Lecture 20 - Teeth and Mastication

Question 1

Tooth Anatomy

Answer 1

Question 2

Which tooth tissues comprise the crown?

Answer 2

-enamel, dentine, pulp

Question 3

Which tooth tissues comprise the roots?

Answer 3

-cementum, dentine, pulp

Question 4

Peridontal Ligament

Answer 4

• anchors tooth in jaw
• site of many nerves that sense pain, pressure

Question 5

Tooth Anatomical Directions

Answer 5

• mesial = medial
• lingual = towards tongue (tongue side)
• buccal = towards cheek (cheek side)
• labial = towards lips (lip side)
• occlusal surface = surface of teeth

Question 6

What are the 4 types of human teeth?

Answer 6

Question 7

What is the human dental formula?

Answer 7

2. 1.2.3 per quadrant
   - 2 incisors, 1 canine, 2 premolars, 3 molars per quadrant

Question 8

What is field theory?

Answer 8

-canines set up a field that demarcates what tooth grows there

Question 9

Steps for growing a tooth

Answer 9

1. Thickening of the oral epithelium above condensing mesenchyme (stem cells) below
2. Epithelium invaginates into mesenchyme, tooth shape begins to develop
3. Dental tissues start to develop
4. Erupted tooth

*interaction b/w epithelium and mesenchyme: ectoderm gives rise to teeth (EMT)

Question 10

What does the size of the teeth determine?

Answer 10

The number of teeth formed

Question 11

What is the shape organizer?

Answer 11

• enamel knot: located at the future tips of cusps
• # enamel knots = # cusps

Question 12

What two cells form hard tooth tissue?

Answer 12

• odontoblasts: secrete dentine, creating a single dentine tubule (70% mineral) (1 step)
• ameloblasts: secrete enamel matrix, creating a single enamel prism. then, hydroxyapetite crystals grow and encompass this matrix (96% mineral) (2 steps)

Question 13

What is the EDJ?

Answer 13

• odontoblasts and ameloblasts line either side of the enamel-dentine junction
• each cell moves away from the EDJ (odontoblasts inward, ameloblasts outward) secreting their substances as they move

Question 14

How can you tell how long it took a fossil to grow a tooth?

Answer 14

-ameloblasts and odontoblasts secretion pauses everyday (circadian rhythym), leaving marks in tissues

[daily: cross striations (enamel) vs von Ebner’s lines (dentine)]

[long term: retzius lines (enamel) vs Andresen’s lines (dentine)]

• 1st molar formed at birth = birth line
• count from birth line to determine how long it took tooth to grow (like tree rings)

Question 15

Why do we want to determine how long it took fossils to grow teeth?

Answer 15

• linked to overall development rates
• slower development = larger brains, longer childhood, more complex social systems

Question 16

Why are teeth called inside scales instead of outside bones?

Answer 16

-shark denticles (scale-like) gave rise to teeth

Question 17

Homodonty

Answer 17

• one type of tooth
• most fish and early tetrapods
• single cusped teeth, good for catching prey

Question 18

Heterodonty

Answer 18

• mammalian innovation
• different types of teeth, some with multiple cusps

*multiple “mortars and pestles” to make digestion easier is more energy efficient

*heterodonty reduces overall energetic cost of eating

Question 19

Tribosphenic Molar

Answer 19

• addition of a grinding wedge and surface
• requires precision occlusion between upper/lower teeth

Question 20

Permanent Teeth

Answer 20

• evolutionarily lost P¹ and P²
• 3rd molars = wisdom teeth
• 32 teeth total (8 per quadrant)

Question 21

Incisors

Answer 21

• single, blade like cusp
• single root

Question 22

Canines

Answer 22

• single, pointed cusp
• single root

Question 23

Premolars

Answer 23

• 2 cusps
• single root

Question 24

Molars

Answer 24

• 4-5 cusps
• lower have 2 roots
• upper have 3 roots

Question 25

Incision vs Mastication

Answer 25

_Incision_: biting, using incisors - opening stroke: protraction, depression - closing stroke: elevation _Mastication_: chewing, using premolars and molars -concentrates forces on one side \*canines have no use/function in humans

Question 26

How does diet relate to tooth shape and function?

Answer 26

- grinding teeth: good for grinding brittle, stiff foods - shearing teeth: good for ductile (malleable) foods \*human/ape postcanines good for grinding brittle, stiff foods

Question 27

Diphyodonty

Answer 27

- having baby and then adult teeth - deciduous human dental formula: 2.1.2 \*no molars in babies, premolars look like molars \*20 baby teeth vs 32 adult teeth -roots send signals for baby teeth to disintegrate, adult enamel pushes up

Question 28

Odontoclasts

Answer 28

-cells responsible for root resorption

Question 29

TMJ

Answer 29

- temporomandibular joint - glenoid fossa ligments: sphenomandibular, lateral, TMJ capsule, stylomandibular, articular disc

Question 30

TMJ Movements

Answer 30

depression/elevation: TMJ rotation up and down retraction/protraction: TMJ sliding anterior/posterior Bennett Shift: medial-lateral shift

Question 31

What are the four masticatory muscles?

Answer 31

- Temporalis - Masseter - Medial Pterygoid - Lateral Pterygoid

Question 32

Temporalis

Answer 32

Attachment: lateral crania, coronoid process Action: elevates mandible Innervation: CN V³

Question 33

Masseter

Answer 33

Attachment: zygomatic arch, ramus, mandibular angle Actions: elevates mandible, protraction, medio-lateral shifts Innervation: CN V³

Question 34

Medial Pterygoids

Answer 34

Attachments: sphenoid lateral pterygoid plate, ramus, mandibular angle Actions: elevates mandible, protraction, medio-lateral shifts Innervation: CN V³

Question 35

Medial-Lateral Movement

Answer 35

-requires activation of the masseter on one side and the medial pterygoid on the other side

Question 36

Lateral Pterygoid

Answer 36

Attachments: sphenoid lateral pterygoid plate, TMJ, neck of the condyle Action: protraction Innervation: CN V³