FUNCTIONAL ANATOMY

OF TMJ

CONTENTS

• Introduction• Types of joint• Development of TMJ• Mandibular fossa• Condyle• Articular disc• Histology of articular surfaces• Innervation of TMJ• Vascularization of TMJ• Ligaments• Muscles of mastication• Biomechanics• Conclusion• References

INTRODUCTION

• The Temporomandibular joint is that which connects the mandible to the skull and regulates mandibular movement.

• It is a bicondylar joint in which the condyles, located at the two ends of the mandible, function at the same time.

TYPES OF JOINTA Joint is an articulation between two bones.1. Fibrous Joint: immovable joint–Suture - skull–Gomphosis - teeth–Syndesmosis – interosseous

2.Cartilaginous Joint: limited movement–Primary or synchondroses• Hyaline cartilage at ends of long bones

–Secondary or symphysis• Bone-cartilage-fibrous tissue-cartilage-bone; symphysis menti

3.Synovial Joint: permits free movement between two bones; surrounded by capsule enclosing joint cavity filled with synovial fluid. According to shape of articulating surface:– Ginglymoid– Pivot– Condyloid– Ball-and-socket

Craniomandibular articulation – TMJ Complex joint in the body

Hinging movement – ginglymoid joint Gliding movements - arthrodial joint

ginglymoarthrodial joint

hence TMJ is a complex diarthrodial sliding-ginglymoid synovial joint, which attaches the mandible to petrous part of temporal bone of the cranium.

Seperating these two bones from direct articulation is the Articular disc.

TMJ – Classified as Compound joint

articular disc – serve as non ossified bone that permits complex movements of the joint.

Artricular disc - interposed between the condyle of the mandible and the glenoid fossa of the temporal bone.

The articular surface of the temporal bone has a

posterior concave part – mandibular fossa

Anterior convex part – articular tubercle or eminence

DEVELOPMENT OF TMJ

• The TMJ develops from mesenchyme lying between the developing mandibular condyle below and the bone above, which develop intramembranously.

• During the 12th week of IU life ,2 clefts appear in the mesenchyme –producing the upper and lower joint cavities.

• The remaining intervening mesenchyme becomes the intra – articular disc.

• The joint capsule develops from a condensation of mesenchyme surrounding the developing joint

• Mandibular fossa is flat at birth and there is no articular eminence , this becomes prominent only following the eruption of the decidous dentition.

MANDIBULAR FOSSA

Bounderies-• Anterior aspect articular

eminence • Posterior non articular

fossa Is a part of temporal squama and is formed by tympanic plate which also forms the anterior bony wall of external auditory meatus

• As temporal squama and tympanic plate converge medially on the spine of the sphenoid bone – intersposed is the bony edge of the roof of the tympanic cavity –tegmen tympani

• Squamotympannic fissure - fissure between the temporal squama and tympannic bone

• It is divided medially into anterior part -petrosquamous fissure and posterior part petrotympannic fissure/glaserian fissure.

• Laterally petrotympannic fissure allows passage of chorda tympani nerve.

• At the posterior border of the fossa – a tubercle or cone shaped process present laterally between tympanic bone and fossa.

• This prevents direct impingement of condyle on the tympanic plate.

• the medial border of articular fossa also contains a bony lip which extends into angular spine of sphenoid bone .

• These two bone processes or lips limit condylar displacement distally and laterally as well as vertically.

A IKAI et al (ajodo 112;634:8)

• Studied the relationship between temporal component of TMJ – mandibular fossa and articular eminence) with facial bone structure.

• The angle between the line deepest point of the fossa- the midpoint of the eminence and FH plane (middle angle) was negatively correlated only with ANB angle suggesting that a steeper middle angle of eminence is related to retrusive maxilla or protrussive mandible.

CONDYLEBarrel shape –

measuring – 20mm – mediolateral 10mm – anteroposterior

• Perpendicular to ascending ramus of the mandible

• Oriented 10 – 30 degrees with frontal plane.

