Neuromuscular Basis of Mastication

preplanning restorative care can be used for what 6 things

1) diagnostic wax up to preplan occlusion

2) fabricate preparation guide

3) design esthetic temporaries

4) lab communication

5) patient reassurance

6) fabcriate surgical implant guide

preplanning restorative care saves _____ and has ______ results for occlusion

time; better

what is mastication

the process whereby ingested food is cut or crushed into small pieces mixed with saliva and formed into a bolus in preparation for swallowing

what is heterodonty

having different/specialized tooth forms for the specific preparation of food

what are the 7 characteristics of mastication

1) a learned activity

2) enables the food bolus to be easily swallowed

3) enhance the digestibility of food

4) provides reflex stimulation for secretions

5) mixes food with saliva to initiate the digestion process

6) prevents irritation of the GI system and damage to the masticatory system

7) ensures healthy growth and development

recall the hierarchy of physiology of muscle contraction

muscle —> muscle fascicles/motor units —> muscle fibers —> myofibrils —> thick/thin filaments

muscles contract by what

by shortening in length

what is a sarcomere

the all or none unit of contraction

myosin heads of the thick filaments bind to what

the active sites on the actin thin filaments

what theory describes the main driver of contraction

sliding filament theory

contraction is triggered by what kinds of ions

calcium ions

muscle contraction is fueled by what

ATP

strength in muscles = number of __________ acting in parallel

sarcomeres

what is the strength of contraction per square centimeter

5.6 to 7.4 pounds

mandible pictures

temporal bone pictures

TMJ and ligaments pictures

lateral ligament: intrinsic thickening of the joint capsule that runs from neck of mandible to articular tubercle; strengths the joint laterally and helps prevent dislocation

sphenomandibular ligament: extrinsic ligament that runs from sphenoid bone to mandible's lingula; supports joint and acts as a prop during hinge movements

stylomandibular ligament: extrinsic ligament that runs from temporal bone's styloid process to mandible's angle; strengths joint

when giving a correct inferior alveolar nerve block, which ligament would you be closest to?

sphenomandibular ligament (IA nerve goes through the lingula on the mandible)

what is the basic unit of muscle contraction called

motor unit or fascicle

each muscle may have how many muscle fibers

10 to several hundred

muscles have ____ nerve cell connection

one

muscles have an ____ or _____ response

all or nothing

sustained muscle contractions are possible by timing of what

timing of nerve stimulus

muscle tone is important in maintaining what

posture and/or interocclusal rest space

muscle tone can be affected by what 4 things

stress, age, pain, and loss of teeth

muscle tone is also important in the maintenance of what

maintenance of airway

myotactic stretch reflex protects skeletal muscle from excessive ?; sensitive to muscle ?

stretching; length

describe the myotactic stretch reflex

rapid stretching of a muscle results in reflex contraction of the same muscle

what is the temporalis muscle

principle elevator of the mandible; significant positioning muscle

the temporalis muscle aids in what 3 things

retraction, positioning, and clenching

the temporalis muscle has a ______ origin and a ______ insertion

large origin (temporal fossa, parietal bone, frontal bone, occipital bone) , small insertion (coronoid process of mandible)

the temporalis muscle contracts by how many sections

contracts can be one or more of the 3 sections, OE all at once

contraction of the entire temporalis muscle produces what action

elevation

the anterior fibers of the temporalis run in which orientation and does what

vertical; elevates mandible

the middle fibers of the temporalis do what

elevate and slightly retrude the mandible

the posterior fibers of the temporalis do what

cause retrusion

the deep head of the masseter muscle aids in what

stabilizes the condyle when biting on incisors

what is the action of the masseter muscle

elevates the jaw and clenches the teeth

what is the origin and insertion of the masseter muscle

origin: the outer surface of the zygoma

insertion: lower border of the ramus

the superficial head of the masseter muscle aids in what

protrusion

what is the masseter muscle

primary muscle for chewing force

what is the origin and insertion of the newly identified third layer of the masseter muscle

origin: inferior border of zygomatic arch/posterior to zygomatic suture

insertion: masseteric tuberosity/coronoid process

what is the action of the newly identified third layer of the masseter muscle

assists retractor function of the mandible

medial and lateral pterygoid pictures

the lateral pterygoid muscle is the most important indicator of what

occlusal harmony

the lateral pterygoid muscle is highly active in what movements

opening/closing and excursive movements

the lateral pterygoid muscle is the only muscle to insert into where

the TMJ capsule

the inferior lateral pterygoid is active in what action

protrusion

when the inferior lateral pterygoid is in concert with depressor muscles, it will cause what kinds of movements

working and nonworking movements

the active side of inferior lateral pterygoid muscle contraction is the ___-__________ side

non-working

the superior head of the lateral pterygoid is _____ as large as the inferior head of the lateral pterygoid

