Functional Anatomy of Mastication Flashcards
Phases of Eating
- Ingestion: bringing a sold/liquid into the mouth
- Stage I Transport: moving food from incisors to molars
- Food processing: mastication (chewing) and stage II transport (bolus formation and accumulation)
- Deglutition: swallowing (pharyngeal and esophagus phases)
Ingestive phase
- Manipulation of food item with the lips and tongue
- extrinsic and intrinsic tongue muscles
- muscles of facial expression: orbicularis oris m., buccinator m.
- Incision of the food: biting off small pieces using the incisors and canines
Masticatory skeleton: Temporal bone
- temporal bone (squamous portion)
- mandibular fossa: articulates with mandibular condyle
- articular tubercle: anterior to fossa, prevents anterior dislocation of TMJ
Masticatory Skeleton: Mandible
- Corpus: body of the mandible, supports the alveolar processes
- Mandibular symphysis: midline fusion of the two halves of the mandible, originally a fibrocartilaginous joint (fuses by age 1 year)
- Ramus: vertivle portion of the mandible that supports the condyle and muscular attachments
- Neck: attachment for the inferior head of the lateral pterygoid m. (laterally)
- Condyle: forms the articulation with the temporal bone
- Coronoid process: attachment for the temporalis m.
- Angular process: attachment for the masseter m. (laterally), and medial pterygoid m. (medially)
Knee joint and TMJ articular surfaces and meniscus/disk
Masticatory ligaments: Sphenomandibular ligaments
- From sphenoid bone to mandibular lingula
- Limits inferior displacement of the mandible
Masticatory ligaments: Stylomandibular ligaments
- From styloid process to mandibular angle
- Limits anterior displacement and mandibular depression
Masticatory ligaments: Temporomandibular ligament
- Also called the lateral capsular ligament
- Prevents posterior displacement of the condyle
Masticatory ligaments: discal ligaments
- Hold the articular disc to the condyle
TMJ Anatomy
- Articular disc
- Synovial compartments
- Superior: tranlsated movements
- Inferior: rotational movements
- Ligaments and capsule: stabilize joint, holds disc to condyle
- Articular eminence: prevents anterior dislocation
- Retrodiscal pad: a mass of fatty, vascularized tissue behind the joint the prevents posterior dislocation
What type of joint is ginglymoarthrodial joint?
hinge and sliding joint
TMJ movements
modified hinge joint (rotation and sliding)
Wide jaw opening requires both depression (rotation) and protrusion (sliding)
Movement terms
- depression: rotational opening of the mouth
- elevation: rotational closing of the mouth
- protrusion: anteriorlu-directed translational sliding
- retrusion: posteriorly-directed translational sliding
Muscles of mastication (and their innervation)
- innervated by branches of V3 (mandibular nerve)
- temporalis m.
- masseter m.
- lateral pterygoid m.
- medial pterygoid m.
Temporalis muscle (anterior/posterior parts, fossa and innervation)
- anterior part: elevates jaw
- posterior part: retracts jaw
- temporal fossa to coronoid process
- innervation: deep temporal nerves
Masseter muscle (superficial/deep parts and innervation)
- superficial part: protracts and elevates jaw
- anterior zygomatic arch to angle of mandible
- deep part: elevates jaw
- zygomatic arch to mandibular ramus
- unilateral contractions will move jaw laterally
- innervation: messeteric nerve
Medial pterygoid muscle (what it does, supperficial/deep parts, and innervation)
- elevates and protrudes the jaw
- superficial part: maxillary tuberosity and palatine bone to the medial aspect of the mandibular angle
- deep part: medial aspect of lateral pterygoid plate to the medial aspect of the mandibular angle
- innervation: nerve to medial pterygoid muscle
Lateral pterygoid muscle: (what it does, supperficial/inferior parts, and innervation)
- Protrudes jaw
- Unilateral contractions move the jaw laterally
- Superior part: greater wing of sphenoid to TMJ capsule
- Inferior partL lateral aspect of lateral pterygoid plate to the neck of the mandibular condyle
- Innervation: nerve to lateral pterygoid
Movements of mastication
- unilateral protrusion (balancing side) causes jaw rotation towards the working side
- this motion is driven by the lateral pterygoid m.
Movements of mastication (opening stroke, closing stroke and power stroke)
- opening stroke
- jaw depression
- protraction of balancing side
- lateral movement to working side (bolus)
- closing stroke
- jaw elevation
- fast closing: movement towars WS
- slow closing: start of lateral movement back to BS
- power stroke
- teeth in occlusion
- protraction to WS
- lateral movement back to BS
- ratuens jaw to midline
Functional groups of masticatory muscles: unilateral protractors and vertical closers
- unilateral protractors: move jaw towards working side (WS) during opening, towards balancing side (BS) during closing
- lateral pterygoid muscle
- vertical closers: initiate closing from maximum gape (start of closing stroke)
- deep masseter m.
- anterior temporalis m.
Functionsla groups of masticatory muscles: triplets, triplet I, triplet II
- triplets: groups that provide the bite force during closing and occlusion
- triplet muscles are ones that are capable of jow closing and either protraction/retraction
- triplet I: continues to move jaw towards WS in preparation for power stroke; active during closing stroke
- BS superficial masseter and medial pterygoid mm., WS posterior temporalis m.
- triplet II: moves haw towards BS/midline; active at the end of closing stroke through power stroke
- WS superficial masseter and medial pterygoid mm., BS posterior temporalis m.
Jaw Opening: Muscles involves in jaw depression
supra- and infra-hyoid muscles
Jaw opening: muscles involved in lateral movement towards WS
lateral pterygoid m. (BS)
Jaw closing: jaw elevation muscles
jaw elevation: vertical closers
anterior temporalis and deep masseter
Jaw closing: fast closing muscles
jaw closing: jaw moves towards WS
vertical closers and triplet I
Jaw closing: slow closing mucsles
jaw closing: jaw moves towards BS
vertical closers and triplet II
Power stroke
- triplet II continues to be active through power stroke, providing a combination of elevation and lateral movement for bite force
- WS lateral pterygoid also moves teh jaw back towards the midling (towards BS)
TMJ innervation
- sensory innervation (GSA), CN V3
- auriculotemporal nerve (passes behind condyle)
- masseteric nerve (passes through mandibular notch)
- deep temporal nerve
MAD
TMJ arterial supply
superficial temporal a.
note that the central part of the articular disc is avascular
TNJ dysfunction: signs and symptoms and common representation
- signs and symptoms
- pain and tenderness
- muscular pain
- joint pain
- limited range of movement
- noises during movement
- pain and tenderness
- common presentation
- anterior disc displacement
Mandibular nerve blocks: inferior alveolar block
- landmark: lingula near mandibular foramen
- target: inferior alveolar and lingual nn.
Mandibular nerve blocks: gow-gates block
- landmark: neck of mandibular condyle
- target: inferior alveolar n., lingual n., buccal n.
Mandibular nerve blocks: misplaced injections (posterior and medial)
- posterior: pierce parotid gland, causing transient facial paralysis (CN VII)
- medial: pierce medial pterygoid m., causing trismus (spasms)