Medial pole more prominent than lateral pole

Articular surface of Posterior aspect > anterior aspect

• In the frontal view – articular eminence often is concave and fits roughly to superior surface of condyle

• Bony surface of condyle and articular part of the temporal bone – covered with dense fibrous connective tissues with irregular cartilage like cells

• The number of cells increases with age and stress on the joint.

ARTICULAR DISC• Biconcave oval structure –

intersposed between the condyle and the temporal bone.

• Consists of dense collagenous tissue that is avascular , hyaline and devoid of nerve tissues in the central area but has vessels and nerves in the peripheral area.

• Divided into 3 regions in the Saggital plane

• Intermediate zone • Posterior • Anterior

• Articular surface situated in the intermediate zone

Anterior view – disc thicker medially than laterally

Shape of disc – determined by morphology of condyle and mandibular fossa.

• During movement the disc is flexible to some extent and can adapt to the functional demands of the articular surfaces.

• The disc maintains its morphology unless destructive forces or structural changes occur in the joint.

• If these changes occur , the morphology of the disc can be irreversibly altered producing biomechanical changes during function.

• ATTACHMENTS OF DISC -

• Retrodiscal tissue - posterior attachment highly vascularized

• Superior retrodiscal lamina – elastic fibres

• Inferior retrodiscal lamina - collagenous fibres.• Remaining – large venous plexus which fills with

blood as condyle moves forward.

Anteriorly–superior and inferior attachments of the disc– capsular ligament

• Superior attachment –articular surface of temporal bone

• Inferior attachment – articular surface of condyle• Composed of collagen fibres• Between the capsular ligament attachment – superior

lateral pterygoid muscles.

Capsular ligament attachment medially and laterally also – dividing joint into 2 cavities.

Superior cavity – mandibular fossa and superior surface of disc.

Inferior cavity –mandibular condyle and inferior surface of disc

• The internal surface of the cavities are surrounded by specialized endothelial cells that form a synovial lining.

• This lining along with a specialized synovial fringe located at the anterior border of the retrodiscal tissue produces synovial fluid which fills both the joint cavities

• TMJ – synovial joint.

Synovial fluid serves 2 purposes

1. Medium for providing metabolic requirements to the non vascular articular surface of the joint.

2. Lubricant between articular surfaces during function.

2 mechanisms by which synovial fluid lubricates are3. Boundary lubrication4. Weeping lubrication

Boundary lubrication• Occurs when joint is moved and synovial fluid is

forced from one area of cavity into another.

• The synovial fluid located in the border or recess areas is forced on the articular surface thus providing lubrication.

• Weeping lubrication• Refers to the ability of articular surfaces to absorb a

small amount of synovial fluid• During function of a joint , forces are created

between the articular surfaces • These forces drive a small amount of synovial fluid in

and out of articular tissues.• This is the mechanism by which metabolic exchange

occurs.

Under compressive forces therefore, a small amount of synovial fluid is released.

This synovial fluid acts as a lubricant between articular tissues to prevent sticking,

Weeping lubrication helps eliminate friction in compressed but not a moving joint.

Only a small amount of friction is eliminated by weeping lubrication.

Therefore prolonged compressive forces to the articular surfaces will exhaust this supply.

HISTOLOGYOF ARTICULAR SURFACES

The articular surfaces of the condyle and the mandibular fossa are composed of four distinct layers or zones.

• Articular zone

• Most superficial layer• Found adjacent to the joint cavity and forms the

outermost functional surface.• Made up of dense fibrous connective tissue .• The collagen fibres are arranged in bundles and

oriented nearly parallel to the articular surface.

• The fibres are tightly packed and are able to withstand the forces of movement.

• It is less susceptible to the effects of aging and therefore is less likely to breakdown over time.

• It also has much better ability to repair than does hyaline cartilage.

• The importance of these two factors is significant in tmj function and dysfunction.

• Proliferative zone

• Undifferentiated mesenchymal tissue –

• This is responsible for the proliferation of articular cartilage in response to the functional demands placed on articular surfaces during loading.

