Control Of jaw Posture and movement

1. Control Of jaw Posture and
movement

2. • Determinants of occlusion:
• 1) TMJ (right and left) and its suspensory
ligaments as well as the condyles ( right and
left) the post Determinants of occlusion
• 2) the teeth : consist of the inter-occlusal
contacting points and inclines of cusps of the
opposing arches  Anter determinants of
occlusion
• 3) the neuromuscular system.

3. • Five requirements for the equilibrium of the masticatory
system:
1) Stable and comfortable TMJ (even when loaded)
2) Anter. Guidance in harmony with functional movement of
the mandible
3) Noninterference of post teeth:
-equal intensity contacts in centric relation
-post disclusion when the condyle leaves centric relation
4) All teeth in vertical harmony with the repetitive contracted
length of the closing muscle
5) All teeth in horizontal harmony with the neutral zone.

4. • Muscle of mastication :
• They are attached to the mandible:
-Elevators
-Depressors
• Assisting muscles :
-Infrahyoid
-Muscles of lips and cheek
-Tongue muscles
-Head and neck muscle

5. Cont’d
• Elevators Muscles:
• Masseters(anter. Fibers )
• Temporalis
• Medial Pterygoids

6. Cont’d
• Different part of a muscle produce different
movements : E.g. temporalis :
-anterior Fibers(Vertical) elevate the mandible
-Posterior Fibers(horizontal ) retract mandible
Unilateral contraction  lateral movemnt of
mandible (chewing )

7. ligaments
• The sphenomandibular and stylomandibular are
considered accessory ligaments. these are
responsible for limitation of mandibular
movements.
• The temporomandbiular ligaments  provide
lateral reinforcement for the capsule, and
prevents post and infer. Displacement of the
condyle. ( the main stablizing ligament)
• Collateral ligaments ( medial and lateral ) (discal
ligaments)  restrict movement of the disc away
from the condyle during function

8. Rest Position
• Teeth are held slightly separate .
• Mandible is held by the sling of Medial
Ptrygoid and Masseter
• TMJ is not loaded.
• The interocclusal space with the mandible in
the rest position and head in upright position
is about 1-3 mm at the incisors but has
considerable normal variance even up to 8 to
10 mm without evidence of dysfunction.

9. • Three basic Jaw Positions:
• Centric occlusion ( ICP) :the maximum intercuspation of the teeth . Its is
tooth Guided
• The rest position of the mandible (postural position) : determined mostly
by the musculature. The usual reflex cited as the basis for the postural
position of the mandible is the tonic stretch reflex of the mandibular
levators (i.e myotatic reflex). It is muscle-guided position
• Centric relation (RCP):is a position (or path of opening and closing without
translation of the condyles) of the mandible in which the condyles are in
their uppermost, Midmost positions in the mandibular fossae and
related anteriorly to the distal slope of the articular eminence.Because
mandible appears to rotate around a transverse axis through the condyle
in centric relation movement, guidance of the jaw by the dentist in
opening and closing movements that do not have translation is referred to
as hinge axis movement. In this position (CR) the condyles are considered
to be in the terminal hinge position .it is ligament guided position

10. Note
• The mandible cannot be forced into centric
relation from the rest position because the
patient’s reflex neuromuscular defense would
resist the applied force. The mandible should
be relaxed and gently guided into centric
relation.

11. • Lateral Movement of the mandible is referred to as
transtrusion , this movement has two components:
• 1- laterotrusion: the lateral movement of the working or
rotating condyle
• 2-mediotrusion: the medial movement of the balancing or
nonworking condyle.
• In later movement the balancing non working condyle
goes downward , forward and medially. The working
condyle moves laterally
• Since mandible is a solid bone, the amount that the non-
working condyles moves medially determines how far the
working condyle mover laterally. This lateral movement is
know as Bennett movement or side shift of the mandible.

12. • Protrusive movement:
• Results form the contraction of both lateral Pterygoid, they
don’t need assistance for this movement
• Is accomplished when the mandible is moved straight
forward until the maxillary and mandibular incisors contact,
edge-to-edge.
• This movement is bilaterally symmetrical in that both sides
of the mandible move in the same directions
• The condyles of the mandible have moved in a downward
and forward direction. The translation is performed as the
mandible moves from pure protrusive movement from the
maximum intercuspal position to a maximum protruded
position

13. • Anterior Guidance : is the Guidance provided by the anterior teeth
when the mandible goes into a lateral or protrusive movement
• It is determined by the OverJet(horizontal overlap) and
OverBite(vertical overlap) .
• This overlapping produces disclusion of the post. teeth when the
mandible protrudes and moves to either side.
• Anterior teeth have a mechanical advantage over post. Teeth
because they are farther away form the fulcrum (condyles) , giving
better leverage to offset the closing musculature. The further away
from the site of muscle action, the less force is exerted.
• SO if Anter Guidance can be accomplished the least amount of
force will be placed during muscular contraction

14. Empty mouth Swallowing
• Occurs Frequently throughout the day and is an
important function that rids the mouth of saliva and
helps to moisten the oral structures.
• The Hourly rate of non-masticatory swallowing is
related to the amount of salivary.
• Its an involuntary reflex activity
• That Masseter muscles contract and the top of the
tongue touches the roof of the mouth during normal
swallowing
• Tooth contacts are of Longer duration in swallowing
than in chewing but there is wide variation in
frequency and duration from one person to another