Lecture 5: Jaws And Teeth Flashcards
Describe the relative size and position of the temporalis muscle in humans vs. chimps
Smaller in humans
More muscle on medial side in chimps
Describe the possible and impossible range of mandibular excursion
The lateral view of the temporalis suggests 30 mm of movement, but the bipennate structure only permits 15 mm
Compare the masseter muscle in humans vs. other primates
In primates it is much larger and more complex - they have superficial and deep component
It is multipennate in both so there is not a lot of movement but it is very strong
Of the muscles of mastication: medial and lateral pterygoid, which has dual heads?
Lateral pterygoid
True or false: the medial pterygoid is multipennate
True
The lower head of the lateral pterygoid acts as a ________________ ______________
Protruder depressor
In terms of the depressors of the jaw or elevators of the hyoid, the _____________ is associated with the jaw and the ___________ is associated with the chin
Mylohyoid
Geniohyoid
The ______ and ______ hyoid muscles can both depress the jaw and elevate and protrude the hyoid bone
Supra
Infra
It is important to note that jaws don’t just hinge, they also protrude. Excursion happens onto __________ _________. Condyle rotates AND slides forward onto this structure and takes __________ ________ with it. As a result, the jaw drops down and forward with full mouth opening
Articular eminence
Articular disc
What muscle allows the excursion of the condyle of the mandible?
Lateral pterygoid
The temporalis elevates the mandible with its _____________ fibers.
It retracts the protruded mandible with its ____________ ___________ fibers.
___________ __________: mastication that moves the mandibular head on the balance side forward
Vertical
Horizontal posterior
Unilateral contraction
The masseter ______ and ______ the mandible
Elevates and protrudes
The medial pterygoid ________ the mandible
Elevates
___________ ____________ of the lateral pterygoid: initiates mouth by ___________ the mandible and moving the articular disk forward.
____________ __________ of the lateral pterygoid: ________ the mandible to the opposite side during mastication
Bilateral contraction; protruding
Unilateral contraction; elevates
What are the glenoid variations among hominids?
Medial translation
Medial excursion
In Parathropus boisei
What are the types of mandibular strain?
Symphysial shear and compression
Twisting and bending of corpora
During __________ mandibular strain, it is counteracted with __________ symphyseal height
Shear; greater
________________ during “wishboning” in mandibular strain is counteracted with ___________ symphyseal AP depth
Compression; Greater
During ___________ mandibular strain, it is counteracted with __________ corpus breadth
Twisting; Greater
During ____________ mandibular strain, it is counteracted with _________ corpus height
Bending; Greater
Describe the structures of TMJ when chewing
The horizontal band is taut on the working side after balancing side excursion during chewing
What happens to the center of rotation during TMJ excursion?
Articular disc drops vertically when fully abducted
Compare the symphyseal anatomy of the mandible between humans, orangutan and A. afarensis
Humans and orangutan have simian shelf to reinforce bone on jaw
A. Afarensis does not have a simian shelf
Compare the hominid corpora and the size of the mandible
Overall size of mandible is reflected by cross sectional area
In overall build, the mandibles of Homo are less robust than those of other hominids
Compare the shape and size of the hominin mandible and teeth between males and females in A. afarensis
In females: have smaller mandible and the last molar lies wide of the dental arcade and creates the v shaped arch
In males: posterior teeth form straight rows and dental arch is narrow
To avoid discussion of TMJ the ________ of all muscle force vectors must stay within a triangle of support
Resultant
The jaw is actually two ______ class levers attached _______
third; anteriorly
The jaw moves ______ if the amount of force does not _______ on the balancing side when biting
out; decrease
What is the adult dental formula?
2.1.2.3/2.1.2.3
What is the deciduous dental formula?
2.1.0.2/2.1.0.2
True or false:
You can still make enamel after it emerges from the mandible.
False
Ameloblasts and odontoblasts make enamel shape in the mandible and emerges. Cannot make more enamel
What is the purpose of the interlocking enamel prisms?
Increase toughness of enamel
Describe the dentition and diet of fruit eaters
Broad incisors
Low rounded molar cusps
Long small intestine
Describe the dentition and diet of leaf eaters
Small incisors
Developed molar crests for shearing and grinding
Complex stomach or enlarged large intestine
Describe the dentition and diet of insect eaters
Sharp cusps
Short, simple gut
What is the pattern of hominin molars?
5Y pattern in lower molar
What is the relationship between molars and bite force in hominins?
The bigger the molar teeth, the harder you can bite
How can shearing efficiency improve in hominins?
Through wear
What does it appear the wear was due to in neanderthals?
Para masticatory behavior
What are some hominin characteristics of dentition?
- Thick enamel layer
- Modified keyhole pattern of enamel points
- Anterior dentition reduced in size
- Canines wear at tip
- All premolars bicuspid
- Molars greatly enlarged in early hominids
What is the dental arcade shaped like in hominins?
Parabolic in shape
Describe the hominin characteristics of the human skull
- Chewing involved significant lateral motions of the mandible
- Expansion of the brain and braincase