• Fibrocartilagenous zone

• Collagen fibrils are arranged in bundles in a crossing pattern.

• The fibrocartilage appears in a random orientation ,providing three dimensional network that offers resistance against compressive and lateral forces.

• Calcified zone

• Made up of chondrocytes and chondroblasts distributed throughout the articular cartilage.

• In this zone , the chondrocytes become hypertrophic, die and have their cytoplasm evacuated , forming bone cells from within the medullary cavity.

• The articular cartilage is composed of chondrocytes and intercellular matrix.

• The chondrocytes produce collagen , proteoglycans , glycoproteins , and enzymes that form the matrix.

• Proteoglycans – complex molecule composed of a protein core and glycosaminoglycan chains.

• The proteoglycans are connected to a hyaluronic acid chain , forming proteoglycan aggregates that make up a great protein of the matrix.

• These aggregates are very hydrophilic and are intertwined throughout the collagen network .

• Since these aggregates tend to bind water ,the matrix expands and the tension in the collagen fibrils counteracts the sweeping pressure of the proteoglycan aggregates.

• In this way the interstitial fluid contributes to support joint loading .

• The external pressure resulting from joint loading is in equilibrium with the internal pressure of the articular cartilage.

• As joint loading increases , tissue fluid flows outward until a new equilibrium is achieved.

• As loading is decreased , fluid is reabsorbed and the tissue regains its original volume.

• Joint cartilage is nourished predominantly by diffusion of synovial fluid, which depends on this pumping action during normal activity.

• The pumping action is the basis for the weeping lubrication, and this action is thought to be very important in maintaining healthy articular cartilage.

Vincent .P. Willard Archieves of oral biology (2012) 599- 606

• Vincent concluded that although the TMJ disc and its attachments form a seamless complex within the joint ,a closer look at the biochemical constituents reveals that these 2 components are distinct .

• While the disc and attachments both contain the same major constituents ,the relative amounts of these components vary based on functional requirements of the tissue

• Disc region have more higher sulfated GAG and collagen content than the attachment regions.

• In contrast attachment regions –contains more DNA content than disc region.

INNERVATION OF TMJ

• Most innervation is provided by the auriculotemporal nerve as it leaves the mandibular nerve behind the joint and ascends laterally and superiorly to wrap around the posterior region of the joint

• Additional innervations by – deep temporal and massetric nerve.

VASCULARIZATION OF TMJ

• Predominant vessels are • Superficial temporal artery - from the posterior• Middle meningeal artery - from the anterior• Internal maxillary artery – from the inferior• Other important arteries are – the deep

auricular ,anterior tympanic and ascending pharyngeal arteries.

• The condyle – through marrow spaces by way of the inferior alveolar artery .

Superficial temporal artery Middle meningeal artery Maxillary artery

LIGAMENTS

• Ligaments play an important role in protecting the structures

• The ligaments of the joints are made up of collagenous connective tissue, which do not stretch.

• They do not enter actively into joint function but instead act as a passive restraining devices to limit and restrict border movements.

• 3 funtcional ligaments support the TMJ :1. Collateral ligaments 2. Capsular ligament 3. TM ligament

2 accessory ligaments4. Sphenomandibular ligament5. Stylomandibular ligament

• Collateral (discal) ligaments• Attach the medial and lateral

borders of the articular disc to the poles of the condyle

• Commonely called as discal ligaments – medial and laterlal

• Medial discal ligament – attaches the medial edge of the disc to the medial pole of the condyle.

• Lateral discal ligament – attaches the lateral edge of the disc to the lateral pole of the condyle,

• These ligaments are responsible for dividing the joint mediolaterally into the superior and inferior joint cavities.

• The discal ligaments are true ligaments ,composed of collagenous connective tissue fibres , therefore they do not stretch.

• They allow the disc to move passively with the condyle as it glides anteriorly and posteriorly on the articular surface of the condyle

• Thus these ligaments are responsible for the hinging movement of the TMJ , which occurs between the condyle and the articular disc.

