Oral Functions - Muscles

Question 1

What are the muscles of mastication

Answer 1

Temporalis
Masseter
Medial pterygoid
Lateral 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 the mandible

Question 3

How should the masseter be examined

Answer 3

Place one finger intra-orally and two fingers on the cheek to palpate the muscle

Question 4

What is the origin, insertion and action of the temporalis

Answer 4

Origin - floor of temporal fossa
Insertion - coronoid process and anterior border of ramus
Action - elevates and retracts the mandible

Question 5

Which patients may have a tender masseter

Answer 5

Those with a clenching habit

Question 6

Which patients may have a tender temporalis

Answer 6

Those with a bruxism habit

Question 7

How is the temporalis examined

Answer 7

Palpate its origin by asking patient to clench teeth

Question 8

What is the origin, insertion and function of the medial pterygoid

Answer 8

Origin - medial surface of lateral pterygoid plate
Insertion - medial surface of angle of mandible
Action - elevated and assists in protrusion of the mandible

Question 9

How is the medial pterygoid examined

Answer 9

Muscle cannot be palpated so there is no reliable way of examining the muscle

Question 10

What is the origin, insertion and function of the lateral pterygoid

Answer 10

Origin - lateral surface of the lateral pterygoid plate
Insertion - anterior border of the condyle and intra-articular disc via two independent heads
Function - protrudes and laterally deviates the mandible and the inferior head functions with the mandible depressors during openings

Question 11

What does the lateral pterygoid plate attach and insert to

Answer 11

Inferior belly attaches to the head of the condyle

Superior belly inserts into the intra-articular disc

Question 12

How is the lateral pterygoid examined

Answer 12

By recording its response to resisted movement

Ask patient to move jaw to side or open mouth and resist it

Question 13

What is the maximum biting force of teeth

Answer 13

In molars - between 200 and 700N

Question 14

What factors affect maximum biting force

Answer 14

Psychological - fear of fracture
Muscle mass - bigger muscles mean larger forces
Parafunction (bruxism)

Question 15

What are the movements of the TMJ

Answer 15

Rotation - initial opening of 20mm

Translation - wider opening

Question 16

Describe rotation of the TMJ

Answer 16

Rotation of the condyle around the hinge

Question 17

Describe translation of the mandible

Answer 17

As the mandible moves during protrusion, both condyle leave their fossa and move forward along the articular eminences
When the mandible retrudes, both condyle leave the eminences and move back into their respective fossae

Question 18

Which muscle fibre types are found in the jaw and which is more common

Answer 18

Type I - slow, low forces
Type II - fast, stronger forces
Sub-types - IIA, IIX, IIB
Predominant type varies depending on jaw morphology and diet

Question 19

What are the suprahyoid muscles

Answer 19

Digastric
Mylohyoid
Geniohyoid
Stylohyoid

Question 20

What are the infrahyoid muscles

Answer 20

‘Strap’ muscles
Sternohyoid
Omohyoid 
Thyrohyoid
Sternothyroid

Question 21

When the hyoid bone is fixed by contraction of the infrahyoids, which muscles act as depressors

Answer 21

Digastric
Mylohyoid
Geniohyoid

Question 22

What are the intrinsic tongue muscles and what are their function

Answer 22

Longitudinal, vertical and transverse

Alter shape of the tongue

Question 23

What are the extrinsic muscles of the tongue and what are their function

Answer 23

Genioglossus
Hyoglossus
Palatoglossus
Styloglossus
Alter shape and position of the tongue