MANDIBULAR MOVEMENTS

•

• By • PALLAWI SINHA

TABLE OF CONTENTS• TYPES OF MOVEMENTS RotationalAxis of rotation:• horizontal• frontal• sagittal Translational • BORDER MOVEMENTS• FUNCTIONAL MOVEMENT • ENVELOPE OF MOTION• REVIEW OF LITERATURE• SUMMARY • CONCLUSION

MANDIBULAR MOVEMENTS:

• It is determined by combined and simultaneousactivities of both TMJs.

.

Mandibular movements are related to 3planes of the skull

Mandibular movements (GPT 8)- any movement in lower jaw.

Factors That Determine The Mandibular Movements:

Mandibular movements are influenced by

Function:

Masseter contracts

Elevation of mandible

Superficial portion

Aid in protrusion of the mandible

When the mandible is protruded &biting force is applied,the fibres of the deep portion stabilize the condyle againstthe articular eminence.

ANTERIOR FIBRES

POSTERIOR FIBRES

(….fibres below the rootof the zygomatic process are the only significant ones)

Vertically raised….elevation

MIDDLE FIBRES…elevates& retrude the mandible.

MEDIAL PTERYGOID:

Function :

Along with masseter it forms a muscular sling that supports the mandible at mandibular angle.

When fibers contract the mandible is elevated.Muscle is active in protruding the mandible.

Unilateral contraction will bring about mediotrusive movement of the mandible.

LATERAL PTERYGOID:

Two bellies:

Inferior lateral pterygoid- outer surface of lateral pterygoid plate &extends backward, upward& outward……inserted on to the neck of the condyle.

Superior lateral pterygoid- infratemporal surface of the greater wing of sphenoid…..inserted on the articular capsule, the disc & the neck of the condyle.

Funtions :

Inferior lateral pterygoid:

Opening ,protracting ,Lateral movement in contralateral direction

Superior lateral pterygoid:

During opening… inferior pterygoid active superior pterygoid remains inactive

Become active only in conjunctionwith the elevator muscles

Closing ,Retracting ,Lateral movement ipsilateral in direction

The combinded efforts of the Digastrics and Lateral Pterygoids provide for natural jaw opening.

Medial and lateral pterygoid act together to protrude the mandible

Other muscles which are important for mandibular function are:

Suprahyoid musclesInfrahyoid muscles

SternocleidomastoidPosterior cervical muscles

Stabilizes the skull& enables controlledmovement of the mandible

STRUCTURE OF THE TEMPOROMANDIBULAR JOINT:

The TMJ is the most complex joints in the body and is the area in which the mandible articulates with the cranium.

Hinging movement in Provides for gliding one plane movement

GINGLYMOID JOINT ARTHRODIAL JOINT

GINGLYMOARTHRODIAL JOINT

COMPOUND JOINT

SYNOVIAL JOINT

ARTICULAR DISC:

SAGITTAL PLANE

It is a firm, oval, fibrous plate positioned between mandibular condyle and the articular fossa and eminance.

Most part devoid of any blood vessels or nerve fibres…..however extreme periphery is slightly Innervated.

It serves as a nonossified bone. Thus making TMJ as the compound joint.

SUPERIOR JOINT CAVITY

INFERIOR JOINT CAVITY

The bony elements of the temporomandibular articulation are the mandibular condyles below and the squamous temporal bone above.

An articular disc composed of fibrous tissue is interposed between the temporal bone and the mandible.

Gliding movementHinge movement

Upper compartment Lower compartment

Disk merges with the capsule at the periphery and is firmly attached to the condyle at its medial and lateral pole .Disk is not attached to temporal bone ,thus it moves with the condyle as the latter translates in relation to the articular eminence

The central area of disk is thinner and is called intermediate zone with thicker peripheral

MANDIBULAR CONDYLE:

ANTERIOR VIEW

POSTERIOR VIEW

Convex portion of the mandible that articulates with the cranium,around which movement occurs.

