Oral function muscles Flashcards
What are the 4 essential muscles for mastication (mandibular muscles)?
- Masseter
- Temporalis
- Lateral pterygoid
- Medial pterygoid
What is the ‘origin’ of the masseter muscle?
- The zygomatic arch
What is the ‘insertion’ of the masseter muscle?
- The lateral surface and angle of the mandible
What is the ‘action’ of the masseter muscle?
- Elevates the mandible
How would you examine the masseter muscle?
- Place one finger intra-orally and the other on the cheek
In which patients would the masseter muscle be tender?
- In patients who have a clenching habit
What is the ‘origin’ of the temporalis muscle?
- The floor of the temporal fossa
What is the ‘insertion’ of the temporalis muscle?
- The coronoid process and anterior border of the ramus
What is the ‘action’ of the temporalis muscle?
- Elevates and retracts the mandible
In which type of patient will the temporalis muscle be tender?
- Patients who have a Bruxism habit
How would you examine the temporalis muscle?
- 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
What is the ‘origin’ of the lateral pterygoid muscle?
- From the lateral surface of the lateral pterygoid plate
What is the ‘insertion’ of the lateral pterygoid muscle?
- Anterior border of the condyle and intra-articular disc via two independent heads
What is the ‘function’ of the lateral pterygoid muscle?
- Protrudes and laterally deviates the mandible and the inferior head functions with the mandibular depressors during opening
Where does the inferior belly of the lateral pterygoid attach to?
- The head of the condyle
Where does the superior belly of the lateral pterygoid insert into?
- The intra-articular disc
If someone has a clicking TMJ. Which muscle has been affected?
- Spasm of the lateral pterygoid which pulls on joint
Can you examine the lateral pterygoid muscle by manual palpation?
- No
How would you examine the lateral pterygoid muscle?
- Best examined by recording its response to resisted movement
- There is a good correlation between the resisted movement test and the muscle being tender to palpation
What is the ‘origin’ of the medial pterygoid?
- Deep head; medial surface of the lateral pterygoid plate
- Superficial head: tuberosity of maxilla
What is the ‘insertion’ of the medial pterygoid?
- Medial surface of the angle of the mandible
What is the ‘action’ of the medial pterygoid?
- Elevates and assist in protrusion of the mandible
Is the medial pterygoid muscle able to be manually palpated?
- No, because of the location of the medial pterygoid, on the inside of the jaw, this muscle in not available for palpation
Can the medial pterygoid muscle be examined by resisted movement tests?
- No, it does not respond well to these
Hoe can we examine the medial pterygoid muscle?
- Unfortunately there is no reliable way of examining this muscle
Following an La injection, your patient was unable to open their mouth fully the following day. Which muscle was accidently hit by your needle?
- The medial pterygoid muscle
Hitting the medial pterygoid muscle accidently when giving an ID block might cause ‘trismus’. What does this mean?
- Inability to open mouth as wide as should be able to
- Limited mouth opening
What are the 2 movements of the TMJ?
- Rotation - initial movement
- Translation - Wider opening
What kind of movement is the ‘rotation - initial opening’ of the TMJ?
- A hinge movement
The translation movement of the TMJ causes a wider opening on the mouth. These can be protrusive or retrusive movements. How does this occur?
- 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
What is the name for the chart that represents the border movements of the jaw?
- Posselt’s envelope
What are the general maximum biting forces of molars?
200-700N
What is an example of a psychological factor in relation to max biting forces?
- Fear of tooth fracture when maximum forces are used
- This could limit the max biting force recorded
In relation to muscle mass, how does this affect the max biting force of an individual?
- Bigger muscles leads to larger forces
What is an example of a parafunction in relation to max biting forces and muscle mass of the jaw?
- Bruxism
What are the characteristics of Type I muscle fibres? (2 points)
- Slow, low forces
What are the characteristics of Type II muscle fibres? (2 points)
- Fast, strong forces
What are different sub-types of type 2 muscle fibres? (3 points)
- IIA, IIX, IIB
- Predominant fibre type varies, depending on the jaw morphology and diet
What is there evidence of with people who have square jaws?
- Tend to have more Type II fibres and can generate stronger biting forces
Why ate anterior teeth weaker than posterior teeth? (3 points)
- Smaller surface area of root
- Posterior are nearer the centre of the force
- Occlusal surface is larger
Which teeth generate the greatest biting forces between them and why?
- 1st molars
- Position relative to TMJ and muscles (molars are nearer the force generating muscles and the fulcrum)
- Root area large (PDL support)
The Suprahyoid and the Infrahyoid muscles are also muscles involved in mastication. What do they do?
- Stabalise the hyoid bone
What are the 4 suprahyoid muscles?
- Digastric*
- Mylohyoid*
- Geniohyoid*
- Stylohyoid
- When the hyoid bone is fixes, by the contraction of the infrahyoid’s, the starred muscles act as jaw depressors
What are the 4 infrahyoid (‘strap’) muscles?
- Sternohyoid
- Omohyoid
- Thyrohyoid
- Sternothyroid
The intrinsic muscles of the tongue alter the shape of the tongue. What are the names of the intrinsic tongue muscles? (3 points)
- Longitudinal
- Vertical
- Transverse
The extrinsic muscles of the tongue alter the shape and position of the tongue. What are the names of the extrinsic tongue muscles? (4 points)
- Genioglossus
- Hyoglossus
- Palatoglossus
- Styloglossus
Which 2 facial muscles help to control the food bolus and prevent spillage out of the mouth?
- Orbicularis oris
- Buccinator
