oral function - muscles

Question 1

what are mandibular muscles

Answer 1

a different name for muscles of mastication

- masseter, temporalis, medial pterygoid and lateral pterygoid

Question 2

what is misleading about the 4 muscles masseter, temporals, medial pterygoid and lateral pterygoid being named muscles of mastication?

Answer 2

because there are many other muscles involved in mastication

Question 3

what is the origin of the masseter

Answer 3

zygomatic arch

Question 4

what is the insertion of the masseter

Answer 4

lateral surface and angle of the mandible

Question 5

what is the action of the masseter

Answer 5

elevates mandible

Question 6

how do you examine the masseter

Answer 6

• it is tender in patients with a clenching habit

- place one finer intra-orally and the other on the cheek (zygomatic arch) and get patients to clench

Question 7

what is the origin of the temporalis

Answer 7

floor of the temporal fossa

Question 8

what is the insertion of the temporalis

Answer 8

coronoid process and anterior border of ramus

Question 9

what is the action of the temporalis

Answer 9

elevates and retracts the mandible

Question 10

how can you examine the temporalis

Answer 10

• it can be tender in patients with a bruxism habit
• examine the origin not insertion
• palpate the origin by asking the patient to clench their teeth together
• digital palpation is performed between the superior and inferior temporal lines just above the ear, extension forwards towards the supra-orbital region

Question 11

what is the origin of the lateral pterygoid

Answer 11

from lateral surface of the lateral pterygoid plate

Question 12

what is the insertion of the lateral pterygoid

Answer 12

anterior border of the condyle and intra-articular disc via two independent heads (superior and inferior heads)

Question 13

what is the function of the lateral pterygoid

Answer 13

• protrudes and laterally deviates the mandible and the inferior head functions with the mandibular depressions during openings
• lateral movement and opening of the jaw (depression of the jaw)

Question 14

where does the inferior belly of the lateral pterygoid attach

Answer 14

to the head of the condyle

Question 15

where does the superior belly of the lateral pterygoid go

Answer 15

inserts into the intra-articular disc

Question 16

why do those who grind their teeth overnight sometimes wake up unable to open their mouth fully

Answer 16

because they have ‘tired out’ the lateral pterygoid muscle

Question 17

what is most often the cause of a ‘click’

Answer 17

spasm of the lateral pterygoid muscle

Question 18

how can you examine the lateral pterygoid

Answer 18

• it is not accessible to palpitation as its inside
• nest examined by recording its response to resisted movement
• there is good correlation between resisted movement test and muscle being tender to palpation
• if it hurts or can’t resist movement, then muscle is not right

Question 19

what is the origin of the medial pterygoid

Answer 19

deep head - medial surface of the lateral pterygoid plate

superficial head - tuberosity of maxilla

Question 20

what is the insertion of the medial pterygoid

Answer 20

medial surface of angle of the mandible

Question 21

what is the action of the medial pterygoid

Answer 21

elevates and assists in protrusion of the mandible

Question 22

why can’t the medial pterygoid be palpated

Answer 22

because it sits on the inside of the jaw

Question 23

does the medial pterygoid respond well to resistive movement tests

Answer 23

no

Question 24

is there any reliable way of examining the medial pterygoid

Answer 24

no

Question 25

what muscles are near the angle of the mandible

Answer 25

- masseter is on the lateral side | - medial pterygoid is on the mesial side

Question 26

what can cause trismus

Answer 26

- if the medial pterygoid muscle is accidentally hit when doing an injection - occurs when carrying out inferior alveolar nerve block (ID block) - causes inability to open mouth to the same extent as before

Question 27

what should be hit when doing an ID block

Answer 27

bone, ensures correct position within the pterygomandibular triangle and not hit the soft tissues

Question 28

what are the 2 movements of the TMJ

Answer 28

- rotation (initial opening) | - translation (wider opening)

Question 29

what is rotation of the TMJ

Answer 29

- 1st movement - hinge movement - rotates around the hinge axis

Question 30

what is translation of the TMJ

Answer 30

- 2nd movement - protrusive or retrusive movements - as mandible moves during protrusion, both condyles leave their fosse and move forward along the articular eminences - when mandible retrudes, both condyles leave eminences and move back into their respective fosse

Question 31

what is the outline of the movement of the TMJ called

Answer 31

the fossae envelope

Question 32

who founded the fossae envelope

Answer 32

Ulf Posselt in 1953 | - he got graphical recordings in the occlusal and sagittal plane for the movement and all had the same shape of envelope

Question 33

what is the maximum biting/clenching forces

Answer 33

- varies between teeth - maximum between 200-700N in molars (forces of 1200-1500N reported in Eskimo's and world record is 4300N)

Question 34

how can psychological factors affect biting/clenching forces

Answer 34

- fear of tooth fracture when max forces are used | - limits max forces used

Question 35

what other factors can affect maximum biting/clenching forces

Answer 35

- muscle mass = bigger muscles cause larger forces - parafunction = bruxism, can fracture tooth with high occlusal forces and can get hypertrophic masseter muscle from excessive use

Question 36

what are the muscle fibre types

Answer 36

- type 1 = slow, low forces - type 2 = fast, stronger forces - sub types = IIA, IIX, IIB

Question 37

what is the most predominant fibre type

Answer 37

- predominant fibre type varies depending on jaw morphology, diet etc - there is evidence however that people with squarer jaws have more type II fibres and can generate stronger bite

Question 38

where is greatest biting forces generated

Answer 38

between 1st molars

Question 39

why do 1st molars have greatest biting force

Answer 39

- they are closer to the muscle generating the force and the fulcrum so - this means that only a small amount of force is needed here to break food, if you bit food at the front of the mouth, a much larger force would be needed which could then fracture the tooth

Question 40

what support does the root area of a tooth have

Answer 40

PDL support

Question 41

what are some other muscles in mastication

Answer 41

- supra hyoid - infra hyoid - hyoid bone - tongue muscles - facial muscles

Question 42

what are the supra hyoid muscles

Answer 42

- digastric - mylohyoid - geniohyoid - stylohyoid

Question 43

what are the infra hyoid muscles

Answer 43

- 'strap muscles' - sternohyoid - omohyoid - thyrohyoid - sternothyroid

Question 44

what happens with the hyoid bone

Answer 44

- when the hyoid bone is fixed by contraction of the infra hyoids, the supra hyoids (apart from the stylohyoid) act as depressors

Question 45

what are the 2 types of tongue muscles

Answer 45

- intrinsic and extrinsic

Question 46

what are the intrinsic tongue muscles and what do they do

Answer 46

- longitudinal, vertical and transverse | - alter shape

Question 47

what are the extrinsic tongue muscles and what do they do

Answer 47

- genioglossus, hypoglossus, palatoglossus, styloglossus | - alter shape and position

Question 48

what is the main role of facial muscles

Answer 48

for expression

Question 49

what is an additional role of some of the facial muscles

Answer 49

keeps the blogs in the oral cavity

Question 50

which facial muscles keep the bolus in the oral cavity

Answer 50

- orbicularis oris | - buccinator