Mediolateral length=15-20mmAnteroposterior length=8-10mm

Articulating surface—extends both anteriorly and posteriorly to the most superior aspect of condyle.

Medial pole serves as a point of rotation.

LIGAMENTS:

Ligaments of the joints are made up of collagenous connective tissue. Muscles move and ligaments limit. They do not stretch.

Ligaments do not enter actively into joint function ,rather they act as passive restraining devices to limit & restrict border movements.

3 functional ligaments that support TMJ are : Collateral ligament

Capsular ligament Temporomandibular ligament

2 accessory ligaments are:-

SphenomandibularligamentStylomandibular ligament

COLLATERAL OR DISCAL LIGAMENTS:

Disc is designed to rotate on the condyle like a bucket handle that attaches to medial and lateral poles of the condyle by DISCAL LIGAMENTS.

There are 2 types: Medial discal ligament Lateral discal ligament

True ligaments:> composed of collagenous CT fibres. therefore they do not stretch.

CAPSULAR LIGAMENTS:

It is the synovial capsule that completely surrounds and encompasses the TMJ.

Function :

LATERAL VIEW

Resist medial ,lateral, or inferior forces that tend to separate or dislocate the articular surfaces .

Retains the synovial fluid .

Well innervated so gives proprioceptive feedback regarding position and movement of the joint.

TEMPOROMANDIBULAR LIGAMENT:

Lateral aspect of the capsular ligament is reinforced by

strong, tight fibers that make up the lateral or

temporomandibular ligament.

LATERAL VIEW

Composed of

Outer oblique portion

Inner horizontal portion

This ligament of the joint does not come into function until jaw opens to 20mm or more.

Oblique portion Inner portion

Resists excessive droppingof the condyle. Therefore limiting the mouth opening.

Limits posterior movement of the condyle&disc thusprotects the retrodiscal tissuefrom trauma.

influence the normalopening movement of the mandible

Prevents lateral pterygoidmuscles from overextension

SPENOMANDIBULAR LIGAMENT

STYLOMANDIBULARLIGAMENT

ACCESSORY LIGAMENTS:

Spenomandibular ligament.. no significant limiting effect

Stylomandibular ligament

•Becomes taut when mandible is protruted.But mostrelaxed when mandible is opened.

•Therefore limits excessive protrusive movementof mandible.

Occlusion

CONDYLAR GUIDANCE:

Defined as “mandibular guidance generated by the condyle and the articular disc traversing the contours of the glenoid fossa ”GPT

It is the path of movement taken by the condyle in the glenoid fossa, this is dictated by the shape of the glenoid fossa.

Defined as the influence of the contacting surface of the mandibular and the maxillary anterior teeth during mandibular movements .”GPT

This is influenced by the lingual surfaces of the maxillary anteriors which guide the mandible during the protrusive movement.

INCISAL GUIDANCE

NEUROMUSCULAR FACTORS

The muscles that move, hold, or stabilize the mandible ---------- because they receive impulses from the central nervous system

NEUROMUSCULAR REGULATION OF MANDIBULAR MOTION:

Impulses….>conscious level….>voluntary mandibular movements

Impulses..>subconscious level of CNS.>involuntary mandibular movements or modification of voluntary movements….as a result of stimulation of oral receptors ,muscle receptors

PROPRIOCEPTORS..>receptors present principally in the mandibular muscles and ligaments ,which provideinformation about the location of the mandible in space.

CLASSIFICATION OF MANDIBULAR MOVEMENTS:

According to sharry:

Based on axis of movement:

Rotation around the transverse or hinge axisRotation around the anteroposterior or sagittal axisRotation around the vertical axis

Based on the direction of movement:

Opening movements Closing movementsProtrusive movementsLateral movements

Based on the extent on movement:

Border movements Intra border movements

Based on habitual movements:

Speech Mastication Deglutition Respiration

CNS:

Innate..>breathing &swallowingLearned ..>chewing &speech

Nonfunctional movements

Bruxism

ACCORDING TO OKESON:

Based on type of movement within the TMJ:

•Rotational movement•Translational movement

Based on the plane of border movements:

•Border movement in horizontal plane•Border movement in frontal plane(vertical) •Border movement in sagittal plane

TYPE OF MOVEMENTS

•1.ROTATIONAL MOVEMENTS

• 2.TRANSLATORY MOVEMENTS

ROTATIONAL MOVEMENT:

In the TMJ, the rotation occurs as movement within the Inferior joint cavity.

