The process by which food is crushed and ground by teeth The first step of digestion Increases the surface area of food to allow more efficient breakdown by enzymes Food after swallowing is called BOLUS
Mastication is the repetitive sequence of jawopening and closing with a profile in the verticalplane called CHEWING CYCLE.THREE PHASES: 1. OPENING PHASE the mouth is opened and the mandible is depressed
2. CLOSING PHASE -the mandible is raised towards the maxilla3. OCCLUSAL OR INTERCUSPAL PHASE -the mandible isstationary and the teethfrom both upper and lowerarches approximate
COMMON CHARACTERISITICS: 1. All are inserted to the mandible 2. All are innervated by the mandibular division of the trigeminal nerve 3. All are concerned un biting and chewingFUNCTIONS: 1. To move the mandible 2. To secure then stabilize the mandibular positions 3. To determine the direction of mandibular movements
MASSETER MUSCLE It is a flat quadrangular muscle, partly tendinous, partly fleshy. It overlies the lateral surface of the mandibular ramus.
Superficial part ORIGIN: maxillary process of zygomatic bone and anterior 2/3 of the zygomatic process of the maxilla INSERTION: angle of the mandible and posterior part of ramusDeep part ORIGIN: medial aspect of the zygomatic arch ACTION: elevate the INSERTION: central and jaw, with the superficial upper part of ramus as fibers causing high as the coronoid protraction
TEMPORALIS MUSCLE It is a large, fan- shaped muscle at the sides of the head.
ORIGIN: the floor oftemporal fossa andtemporal fasciaCOURSE: anterior fibers runvertically downwardswhile the posterior fibersare almost horizontal inpositionINSERTION: the apex and ACTION: anteriordeep surface of the fibers elevate thecoronoid process and mandible, while thealong the anterior border posterior fibersof the ramus retract the mandible
LATERAL (or EXTERNAL) PTERGOID MUSCLE It is a thick and triangular muscle with two heads. It is the muscle of mastication that occupy primarily a horizontal position.
ORIGIN: Superior portion –infratemporal surface ofgreater wing of sphenoid.Inferior portion – lateralsurface of lateral pterygoidplateINSERTION: fibers a redirected laterally andbackwards into the front ofthe pteygoi plateACTION: depress, proturudeand move the mandiblefrom side to side
MEDIAL (or INTERNAL)PTERYGOID MUSCLE It is almost a mirror-like image of the masseter muscle. It is rhomboidal and runs practically in the same direction on the inner surface of the mandible
ORIGIN: medialsurface of lateralpterygoid plate, theposterior surface ofthe tubercle ofpalatine bone andtuberosity of maxillaINSERTION: pterygoidtuberosity ACTION: elevates and protracts the mandible. It also moves the jaw from side to side when acting singly.
SPHENOMANDIBULAR MUSCLE This is one a part of the accessory ligament of TMJ, now regarded as the 5th muscle of mastication. It run medial to the TMJ
ORIGIN: spine of sphenoid bone at the baseof the skullINSERTION: lingula on the mesial side of theramus