Chapter 6: Mandibular dynamics Flashcards
Ideal occlusion:
- CO position
- 2mm overjet
- 2mm overbite
What happens if the overbite and overjet are more than 2mm?
It will compromise the posterior disocclusion
Why is it important to have a 2mm overjet and overbite?
To allow proper anterior guidance
Prematurities are related to what movement?
Opening/Closing
Interferences are related to what movements?
Laterality and Protrusion
How to measure the lower interincisal point on the different planes?
- Sagittal plane: modified posset diagram
- Horizontal plane: modified Guys gothic arch
- Frontal plane: modified Hildebrand scheme
How to measure the mandibular condyle on the different planes?
- Sagittal plane: condylar path inclination
- Horizontal plane: Bennett angle and Bennett movement
- Frontal plane: not possible
What is the normal value of the total opening of the posterior border movement? What if this value is increased or decreased?
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
What movements do we talk about in the Modified posset diagram
- The posterior border movement
- The upper border protrusion
- The anterior opening border
Upper border protrusion characteristics:
- Descends 2 mm, advances 2 mm (with contact) and upward 1mm
- Advances 10 mm again (with no teeth contact)
- Total protrusion: 15 mm
Why can we go only 1mm upwards?
Because the molars will be contacting each other
What is the anterior opening border?
The maximum opening at the maximum protrusion.
In the usual opening, there are condylar rotation and translation from the beginning (intraborder movement).
What is the Condylar Path Inclination (CPI)?
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
The average value of the CPI according to the Frankfurt plane
40-45 degrees (up to 50 with teeth contact)
The average value of CPI according to the Camper plane
30-35 degrees
Laterality in Gysi gothic arc
- 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
Protrusion in Gysi gothic arc
- 1st gothic arc
- Maximum 16 mm
What does the double Gusi gothic arc include?
- 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
Protrusion in the horizontal plane
The advance of both condyles
Laterality in the horizontal plane
- The WS rotates
- The non-working condyle goes forward and goes medially (displaced downwards, inwards and frontwards)
The Bennett angle in the horizontal plane
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)
The average value of Bennett angle
15 degrees
Opening in the modified Hildebrand scheme
- It is a straight path of 45 mm
- The condyle advance and descends
Laterality in the modified Hildebrand scheme
- 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
