What are the two influences that move the mandible relative to the maxilla?
Neuromuscular Control – locomotive forces are provided by the muscles under control of the nervous system
Hard Tissue Guidance Systems – the temporomandibular joint and the occlusal surfaces of the teeth.
What are the muscles involved in mandibular movement?
Muscles of Mastication
* Involved in depression, elevation and lateral movements of the mandible
Suprahyoid Muscles
* Elevate the hyoid bone or depress the mandible
What actions do the MOM carry out?
Temporalis (T)
* Elevates and retracts the mandible
* Assists in rotation
Lateral Pterygoid
* positions disc in closing (superior - SLP)
* Protrudes and depresses mandible and causes lateral movement (inferior - ILP)
Medial Pterygoid (MP)
* Elevates the mandible
* Lateral movement and protrusion
Masseter (SMA)
* Elevates and protracts the mandible
* Assists in lateral movement
What muscles are responsible for opening and for closing?
** Jaw Closing**
- Masseter
- Temporalis
- Medial pterygoid
Jaw Opening
- Lateral Pterygoid (- Digastric)
What happens anatomically during rotation of the mandible?
- Small amount of mouth opening (up to 20mm)
- Condyle and disc remains within the articular fossa
- No downwards or forwards movement
- Also known as “hinge movement”
What are hinge movements?
- Rotation of the condylar heads
around an imaginary horizontal line
through the rotational centers of
the condyles - The imaginary line is termed the
terminal hinge axis
What does a facebow record?
- terminal hinge axis
- distance between the condyles
What happens anatomically during translation of the mandible?
- Lateral pterygoid contracts
- Articular disc and condyle begin to move
- Travels downwards and forwards along the incline of the articular eminence
- May also travel laterally (laterotrusive movement)
What is posselts envelope?
- Extremes of mandibular movement
- Border movements of the mandible in the Sagittal Plane
What is ICP?
Intercuspal Position (ICP)
* Tooth position regardless of the condylar position
* The comfortable bite
* Best fit of the teeth
* Maximum interdigitation of the teeth
* Can be called centric occlusion (CO)
What is edge to edge?
- Tooth position
- Teeth slide forward from ICP guiding on palatal surfaces of anterior teeth
- Incisal edges of upper and lower incisors touch
What is protrusion?
- Condyle moves forwards and downwards on articular eminence
- Only incisors +/- canines touch
- No posterior tooth contacts
- Eventually no tooth contacts
What is maximum opening (T)?
- No tooth contacts
- Mouth wide open
- Full translation of the condyle over the articular eminence
What is retruded axis position?
- No tooth contacts
- Most superior posterior position of the condylar head in the fossa
- Terminal hinge axis
What is retruded contact position?
how many mm is it from icp
- First tooth contact when the mandible is in retruded axis position
- ICP is approximately 1mm anterior to RCP in 90% of the population
What is anterior guidance and what is posterior guidance provided by?
Anterior Guidance
- provided by the occlusal contacts of the teeth. (ICP-RCP and ICP-Protrusion)
Posterior Guidance
-provided by the temporomandibular joint. (Opening-RCP)
What is lateral translation? What is this movement called
mandible moving to right
right = working side
mandible moving away from the left
left = non-working side
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