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7/31/2019 Oral Physio Slides -5.Mastication Dynamics of Occlusion
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MASTICATION & DYNAMICS
OF OCCLUSION
Oral PhysiologyDent 207
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Sequence of food intake
Incision Fragmentation of food by
approximation (occlusion)
Moving mandible againstmaxilla
Rotation about the 2 TMJs
Transport To & between PM & M teeth
Mastication Fragmentation of food by
approximation (occlusion)
Moving mandible againstmaxilla
Transport preparatory toswallowing
Deglutition (swallowing)
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The Muscles of mastication
Attached to the mandible
Elevators
Depressors Only when the hyoid bone is fixed by infrahyoid muscles
Assisting muscles
Infrahyoid muscles (are they masticatory?)
Muscles of the lips & cheeks
Tongue muscles Head & neck muscles
When greater forces are needed
Food capture & incision
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Elevators muscles
Masseter
Temporalis
Medial pterygoid
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Masseter
Quadrilateral
Deep & superficial portions
Superficial Origin
Zigomatic process Anterior 2/3s of zygomatic arch
Insertion Angle of the mandible
Lower of ramus
Deep Origin
Medial surface of zygomatic arch
Posterior 1/3 of lower border of zygomaticarch
Insertion Lateral surface of coronoid
Upper of ramus
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Temporalis
Large fan-shaped
Temporal fossa centraltendon coronoid
Coronoid insertion
Medial surface
Apex
Anterior border or coronoid &ramus
Most posterior fibers retrudethe mandible
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Medial pterygoid
Origin
Lateral pterygoid plate medial surface
Tubercle of palatine bone(pyramidal process)
Insertion
Lower & posterior portionsof the medial of ramus
Angle of the mandible
Masseter & m. pterygoid
sling around the mandible
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Lateral pterygoid
Not an elevator
For lateral displacement & protrusion
Origin
Upper head: infratemporal surface & crest ofsphenoid
Lower head: lateral pterygoid plate lateral
surface Insertion
Neck & disc
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Depressors
Suprahyoid
Digastric maindepressor
Mylohyoid Stylohyoid
Geniohyoid
Infrahyoid Sternohyoid
Thyrohyoid
Omohyoid
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Direction of forces by masticatory
muscles
Different parts of a
muscle produce different
movements
E.g.Temporalis Anterior fibers elevation
(vertical)
Posterior fibers retrusion
(horizontal)
Mandibular elevation a
composite activity of a
number of muscles
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Characterization of masticatory
muslces Masseter & MP
Power production
Temporalis Stabilizing of mandibular position
Allowing masseter to take action
LP Continuous workload at low forces with fatiguing
Stabilizing the position of TMJ
Digastric Slow fatigue resistance
Brake the elevator activity as teeth are occluded
Depression is faster than elevation
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Sensory receptors in masticatory
muscles
Control of muscle movement
Unevenly distributed in the muscles of mastication
Muscle spindles
Many in elevators and tongue muscles Few in depressors
Golgi tendon organs
Not known if they exist in elevators
Protect against overdevelopment of muscle tension Performed by PDL receptors limit force applied in
mastication
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Electromyography of masticatory
muscles
Complex combinations of activation in specificmovements
M, TP & MP activated in a sequence during
mandibular approximation Digastric bursts of activity during elevation to brake
the rate of occlusion force
Activity in M
begins late during elevation Ceases before the stroke is completed
SCM is active in clenching
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Occlusion
The envelop of motion of themandible
Occlusion
Teeth contact position
Centric occlusion CO =
intercuspal position ICP Teeth in light contact
CO Intercuspal clenching
position ICCP
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Occlusion
In CO location of the head of condyle
CO in complete dentures
ICP & ICCP are static Median occlusal position
Light tooth contact position reached in a
normal chewing cycle
Very close to CO
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Clench positions
ICCP
Incisal clenching position
Lateral clench extreme of lateral movement
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Rest position
Teeth are held slightly separate
Mandible is held by the sling of MP & M
TMJ is not loaded Is M contracted? conflicting evidence
Freeway space = interdental space = speech
space
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Teeth articulation
Contact between upper & lower jaws via teeth
PDL receptors
Articular receptors
Monitor load upon the articulating surfaces
Pressure receptors found in apical area of PDL
Equivalent to Golgi tendon organs
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Incision
Consists of Protrusive movement
Condylar heads sliding forwards &downwards onto articular eminence
Depression in protruded position Hinge movement to elevate the
body to edge-edge incisal position
Acting muscles Protrusion LP
Final elevation MP & M
Maximum separation 3 cm
Beyond that - dislocation
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Dislocation of condyle
Excessive jaw separation
During yawning reflex rather
than during incision
Condyle moving beyond
articular eminence
Reduction by downward &backward pressure in 3rd molar
region on both sides
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Incising resistant food
Mandible begins to retrude but stops as resistance is
felt
Teeth pressed into food
Side-to-side oscillating retrusive slide
Some lateral movement in protrusion (sawing
motion)
Food portion separates Mandible drops slightly to release the particle
Lips guide it toward cheek teeth
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Incising moderately resistant & soft
food
Moderately resistant food
Mandible slides back to ICP
Food portion separates in scissor-blade movement
Soft food
Sheared by incisors
Not cut through
Food thins and parts
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Incision & head movement
More apparent in carnivores
Incisors grip food
Fracture by a downward jerk of the head
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Food transport muscles
Tongue, lips & cheek muscles
Pass food back & forth between the teeth
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Extrinsic muscles of the tongue
Genioglossus
Hyoglossus
Chondroglossus Styloglossus