• These ligaments have a vascular supply and are innervated .

• Strain on these ligaments produces pain.

Capsular ligament• The entire TMJ is

surrounded and encompassed by the capsular ligament .

• The fibres of the capsular ligament are attached superiorly to the temporal bone along the borders of the articular surface of the mandibular fossa and articular eminence

• Inferiorly the fibers of the capsular ligament attach to the neck of the condyle.

• The capsular ligament -resist any medial, lateral or inferior forces that tend to separate or dislocate the articular surfaces.

• 1 significant function – to encompass the joint thus retaining the synovial fluid.

• Capsular ligament is well innervated and provides proprioceptive feedback regarding position and movement of joint.

• Temporomandibular ligament

The lateral aspect of the

capsular ligament is reinforced by strong , tight fibres – lateral ligament or TM ligament.

TM ligament has 2 parts • Outer oblique portion• Inner horizontal portion

• Outer portion – extends from outer surface of the articular tubercle and zygomatic process posteroinferiorly to the outer surface of the condylar neck.

• Inner horizontal portion – extends from the outer surface of the articular tubercle and zygomatic process posteriorly and horizontally to the lateral pole of the condyle and posterior part of articular disc.

• Oblique portion – resists excessive drooping of the condyle – limiting the extent of mouth opening.

• During the initial phase of opening ,the condyle can rotate around a fixed point until the TM ligament becomes tight as its point of insertion on the neck of the condyle is rotated posteriorly.

• When the ligament is taut , the neck of the condyle cannot rotate further .

• If mouth were to be opened wider- the condyle has to move downward and forward across the articular eminence.

• Clinically tested by – closing the mouth and applying mild posterior force to the chin-jaw easily rotates until teeth are 20 – 25mm apart after which a resistance is felt when the jaw is opened wider.

• This resistance is brought about by the tightening of TM ligament.

This unique feature of TM ligament which limits rotational opening is found only in humans.

• The inner horizontal portion of TM ligament limits posterior movement of condyle and disc.

• When force applied to the mandible it displaces the condyle posteriorly , this portion of ligament becomes tight and prevents the condyle from moving further into the posterior region of the mandibular fossa.

• Hence it protects the retrodiscal tissues from trauma created by posterior displacement of the condyle.

• Also protects the lateral pterygoid muscle from overextension or overlengthening.

• The effectiveness of TM ligament is demonstrated during cases of extreme trauma to the mandible.

• In such cases the neck of the condyle is seen to fracture before the retrodiscal tissues are severed.

• Sphenomandibular ligament

• Accesory ligament of the TMJ• Arises from the spine of the

sphenoid bone and extends downwards to a small bone prominence on the medial surface of the ramus of the mandible called the lingula.

• It does not have any significant limiting effects on mandibular movement.

• Stylomandibular ligament

• It arises from the styloid process and extends downwards and forward to the angle and posterior border of the ramus of the mandible.

• It becomes taut when the mandible is protruded but is most relaxed when the mandible is opened.

• The stylomandibular ligament therefore limits the excessive protrusive movements of the mandible.

MUSCLES OF MASTICATION

The skeletal components of the body are held together and moved by the skeletal muscles.

• Muscles fibers ranging between 10 – 80mm subunits According to amount of myoglobin Muscles slow/type1 muscle fibers

fast/type ll fibers.

• Slow muscle fibers- • Deeper in red color due to higher concentration of

myoglobin,• Capable of slow but sustained contraction• Well developed aerobic metabolism therefore

resistant to fatigue.

• Fast muscle fibers –• Whiter due to lower concentrations of myoglobin • Have fewer mitochondria and rely more on

anaerobic activity for function.• Capable of quick contraction but fatigue more quickly

• All skeletal muscles contain a mixture of fast and slow fibers in varying proportions, which reflect the function of that muscle.