Horizontal axis of rotation:

.

TERMINAL HINGE AXIS:

•When the condyles are in their most superior position in the articular fossae and the mouth is purely rotated open, the axis around which movement occurs.

Frontal (vertical) axis of rotation:

Mandibular movement around the frontal axis occurs when one condyle moves anteriorly out of terminal hinge position with the vertical axis of opposite condyle

remaining in the terminal hinge position.

Sagittal axis of rotation:

Mandibular movement around the sagittal axis occurs when one condyle moves inferiorly while the other remains in the terminal hinge position.

TRANSLATIONAL MOVEMENT:

Defined as a movement in which every point of the moving object has simultaneously the same velocity &direction .

Ex: During protrusion

During most normal movements of the mandible ,both rotation &translation occur simultaneously.

This results in complex movements that are extremely difficult to visualize.

.

When the mandible moves through the outer range of motion, reproducible and describable limits result, which are called BORDER MOVEMENTS

Mandibular movements are limited by ligaments and articular surface of TMJ’s as well as the morphology and alignment of the teeth

Sagittal border & functional movementsHorizontal border & functional movementsFrontal border & functional movements

SINGLE-PLANE BORDER MOVEMENTS

Based on extent of movement

Border movement Intraborder movement

Border movement -Mandibular movement at the limits dictated by anatomic structure as viewed in a given plane.

SAGITTAL PLANE BORDER & FUNCTIONAL MOVEMENTS:

Four distinct movement components:

Posterior opening borderAnterior opening borderSuperior contact borderFunctional

Posterior & anterior opening border movements

Limited primarily by the ligaments &the morphology of the TMJs.

Superior contact border movements

Determined by the occlusal&incisal surfaces of the teeth.

Functional movements Not considered border movement., becoz not

determined by an outer range of motion. Determinedby the conditional responses of the neuromuscular

POSTERIOR OPENING BORDER MOVEMENTS:

In the sagittal plane occurs as two-stage hinging movement.

First stage:

.In CR the mandible can be rotated around the horizontal axis

20-25mm

At this point TM ligaments tighten continued opening results in anterior and inferior translation of the condyle.

Second stage:

Opening beyond 20-25mm

Condyles translate

Location of the axis of Rotation shifts to the rami

Condyles moving anteriorly& inferiorly & the anterior portion of mandible is moving posteriorly and inferiorly

Maximum opening is reached when the capsule ligament prevent further movement of condyles

Maximum opening is in range of ---40-60mm

ANTERIOR OPENING BORDER MOVEMENTS:

If the condyle were stabilized in this anterior position, a hinge movement can occur ,when mandible is closing from maximally opened to maximum protruded position..

.

Not a pure hinge movement…>because produces eccentricity in the anterior border movement

Because the maximum protrusive position is determined in part by stylomandibular ligaments, when closure occurs, tightening of ligaments produces a posterior movement of the condyles

SUPERIOR CONTACT BORDER MOVEMENTS:

of the occluding surfaces of the teeth

.Its precise delineation depends on 5 factors:

• Amount of variation between centric relation and maximum intercuspation.

• The steepness of the cuspal inclines of the posterior teeth.

• Amount of vertical and horizontal overlap of anterior teeth.

• Lingual morphology of maxillary anterior teeth.

• General interarch relationships of the teeth.

In centric relation position:

Initial tooth contacts in terminal hinge closure occurs b/n

If muscular force is appliedto the mandible, a Supero-anterior movement or shift will occur untill the intercuspation position is reached.

This CR to maximum intercuspation have a lateral component.

