Mastication & Dynamics of Occlusion

MASTICATION & DYNAMICS MASTICATION & DYNAMICS OF OCCLUSIONOF OCCLUSION

Oral PhysiologyOral PhysiologyDent 207Dent 207

Sequence of food intakeSequence of food intake IncisionIncision

Fragmentation of food by Fragmentation of food by approximation (occlusion)approximation (occlusion)

Moving mandible against Moving mandible against maxillamaxilla

Rotation about the 2 TMJsRotation about the 2 TMJs TransportTransport

To & between PM & M teethTo & between PM & M teeth MasticationMastication

Fragmentation of food by Fragmentation of food by approximation (occlusion)approximation (occlusion)

Moving mandible against Moving mandible against maxillamaxilla

Transport preparatory to Transport preparatory to swallowingswallowing

Deglutition (swallowing)Deglutition (swallowing)

The Muscles of masticationThe Muscles of mastication

Attached to the mandibleAttached to the mandible ElevatorsElevators DepressorsDepressors

Only when the hyoid bone is fixed by infrahyoid musclesOnly when the hyoid bone is fixed by infrahyoid muscles

Assisting musclesAssisting muscles Infrahyoid muscles (are they masticatory?)Infrahyoid muscles (are they masticatory?) Muscles of the lips & cheeksMuscles of the lips & cheeks Tongue musclesTongue muscles Head & neck musclesHead & neck muscles

When greater forces are neededWhen greater forces are needed Food capture & incisionFood capture & incision

Elevators musclesElevators muscles

MasseterMasseter TemporalisTemporalis Medial pterygoidMedial pterygoid

MasseterMasseter QuadrilateralQuadrilateral Deep & superficial portionsDeep & superficial portions SuperficialSuperficial

OriginOrigin Zigomatic processZigomatic process Anterior 2/3s of zygomatic archAnterior 2/3s of zygomatic arch

InsertionInsertion Angle of the mandibleAngle of the mandible Lower ½ of ramusLower ½ of ramus

DeepDeep OriginOrigin

Medial surface of zygomatic archMedial surface of zygomatic arch Posterior 1/3 of lower border of zygomatic Posterior 1/3 of lower border of zygomatic

archarch InsertionInsertion

Lateral surface of coronoidLateral surface of coronoid Upper ½ of ramusUpper ½ of ramus

TemporalisTemporalis

Large fan-shapedLarge fan-shaped Temporal fossa – central Temporal fossa – central

tendon – coronoidtendon – coronoid Coronoid insertionCoronoid insertion

Medial surfaceMedial surface ApexApex Anterior border or coronoid & Anterior border or coronoid &

ramusramus Most posterior fibers retrude Most posterior fibers retrude

the mandiblethe mandible

Medial pterygoidMedial pterygoid

OriginOrigin Lateral pterygoid plate – Lateral pterygoid plate –

medial surfacemedial surface Tubercle of palatine bone Tubercle of palatine bone

(pyramidal process)(pyramidal process) InsertionInsertion

Lower & posterior portions Lower & posterior portions of the medial of ramusof the medial of ramus

Angle of the mandibleAngle of the mandible Masseter & m. pterygoid – Masseter & m. pterygoid –

sling around the mandiblesling around the mandible

Lateral pterygoidLateral pterygoid

Not an elevatorNot an elevator For lateral displacement & protrusionFor lateral displacement & protrusion OriginOrigin

Upper head: infratemporal surface & crest of Upper head: infratemporal surface & crest of sphenoidsphenoid

Lower head: lateral pterygoid plate – lateral Lower head: lateral pterygoid plate – lateral surfacesurface

InsertionInsertion Neck & discNeck & disc

DepressorsDepressors

SuprahyoidSuprahyoid Digastric – main Digastric – main

depressordepressor MylohyoidMylohyoid StylohyoidStylohyoid GeniohyoidGeniohyoid

InfrahyoidInfrahyoid SternohyoidSternohyoid ThyrohyoidThyrohyoid OmohyoidOmohyoid

Direction of forces by masticatory Direction of forces by masticatory musclesmuscles

Different parts of a Different parts of a muscle produce different muscle produce different movementsmovements

E.g.TemporalisE.g.Temporalis Anterior fibers – elevation Anterior fibers – elevation