1/3

the superior lateral pterygoid inserts onto where

onto the TMJ capsule and has some fibers that insert onto the disc

the superior lateral pterygoid is inactive during ______ and highly active during ________

opening; closure

the superior lateral pterygoid contracts while ?

while lengthening

the superior lateral pterygoid is most susceptible to what

to injury

what is the action of the medial pterygoid muscle

elevator of the mandible

the medial pterygoid muscle supports the activity of which muscle

lateral pterygoid muscle

the medial pterygoid muscle is highly active during what kinds of movement

rotary or protrusive movements

origin and insertion of medial pterygoid muscle

origin- pterygoid fossae of sphenoid bone

insertion- medial angle of mandible

origin and insertion of lateral pterygoid muscle

origin of superior head: inferior surface of greater wing of sphenoid (roof of infratemporal fossa)

origin of inferior head: lateral surface of lateral pterygoid plate

insertion: pterygoid fovea of mandible (on the neck of the condyle) - both run posteriorly from their origin to their insertion (superior also inserts onto TMJ capsule and some fibers into the disc)

the suprahyoid muscles act as the __________ of the hyoid bone and the __________ __________ of the mandible

elevators; depressor retractors

origin and insertion of digastric muscle (posterior head)

origin: mastoid portion of temporal bone

insertion: hyoid bone

origin and insertion of stylohyoid muscle

origin: styloid process of temporal bone

insertion: body of hyoid

what are the 4 suprahyoid muscles

digastric, stylohyoid, mylohyoid, geniohyoid

how are the suprahyoid muscles and the tongue related

extrinsic muscles of the tongue act as depressor retractors and the suprahyoid muscles can elevate the tongue

what is the action of the geniohyoid

elevates the hyoid bone and the tongue

what is the origin and insertion of the geniohyoid

origin: mandible

insertion: hyoid

what is the action of the mylohyoid

elevates the hyoid bone, base of tongue, and raises the floor of the mouth

what is the origin and insertion of the mylohyoid

origin: mylohyoid line of the mandible

insertion: mylohyoid raphe and the body of the hyoid

what is the action of the digastric

raises the hyoid bone and the base of the tongue

what is the action of the stylohyoid

elevates the hyoid bone and the base of the tongue

what 4 muscles make up the infrahyoid muscles

sternohyoid, omohyoid, sternothyroid, thyrohyoid

all of the infrahyoid muscles act to _______ the hyoid bone

fixate

diagram of muscles of the hyoid bone

3/4 infrahyoid muscles are attached (3)

all suprahyoid muscles are attached (4)

genioglossus and hyoglossus (2)

total 9 muscles are attached to hyoid bone

mandibular muscles demonstrate standard __________ ___ _________ in healthy subjects during the vertical and horizontal movements of the mandible

patterns of activity

which muscle initiates the activity of mandibular opening, be specific

the inferior head of lateral pterygoid

which kinds of muscles help to follow the mandibular opening action to completion (general)

depressor/retractors

normal mandibular opening is a _________ function

depressor

forced (isometric) mandibular opening activates which muscle as soon as the lateral pterygoids are activated

digastric muscle

which 2 muscles act as assists during mandibular opening

temporalis and masseter muscles

which 3 muscles are active during elevation in unrestricted normal closing

medial pterygoid, anterior temporalis, and masseter muscles

which muscle group relaxes during unrestricted normal closing

suprahyoid muscles

in unrestricted normal closing, the _________ lateral pterygoid relaxes to the action of the _________ lateral pterygoid

inferior; superior

which 2 muscle fibers or the temporalis contract to aid positioning in unrestricted normal closing

posterior and middle

which 2 muscles can add power in centric?

masseter and temporalis

power muscles provide what kinds of capabilities to the mandible

crushing capabilities

what is the average power of the power muscles

320 pounds

what is the envelope of border movements

the volume of space within which all movements of a specified point on the mandible occur

what are chewing cycles

a pathway of symmetrical movements formed by the repeated opening and closing of the mandible during mastication

example of root angulations and maxillary occlusal plane

the envelope of border movements is limited by anatomical considerations such as?

ligaments and tooth contacts

most natural movements do not utilize this maximum volume but occur ____ ______ the envelope

well within

example of frontal plane envelope of border movements

shield shape

figures of sagittal and frontal plane envelope of border movements

complex chewing movements can be better understood when they are related to the more familiar _______ _________

border movements

these relationships between chewing movements and border movements show where the chewing and border paths ______ and indicate where ________ _______ occur during chewing

coincide; occlusal contacts

unilateral chewing is characterized by wide _______ __________ movements and frequent ________ contacts between opposing teeth

lateral closing; sliding

time for the entire chewing cycle is ____ seconds with an average speed of what

0.7 seconds with average speed of 7.5 cm/second

what are the 3 phases of the chewing cycle

1) closing stroke

2) masticatory or power stroke

3) opening stroke or free movement phase

what happens in the closing stroke in the chewing cycle

mandible is brought upward and outward to come into initial contact with the food