Week 9 TMJ and Respiratory Biomechanics

What type of joint is the TMJ?

The TMJ is a synovial joint.

What are the two main surfaces of the TMJ?

The convex mandibular condyle and the concave mandibular fossa.

Mandibular fossa

articular and non articular

Articular (mandibular) Fossa

articular eminence

articular eminence

Load bearing surface that's made of thick compact bone lined with fibrocartilage

Non-articular mandibular fossa

Thin bone and fibrocartilage of superior dome of the fossa

Large upward force applied to chin can fracture

Non-articular mandibular fossa

Full opening of the mouth requires each condyle to

slide forward across the articular eminence

Shear at the interface of the TMJ

may compress and fragment the fibrocartilage

Indicator of degenerative arthritis at the TMJ

Inflammation and fragmentation from shear forces

TMJ is made of

fibrocartilage

TMJ blood and sensory nerves location

only in periphery

What is the role of the TMJ disc?

The disc maximizes congruence of the TMJ, reduces contact pressure, provides stability, and cushions large forces during mastication.

What are the three parts of the TMJ disc?

Posterior, intermediate, and anterior parts.

Posterior TMJ capsule

Convex superiorly

Concave inferiorly

Accepts mandibular condyle

Posterior tmj attaches to

retrodiscal lamina

Inferior retrodiscal lamina

Collagenous fibers, attaches disc to posterior margin of articular surface of the condyle

superior retrodiscal lamina

Elastic properties that allow the disc to move forward and bring it back

Maintains meniscus between the condyle and eminence

intermediate TMJ capsule

Concave inferior

Flat superior

Anterior TMJ

Nearly flat inferior

Concave superiorl

Superior head of the Lateral Pterygoid tendon attaches here

Temporal Bones also attach here

Anterior TMJ capsule

Disc cushions large forces inherent to

muscles of mastication

Inferior synovial joint cavity

Between the disc and mandibular condyle

superior mandibular cavity

Between disc and mandibular fossa and articular eminence

What is the function of the lateral ligament of the TMJ?

It stabilizes the lateral side of the capsule and limits depression and retrusion of the mandible.

Tears of the lateral ligament may cause what

the disc to migrate medially

what tears the lateral ligament

Caused by pull of lateral pterygoid superior head

obliques lateral ligament

limits depression and retrusion of the mandible

horizontal lateral ligament

prevents posterior displacement of the condyle and disc

What are the accessory ligaments of the TMJ?

Stylomandibular ligament and sphenomandibular ligament.

Accessory ligaments of the TMJ job

help suspend the mandible from the cranium

How does the TMJ capsule contribute to joint stability?

The fibrous capsule attaches to the rim of the mandibular fossa and the periphery of the disc, providing stability during lateral movements.

What might indicate degenerative arthritis in the TMJ?

Shear at the interface of the TMJ that may compress and fragment the fibrocartilage.

What is the significance of the retrodiscal lamina in the TMJ?

The inferior retrodiscal lamina connects the disc to the mandibular condyle and TMJ capsule,

the superior retrodiscal lamina connects

to the temporal bone.

What are the consequences of a large upward force applied to the chin?

It can fracture the non-articular area of the TMJ and send bone fragments into the cranium.

What are the two synovial cavities created by the TMJ disc?

The inferior cavity (between the disc and mandibular condyle) and the superior cavity (between the disc and mandibular fossa/articular eminence).

What is capsular fibrosis and how can it develop?

Capsular fibrosis can develop from repeated episodes of acute capsulitis and inflammation, exacerbated by stress and faulty posture.

What are the osteokinematic movements involved in protrusion of the mandible?

Anterior translation of the mandible.

What are the arthrokinematic movements during protrusion?

The mandibular condyle and disc translate anteriorly, with the mandible sliding slightly down.

retrusion osteokinematics

posterior translation

retrusion arthrokinematics

Mandibular condyle and disc translate posteriorly

mandible during retrusion

slides slightly upwards

Is there any rotation during protrusion and retrusion?

No

What is lateral excursion in terms of osteokinematics?

Lateral excursion involves side-to-side translation, usually combined with slight horizontal plane rotation.

What factors guide the path of movement during lateral excursion?

occlusion, muscle actions, shape of the mandibular fossa, and position of the disc.

occlusion of the TMJ

contact between upper and lower teeth

Lateral excursion arthrokinematics

contralateral condyle protrudes anteriorly and medially; ipsilateral condyle is the pivot point of translation and slight rotation (side-to-side translation)

depression osteokinemtaics

Anterior and inferior translation

Depression aka

opening of the mouth

Mastication only requires

38% of max opening

What is the normal range of mouth opening during depression?

