Anatomy and Anatomy and biomechanics of the TMJbiomechanics of the TMJ

By Dr. Rabia Aziz

INTRODUCTIONINTRODUCTION

Area Of Craniomandibular Area Of Craniomandibular ArticulationArticulation Mandibular condyle – Mandibular condyle – Mandibular fossa of the temporal bone.Mandibular fossa of the temporal bone.

Ginglymoarthrodial JointGinglymoarthrodial Joint “ “Ginglymoid jointGinglymoid joint” – hinging ” – hinging

movements.movements. “ “Arthrodial jointArthrodial joint” – gliding movements.” – gliding movements. Compound JointCompound Joint – a joint requires – a joint requires

presence of at least three bones.presence of at least three bones. Synovial JointSynovial Joint – synovial fluid– synovial fluid

TMJ - LOCATIONTMJ - LOCATION

Anatomy Of The TMJAnatomy Of The TMJ

Structures Structures involved are:involved are:

Mandibular Mandibular condyle condyle

Mandibular Mandibular fossa of the fossa of the temporal bone.temporal bone.

Articular discArticular disc

Articular DiscArticular Disc

Sagittal PlaneSagittal Plane It can be divided into It can be divided into

three regions:three regions:1.1. Intermediate zone – Intermediate zone –

thinnest zonethinnest zone2.2. Anterior region – thicker Anterior region – thicker

zonezone3.3. Posterior region – Posterior region –

thickest zonethickest zone Frontal ViewFrontal View thicker medially thicker medially

than laterally than laterally

Posterior Attachments Of Posterior Attachments Of The Articular DiscThe Articular Disc

Bilaminary Bilaminary ZoneZone

1. Retrodiscal 1. Retrodiscal tissuetissue

2. Retrodiscal 2. Retrodiscal laminalamina

Posterior Attachments Posterior Attachments Of The Articular DiscOf The Articular Disc

i. i. Superior Superior retrodiscal retrodiscal laminalamina: :

It attaches the It attaches the

articular disc articular disc posteriorly to posteriorly to the tympanic the tympanic plate.plate.

Posterior Attachments Posterior Attachments Of The Articular DiscOf The Articular Disc

ii.ii. Inferior Inferior retrodiscal retrodiscal laminalamina: :

It attaches the It attaches the inferior border of inferior border of the post edge of the post edge of the disc to the post the disc to the post margin of the margin of the articular surface of articular surface of the condyle. the condyle.

Anterior Attachments Of Anterior Attachments Of The Articular DiscThe Articular Disc

1. 1. Superior attachmentSuperior attachment:: It is to the ant. It is to the ant. margin of the articular margin of the articular surface of the temporal surface of the temporal bone.bone.

2.2. Inferior attachmentInferior attachment: : It is to the ant It is to the ant margin of the articular margin of the articular surface of the condyle.surface of the condyle.

3.3. Middle attachmentMiddle attachment: : It is to the It is to the superior lateral pterygoid superior lateral pterygoid muscle by tendinous muscle by tendinous fibers.fibers.

Lateral and medial Lateral and medial attachments of the attachments of the articular discarticular disc

These divide the joint into two These divide the joint into two cavities:cavities:

1. Upper or superior cavity1. Upper or superior cavity

2. Lower or inferior cavity2. Lower or inferior cavity

TMJ – SYNOVIAL JOINTTMJ – SYNOVIAL JOINT

Synovial Lining – secretion of synovial fluid. Synovial Lining – secretion of synovial fluid. Purpose of the synovial fluidPurpose of the synovial fluidi.i. Acts as a medium for metabolic Acts as a medium for metabolic

requirements.requirements.ii.ii. Acts as a lubricant to reduce friction.Acts as a lubricant to reduce friction.Mechanisms of lubricationMechanisms of lubrication There are two mechanisms:There are two mechanisms:i.i. Boundary lubricationBoundary lubricationii.ii. Weeping lubrication Weeping lubrication

LIGAMENTSLIGAMENTS

Protect the structures in any joint Protect the structures in any joint system.system.

Made up of collagenous Made up of collagenous connective tissue.connective tissue.

can not be stretched due to can not be stretched due to above said characteristic.above said characteristic.

Limit and restrict joint Limit and restrict joint movements within normal limits.movements within normal limits.

Ligaments Related To Ligaments Related To TMJTMJ

There are There are three functional ligamentsthree functional ligaments related to TMJ:related to TMJ:

1.1. Collateral (discal) ligamentsCollateral (discal) ligaments

2.2. Capsular ligamentsCapsular ligaments

3.3. Temporomandibular ligamentsTemporomandibular ligaments There are also There are also two accessory two accessory

ligamentsligaments::

1.1. Sphenomandibular Sphenomandibular

2.2. StylomandibularStylomandibular

Collateral (Discal) Collateral (Discal) LigamentsLigaments Attach the medial and lateral borders Attach the medial and lateral borders

of the articular disc to the poles of the of the articular disc to the poles of the condyle.condyle.