• Muscles that respond quickly – predominantly white fibers• Muscles for slow continuous activity – higher concentration of slow fibers

• 4 pairs of muscles – muscles of mastication1. Masseter2. Temporal3. Medial pterygoid 4. Lateral pterygoid

Masseter muscle• Orgin -Rectangular muscle that originates from the

zygomatic arc and extends downward to the lateral aspect of the lower border of the ramus of the mandible.

• Insertion - extends from the region of the second molar in the mandible at the inferior border posteriorly to include the angle.

• 2 portions – • superficial portion (fibers

run downward and slightly backward)

• Deep portion (fibers run predominantly in vertical direction)

Function – elevation of mandible and teeth brought into contact• Superficial portion – aid in protruding the mandible• When the mandible is protruded and biting force is

applied ,the fibers of deep portion stabilize the condyle against the articular eminence.

Acta Odontologica Scandinavica, 2008; 66: 2330

Studies concluded that there is a significant association between the posterior-to-anterior facial height ratio and the masseter muscle in children, indicating that subjects with stronger masseter muscles have an increased posterior facial height for a given anterior facial height. Girls show greater associations than boys between

the masseter muscle and vertical craniofacial morphology.

Stavros Kiliaridis et al ,European Journal of Orthodontics 25 (2003) 259–263

Studied the relationship between thickness of masseter muscle and width of maxillary dental arch and results showed that -

• Masseter muscle thickness was greater in older individuals and in males.

• In the female group, maxillary intermolar width showed a direct, significant association with masseter thickness both during contraction and relaxation i.e. females with thicker masseter muscles had a wider maxillary dental arch.

• The findings of this study indicate that the functional capacity of the masticatory muscles may be considered as one of the factors influencing the width of the maxillary dental arch.

• Temporal muscle• Orgin-Large fan shaped

muscle that originates from the temporal fossa and lateral surface of the skull.

• Divided into 3 distinct areas according to fiber direction and ultimate function -anterior, middle and posterior portion

• Anterior portion – vertically directed fibers

• Middle portion -obliquely across lateral aspect of the skull

• Posterior portion –horizontally alligned fibers

Function - elevates mandible and teeth brought into contact

• Contraction of anterior portion – mandible raised vertically• Contraction of middle portion –elevates and retrudes • Contraction of posterior portion – elevation and slight retrusion

• Because the angulation of its muscle fibers varies , the temporal muscle is capable of co ordinating closing movements. It thus is a significant positioning muscle of mandible.

• Clinical examination:• "Ask the patient to clench their teeth while you

palpate both masseter muscles above the angles of the jaw and then while you palpate both temporalis muscles over the temples."

• Medial pterygoid muscle

• Origin - from the pterygoid fossa and extends downward, backward and outward to insert along the medial surface of the mandibular angle.

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

Function – mandible elevated and teeth brought into contact - also active in protruding the mandible. - unilateral contraction brings about a mediotrusive movement of the mandible

Lateral pterygoid muscle• Divided into 2 –since their functions are nearly

opposite - inferior lateral pterygoid muscle superior lateral pterygoid muscle

Inferior lateral pterygoid muscle

• Origin- at the outer surface of the lateral pterygoid plate and extends backward, upward and outward to its insertion primarily on the neck of the condyle.

• function – when the inferior right and left lateral pterygoid muscle contracts simultaneously –condyles are pulled down their articular eminences and mandible is protruded.

• Superior lateral pterygoid muscle

• Smaller than inferior muscle

• Origin- at infra temporal surface of the greater sphenoid wing , extending almost horizontally , backward and outward to insert on the articular capsule, the disc and the neck of the condyle.

• While the inferior lateral pterygoid muscle is active during opening ,the superior lateral pterygoid muscle remains inactive ,becoming active only in conjugation with the elevator muscles.

• Function -Superior lateral pterygoid muscle is especially active during power stroke (movements that invovle closure of mandible against resistance, such as chewing or clenching the teeth together)

• Approximately 80% of the fibers that make up both lateral pterygoid muscles are slow muscle fibers /type I which suggest that these muscles are relatively resistant to fatigue and may serve to brace the condyle for long periods of time without difficulty.

