What is condylar angle defines as?
Angle at which the condyle moves away from a horizontal reference plane
Can a condylar angle be recorded (estimated) on a patient?
Yes
How can a condylar angle be recorded via?
A protrusive movement or via lateral movements
What is the angle influenced by in protrusive movement?
Posterior slope of the articular eminence (the angle the posterior slope of the articular eminence varies among individuals)
What is the condylar angle measured via?
Lateral movement
What is the condylar angle influenced by?
The steepness of the medial wall of the articular fossa (non-working side)
Where does the non-working side condyle move in lateral movement?
- Downards, forwards, and medially
- over the steeper medial wall of the articular fossa
Can the condylar angle be recorded in lateral movement?
Yes
- usually slightly steeper than when recorded in protrusion
What is fischer’s angle?
The angle formed by the intersection of the protrusive and non-working condylar paths as viewed in the sagittal plane
What is fischer’s angle a difference between?
The condylar angle recorded with a protrusive and lateral record
What is the medial wall of articular fossa like in fischer’s angle?
Medial wall is generally steeper than the posterior slope of the articular eminence
What are the degrees of fischer’s agle?
5-10 degrees
What is Bennett angle?
The angle at which the NWS condyle moves medially away from a sagittal reference plane as viewed in the horizontal plane during a lateral movement
What is lateral translation?
Bodily movement of the mandible during lateral excursive movement (bennett movement)
- sometimes theworking side condyle doesn’t simply rotate but also shifts laterally during the lateral movement
Describe the condyles during protrusion
- both condyles translate
- condyles move forwards and downwards
- condyles move down the posterior slope of the articular eminence
- condylar guidance angle can be calculated from this movement