Divide the joint mediolaterally into Divide the joint mediolaterally into superior and inferior joint cavities.superior and inferior joint cavities.

Restrict movement of the disc away Restrict movement of the disc away from the condyle.from the condyle.

Responsible for hinging movement of Responsible for hinging movement of TMJ which occurs between the condyle TMJ which occurs between the condyle and the articular disc.and the articular disc.

Capsular LigamentsCapsular Ligaments

Surrounds the entire TMJ.Surrounds the entire TMJ. Superiorly, attached to the temporal Superiorly, attached to the temporal

bone along the borders of the articular bone along the borders of the articular surfaces of the mandibular fossa and surfaces of the mandibular fossa and articular eminence.articular eminence.

Inferiorly, attached to the neck of the Inferiorly, attached to the neck of the condyle.condyle.

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

Retain the synovial fluid.Retain the synovial fluid.

Temporomandibular Temporomandibular LigamentLigament

Reinforced the lateral aspect of Reinforced the lateral aspect of capsular ligament.capsular ligament.

Composed of two partsComposed of two parts

1.1. Outer oblique portionOuter oblique portion

2.2. Inner horizontal portionInner horizontal portion

1.1. Outer Oblique Outer Oblique PortionPortion

Extends from the outer surface of the Extends from the outer surface of the articular tubercle and zygomatic articular tubercle and zygomatic process posteroinferiorly to the outer process posteroinferiorly to the outer surface of the condylar neck.surface of the condylar neck.

Acts to limit the extent of mouth Acts to limit the extent of mouth opening opening

Resists the impingement of mandible Resists the impingement of mandible on the vital submandibular and on the vital submandibular and retromandibular structures of the neck.retromandibular structures of the neck.

2. 2. Inner Horizontal Inner Horizontal PortionPortion

Extends from outer surface of the articular Extends from outer surface of the articular tubercle and zygomatic process posteriorly tubercle and zygomatic process posteriorly and horizontally to the lateral pole of the and horizontally to the lateral pole of the condyle and posterior part of the articular condyle and posterior part of the articular discdisc

Limits posterior movement of the condyle Limits posterior movement of the condyle and disc.and disc.

Protects the retrodiscal tissues from Protects the retrodiscal tissues from trauma.trauma.

Protects the lateral pterygoid muscle from Protects the lateral pterygoid muscle from overlengthening or extension. overlengthening or extension.

Accessory LigamentsAccessory Ligaments

1.1. SphenomandibulSphenomandibular Ligamentar Ligament

Arises from the spine Arises from the spine of the sphenoid bone of the sphenoid bone and extends downward and extends downward to a small bony to a small bony prominence on the prominence on the medial surface of the medial surface of the ramus of the mandible ramus of the mandible called the lingula.called the lingula.

Not have any Not have any significant effects on significant effects on mandibular movementmandibular movement

Arises from the Arises from the styloid process and styloid process and extends downward extends downward and forward to the and forward to the angle and posterior angle and posterior border of the border of the ramus of the ramus of the mandible.mandible.

Limits excessive Limits excessive protrusive protrusive movements of the movements of the mandible by mandible by becoming taut.becoming taut.

2.Stylomandibular 2.Stylomandibular LigamentLigament

Muscles Of MasticationMuscles Of Mastication

There are four pairs of muscles:There are four pairs of muscles:

1.1. MasseterMasseter

2.2. TemporalisTemporalis

3.3. Medial pterygoidMedial pterygoid

4.4. Lateral pterygoid.Lateral pterygoid.

1.1. MasseterMasseter

Originate from Originate from zygomatic arch zygomatic arch and extends and extends downward to the downward to the lateral aspect of lateral aspect of the lower border the lower border of the ramus of of the ramus of the mandible. the mandible.

Superficial portionSuperficial portion – runs downward – runs downward and slightly and slightly backwardbackward

Deep portionDeep portion – runs – runs predominantly in predominantly in vertical direction.vertical direction.

ActionAction – elevate – elevate and protrude the and protrude the mandiblemandible

22. . TemporalisTemporalis

Originate from temporal Originate from temporal fossa and the lateral fossa and the lateral surface of the skull.surface of the skull.

All fibers come together All fibers come together as they extend downward as they extend downward between the zygomatic between the zygomatic arch and lateral surface of arch and lateral surface of the skull to form a tendon the skull to form a tendon that inserts on the that inserts on the coronoid process and coronoid process and anterior border of the anterior border of the ascending ramus.ascending ramus.

Anterior FibersAnterior Fibers – – elevate the elevate the mandiblemandible

Middle And Middle And Posterior FibersPosterior Fibers – – elevate and elevate and retrude the retrude the mandible. mandible.

3. 3. Medial PterygoidMedial Pterygoid

Originates from Originates from pterygoid plate and pterygoid plate and extends downward, extends downward, backward and outward backward and outward to insert along the to insert along the medial surface of the medial surface of the mandibular angle.mandibular angle.