Palatoglossus
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Intrinsic tongue muscles
Superior longitudinal
Shorten the tongue & elevates its edges
Inferior longitudinal
Shorten the tongue & depresses its edges
Transverse
Elongate & narrow the tongue
Vertical
Broaden & flatten the tongue
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Facial muscles involved in food
transport
Buccinator
Pushes food back between occlusal
surfaces
Opposes outward pressure of the tongue Aids in transverse movement of food
during mastication
Storage of food during mastication less
important in humans Perioral muscles
Same functions as buccinator during
mastication but anteriorly
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Mastication
Is a complex process
Movement of the body of the mandible In a vertical plane
In a horizontal plane
Movement of the tongue, lips & cheeks
To control position and form of food Food reduced in size by
Teeth
Tongue against palate Food mixed with saliva softened mass (bolus)
Precision rarity of biting tongue, lips or cheeks
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Mastication
Masticatory stroke (chewing cycle) 3 phases
Jaw opening phase
Increasing separation of occlusal teeth
Rapid jaw closing phase
Occlusal surfaces are brought together
Slow jaw closing phase
Food particles are crushed between occlusal surfaces Tooth contact phase power phase
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Jaw opening phase
Sequence of muscular activation Mylohyoid muscle
Digastric Hyoid bone needs to be fixed by infrahyoid muscles
Inferior head of LP Degree of separation
depends on size & consistency of food
Varies in one person
Lower incisors move 10 15 mm downwards May be divided into 2 phases
Slow opening followed by
Rapid opening
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Rapid jaw closing phase
Chewing stroke swings to the preferred
chewing side
Activity in LP ceases mandibular depression
is zero
Activity
Elevatory component - M, MP & TP
Lateral deviation LP
Contralateral MP contracts before ipsilateral
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Rapid jaw closing phase
Working side condyle moves back horizontally
Balancing condyle moves upwards & backwards
Terminal position before slow closing phase
Both condyles are displaced laterally Working side condyle 0.25 mm below its original starting
position
Sequence of muscle activity
Working side LP, TPa & TPp, deep M, MP, deep M
Balancing side MP, deep M
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Slow jaw closing phase
Rapid phase ends when resistance is detected between theteeth
Slow closure follows
Slide of mandibular teeth against cuspal inclines of maxillary
teeth Three possible outcomes
Failure to penetrate food particle even after the power stroke
Slow penetration of food particle & tooth contact
Sudden breakage of food particle unloading reflex separation
Next cycle is initiated by stimulation of PDL receptors
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Slow jaw closing & power stroke
Increasing force of contraction in all elevator
muscles of both sides
TPa & TPp, Md & Ms, MP, LPu & LPl
Power stroke returns
Working side condyle to its starting position
Upwards & medially
Balancing side condyle at original higher positionon anterior slope of the fossa
Laterally
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Control of mastication
Voluntary initiation
Involuntary periods also occur
Reflex activity
Can be overridden by voluntary control
Mastication is involuntarily initiated by
stimulating the anterior sensorimotor cortex
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Control of mastication
Central rhythm generator
Responsible for the automatic rhythmic activity
Operate by neurons
Stimulating elevator muscles, & simultaneously
Inhibiting active depressor muscles
Activity modified by sensory inputs from intraoral
muscle & joint receptors
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Control of mastication
Incision / food taken into the mouth
Rhythmic pattern of mastication
Receptors in PDL, muscles, joints
Pressure & touch receptors in tongue & palate
Monitor hardness of food & degree of comminution
Feedback to
Motor neurons
Rhythm generator
Cerebellum Adjust the activity of the muscles
Soft food is chewed faster than hard food
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Control of mastication
Cycle is longer at beginning of ingestion
Different types of food fragment in different
ways
Food bolus is judges by oral receptors to be
ready for swallowing
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Control of mastication
Amount of chewing before swallowing
Characteristic of the individual
Influenced by nature of food
Number of strokes before swallowing
Men > women
Women > children
Not markedly influenced by state of dentition
Influenced by efficiency of food comminution
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Bite force
Maximum force for typical European food 80 N
64 N in denture wearers
Force measured by a gnathodynamometer
Maximum atypical forces
440 N molar region
150 N canine region
Males 520 N females 340 N
Western diet needs less force
Force increased by training Eskemo women chew sealskin to use in clothing
Force can reach 1450 & 1700 N
Limit on force Stimulation of pain receptors in PDL
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Functions of chewing
No large particles damaging the esophageal or
gastric mucosa
Reduce amount of digestion in stomach
Maintenance of oral mucosal health
Psychological value
Fulfilling emotional needs (gum & tobacco
chewing
Satisfaction or calming effect
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Masticatory reflexes
Modification of central rhythm
Jew jerk reflex
Jaw opening reflex
Unloading reflex
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Jaw jerk reflex
Stretch reflex
Similar to knee jerk reflex
Induced by a sharp downward tap on the chin when
the mandible is held loosely in the rest position
Reflex generated by muscle spindles in M
Contraction of masseter muscle
Teeth are brought to occlusion No muscle spindles in depressors - no jerk reflex
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Jaw opening reflex
Mechanical or electrical stimulation of
Lips, oral mucosa, teeth (PDL)
Inhibition of activity of elevators
No simultaneous contraction of depressors
Similar effect when a hard particle stops
mandibular elevation
Other animals contraction of depressors
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Unloading reflex
Control of mastication a protective
mechanism
Sudden reduction in the resistance of a food
particle
Sudden inactivation of massetric muscle
spindles
Massetric activity is decreased
Immediate stop in closure