(vertical)(vertical) Posterior fibers – Posterior fibers –

retrusion (horizontal)retrusion (horizontal) Mandibular elevation – a Mandibular elevation – a

composite activity of a composite activity of a number of musclesnumber of muscles

Characterization of masticatory Characterization of masticatory muslcesmuslces

Masseter & MPMasseter & MP Power productionPower production

TemporalisTemporalis Stabilizing of mandibular positionStabilizing of mandibular position Allowing masseter to take actionAllowing masseter to take action

LPLP Continuous workload at low forces with fatiguingContinuous workload at low forces with fatiguing Stabilizing the position of TMJStabilizing the position of TMJ

DigastricDigastric Slow fatigue resistanceSlow fatigue resistance Brake the elevator activity as teeth are occludedBrake the elevator activity as teeth are occluded Depression is faster than elevationDepression is faster than elevation

Sensory receptors in masticatory Sensory receptors in masticatory musclesmuscles

Control of muscle movementControl of muscle movement Unevenly distributed in the muscles of masticationUnevenly distributed in the muscles of mastication Muscle spindlesMuscle spindles

Many in elevators and tongue musclesMany in elevators and tongue muscles Few in depressorsFew in depressors

Golgi tendon organsGolgi tendon organs Not known if they exist in elevatorsNot known if they exist in elevators Protect against overdevelopment of muscle tensionProtect against overdevelopment of muscle tension Performed by PDL receptors – limit force applied in Performed by PDL receptors – limit force applied in

masticationmastication

Electromyography of masticatory Electromyography of masticatory musclesmuscles

Complex combinations of activation in specific Complex combinations of activation in specific movementsmovements

M, TP & MP activated in a sequence during M, TP & MP activated in a sequence during mandibular approximationmandibular approximation

Digastric – bursts of activity during elevation to brake Digastric – bursts of activity during elevation to brake the rate of occlusion forcethe rate of occlusion force

Activity in MActivity in M begins late during elevationbegins late during elevation Ceases before the stroke is completedCeases before the stroke is completed

SCM is active in clenchingSCM is active in clenching

OcclusionOcclusion The envelop of motion of the The envelop of motion of the

mandiblemandible OcclusionOcclusion

Teeth contact positionTeeth contact position Centric occlusion CO = Centric occlusion CO =

intercuspal position ICPintercuspal position ICP Teeth in light contactTeeth in light contact

CO CO ≠≠ Intercuspal clenching Intercuspal clenching position ICCPposition ICCP

OcclusionOcclusion

In CO – location of the head of condyleIn CO – location of the head of condyle CO in complete denturesCO in complete dentures ICP & ICCP are staticICP & ICCP are static Median occlusal positionMedian occlusal position

Light tooth contact position reached in a Light tooth contact position reached in a normal chewing cyclenormal chewing cycle

Very close to COVery close to CO

Clench positionsClench positions

ICCPICCP Incisal clenching positionIncisal clenching position Lateral clench – extreme of lateral movementLateral clench – extreme of lateral movement

Rest positionRest position

Teeth are held slightly separateTeeth are held slightly separate Mandible is held by the sling of MP & MMandible is held by the sling of MP & M TMJ is not loadedTMJ is not loaded Is M contracted? – conflicting evidenceIs M contracted? – conflicting evidence Freeway space = interdental space = speech Freeway space = interdental space = speech

spacespace

Teeth articulationTeeth articulation

Contact between upper & lower jaws via teethContact between upper & lower jaws via teeth PDL receptorsPDL receptors

Articular receptorsArticular receptors Monitor load upon the articulating surfacesMonitor load upon the articulating surfaces Pressure receptors found in apical area of PDLPressure receptors found in apical area of PDL

Equivalent to Golgi tendon organsEquivalent to Golgi tendon organs

IncisionIncision Consists ofConsists of

Protrusive movementProtrusive movement Condylar heads sliding forwards & Condylar heads sliding forwards &

downwards onto articular eminencedownwards onto articular eminence Depression in protruded positionDepression in protruded position Hinge movement to elevate the Hinge movement to elevate the

body to edge-edge incisal positionbody to edge-edge incisal position Acting musclesActing muscles

