Mastication

Question 1

Function of incisors during mastication

Answer 1

Used to grab and cut food to bring into the oral cavity

Question 2

Function of canines during mastication

Answer 2

Piercing or tearing

Question 3

Function of premolars and molars during mastication

Answer 3

Grinding and reduction in size of food bolus

Question 4

Food classification overview

Answer 4

Food is classified based on the amount of reduction required- class 1 are most difficult to chew, class 2 are moderately easy, class 3 are most soft and need little to no mastication

Question 5

What are the categories mandibular movements are divided into?

Answer 5

Asymmetrical (side to side) vs symmetrical (depression, elevation, protrusion, retrusion)
Ipsilateral (movements on the same side) vs contralateral (movements on the opposite side)

Question 6

Describe protrusion

Answer 6

Largely controlled by contraction of inferior head of lateral pterygoid.
Also involves medial pterygoid and masseter muscle

Question 7

Describe retrusion

Answer 7

Largely controlled by contraction of inferior head of lateral ptergoid and posterior horizontal fibres of temporalis muscle

Question 8

Describe depression

Answer 8

Largely controlled by contraction of inferior head of lateral pterygoid and suprahyoid muscles

Question 9

Describe elevation

Answer 9

Contraction of anterior vertical fibres of temporalis muscle, masseter muscle and medial pterygoid

Question 10

Describe side to side movement

Answer 10

Contraction on one side only of the medial and lateral pterygoid muscles

Question 11

What is the envelope of motion?

Answer 11

Describes the initial incising in which the mandible opens and protrudes forward.

Question 12

What are the 3 main phases of mandibular movement?

Answer 12

1. Closing stroke
   Anterior teeth brought into contact with food (also called buccal phase)
2. Power stroke
   Food crushed between premolars and molars and reduced in size (intercuspal phase)
3. Opening stroke
   Mandible lowered and process starts again (lingual phase)

Question 13

What are the major salivary glands?

Answer 13

• Parotid gland
• Submandibular gland
• Sublingual gland

Question 14

What are the main functions of saliva?

Answer 14

• Food must be moist in order to be able to taste it, saliva facilitates this
• Saliva is antibacterial and also acts as a bicarbonate buffer protecting teeth from acidic environments
• Saliva initiates starch digestion due to salivary amylase

Question 15

Is saliva continuously produced?

Answer 15

Yes- there is a very low level of constant parasympathetic excitation keeping the oral cavity constantly moist

Question 16

What are the 2 categories of saliva production?

Answer 16

1. Simple, unconditional reflex: under control of chemoreceptors (smell or taste) and mechanoreceptors (e.g. placement of dental instruments in mouth)
2. Acquired, conditional reflex: Pavlov’s dogs

Question 17

Describe the role of the tongue in mastication

Answer 17

• Manipulates the food, repositions food onto premolars and molars
• Helps mix food and saliva to form a bolus
• Transports bolus to the back of the mouth for swallowing

Question 18

What controls the multitude of actions involved in mastication?

Answer 18

1. Rhythmic pattern generator in medulla oblongata (CNS)
2. Motor response causing coordinated contraction of muscles of mastication
3. Mandible moves
4. Teeth brought together
5. Sensory feedback loop (e.g. is food hard and needs to be chewed more)
6. Food forms soft bolus
7. Bolus swallowed

Question 19

Name 3 parafunctional tooth contacts

Answer 19

• Biting on hard objects (e.g. pens)
• Biting on soft objects (cheeks, lips)
• Jaw clenching/bruxism

Question 20

Describe the jaw jerk reflex

Answer 20

• Used to test CN V
• Chin tapped at a downward angle whilst mouth is slightly open
• Causes masseter muscle to contract and bring the mandible upwards

Monosynaptic reflex
(Very slight)

Question 21

Describe the jaw opening reflex

Answer 21

• Caused by mechanical or chemical stimuli
• If mouth is overloaded or tastes something bad the mandible opens so food can be expelled from the mouth

Polysynaptic reflex (more complex)