Oral Physio Slides -5.Mastication Dynamics of Occlusion

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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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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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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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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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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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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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

Oral Physio Slides -5.Mastication Dynamics of Occlusion

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