Protrusion – LPProtrusion – LP Final elevation – MP & MFinal elevation – MP & M

Maximum separation 3 cmMaximum separation 3 cm Beyond that - dislocationBeyond that - dislocation

Dislocation of condyleDislocation of condyle

Excessive jaw separationExcessive jaw separation During yawning reflex rather During yawning reflex rather

than during incisionthan during incision Condyle moving beyond Condyle moving beyond

articular eminencearticular eminence Reduction by downward & Reduction by downward &

backward pressure in 3backward pressure in 3rdrd molar molar region on both sidesregion on both sides

Incising resistant foodIncising resistant food

Mandible begins to retrude but stops as resistance is Mandible begins to retrude but stops as resistance is feltfelt

Teeth pressed into foodTeeth pressed into food Side-to-side oscillating retrusive slideSide-to-side oscillating retrusive slide Some lateral movement in protrusion (sawing Some lateral movement in protrusion (sawing

motion)motion) Food portion separatesFood portion separates Mandible drops slightly to release the particleMandible drops slightly to release the particle Lips guide it toward cheek teethLips guide it toward cheek teeth

Incising moderately resistant & soft Incising moderately resistant & soft foodfood

Moderately resistant foodModerately resistant food Mandible slides back to ICPMandible slides back to ICP Food portion separates in scissor-blade movementFood portion separates in scissor-blade movement

Soft foodSoft food Sheared by incisorsSheared by incisors Not cut throughNot cut through Food thins and partsFood thins and parts

Incision & head movementIncision & head movement

More apparent in carnivoresMore apparent in carnivores Incisors grip foodIncisors grip food Fracture by a downward jerk of the headFracture by a downward jerk of the head

Food transport musclesFood transport muscles

Tongue, lips & cheek musclesTongue, lips & cheek muscles Pass food back & forth between the teethPass food back & forth between the teeth

Extrinsic muscles of the tongueExtrinsic muscles of the tongue

GenioglossusGenioglossus HyoglossusHyoglossus ChondroglossusChondroglossus StyloglossusStyloglossus PalatoglossusPalatoglossus

Intrinsic tongue musclesIntrinsic tongue muscles

Superior longitudinalSuperior longitudinal Shorten the tongue & elevates its edgesShorten the tongue & elevates its edges

Inferior longitudinalInferior longitudinal Shorten the tongue & depresses its edgesShorten the tongue & depresses its edges

TransverseTransverse Elongate & narrow the tongueElongate & narrow the tongue

VerticalVertical Broaden & flatten the tongueBroaden & flatten the tongue

Facial muscles involved in food Facial muscles involved in food transporttransport

BuccinatorBuccinator Pushes food back between occlusal Pushes food back between occlusal

surfacessurfaces Opposes outward pressure of the tongueOpposes outward pressure of the tongue Aids in transverse movement of food Aids in transverse movement of food

during masticationduring mastication Storage of food during mastication – less Storage of food during mastication – less

important in humansimportant in humans Perioral musclesPerioral muscles

Same functions as buccinator during Same functions as buccinator during mastication but anteriorlymastication but anteriorly

MasticationMastication Is a complex processIs a complex process Movement of the body of the mandibleMovement of the body of the mandible

In a vertical planeIn a vertical plane In a horizontal planeIn a horizontal plane

Movement of the tongue, lips & cheeksMovement of the tongue, lips & cheeks To control position and form of foodTo control position and form of food

Food reduced in size byFood reduced in size by TeethTeeth Tongue against palateTongue against palate

Food mixed with saliva – softened mass (bolus)Food mixed with saliva – softened mass (bolus) Precision – rarity of biting tongue, lips or cheeksPrecision – rarity of biting tongue, lips or cheeks

MasticationMastication

Masticatory stroke (chewing cycle) – 3 phasesMasticatory stroke (chewing cycle) – 3 phases Jaw opening phaseJaw opening phase

Increasing separation of occlusal teethIncreasing separation of occlusal teeth Rapid jaw closing phaseRapid jaw closing phase

Occlusal surfaces are brought togetherOcclusal surfaces are brought together Slow jaw closing phaseSlow jaw closing phase

Food particles are crushed between occlusal surfacesFood particles are crushed between occlusal surfaces Tooth contact phase – power phaseTooth contact phase – power phase