It is normal to fit 3 knuckles in the mouth.

What occurs during the early phase of depression?

The condyles roll posterior, swinging the mandible body inferior and posterior.

Early phase of mandibular depression

First 30-50% of ROM

mandibular depression stretches what

oblique lateral ligament

What happens in the late phase of depression?

There is a transition from rotation to translation, with anterior and inferior translation of the disc and condyle.

late phase of depression

Disc and condyle moves together anterior and inferior

What limits full opening of the mouth?

Full opening is limited by the stretched superior retrodiscal laminae.

Full opening of the mouth maximally stretches and pulls the disc

anterior

Early phase of mandibular elevation

Disc and condyle Translation posterior and superior

early phase of elevation is initiated by

tension in superior retrodiscal lamina-retracts disc

late phase of elevation

Rotation

Condyles roll anterior

What are the primary muscles of mastication?

Masseter, temporalis, medial pterygoid, and lateral pterygoid.

What is the primary function of the masseter?

To elevate the mandible and create large forces between the molars.

Bilateral masseter

Elevates and protrudes mandible

How does unilateral contraction of the masseter affect movement?

It allows for ipsilateral excursion

best leverage for masseter

if mandible already positioned in contralateral excursion

Masseter binding force

ability to combine lateral excursion with a strong bite force

temporalis bilateral action

elevation and retrusion

temporalis unilateral action

ipsilateral excursion

temporalis best leverage

if mandible already positioned in contralateral excursion

Deep head of medial pterygoid

Larger and attaches to medial side of lateral pterygoid plate of the sphenoid bone

Superior Head of Medial Pterygoid

Attaches to the posterior side of the maxilla above the third molar

How do the heads of the medial pterygoid compare to the masseter?

Both heads are almost parallel to the masseter and attach on the internal surface of the ramus near the angle.

medial pterygoid bilateral action

elevates and protrudes mandible

Unilateral contraction of the medial pterygoid

contralateral excursion

superior head of lateral pterygoid

stabilizes the articular disk

inferior head of lateral pterygoid

Runs from lateral surface of lateral pterygoid plate→Maxilla→pterygoid fovea

What is the function of bilateral contraction of the lateral pterygoid?

Elevates the mandible and causes slight protrusion.

What happens during unilateral contraction of the lateral pterygoid?

It causes contralateral excursion and rotates the ipsilateral condyle anteromedially.

Where does the superior head of the lateral pterygoid run from and to?

From the greater wing of the sphenoid bone to the joint.

What muscles are involved in lateral excursion of the mandible to the Left

The right lateral and medial pterygoids cause contralateral excursion, while the left masseter and temporalis cause ipsilateral excursion.

Low bite resistance

intermediate disc region positioned between condyle and articular eminence

High bite resistance

→momentary reduction in joint pressure in ipsilateral TMJ

→superior head of lateral pterygoid pulls disc forward

secondary muscles of mastication

suprahyoids and infrahyoids

What is the role of the suprahyoids in mouth opening?

They assist with depression of the mandible and opening of the mouth when the hyoid bone is stable.

When hyoid bone is stable because of infrahyoid pull,

the suprahyoids can assist with depression of the mandible and opening of the mouth

What muscles are responsible for closing the mouth against resistance?

Masseter, medial pterygoid, and temporalis.

Oblique fibers of the temporalis can

etrude the mandible

Superior head of Lateral Pterygoid acts eccentrically to

slowly return the disc and condyle back to fossa

Forward tension helps to stabilize

the disc between the condyle and articular eminence

What muscles open the mouth using a force couple

Inferior head of Lateral pterygoid and suprahyoids

What occurs during full opening of the mouth?

The inferior head of the lateral pterygoid pulls the disc anteriorly, leading to contact with the articular eminence.

Loading on TMJ (highest to lowest)

-Resisted closing

-Full opening

-Unresisted closing

Resisted closing of the mouth

Generates much greater joint loading and disc compression

Age related changes of the TMJ

Degenerative changes, OA

Degenerative changes and cadavers

59% of older cadavers had disc perforations, roughness, thinning

Degenerative changes in the TMJ not necessarily related

to aging and not necessarily associated w/ symptoms of dysfunction

What are the degenerative changes seen in the TMJ with age?

Disc perforations, roughness, thinning, and osteoarthritis in 14-40% of adults.

What inflammatory conditions can affect the TMJ?

Capsulitis and synovitis