Mechanics of Mandibular Movements

Question 1

Terminal hinge axis represents what mandibular movement?

Answer 1

rotation - in the very beginning and anything beyond this point the mandible starts to translate as well

Question 2

Five factors of mandibular movement

Answer 2

1. initiating position (centric relation)
2. types of motion - rotation and translation
3. direction of motion (planes)
4. degree of movement
5. clinical significance of movements

Question 3

clinical importance of CR?

Answer 3

START POINT -where you start with any restorative procedures

Question 4

Rotation

definition and where

Answer 4

process of moving around an axis - motion of a body around its center

around horizontal axis
around frontal (vertical axis)
around sagittal axis

Question 5

translation

definition and where

Answer 5

Motion of a body in which all of its points move in the same direction at the same velocity

Question 6

*functional border starts where?

Answer 6

MIP

Question 7

how far open when just doing rotation? what axis?

Answer 7

only the horizontal hinge axis

opens approx. 20-25 mm as measured between incisal edges

Question 8

Direction of movement of mandible when translate and condyles when translate (in sagittal plane)

Answer 8

Condyles : move anterior and inferior

Mandible: moves inferior and posterior (40-60 mm)

Question 9

center of rotation when go into translation?

Answer 9

moves from condyle to the body of ramus

Question 10

when is condyle in most anterior position?

Answer 10

when the mandible is in maximum opening

Question 11

how is maximum protrusion limited?

Answer 11

in part by the stylomandibular ligaments, which when close, produce a posterior movement of the condyle

Question 12

posterior opening border in sagittal plane

Answer 12

Rotation (terminal hinge axis) and translation into MO

Question 13

Anterior opening border in sagittal plane

Answer 13

maximum opening o maximum protrusion

Question 14

superior contact border in sagittal plane

start – finish and what is in between

Answer 14

CR to maximum protrusion

1. CR (posterior to MIP)
2. anterior to MIP
3. in presence of anterior guidance there is INFERIOR movement of mandible
4. In protrusion, as incisal edges contact - EDGE to EDGE there is HORIZONTAL movement
5. as pass each other from edge to edge - mandible moves superior and posterior teeth contact
6. Continued protrusive movement is affected by the cuspal height of posterior teeth and limited by the ligaments

Question 15

sagittal plane functional border

Answer 15

STARTS at MIP *

“clinical rest position” is found within this functional border, usually 2-4 mm below MIP

Question 16

amount of normal vertical overlap?

horizontal?

Answer 16

2-3 mm

horizontal want to limit this

Question 17

*5 things that affect the superior contact border?

Answer 17

1. amount of variation between centric relation and maximum intercuspation (freeway space)
2. steepness of the cuspal inclines of the posterior teeth
3. amount of vertical and horizontal overlap of the anterior teeth
4. lingual morphology of maxillary anterior teeth (relationship with anterior guidance)
5. general inter-arch relationships of the teeth

Question 18

does functional movement look the same if the patient has flat teeth?

Answer 18

no - flat more movement side to side

Question 19

4 anatomic determinants of mandibular motion

Answer 19

1. Right condyle
2. left condyle
3. Dentition (occlusion of permanent dentition)
4. R/L TMJ joints and muscles

Question 20

Frontal plane border movement : left lateral superior
Starts?
determined by?

Answer 20

Starts in CR
Nature of movement is determined by the morphology and interarch relationship of the opposing posterior teeth

the maximum extend of the movement is determined by the ligaments of the relating joint

Question 21

Frontal plane border movement : left lateral opening
Starts?
what happens at max opening?

Answer 21

Starts at the maximum left lateral movement
jaw will take a convex path towards the midline (at bottom of drop near max opening)

at maximum opening the ligaments tighten and the mandible moves to midline

Question 22

horizontal plane border movement
starts?
name all positions and locations within border

Answer 22

BORDER STARTS AT CR - which is posterior to the MIP

looks like a diamond

1. left lateral
2. continued left lateral with protrusion
3. right lateral
4. continued right lateral with protrusion

Question 23

posterior intersection in horizontal plane?

Answer 23

marked centric relation

Question 24

left lateral in horizontal plane

Number in picture?

Answer 24

Number 1.
Left condyle = rotating
Right condyle = orbiting

Goes from CR – left lateral and as it does the INFERIOR PTERYGOIDS ON THE RIGHT BRING THE RIGHT CONDYLE INFERIOR ANTERIOR AND MEDIAL

Question 25

continued left lateral in horizontal plane

Number in picture?

Answer 25

Number 2.
With continued lateral there is also protrusion occuring so now the LEFT INFERIOR LATERAL PTERYGOID IS CONTRACTING TOO - along with the continued contraction of the right lateral pterygoid

overall – the left condyle will begin to move anteriorly and to the right (to follow the motion of the border we see)

so duel * contraction of the inferior lateral pterygoids

Question 26

action of the inferior lateral pterygoids

Answer 26

active during opening in conjuction with the mandibular depressors and also active in protrusion

UNILATERAL contraction is responsible for mediotrusive movements

Question 27

how to trace horizontal plane movement>

Answer 27

Gothic arch tracing

tracing made using static plate attached to maxilla and a stylus point attached to mandible

ask patient to make protrusive RL and LL movements

Question 28

how to find centric relation position for complete denture patients?

Answer 28

gothic arch tracing

Question 29

relationship to opening and size of the gothic arch tracing?

Answer 29

as the mandible is opened more – the ability of the jaw to move side to side decreases - thus the tracing becomes smaller at maximum opening
- limited/ restricted by ligaments in excessive motions

Question 30

what is H in sagittal view?

Answer 30

Terminal hinge axis