Jaw opening phaseJaw opening phase Sequence of muscular activationSequence of muscular activation

Mylohyoid muscleMylohyoid muscle DigastricDigastric

Hyoid bone needs to be fixed by infrahyoid musclesHyoid bone needs to be fixed by infrahyoid muscles Inferior head of LPInferior head of LP

Degree of separationDegree of separation depends on size & consistency of fooddepends on size & consistency of food Varies in one personVaries in one person Lower incisors move 10 – 15 mm downwardsLower incisors move 10 – 15 mm downwards

May be divided into 2 phasesMay be divided into 2 phases Slow opening followed bySlow opening followed by Rapid openingRapid opening

Rapid jaw closing phaseRapid jaw closing phase

Chewing stroke swings to the preferred Chewing stroke swings to the preferred chewing sidechewing side

Activity in LP ceases – mandibular depression Activity in LP ceases – mandibular depression is zerois zero

ActivityActivity Elevatory component - M, MP & TPElevatory component - M, MP & TP Lateral deviation – LPLateral deviation – LP Contralateral MP contracts before ipsilateralContralateral MP contracts before ipsilateral

Rapid jaw closing phaseRapid jaw closing phase

Working side condyle moves back horizontallyWorking side condyle moves back horizontally Balancing condyle moves upwards & backwardsBalancing condyle moves upwards & backwards Terminal position before slow closing phaseTerminal position before slow closing phase

Both condyles are displaced laterallyBoth condyles are displaced laterally Working side condyle 0.25 mm below its original starting Working side condyle 0.25 mm below its original starting

positionposition Sequence of muscle activitySequence of muscle activity

Working sideWorking side LP, TPa & TPp, deep M, MP, deep MLP, TPa & TPp, deep M, MP, deep M

Balancing sideBalancing side MP, deep MMP, deep M

Slow jaw closing phaseSlow jaw closing phase Rapid phase ends when resistance is detected between the Rapid phase ends when resistance is detected between the

teethteeth Slow closure followsSlow closure follows Slide of mandibular teeth against cuspal inclines of maxillary Slide of mandibular teeth against cuspal inclines of maxillary

teethteeth Three possible outcomesThree possible outcomes

Failure to penetrate food particle even after the power strokeFailure to penetrate food particle even after the power stroke Slow penetration of food particle & tooth contactSlow penetration of food particle & tooth contact Sudden breakage of food particle – unloading reflex – separationSudden breakage of food particle – unloading reflex – separation

Next cycle is initiated by stimulation of PDL receptorsNext cycle is initiated by stimulation of PDL receptors

Slow jaw closing & power strokeSlow jaw closing & power stroke

Increasing force of contraction in all elevator Increasing force of contraction in all elevator muscles of both sidesmuscles of both sides TPa & TPp, Md & Ms, MP, LPu & LPlTPa & TPp, Md & Ms, MP, LPu & LPl

Power stroke returnsPower stroke returns Working side condyle to its starting positionWorking side condyle to its starting position

Upwards & mediallyUpwards & medially Balancing side condyle at original higher position Balancing side condyle at original higher position

on anterior slope of the fossaon anterior slope of the fossa LaterallyLaterally

Control of masticationControl of mastication

Voluntary initiationVoluntary initiation Involuntary periods also occurInvoluntary periods also occur

Reflex activityReflex activity Can be overridden by voluntary controlCan be overridden by voluntary control

Mastication is involuntarily initiated by Mastication is involuntarily initiated by stimulating the anterior sensorimotor cortexstimulating the anterior sensorimotor cortex


Central rhythm generatorCentral rhythm generator Responsible for the automatic rhythmic activityResponsible for the automatic rhythmic activity Operate by neurons Operate by neurons

Stimulating elevator muscles, & simultaneouslyStimulating elevator muscles, & simultaneously Inhibiting active depressor musclesInhibiting active depressor muscles

Activity modified by sensory inputs from intraoral Activity modified by sensory inputs from intraoral muscle & joint receptorsmuscle & joint receptors

