Oral functions - muscles

Question 1

what are the muscles involved in mastication?

4

Answer 1

masseter
temporalis
lateral pterygoid
medial pterygoid

Question 2

what is the origin, insertion and action of the masseter?

Answer 2

origin: zygomatic arch
insertion: lateral surface and angle of mandible
action: elevates mandible

Question 3

how do you examine the masseter?

Answer 3

place one finger intra-orally and the other on cheek
tender in patients that have a clenching habit

Question 4

what is the origin, insertion and action of the temporalis?

Answer 4

origin: floor of temporal fossa
insertion: coronoid process adn anterior border of ramus
action: elevates and rettracts the mandible

Question 5

how do you examine the temporalis?

Answer 5

palpate origin by asking pt to clench teeth
palpate between superior and inferior temporal lines just above the ear, extending towards the ssupra-orbital region
tender in pts with a bruxist habit

Question 6

what is the origin, insertion and function of the lateral pterygoid?

Answer 6

origin: lateral surface of the lateral pterygoid plate
insertion: anterior border of the condyle (inferior head) and intra-articular disc (superior head)
function: protrudes and laterally deviates the mandible and inferior head functions with the mandibular depressors during openings

Question 7

how do you examine the lateral pterygoid?

Answer 7

not accessible by manual palpitation
best examined by recording its response to resisted movement

Question 8

what is the origin, insertion and action of the medial pterygoid?

Answer 8

origin: medial surface of lateral pterygoid plate (deep head) and tuberosity of maxilla (superficial head)
insertion: medial surface of angle of mandible
action: elevates and assists in protrusion of mandible

Question 9

how do you examine the medial pterygoid?

Answer 9

no accessible to manual palpitation as inside of jaw does not respond well to resistive movement tests

Question 10

how would you ensure correct position when performing an inferior alveolar nerve block? what can incorrect performance lead to?

Answer 10

bone should always be contacted to ensure correct position within the pterygomandibular triangle and not hit soft tissues
hitting medial pterygoid muscle might cause trismus (restriction of movement of jaw)

Question 11

describe the movement of the TMJ

Answer 11

rotation - initial opening (first 20mm), hinge movement
translation - wider opening

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

Question 12

what factors affect maximum bite force?

Answer 12

fear of tooth fracture
muscle mass - bigger muscles = larger forces
parafunction (bruxism) - use of a musclce outside their main function

Question 13

why are molars the strongest teeth?

Answer 13

positioned closest to the TMJ and muscles (fulcrum) so less force is required

Question 14

what are the different types of muscle fibres?

3

Answer 14

type 1 - slow, low forces
type 2 - fast, stronger forces
subtypes (2A, 2X, 2B) - predominant fibre type varies, depending on jaw morphology, diet

Question 15

what are the suprahyoid muscles?

4

Answer 15

• digastric
• mylohyoid
• geniohyoid
• stylohyoid

when the hyoid bone is fixed, by contraction of the infrahyoids, the digastric, mylohyoid and geniohyoid muscles act as jaw depressors

Question 16

what are the infrahyoid ‘strap’ muscles?

4

Answer 16

• sternohyoid
• omohyoid
• thyrohyoid
• sternothyroid

Question 17

what do the intrinsic tongue muscles do? what muscles does it include?

Answer 17

alter shape of tongue
* longitudinal
* vertical
* transverse

Question 18

what do the extrinsic tongue muscles do? what muscles does it include?

Answer 18

alter shape and position of tongue
* genioglossus
* hyoglossus
* palatoglossus
* styloglossus

Question 19

what muscles help to control food bolus and prevent spillage?

Answer 19

buccinator
orbicularis oris