ActionAction – elevate and – elevate and protrude the mandibleprotrude the mandible

4. 4. Lateral PterygoidLateral Pterygoid

This muscle has two This muscle has two bellies bellies

1.1. Inferior bellyInferior belly Originates at the Originates at the

outer surface of outer surface of the pterygoid the pterygoid plate and extends plate and extends backward upward backward upward and outward to its and outward to its insertion primarily insertion primarily on the neck of the on the neck of the condyle.condyle.

2.2. Superior bellySuperior belly Originates at the Originates at the

infratemporal surface infratemporal surface of the greater of the greater sphenoid wing, sphenoid wing, extending almost extending almost horizontally, horizontally, backward and backward and outward to insert on outward to insert on the articular capsule, the articular capsule, the disc and the neck the disc and the neck of the condyle.of the condyle.

Action:Action:

1.1. Protrusion of the mandibleProtrusion of the mandible

2.2. Side to side movementSide to side movement

Biomechanics Of The Biomechanics Of The TMJTMJ

The TMJ is a compound joint. Its The TMJ is a compound joint. Its structure and function can be divided structure and function can be divided into two distinct systems:into two distinct systems:

1.1. Inferior Joint SystemInferior Joint System2.2. Superior Joint SystemSuperior Joint System

1.1. Inferior Joint SystemInferior Joint System

composed of condyle and articular composed of condyle and articular disc.disc.

Disc is tightly bound to the condyle Disc is tightly bound to the condyle by lateral and medial discal by lateral and medial discal ligamentsligaments

Only physiologic movement that can Only physiologic movement that can occur here is rotation of the disc on occur here is rotation of the disc on the articular surface of the condyle.the articular surface of the condyle.

2.2. Superior Joint SystemSuperior Joint System

Here condyle-disc complex Here condyle-disc complex functions against the surface of functions against the surface of the mandibular fossa.the mandibular fossa.

Disc is not tightly attached to Disc is not tightly attached to the mandibular fossathe mandibular fossa

Sliding movements (translation) Sliding movements (translation) are possible here.are possible here.

StabilityStability – maintained by constant – maintained by constant activity of the muscles that pull across activity of the muscles that pull across the joint, primarily the elevators.the joint, primarily the elevators.

Even in resting stage, these muscles are Even in resting stage, these muscles are in a mild stage of contraction called in a mild stage of contraction called tonus.tonus.

Interarticular pressure increases as Interarticular pressure increases as muscle activity increases.muscle activity increases.

Width of the articular disc varies with Width of the articular disc varies with the interarticular pressure.the interarticular pressure.

Superior retrodiscal laminaSuperior retrodiscal lamina – retracts – retracts the disc posteriorly on the condyle.the disc posteriorly on the condyle.

The interarticular pressure and The interarticular pressure and morphology of the disc prevent the morphology of the disc prevent the disc from being overretracted disc from being overretracted posteriorly.posteriorly.

Superior lateral pterygoid muscleSuperior lateral pterygoid muscle – – protracts the disc anteriorly and protracts the disc anteriorly and medially.medially.

Anterior capsular ligament and inferior Anterior capsular ligament and inferior retrodiscal laminaretrodiscal lamina force the disc to force the disc to translate forward with the condyle.translate forward with the condyle.

Tonus of the superior lateral Tonus of the superior lateral pterygoid muscle is greater than pterygoid muscle is greater than the superior retrodiscal lamina.the superior retrodiscal lamina.

At rest, with the mouth closed the At rest, with the mouth closed the condyle will normally be in contact condyle will normally be in contact with the intermediate and with the intermediate and posterior zones of the disc.posterior zones of the disc.

LIGAMENTS AND LIGAMENTS AND MUSCLES INVOLVEDMUSCLES INVOLVED

MAKING IT MAKING IT RIDICULOUSLY EASYRIDICULOUSLY EASY

Basic Orthopedic Basic Orthopedic Principles Related To TMJPrinciples Related To TMJ

1.1. Ligaments do not actively Ligaments do not actively participate in function of the TMJ. participate in function of the TMJ. They act as guide wires, restricting They act as guide wires, restricting certain joint movements while certain joint movements while permitting others. permitting others.

2.2. Ligaments do not stretch. If Ligaments do not stretch. If traction force is applied, they can traction force is applied, they can become elongated which leads to become elongated which leads to compromised joint function.compromised joint function.

3.3. The articular surfaces of TMJ must The articular surfaces of TMJ must be maintained in constant contact. be maintained in constant contact. This contact is produced by the This contact is produced by the muscles that pull across the joint ( muscles that pull across the joint ( the elevators: temporal, masseter, the elevators: temporal, masseter, and medial pterygoid).and medial pterygoid).

A sound understanding of these A sound understanding of these principles is necessary for the principles is necessary for the evaluation and treatment of the evaluation and treatment of the various disorders.various disorders.