This slide present..>90% population

From early 1950’s to more recently the distance between MI and CR has changed from

1.25 mm by Posselt

1.0mm by Schuyler

0.8 to 0.5mm by Ramfjord

0.2mm Dawson and Ramfjord

The 0.2mm discrepancy between optimum condylar position& MI…>Considered physiological.

In ICP the opposing anterior teeth usually contact.when mandible is protruded from maximum intercuspation, contact between incisal edge of mandible teeth and lingual inclines of maxillary teeth results in an anterio-inferior movement of mandible.

Continue till edge to edge position .at this time a horizontal pathway is followed.

This horizontal movement continue till incisal edge of mandibular teeth pass beyond the incisal edge of maxillary teeth. Mandible moves in a superior direction untill the posterior teeth contact.

occlusal surface of posterior teeth then dictate the remaining pathway to the maximum protrusive movement .

FUNCTIONAL MOVEMENTS:

• Occur during functional activity of the mandible.

• Usually occur within border movements

therefore considered free movements.

• require maximum intercuspation and therefore typically begin at & below the intercuspal position.

Functional movements (GPT 8)-all normal, proper, or characteristic movements of the mandible made during speech, mastication, yawning, swallowing, and other associated movements

Rest position is located approximately 2 to 4 mm below the intercuspal position

Rugh JD,Drago CJ: Vertical dimension: a study of clinical rest position and jaw muscle activity, J Prosthet Dent

concluded that the muscles of mastication are apparently at their lowest level of activity when the mandible is positioned approx 8mm infr and 3mm anterior to ICP

The increased level of electromyographic muscle activity in this position are indicative of myotatic reflex .Because this is not a true resting position ,the position in which the mandible is maintained is more appropriately termed the postural position .

Postural position (GPT 8)- any mandibular relationship occurring during minimal muscle contraction

POSTURAL EFFECTS ON FUNCTIONAL MOVEMENTS:

•When head is positioned erect, postural position of mandible-2-4mm• If the face is directed 45 degrees upward as during drinking.• If face is directed 30 degrees downward as during eating-ALERT FEEDING POSITION…..significant in considering the functional relationships of teeth.

HORIZONTAL PLANE BORDER & FUNCTIONAL MOVEMENTS:

Traditionally GOTHIC ARCH TRACER used for recording mandibular movement in horizontal plane.

components:

Left lateral borderContinued left lateral border with protrusionRight lateral borderContinued right lateral border with protrusion

Left lateral border movements:With the condyles in the centric relation position,,

the result will be a left lateral

border movement.

Left condyle…>rotating condyle / working condyleRight condyle…>orbiting condyle/nonworking condyle

left condyle still in the CR

Continued left lateral border movements with protrusion:

With the mandible in the left lateral border position, contraction of the left inferior lateral pterygoid along with continued contraction of right inferior lateral pterygoid will cause the left condyle to move anteriorly to the right.

Cause a shift in the mandibular midline back to coincide with the midline of the face.

Right lateral border movements:

Mandible comes back to the CR the right lateral border movements

Left condyleorbiting condyle…..as it orbitingaround the frontal axis of the right condyle.

Right condylerotating condyle…because the mandible is rotating around it.

Continued right lateral border movements with protrusion:

With the mandible in the right lateral border position, contraction of the right inferior lateral pterygoid along with continued contraction of left inferior lateral pterygoid will cause the right condyle to move anteriorly to the left.

Lateral movements can be generated by varying levels of mandibular opening .

With each increasing degree of opening- smaller tracings will result

Functional movements:

. Occur near the ICP

During chewing the range of jaw movements begins some distance from maximum intercuspal position; but as the food is broken down into smaller particles, jaw action moves closer and closer to intercuspal position.

EC- area used in the early stages of masticationLC-area used in the later stages of masticationEEP-end- to end position of the anterior position

FRONTAL (VERTICAL) BORDER &FUNCTIONAL MOVEMENTS:

A shield-shaped pattern can be seen that has a functional component, & four distinct movement components:-

Left lateral superior border. Left lateral opening border. Right lateral superior border Right lateral opening border

Left lateral superior border movements:

With the mandible in the maximum intercuspation ,a lateral movement is made to the left .