Control of masticationControl of mastication Incision / food taken into the mouth »»Incision / food taken into the mouth »» Rhythmic pattern of mastication »»Rhythmic pattern of mastication »» Receptors in PDL, muscles, jointsReceptors in PDL, muscles, joints Pressure & touch receptors in tongue & palatePressure & touch receptors in tongue & palate Monitor hardness of food & degree of comminution »»Monitor hardness of food & degree of comminution »» Feedback toFeedback to

Motor neuronsMotor neurons Rhythm generatorRhythm generator CerebellumCerebellum

Adjust the activity of the muscles »»Adjust the activity of the muscles »» Soft food is chewed faster than hard foodSoft food is chewed faster than hard food


Cycle is longer at beginning of ingestionCycle is longer at beginning of ingestion Different types of food fragment in different Different types of food fragment in different

waysways Food bolus is judges by oral receptors to be Food bolus is judges by oral receptors to be

ready for swallowingready for swallowing


Amount of chewing before swallowingAmount of chewing before swallowing Characteristic of the individualCharacteristic of the individual Influenced by nature of foodInfluenced by nature of food

Number of strokes before swallowingNumber of strokes before swallowing Men > womenMen > women Women > childrenWomen > children Not markedly influenced by state of dentitionNot markedly influenced by state of dentition Influenced by efficiency of food comminutionInfluenced by efficiency of food comminution

Bite forceBite force Maximum force for typical European food 80 NMaximum force for typical European food 80 N 64 N in denture wearers64 N in denture wearers Force measured by a gnathodynamometerForce measured by a gnathodynamometer Maximum atypical forcesMaximum atypical forces

440 N – molar region440 N – molar region 150 N – canine region150 N – canine region Males 520 N – females 340 NMales 520 N – females 340 N

Western diet needs less forceWestern diet needs less force Force increased by trainingForce increased by training

Eskemo women chew sealskin to use in clothingEskemo women chew sealskin to use in clothing Force can reach 1450 & 1700 NForce can reach 1450 & 1700 N

Limit on forceLimit on force Stimulation of pain receptors in PDLStimulation of pain receptors in PDL

Functions of chewingFunctions of chewing

No large particles damaging the esophageal or No large particles damaging the esophageal or gastric mucosagastric mucosa

Reduce amount of digestion in stomachReduce amount of digestion in stomach Maintenance of oral mucosal healthMaintenance of oral mucosal health Psychological valuePsychological value

Fulfilling emotional needs (gum & tobacco Fulfilling emotional needs (gum & tobacco chewingchewing

Satisfaction or calming effectSatisfaction or calming effect

Masticatory reflexesMasticatory reflexes

Modification of central rhythmModification of central rhythm Jew jerk reflexJew jerk reflex Jaw opening reflexJaw opening reflex Unloading reflexUnloading reflex

Jaw jerk reflexJaw jerk reflex

Stretch reflexStretch reflex Similar to knee jerk reflexSimilar to knee jerk reflex Induced by a sharp downward tap on the chin when Induced by a sharp downward tap on the chin when

the mandible is held loosely in the rest position »»the mandible is held loosely in the rest position »» Reflex generated by muscle spindles in MReflex generated by muscle spindles in M Contraction of masseter muscle »»Contraction of masseter muscle »» Teeth are brought to occlusionTeeth are brought to occlusion No muscle spindles in depressors - no jerk reflexNo muscle spindles in depressors - no jerk reflex

Jaw opening reflexJaw opening reflex

Mechanical or electrical stimulation ofMechanical or electrical stimulation of Lips, oral mucosa, teeth (PDL) »»Lips, oral mucosa, teeth (PDL) »»

Inhibition of activity of elevatorsInhibition of activity of elevators No simultaneous contraction of depressorsNo simultaneous contraction of depressors Similar effect when a hard particle stops Similar effect when a hard particle stops

mandibular elevationmandibular elevation Other animals – contraction of depressorsOther animals – contraction of depressors

Unloading reflexUnloading reflex

Control of mastication – a protective Control of mastication – a protective mechanismmechanism

Sudden reduction in the resistance of a food Sudden reduction in the resistance of a food particle »»particle »»

Sudden inactivation of massetric muscle Sudden inactivation of massetric muscle spindles »»spindles »»

Massetric activity is decreased »»Massetric activity is decreased »» Immediate stop in closureImmediate stop in closure

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Mastication & Dynamics of Occlusion