Week 3 - Mandibular Movements Flashcards
Occlusal Stability
Anatomic and functional harmony caused by the balance between the elevator and depressor muscles
At rest, where is the jaw?
Suspended 2-4 mm in space
(According to this class) What are the muscles of mastication?
Digastric
Masseter
Temporalis
Lateral Ptrygoid
Diagastric muscle
Helps open the jaw
Masseter muscle
Helps close and crush
Temporalis muscle
Closes the jaw
Lateral Pterygoid muscle
Open and orient the jaw
Has two heads that act like oars on a boat
Articulating disc
Biconcave disc in the TMJ to protect the bone from the joint
What two bones are included in the TMJ?
Mandible and Temporal bone
What direction does the jaw move during protrusion?
Down and forward
Midsagittal section of the head
Median plane
Transverse section of the head
Horizontal plane
Coronal section of the head
Frontal plane
Rotation movement of the mandible
Rotating around its long axis
Mandible stays in the same location
Translational movement of the mandible
Leaves the former space and goes to another
In the mandible, this occurs when it moves forward
THA (Terminal Hinge Axis or Transverse Horizontal axis)
Imaginary line that connects the condyles
The mandible rotates around this axis
Working side
The side towards which the mandible moves during lateral movement
Non-working side
The side opposite the working side
What direction does the non-working side move during right lateral movement?
It moves downward, forward, and medial
What direction does the working side move during right lateral movement?
Laterally
Bennett’s Movement/Bennett’s Cone
The working side movement can go anywhere within a cone (called Bennett’s cone)
Bennett’s Side Shift
Mandibular Lateral Rotation
During lateral movement, the jaw has to translate forward slightly, because it is up against a wall and at an angle. When it twists, it has to come forward because it can’t move the skull
What motion does the jaw move during chewing?
It opens and closes in a tear-drop shape
Ulf-Posselt’s Envelope of Motion
Occurs when the mouth is opening and closing
The mandible first rotates and then it translates
Centric relation curve
The curve seen when the mandible first rotates
Curve of translation
When the mandible translates after rotating during opening in Ulf-Posslet’s envelope of motion
Initial Point of contact
In 90% of the population, CO occurs with two teeth and then slide into MI
In 10% of the population, they go straight into MI (CO = MI)
What are the funcitons of Anterior Teeth?
Anterior Guidance Perform Initial acts of mastication Speech Lip Support Esthetics
Anterior Guidance
The anterior teeth overlap, creating an angle, which help guide occlusion
What is anterior guidance dictated by?
Position of the incisal edge of the mandibular anterior teeth relative to the lingual surfaces of the maxillary anterior teeth
Changes in morphology of the lingual surfaces of maxillary anterior teeth
Length of mandibular incisors or canines
What are the 2 forms of anterior guidance, and which is ideal?
Incisal guidance
Canine guidance*
Why is Canine guidance ideal?
Muscle activity is lower, leading to less fatigue
What are the two occlusal schemes, which is ideal?
Anterior guidance
Group Function
Group Funciton
The canines and molars are all touching at the same time
not ideal but sometimes necessary
What are the three functions of the incisal guides on the articulator?
1) When anterior teeth are prepared, the angulations of the custom guide provides anterior guidance in the place of anterior teeth
2) When only posterior teeth are to be replaced, the angulation of the guide serves to estimate the buccolingual and mesiodistal cusp angles so as to avoid interference in both protrusive and on-working excursions
3) Reduce the amount of wear on the stone during excursive movements made on the articulator