Inferiorly concave path.

Path determined by : morphology &interarch relationships of the maxillary& mandibular teeth that are in contact during this movement.

condyle –disc-fossa relationships & morphology of the working or rotating side TMJ.

Left lateral opening border movements:

Laterally convex path.

As maximum opening is approached , ligaments tighten& produce a medially directed movement that causes a shift back in the mandibular midline to coincide with the midline of the face.

Right lateral superior border movements:

From maximum intercuspation position a lateral movement is made to the right.

Slight differences may occur due to tooth contacts.

Right lateral opening border movements

Funtional movements:

Begin and end at the Intercuspal position.

During chewing mandible drops directly inferiorly until desired opening is achieved.

It then shifts to the side on which the bolus is placed and rises up.

in maximum intercuspation bolus is broken down between opposing teeth.

In the final millimeter of closure, the mandible shifts back to the intercuspal position.

ENVELOPE OF MOTION:

Represents maximum range of movement of the mandible.

Given by POSSELT

For ex: during a simple lateral movement ,motion occurs around each axis& simultaneouslyeach axis tilts to accommodate tothe other axes.All this happens within the envelope of motion.

Controlled by the neuromuscular system to avoid injury to any of the oral structures.

. This three dimensional space is called the envelope of motion

ECCENTRIC MANDIBULAR MOVEMENT:

Protrusive

sagittal protrusive condylar pathsagittal protrusive incisal path

Mandibular movement anterior to centric relation .(GPT 8)

Occurs while incising and grasping food. This movement occurs after the condyle rotates about in the TMJ.

Sagittal protrusive condylar path:

The orbit produced by the centres of the right & left condyles during protrusive movement is referred to as the PROTRUSIVE CONDYLAR PATH.

S- shaped curve

Curve more obvious in dentulous patients than in edentulous.

Acc to AULL(1965), 8% form a straight line and 92% form a curve.

The angle formed by the protrusive condylar path and the horizontal reference plane is called the “SAGITTAL INCLINATION OF PROTRUSIVE CONDYLAR PATH.”

Acc to ISAACSON (1959) 35.60

Acc to LUNDEEN & WIRTH (1973) 45-500

Acc to HOBO (1982) 5-550 with a

mean of 30.40

Sagittal protrusive incisal path:

The orbit of the incisal point from maximum intercuspation to the edge-to-edge occlusion is referred to as the PROTRUSIVE INCISAL PATH.

Mean length of this path is 5mm with variable paths in different individuals.

Angle formed by the protrusive incisal path &the horizontal reference plane is called the SAGITTAL INCLINATION OF PROTRUSIVE INCISAL PATH.

Range between

50-70 degrees

Steeper than the condylar path (HOBO, 1978)

LATERAL MOVEMENT

They are generally complex activities in most humans.

Important as they influence the intercuspation of the teeth during mastication.

Occurs when one condyle rotates within the temporomandibular fossa and the other condyle translates forward ,inward & downward.

.In practically all cases,howeverlateral excursion is not a simpleArc like movement

FISCHER (1952)

Lateral movement..>Sagittal plane Horizontal plane

Movement from either right or left of the midsagittal plane (GPT 8).

Sagittal lateral condylar path:

When the orbit of the center of the nonworking condyle is traced on the sagittal plane ….SAGITTAL LATERAL CONDYLAR PATH.

This path is longer and usually steeper than the sagittal protrusive condylar path.

The angle formed between the sagittal protrusive condylar path and sagittal lateral condylar path is called the FISCHER ANGLE ,with a mean of 5 degrees.

The angle formed by the sagittal lateral condylar path and horizontal reference plane is called the SAGITTAL INCLINATION OF LATERAL CONDYLAR PATH.

The sagittal inclination of the lateral condylar path ranges between 11-61 degrees with a mean of 330

WORKING SIDE LATERAL MOVEMENT:

Dr.NORMAN GODFREY BENNETT(1908) initially studied the working condylar path and called it BENNETT MOVEMENT,now referred to as LATEROTRUSION.

