Oral Function - Muscles Flashcards
mandibular muscles
muscles of mastication
- Masseter
- Temporalis
- Lateral Pterygoid
- Medial Pterygoid
origin of masseter
zygomatic arch
insertion of masseter
lateral surface and angle of mandible
action of masseter
elevates the mandible (closing the jaw)
masseter in patients with clenching habit
tender
examining masseter
Place one finger intra-orally and the other on the cheek
origin of temporalis
floor of temporal fossa
insertion of temporalis
coronoid process and anterior border of ramus
action
elevates and retracts the mandible
- closing the jaw and retraction
temporalis is tender in patients who have….
bruxist habit
clenching and grinding teeth at night - parafunction
examining temporalis
Palpate its origin by asking the patient to clench the teeth together, because it is difficult to palpate the insertion area.
Digital palpation is performed between the superior and inferior temporal lines just above the ear, extending forwards towards the supra-orbital region
origin of lateral pterygoid
from the lateral surface of the lateral pterygoid plate
insertion of lateral pterygoid
anterior border of the condyle and intra-articular disc via two independent heads
- superior and inferior heads so 2 points of insertion
clinically important
inferior (top) belly of the lateral pterygoid attaches where
to the head of the condyle
the superior belly of the lateral pterygoid attaches where
into the intra-articular disc
jaw click is a sign of
spasm of lateral pterygoid
Tense pull disc = click
Limited mouth opening - improves with day and click will disappear
function of lateral pterygoid
protrudes and laterally deviates the mandible and the inferior head functions with the mandibular depressors during openings.
Lateral movement and opening of jaw
what does clenching and grinding do to the lateral pterygoid
clenching and grinding wears muscle out
as lateral deviation of the jaw as well as opening
- Physiotherapy or splint can reduce load on muscle
examining lateral pterygoid
Not accessible to manual palpation
Best examined by recording its response to resisted movement.
- Give idea on the muscle
There is a good correlation between the resisted movement test and the muscle being tender to palpation.
Test – try to open jaw and clinician pushes upwards, jaw move to one side and you push it the other way.
- Problem is causes pain
origin of medial pterygoid
deep head
- medial surface of lateral pterygoid plate
superficial head:
- tuberosity of maxilla
insertion of medial pterygoid
medial surface of angle of mandible
Masseter is from the lateral side.
- Together they hold the jaw like a swing
action of medial pterygoid
elevates and assists in protrusion of the mandible
examination of medial pterygoid
Because of the location of the medial pterygoid, on the inside of the jaw, this muscle is not available for palpation.
- It also does not respond well to resistive movement tests.
Therefore, unfortunately, there is no reliable way of examining this muscle.
following an injection, patient was unable to open the mouth fully on the following day.
which muscle was accidentally hit by the needle?
ID block coming from inside
- Inserted into area in cheek
- Medial pterygoid affected as from the inside
Try to avid bulk/mass of muscle when inject
Bone should be contacted to ensure correct position within the pterygomandibular triangle and not t hit soft tissues.
Hitting this muscle by the needle accidentally might cause “trismus”
2 movements of the TMJ
rotation
translation
rotation of TMJ
initial opening
hinge movement
translation
wider opening
Protrusive or Retrusive Movements
- 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
Posselt’s Envelope
full TMJ movement
- 2 movement of TMJ - rotation and translation
- Chart represents the border movements of the jaw/mandible
Important for prosthetics dentistry
Posselt’s Investigation (1953)
65 fit & healthy dental students - Age 20 -29 - 2 or fewer missing posterior teeth - No present dental disease 1 Cadaver
Graphical recordings in Occlusal & Sagittal plane + profile radiography
average maximum biting/clenching forces between molars
200-700N on average
varies between teeth and people
- Forces of 1200-1500N reported in some groups (Eskimo)
- ‘World record’ is >4300N
‘psychological’ factors that impact maximum biting/clenching forces
Fear of tooth fracture when maximum forces are used
- This could limit maximum biting force recorded
Exceed capacity = tooth splits
physical factors affecting maximum biting force
Muscle mass
- Bigger muscles = larger forces
- Parafunction (Bruxism)
(Hypertrophic masseter muscle due to excessive use; Asymmetrical face shape)
only Unilateral chewing (wrong should be bilateral – assess, to avoid muscle effect)
type I muscle fibres
slow, low forces
type II muscle fibres
fast stronger forces
sub types muscle fibres
IIA, IIX, IIB
predominant muscle fibre type in jaw
varies depending on jaw morphology and diet
muscle fibre type in people with ‘squarer’ jaws
more Type II fibres and can generate stronger bite forces
where is the greatest bite force generated?
between the 1st molars
posterior teeth
why is the greatest bite force generated between the 1st molars?
Position relative to TMJ and muscles
- Molars are nearer the force generating muscles and the fulcrum (TMJ)
Root area (PDL support)
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 away from the hinge you will have to use extra force trying to break the nut open; maybe not even cracking it.
- Whereas, if you place the nut close to the hinge, the nut cracks easily with only a modest amount of force. .
Further back = closer to hinge = less force needed (posterior teeth)
what do the suprahyoid and infrahyoid muscles do?
involved in mastication too
- stabilise when you chew
4 suprahyoid muscles
- Digastric
- Mylohyoid
- Geniohyoid
- Stylohyoid
4 infrahyoid muscles
- Sternohyoid
- Omohyoid
- Thyrohyoid
- Sternothyroid
infrahyoid muscles a.k.a
‘strap’ muscles
what suprahyoid muscles act as jaw depressors when the hyoid bone is fixed?
- Digastric *
- Mylohyoid *
- Geniohyoid *
contraction
2 types of tongue muscle
intrinsic
extrinsic
intrinsic tongue muscles role
alter shape
3 types of intrinsic tongue muscle
longitudinal
vertical
transverse
extrinsic tongue muscle role
alter shape and position
4 extrinsic tongue muscles
- genioglossus
- hypoglossus
- palatoglossus
- styloglossus
facial muscles role in mastication
Help to control food bolus and prevent spillage
- Role in keeping the bolus in the centre of the oral cavity
2 facial muscles that have a key role in mastication
- Orbicularis oris
- Buccinator