• Clinical examination of pterygoid muscles

• by forcefully opening the jaw against resistance • with unilateral lateral pterygoid weakness the jaw

deviates to the ipsilateral side as it opens.

• As a person yawns ,the head is brought back by contraction of the posterior cervical muscles , which raises the maxillary teeth .

• This simple example shows that normal functioning of the masticatory system uses many more muscles than those of mastication.

• Muscles of mastication is only a part of this complex system

Other accesory muscles are –

Digastric muscle• Though not a masticatory

muscle-important influence on the function of mandible.

• Divided into 2 –

posterior belly of digastric anterior belly of digastric

Orgin-• Posterior belly –originates from mastoid notch ,

medial to mastoid process – fibers run forward , downward and inward to intermediate tendon attached to hyoid bone.

• Anterior belly - originates at a fossa on the lingual surface of mandible ,close to the midline – fibers run downward and backward to insert at the same intermediate tendon as does the posterior belly.

• Function – • When the right and left digastric muscle contract and

the hyoid bone fixed by suprahyoid and infrahyoid muscles ,the mandible is depressed and pulled backward and teeth are brought out of contact.

• When the mandible is stabilized the digastric muscles with the suprahyoid and infra hyoid muscles elevate the hyoid bone ,which is a necessary function for swallowing.

• The digastric are one of the many muscles that depress the mandible and raise the hyoid bone.

• STERNOCLEIDO MASTOID MUSCLE

• Large superficial muscles of the neck that also play a role during mastication

• Orgin –• the sternal head is tendinous and

arises from the superolateral part of the front of the manibrium sterni

• The clavicular head is musculotendinous and arises from the medial one – third of the superior surface of the clavicle.

• It passes deep to the sternal head and the 2 heads blend below the middle of the neck.

Function -• When one muscle contracts it turns the chin to

opposite side .• When both muscles contract together they draw the

head forwards as in eating and in lifting the head from pillow.

Muscles of Mastication

Temporalis muscleelevation

Medial PterygoidLateral Pterygoid

protrusion

Medial PterygoidTemporalis muscleretrusion

lateral movements Medial PterygoidLateral Pterygoid

depressionMylohyoidInferior bellyof diagastric

BIOMECHANICS OF TMJ

• The TMJ is an extremely complex joint system -2 TMJ connected to the same bone.

• TMJ structure can be divided into 2 systems- 1. Joint system – surrounds the inferior synovial cavity

– condyle and the articular disc(condyle –disc complex)

Since disc is tightly bound to condyle by lateral and medial discal ligaments, the only physiologic movement that can occur between these surfaces is rotation of on the articular surface of condyle .

This joint system responsible for rotational movement in TMJ.

2 Second system is made up of the condyle – disc complex functioning against the surface of the mandibular fossa.

• Since the disc is not tightly attached to the mandibular fossa , free sliding movement is possible between these surfaces in the superior cavity.

• This movement occurs when the mandible is moved forward – transalation.

• Transalation – occurs between superior surface of articular disc and mandibular fossa.

• Thus articular disc – non ossified bone – hence TMJ classified as compound joint.

• The articular surfaces of the joint have no structural attachment or union-yet contact must be maintained for joint stability.

• Joint stability-maintained by constant activity of muscles that pull across the joint.

• Even in resting state ,these muscles are in mild state of contraction –tonus.

• as muscle activity increases –condyle forced against disc and disc against mandibular fossa - resulting in increase in interarticular pressure .

• In the absence of interarticular pressure- articular surfaces separate and joint dislocates.

• Width of articular disc space varies with interarticular pressure.

• When pressure is low- closed rest position – disc space widens.

• When pressure is high – clenching of teeth – disc space narrows.

• As interarticular pressure increases – condyle seats itself on the intermediate zone

• When pressure is decreased –disc space widens and thicker portion of disc is rotated to fill the space.

