oral function - muscles Flashcards
what are mandibular muscles
a different name for muscles of mastication
- masseter, temporalis, medial pterygoid and lateral pterygoid
what is misleading about the 4 muscles masseter, temporals, medial pterygoid and lateral pterygoid being named muscles of mastication?
because there are many other muscles involved in mastication
what is the origin of the masseter
zygomatic arch
what is the insertion of the masseter
lateral surface and angle of the mandible
what is the action of the masseter
elevates mandible
how do you examine the masseter
- 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
what is the origin of the temporalis
floor of the temporal fossa
what is the insertion of the temporalis
coronoid process and anterior border of ramus
what is the action of the temporalis
elevates and retracts the mandible
how can you examine the temporalis
- 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
what is the origin of the lateral pterygoid
from lateral surface of the lateral pterygoid plate
what is the insertion of the lateral pterygoid
anterior border of the condyle and intra-articular disc via two independent heads (superior and inferior heads)
what is the function of the lateral pterygoid
- 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)
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 go
inserts into the intra-articular disc
why do those who grind their teeth overnight sometimes wake up unable to open their mouth fully
because they have ‘tired out’ the lateral pterygoid muscle
what is most often the cause of a ‘click’
spasm of the lateral pterygoid muscle
how can you examine the lateral pterygoid
- 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
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 angle of the mandible
what is the action of the medial pterygoid
elevates and assists in protrusion of the mandible
why can’t the medial pterygoid be palpated
because it sits on the inside of the jaw
does the medial pterygoid respond well to resistive movement tests
no
is there any reliable way of examining the medial pterygoid
no
what muscles are near the angle of the mandible
- masseter is on the lateral side
- medial pterygoid is on the mesial side
what can cause trismus
- 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
what should be hit when doing an ID block
bone, ensures correct position within the pterygomandibular triangle and not hit the soft tissues
what are the 2 movements of the TMJ
- rotation (initial opening)
- translation (wider opening)
what is rotation of the TMJ
- 1st movement
- hinge movement
- rotates around the hinge axis
what is translation of the TMJ
- 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
what is the outline of the movement of the TMJ called
the fossae envelope
who founded the fossae envelope
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
what is the maximum biting/clenching forces
- varies between teeth
- maximum between 200-700N in molars
(forces of 1200-1500N reported in Eskimo’s and world record is 4300N)
how can psychological factors affect biting/clenching forces
- fear of tooth fracture when max forces are used
- limits max forces used
what other factors can affect maximum biting/clenching forces
- 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
what are the muscle fibre types
- type 1 = slow, low forces
- type 2 = fast, stronger forces
- sub types = IIA, IIX, IIB
what is the most predominant fibre type
- 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
where is greatest biting forces generated
between 1st molars
why do 1st molars have greatest biting force
- 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
what support does the root area of a tooth have
PDL support
what are some other muscles in mastication
- supra hyoid
- infra hyoid
- hyoid bone
- tongue muscles
- facial muscles
what are the supra hyoid muscles
- digastric
- mylohyoid
- geniohyoid
- stylohyoid
what are the infra hyoid muscles
- ‘strap muscles’
- sternohyoid
- omohyoid
- thyrohyoid
- sternothyroid
what happens with the hyoid bone
- when the hyoid bone is fixed by contraction of the infra hyoids, the supra hyoids (apart from the stylohyoid) act as depressors
what are the 2 types of tongue muscles
- intrinsic and extrinsic
what are the intrinsic tongue muscles and what do they do
- longitudinal, vertical and transverse
- alter shape
what are the extrinsic tongue muscles and what do they do
- genioglossus, hypoglossus, palatoglossus, styloglossus
- alter shape and position
what is the main role of facial muscles
for expression
what is an additional role of some of the facial muscles
keeps the blogs in the oral cavity
which facial muscles keep the bolus in the oral cavity
- orbicularis oris
- buccinator
