Mastication

Question 1

Is matiscation voluntary or involunatary? conscious or unconscious?

Answer 1

opening your mouth depressing your jaw is voluntary. But the chewing is patterned into the brain stem.
It is voluntary but it begins to become involuntary. When you’re not paying attention to it it starts going again.
Chewing can be conscious but most times we don’t think about it.

BECAUSE OF THIS IF YOU CHANGE ANYTHING IN THE ORAL CAVITY YOU CAN DAMAGE SOMETHING BECAUSE YOUR PATTERN GENERATORS ARE GOING TELLING YOU HOW TO CHEW.

Question 2

what is a persons chewing pattern like?

Answer 2

It’s different for everyone but similar as you chew for each individual person.

Question 3

What are the four main muscles of mastication?

Answer 3

medial pterygoid, lateral pterygoid, temporalis, masseter

Question 4

What elevates the mandible?

Answer 4

masseter, medial pterygoid, temporalis

these are much stronger than the opening muscle

Question 5

What muscle depresses the mandible?

Answer 5

lateral pterygoid. accessory muscles: mylohyoid, digastric (opening)

Question 6

What muscles protrude the mandible and do not laterally deviate?

Answer 6

masseter, medial pterygoid

Question 7

What muscles protrude the mandible and laterally deviate?

Answer 7

lateral pterygoid

Question 8

What muscle retrudes the mandible and is involved in lateral deviation?

Answer 8

temporalis

Question 9

so what two muscles are involved in lateral deviation?

Answer 9

lateral pterygoid, temporalis

Question 10

So what is the main movement in the jaw? what are two other types of movement?

Answer 10

. Main movement is a rhythmic opening and closing - (separation & apposition) of the jaws (depression and elevation)
closing muscles = masseter, temporalis, medial pterygoids)
Opening muscles = lateral pterygoids, digastric, mylohyoid

2. Also small protrusive and retrusive movements
3. Lateral deviation (extrusion) used in grinding

Question 11

What is the so-called “Bennett” movement?

Answer 11

Lateral movement results in lateral displacement of condoyles -
the so-called “Bennett” movement

In most individuals, all of these movements results in chewing that is mainly (approx) symmetrical

Question 12

In about one third of normal chewing strokes, how is the bolus of food chewed? where is the remained concentrated?

Answer 12

Bolus of food only chewed equally on both sides in about one third of normal chewing strokes
Remainder concentrated on one side (primarily left in most patients) although bolus transferred to other side after several strokes

Question 13

What are three factors that affect symmetrical chewing patterns?

Answer 13

Factors that affect symmetrical chewing patterns
sore tooth
inflamed periodontal ligament
missing teeth

Question 14

what’s the most common pattern for chewing?

Answer 14

1. Food initially cut/torn by incisors & canines
2. Broken up into smaller pieces in premolar/anterior molar regions
3. Comminuted (grinding action) by the molars (includes lateral movements)

Question 15

does the mandible move a constant speed or force?

Answer 15

no

Question 16

What are the two main phases of chewing? what are the sub phases to make four total phases of chewing?

Answer 16

opening versus closing.

SLOW OPENING (SO)
FAST OPENING (FO)
FAST CLOSING (FC) 
SLOW CLOSING (POWER STROKE)    SC (PS)

Question 17

Chewing cycles differ with species but patterns are similar within species. WHY?

Answer 17

Chewing patterns will differ depending on whether you are doing a lot of grinding (herbivore) vs. shearing (omnivore) as well as the position of the tongue (the food eaten likely directs the chewing cycle pattern)

Question 18

Which muscles are active during each phase of chewing ( beginning at the point of minimal opening) ?

Answer 18

SO = __mylohyoids, digastric, lat. pterygoid____________

FO = ___mylohyoid, digastrics, lat. Pterygoids. __________

FC= __med. Pterygoids, masster, temporalis____________

PS = __masseter, temporalis, med. Pterygoids. __________

Question 19

during chewing, when does the mandible reach its greatest speed?

Answer 19

toward the end of opening and beginning of closing

Question 20

When do chewing cycles (or cycle time) vary?

Answer 20

Chewing cycles vary depending on what is being ingested
Cycle time (especially the opening phase) is increased for tough sticky foods
Eg., 	carrots = 0.58 sec
	peanut butter = 0.77 sec

Question 21

When else does the cycle time vary?

Answer 21

Cycle time also varies as we comminute the food in the oral cavity.
ie., the time/forces used at the beginning of the cycle for chewing a piece of crunchy carrot are not the same as those at the end (just before we swallow it)

Question 22

What changes to make the time/forces used at the beginning of the cycle for chewing a piece of crunchy carrot not the same as those at the end?

Answer 22

the mechanoreceptor activity will change

Question 23

For opening and closing muscles the RA/SA fire when?

Answer 23

RA/SA:
Fire when teeth in contact,
may still
fire at any time there is input

Question 24

For closing, are the opening muscles inhibited? For opening are the closing muscles inhibited?

Answer 24

Opening muscles are at 0 when closing, so they are not inhibited. The closing muscles are hyperpolarized or below zero and are therefore inhibited. The closing muscles are inhibited. This is because the closing muscles are very strong and will overried what is happening with the opening muscles.

Question 25

What is the direct sequence of action for opening and closing?

Answer 25

Also there is a direct sequence of activation

1. Opening - mylohyoids, digastrics, lat.pterygoids
2. Closing - med. Pterygoids, masseter, temporalis

Question 26

What receptors modulate the output from the chewing centers of the CNS with respect to the forces that are eliminated by the mandible?

Answer 26

Feedback control from the sensory receptors such as pulpal receptors, periodontal receptors, receptors in the surrounding bone and soft tissue and even TMJ receptors plays a role in modulating the output from the chewing centres of the CNS with respect to the forces that are elicited by the mandible

Question 27

What are the normal forces of mastication for north americans?

Answer 27

Normal forces are in the 7 - 15 kg per tooth load
Total load developed can be much greater
Inuit population - 50 - 150 kg per tooth

Question 28

Where is the force of biting hte greatest?

Answer 28

your third molar has a little less but it is highest on your second molar and decreases until you get to your incisors.

Question 29

what factors affect forces of mastication?

Answer 29

pain, exercise, diet (strength)

pain - you get inhibition to bite down
exercise - you can train people who have had strokes for example to chew.

Question 30

What are the muscles of mastication controlled by?

Answer 30

1. the trigeminal motor nucleus (V)
2. the sensory nuclei –
   
   • mesencephalic;
   • main sensory nucleus
   • descending spinal trigeminal nucleus
3. the reticular formation - pattern generators (in pons) + higher centers

Question 31

What is the jaw closing reflex?

Answer 31

The Jaw Closing reflex (jaw-jerk). MONOSYNAPTIC.
Tap chin = stretch muscle spindle = afferent information
to cell bodies in mesencephalic nucleus = monosynaptic
synapse on alpha motor neuron which closes the jaw

Question 32

What is the jaw opening reflex?

Answer 32

Stimulate intraoral mucosal receptors –> afferent info
to trigeminal nucleus–> synapse on interneuron –>
activate alpha motor neuron (digastric)–> open jaw

Question 33

For smooth rhythmic chewing patterns where do these come from?

Answer 33

These all form the substrates for smooth rhythmic chewing patterns
sensory receptors - reflexes
pattern generators (in pons)
higher centers - cerebral cortex, basal ganglia, hypothalamus, cerebellum