Chapter 6: Mandibular dynamics

Question 1

Ideal occlusion:

Answer 1

• CO position
• 2mm overjet
• 2mm overbite

Question 2

What happens if the overbite and overjet are more than 2mm?

Answer 2

It will compromise the posterior disocclusion

Question 3

Why is it important to have a 2mm overjet and overbite?

Answer 3

To allow proper anterior guidance

Question 4

Prematurities are related to what movement?

Answer 4

Opening/Closing

Question 5

Interferences are related to what movements?

Answer 5

Laterality and Protrusion

Question 6

How to measure the lower interincisal point on the different planes?

Answer 6

• Sagittal plane: modified posset diagram
• Horizontal plane: modified Guys gothic arch
• Frontal plane: modified Hildebrand scheme

Question 7

How to measure the mandibular condyle on the different planes?

Answer 7

• Sagittal plane: condylar path inclination
• Horizontal plane: Bennett angle and Bennett movement
• Frontal plane: not possible

Question 8

What is the normal value of the total opening of the posterior border movement? What if this value is increased or decreased?

Answer 8

45 mm
If it is less than 40 mm we would have a TMD
If it is more than 50 mm we would have lunation

Question 9

What movements do we talk about in the Modified posset diagram

Answer 9

• The posterior border movement
• The upper border protrusion
• The anterior opening border

Question 10

Upper border protrusion characteristics:

Answer 10

• Descends 2 mm, advances 2 mm (with contact) and upward 1mm
• Advances 10 mm again (with no teeth contact)
• Total protrusion: 15 mm

Question 11

Why can we go only 1mm upwards?

Answer 11

Because the molars will be contacting each other

Question 12

What is the anterior opening border?

Answer 12

The maximum opening at the maximum protrusion.
In the usual opening, there are condylar rotation and translation from the beginning (intraborder movement).

Question 13

What is the Condylar Path Inclination (CPI)?

Answer 13

It is the angle formed by the line connecting the initial and final position of the condyle in the opening movement with the Frankfurt plane

Question 14

The average value of the CPI according to the Frankfurt plane

Answer 14

40-45 degrees (up to 50 with teeth contact)

Question 15

The average value of CPI according to the Camper plane

Answer 15

30-35 degrees

Question 16

Laterality in Gysi gothic arc

Answer 16

• Contact border made by the anterior guidance 10 mm (upper central incisor width)
• Border laterality with no contact 8mm (upper lateral incisor width)
• Total 16-18 mm

Question 17

Protrusion in Gysi gothic arc

Answer 17

• 1st gothic arc
• Maximum 16 mm

Question 18

What does the double Gusi gothic arc include?

Answer 18

• Maximum opening of 45 mm. The interincisal point moves 30 mm backwards. Second Gothic arc.
• Lateral anterior border movement, maximum laterality to maximum protrusion
• Lateral posterior border movement, maximum laterality at maximum opening

Question 19

Protrusion in the horizontal plane

Answer 19

The advance of both condyles

Question 20

Laterality in the horizontal plane

Answer 20

• The WS rotates
• The non-working condyle goes forward and goes medially (displaced downwards, inwards and frontwards)

Question 21

The Bennett angle in the horizontal plane

Answer 21

It is formed by the line connecting the initial and final position of the non-working condyle in lateral movement (the path made by the condyle in the para-sagittal plane)

Question 22

The average value of Bennett angle

Answer 22

15 degrees

Question 23

Opening in the modified Hildebrand scheme

Answer 23

• It is a straight path of 45 mm
• The condyle advance and descends

Question 24

Laterality in the modified Hildebrand scheme

Answer 24

• The border contacting and non-contacting with descending
• The WS rotates, goes outward only, and rises slightly (not a pure rotation)
• The NWS descends and moves mesially

Question 25

Indicate if the information is true or false regarding the functional movements:

1. They begin and end at the intercuspal position
2. During chewing the mandible goes superiorly until the desired opening is achieved.
3. Then, it shifts to the side on which the bolus is placed and raised up.
4. In maximum intercuspation, the bolus is broken between neighbouring teeth.
5. In the final millimetre of closure, the mandible stays in its position.

Answer 25

1. True
2. False, the mandible drops directly inferiorly
3. True
4. False, the bolus is broken between opposing teeth
5. False, the mandible shifts back to the intercuspal position