Oral functions - muscles

Question 1

What are the 4 muscles of mastication

Answer 1

• temporalis
• masseter
• lateral pterygoid
• medial pterygoid

Question 2

what is the origin of the masseter

Answer 2

zygomatic arch

Question 3

what is the insertion of the masseter

Answer 3

lateral surface and angle of mandible

Question 4

what is the action of the masseter

Answer 4

elevates mandible

Question 5

how do you examine the masseter?

Answer 5

place one finger intra-orally and the other on the cheek

Question 6

what is the origin of the temporalis

Answer 6

floor of the temporal fossa

Question 7

what is the insertion of the temporalis

Answer 7

coronoid process and anterior border of ramus

Question 8

what is the action of the temporalis

Answer 8

elevates and retracts mandible

Question 9

how do you examine the temporalis

Answer 9

palpate its origin by asking the patient to clench the teeth together

digital palpation is performed between the superior and inferior temporal lines just above the ear, extending forwards towards the supra-orbital region

Question 10

why might the temporalis be tender

Answer 10

patients with a bruxist habit

Question 11

why might the masseter be tender

Answer 11

patients with a clenching habit

Question 12

origin of the lateral pterygoid

Answer 12

from the lateral surface of the lateral pterygoid plate

Question 13

insertion of the lateral pterygoid

Answer 13

anterior border of the condyle and intra-articular disc via two independent heads

Question 14

function of the lateral pterygoid

Answer 14

protrudes and laterally deviates the mandible and the inferior head functions with the mandibular depressors during openings

Question 15

where does the inferior belly of the lateral pterygoid attach to

Answer 15

the head of the condyle

Question 16

where does the superior belly of the lateraly pterygoid insert into

Answer 16

the intra articular disc

Question 17

how can we examine the lateral pterygoid muscle

Answer 17

by recording its response to resisted movement

there is good correlation between the resisted movement test and the muscle being tender to palpation

Question 18

origin of the medial pterygoid

Answer 18

deep head: medial surface of lateral pterygoid plate

superficial head: tuberosity of maxilla

Question 19

insertion of the medial pterygoid

Answer 19

medial surface of angle of mandible

Question 20

action of the medial pterygoid

Answer 20

elevates and assists in protrusion of the mandible

Question 21

how can we examine the medial pterygoid

Answer 21

not possible

not available for palpation and doesn’t respond well to resistive movement tests

Question 22

what are the movements of the TMJ

Answer 22

rotation - initial opening

translation - wider opening

Question 23

what type of movement does the TMJ use to achieve rotation

Answer 23

hinge movement

Question 24

what type of movement does the TMJ use to achieve translation

Answer 24

protrusive or retrusive movements

Question 25

describe the TMJ movement of translation

Answer 25

as the mandible moves during protrusion, both condyles leave their fossae and move forward along the articular eminences

when the mandible retrudes, both condyles leave the eminences and move back into their respective fossae

Question 26

who worked out the mandibular movements

Answer 26

Ulf Posselt (1953)

Question 27

what is a normal maximum biting/ clenching force?

Answer 27

varies between teeth
maximum between molars (200-700N)

forces of 1200-1500N reported in some eskimo groups

Question 28

what are factors related to maximum biting force

Answer 28

• fear of tooth fracture when maximum forces are used
• muscle mass (bigger muscles, larger forces)
• parafunction (Bruxism)

Question 29

what are the characteristics of the different muscle fibres types

Answer 29

Type 1
- slow, low forces

Type 2
- fast, stronger forces

Sub-types
- predominant fibre type varies, depending on jaw morphology, diet

Evidence that people with ‘squarer’ jaws have more type 2 fibres and can generate stronger bite forces

Question 30

which teeth generate the greatest bite forces

Answer 30

1st molars

Question 31

why do 1st molars generate the greatest bite force

Answer 31

• position relative to the TMJ and muscles (molars are nearer the force generating muscles and the fulcrum (TMJ)
• root area (PDL support)

Question 32

what kitchen utensil can your jaw be compared to and why

Answer 32

a nutcracker

Your jaw joint would be where the hinge of the nutcracker is.

Your front teeth would be at the ends of the handles and your molars would be close to the hinge itself.

If you place the nut far awayfrom the hinge you will have to use extra force trying to break the nut open; maybe not even cracking it.Whereas, ifyou place the nut close to the hinge, the nut cracks easily with only a modest amount of force

Question 33

what happens when the hyoid jaw is fixed

Answer 33

the suprahyoid muscles (digastric, mylohyoid, geniohyoid and stylohyoid) muscles act as jaw depressors

Question 34

what muscles fix the hyoid bone by contraction

Answer 34

infrahyoids
(strap muscles)
- sternohyoid
- omohyoid
- thyrohyoid
- sternothyroid

Question 35

what do the intrinsic tongue muscles do

Answer 35

alter shape

Question 36

what do the extrinsic tongue muscles do

Answer 36

alter shape and position

Question 37

what are the instrinsic tongue muscles like

Answer 37

longitudinal, vertical and transverse

know positions

Question 38

what are the names of the extrinsic tongue muscles

Answer 38

• genioglossus
• hyoglossus
• palatoglossus
• styloglossus

(know positions)

Question 39

what are the key facial muscles used in eating and what do they do

Answer 39

• orbicularis oris
• buccinator

help to control food bolus and prevent spillage