• Since anterior and posterior bands are thicker than intermediate zone – disc rotates anteriorly or posteriorly to accomplish the task.

• Disc attached posteriorly – retrodiscal tissues which are highly elastic- hence condyle can move out of fossa without creating damage to superior retrodiscal lamina.

• During mandibular opening –condyle is pulled forward down the articular eminence ,the superior retrodiscal lamina becomes increasingly stretched , creating increased forces to retract the disc.

• The interarticular pressure and the morphology of the disk prevent the disc from being overetracted posteriorly.

• Superior retrdiscal lamina –only structure capable of retracting the disc posteriorly on the condyle.

• Anterior border of articular disc attached to -superior lateral pterygoid

• Constantly maintained in a mild state of contraction or tonus –exerts slight anterior and medial force on the disc.

• In the resting closed joint position thus anterior and medial force will normally exceed that of nonstretched Superior retrodiscal lamina.

• Therfore in the resting closed joint position when the interarticular pressure is low and disc space widened –disc will occupy most anterior rotary position on the condyle and the condyle in contact with intermediate and posterior zones of the disc.

• This disc relationship is maintained during minor passive rotational and transalatory mandibular movements.

• As condyle moves more forward – Superior retrodiscal lamina gets stretched –greater force than the superior lateral pterygoid – allows disc to be rotated posteriorly to extent permitted by width of articular disc space.

At rest condyle rests on posterior band; beginning of translation, it lies over the intermediate zone; when mouth is fully open, it lies over the anterior band.

Power stroke –• When resistance is met during mandibular closure (biting hard food) – interarticular pressure on biting

side is decreased –because force of closure applied to food not to joint .

• With condyle forward and disc space increased –tension of Superior Retrodiscal lamina will tend to retract the disc from a functional position-resulting in separation of articular surfaces leading to dislocation.

• To avoid this –superior lateral pterygoid becomes active during power stroke rotating disc forward on condyle so thicker posterior border of disc maintains articular contact-therfore joint stability maintained.

• As teeth pass through the food and approach intercuspation –interarticular pressure is increased –disc space decreased – disc rotated posteriorly so thinner intermediate zone fills the space.

• When the force of closure is discontinued the resting closed joint position is once again assumed.

• Joseph H. Kronman et al (ajodo 1994;105:257-64.)

• Investigated the site of lateral pterygoid muscle insertion into the TMJ disk, and the relationship between that attachment and the disk.

• Results indicated a statistically significant relationship between functional muscle attachment and disk displacement.

• the SLP can maintain disk displacement only when it inserts directly into the disk.

• In cases of normal disk arrangement and condylar attachment, the muscle may not play a clinically significant role in disk displacement because disk attachment at the medial and lateral poles of the condyle allows the disk to move freely with the condyle.

• This movement of the condyle and the disk may overcome the pull of the SLP when normal disk attachment is maintained.

CONCLUSION

• It is impossible to comprehend the fine points of occlusion without an in depth awareness of the anatomy ,physiology ,and biomechanics of the TMJ.

• The first requirement for successful occlusal treatment is stable, comfortable TMJ.

• The jaw joints must be able to accept maximum loading by the elevator muscles with no signs of discomfort.

• It is only through an understanding of how the normal, healthy TMJ functions that we can make sense out of what is wrong when it isn't functioning comfortably.

• This understanding of TMJ is foundational to diagnosis and treatment.

THANKYOUTHANKYOU

References

1. Gray’s Anatomy2. Fundamentals of occlusion and TMJ disorders -- Okeson3. Grant’s Atlas of Human Anatomy4. Occlusion – Ash RamfJord5. Orthodontics Principles and Practice -- T.M.Graber6. Joseph H. Kronman et al (ajodo 1994;105:257-64.)

7. Stavros Kiliaridis et al ,European Journal of Orthodontics 25 (2003) 259–263

8. Acta Odontologica Scandinavica, 2008; 66: 23309. Vincent .P.Willard Archieves of oral biology (2012)

599- 60610. A IKAI et al (ajodo 112;634:8)