Bennett showed that working condyle moves outwards

and nonworking condyle moves inwards.

McCollum considered it the most important determinant of occlusion.

Lateral movement in horizontal plane:

Bennett movement is usually recorded with a pantographic survey.

BENNETT SIDE SHIFT; is the bodily side shift of the mandible on the working side in the horizontal plane.

It is also termed as mandibular lateral translation.

restraining influences of the temporomandibular ligament on the working condyle and to some extent by the medial wall of glenoid fossa on the non working side

The average lateral movement is about 0.75 mm (Lundeen et al; 1978)

NON WORKING SIDE LATERAL MOVEMENT:

The non working side will move forward , downward and medially.

this path of nonworking condyle is traced on horizontal plane it is known as the

HORIZONTAL LATERAL CONDYLAR PATH.

It has two components:

Immediate lateral translationProgressive lateral translation

The Bennett side shift was classified based on the timing of the shift in relation to the forward movement of the non working condyle. (lundeen ;1978)

Immediate lateral translationOccurs when the nonworking condyle moves

from the centric relation straight inward or medially,

Mean movement ….>1mm (Lundeen,Wirth,1973)

In a study using electronic mandibulardevice. (Hobo,Mochizuki,1982)

Value of 0-2.6mmwith a mean of 0.42mm.

When downward forward and inward ,there is no ISS.If medially downward and forward , there is ISS

Progressive lateral translation

Translatory portion of lateral movement that

occur at a rate proportional to forward movement of non working condyle

The progressive side shift determines the value of bennett angle

Bennett angle – angle formed between the sagittal plane and the average path of the advancing condyle as viewed in horizontal plane during lateral mandibular movement

Angle is formed due to anterior and medial movement of non working condyle .

Varies b/n 2-440 with a mean of 16.00

lateral movement occurs during the first 2-3mm of the forward movement of the non working side .

Correlation between Bennett angle , immediate lateral translation & progressive lateral translation:

Increase in the Bennett angle causes increase in the other two elements .

Immediate & progressive side shift can be calculated from the Bennett angle.

This method is effective when using the interocclusal record method to determinethe horizontal lateral condylar path

Bennett movement regulated by

1. Anatomical configuration of glenoid fossa 2. Slackness of capsular ligaments 3. Contraction of medial pterygoid on non working

side

REVIEW OF LITERATURE

•Posselt (1956) J Prosthet Dent With the aid of a gnathothesiometer the area of movement for 3 points on mandible were recorded in the 3 main planes. 1 point was close to infradentale and 2 were in the middle of each condyle.

Joseph R. Jarabak (1956) J Prosthet Dent

Electromyographically mandibular movements in subjects wearing dentures were studied.

It was found that correct vertical dimension of occlusion coupled with an adequate interocclusal distance between the teeth of upper and lower denture is essential to maintain the muscles of mastication at there most efficient functional length.

•Hickey et al. ( 1957) J Prosthet Dent.

In this study 3 identical dentures and various food stuff masticated while electromyographic tracings were made..

• It was concluded that ext. pterygoid and suprahyoid muscles were responsible for uncontrolled opening movement while masseter and temporal muscles for closing movement

• Both external pterygoid muscles were responsible for the protrusion of mandible

• William W Wood ( 1987) J Prosthet Dent

According to this article-• Elevator muscles demonstrate

maximum activity when even bilateral occlusal contacts occur during clenching in the intercuspal position.

• Ferrario et al. (1992) Int J Prosthodont.

They found that males have a significantly greater mean value of vertical rest position than do females. There is no gender difference in mean value of maximum opening.

CONCLUSION• The masticatory system is extremely complex.• Mandibular movements is regulated by an intricate

neurologic control system made up of Brain, Brainstem, and the PNS. Each movement is co-ordinated to maximize function while minimizing damage to any structure

• Precise movement of the mandible by the musculature is required to move the teeth effeciently across each other during function

• The mechanics and physiology of this movement hence are basic to the study of masticatory function.