Mechanics of Mandibular Movement

Question 1

Four anatomic determinants of movement

Answer 1

1. Right TMJ
2. Left TMJ
3. Teeth/Occlusion
4. Neuromusculature

Question 2

1&2

Answer 2

right and left tempormandibular joints (and associated ligaments)

Question 3

3

Answer 3

occlusion of the permanent dentition

Question 4

movements within TMJ (2)

Answer 4

rotational

translational

Question 5

Rotational Movement

Answer 5

– Occurs in the inferior joint compartment

Question 6

Translation Movement

Answer 6

– Occurs in the superior joint compartment

Question 7

Rotation

Answer 7

The process of turning about an axis

Question 8

rotation occurs when

Answer 8

the mouth opens and closes
around a fixed point or axis within the
condyles

Question 9

rotation occurs within the

Answer 9

inferior joint compartment

Question 10

rotation:

condyle rotates on the

Answer 10

inferior aspect of the articular disk

Question 11

rotation occurs for the first — mm of opening

Answer 11

20-25

Question 12

on further opening, — occurs

Answer 12

translation

Question 13

Rotational movements may occur in all

three reference planes in the mandible:

Answer 13

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

Question 14

Horizontal axis that passes through both R and L

condyles is called (3)

Answer 14

– Terminal hinge axis
– Transverse hinge axis
– Horizontal hinge axis

Question 15

Rotation in the Sagittal Plane

around a Horizontal Axis (2)

Answer 15

This movement is clinically identifiable and
recordable
Only rotational movement that can be isolated
clinically

Question 16

2. Frontal Axis of Rotation
   Rotation in the horizontal plane around
   a frontal (vertical) axis (3)

Answer 16

Occurs during lateral movement
Frontal axis is in the working side condyle
Non-working side condyle moves medially 
(and forward) in the horizontal plane 
orbiting around this frontal axis

Question 17

3.Sagittal axis of rotation
Rotation in the vertical plane around a
sagittal center of rotation (3)

Answer 17

Occurs during lateral movement
Sagittal axis is in the working side condyle
Non-working side condyle moves inferiorly
in the frontal plane around the sagittal axis

Question 18

Rotational Center of the condyle

Answer 18

Where all three axes (horizontal, vertical
and sagittal) meet is called the rotational
center of the condyle

Question 19

Translation

Answer 19

Defined as every point in an object
(mandible) simultaneously moving in the
same direction with the same velocity

Question 20

Translation

Occurs: (3)

Answer 20

1. Depression of the mandible (beyond 25 mm), and
   in Protrusion (both condyles translate)
2. In lateral movement:
   non-working condyle: moves Downwards,
   Forwards, and Medially
3. In lateral movement (Lateral Translation of the
   mandible): working side condyle may shift
   laterally. This bodily lateral movement of the
   working side condyle is called the Bennett
   Movement.

Question 21

Working side condyle (2)

Answer 21

– During a lateral movement, this is the condyle
on the side towards which the mandible
moves
– A.k.a. rotating condyle

Question 22

Non-working side condyle (2)

Answer 22

– This is the condyle on the side opposite to
which the mandible moves
– A.k.a. orbiting condyle

Question 23

Working side condyle mainly rotates

around a — axis

Answer 23

vertical

Question 24

Non-working side condyle moves

Answer 24

downwards, forwards and medially

through a series of rotations

Question 25

Condylar Angle

Defined as:

Answer 25

Angle at which the condyle moves

away from a horizontal reference plane

Question 26

Can the condylar angle can be recorded (estimated) on

a patient?

Answer 26

yes

Question 27

condylar angle can be recorder via a — movement or via — movements

Answer 27

protrusive

lateral

Question 28

During PROTRUSIVE MOVEMENT, the angle is

influenced by the

Answer 28

posterior slope of the articular
eminence. (the angle the posterior slope of the
articular eminence varies among individuals)

Question 29

The condylar angle measured via lateral

movement is influenced by the

Answer 29

steepness of the

medial wall of the articular fossa (non-working side)

Question 30

Lateral Movement (4)

Answer 30

Non-working side condyle moves 
downwards, forwards and medially
Moves over the steeper medial wall of the 
articular fossa
Can record the condylar angle from this 
movement also
Condylar angle is usually slightly steeper 
than when recorded in protrusion

Question 31

Fischer’s angle

Answer 31

The angle formed by the intersection
of the protrusive and non-working
condylar paths as viewed in the
sagittal plane.

Question 32

The difference between the condylar angle

recorded with a

Answer 32

protrusive and lateral

record

Question 33

Medial wall of articular fossa is generally
— than the posterior slope of the
articular eminence

Answer 33

steeper

Question 34

Fischer’s angle=

Answer 34

5-10 degrees

Question 35

Bennett Angle

Answer 35

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

Question 36

Lateral Translation

Answer 36

Bodily movement of the mandible during lateral 
excursive movement (Bennett Movement)

Question 37

Bennett Movement

Answer 37

Sometimes the working side condyle does
not simply rotate but also shifts laterally
during the lateral movement. This lateral
movement of the working side condyle is
called the Bennett movement.

Question 38

Both condyles —

Answer 38

translate

Question 39

Condyles move (2)

Answer 39

forwards and downwards

Question 40

Condyles move down the

Answer 40

posterior slope of

the articular eminence

Question 41

— —- —- can be calculated

from this movement

Answer 41

Condylar guidance angle