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1. Biomechanics of
Temporomandibular Joint
T. Sunil Kumar
Dept of Physiotherapy

2. INTRODUCTION
• The temporomandibular (TM) joint is unique
in both structure and function. Structurally, the
mandible is a horseshoe-shaped bone that
articulates with the temporal bone at each
posterior superior end and produces two
distinct but highly interdependent articulations.
• Each TM joint contains a disc that separates
the joint into upper and lower articulations.
• Functionally, mandibular movement involves
concurrent movement in the four distinct joints,
resulting in a complex structure that moves in
all planes of motion to achieve normal function.

4. JOINT STRUCTURE
Articular Structures
• Multiple bones merge to form the structure and
contribute to the function of the TM joints.
• These bones include the mandible, maxillae,
temporal, zygomatic, sphenoid, and hyoid
bones.
• The proximal or stationary segment of the TM
joint is the temporal bone. The condyles of the
mandible sit in the mandibular fossa of the
temporal bone.
• The mandibular fossa is located between the
post-glenoid tubercle and the articular
eminence of the temporal bone

6. • Structurally, the individual TM joints are
considered to be synovial joints formed by the
condyle of the mandible inferiorly and the
articular eminence of the temporal bone
superiorly.
• The condyle of the mandible sits in the
mandibular fossa, but it is not at all appropriate
as an articular surface. So, the articular
eminence contains a major area of trabecular
bone and serves as the primary articular
surface for the mandibular condyle.
• Thus, functionally, the mandibular condyle
articulates with the articular eminence of the
temporal bone. The articular eminence and the
condyle are both convex structures, resulting in
an incongruent joint

7. • The TM joint is classified as a synovial joint,
although no hyaline cartilage covers the
articular surfaces.
• The articular surfaces of the articular eminence
and the mandibular condyle are covered with
dense, avascular, collagenous tissue that
contains some cartilaginous cells.
• Because some of the cells are cartilaginous,
the covering is often referred to as
fibrocartilage.
• The articular collagen fibers are aligned
perpendicular to the bony surface in the deeper
layers to withstand stresses.
• The presence of fibrocartilage rather than
hyaline cartilage is significant because
fibrocartilage can repair and remodel itself

8. Accessory Joint Structures
• The incongruence of the TM joint is addressed
by a unique articular disc.
• A disc located within each TM joint separates
the articulation into distinct superior and inferior
joints with slightly different functions .
• Thus, mandibular motion involves the
simultaneous movement of four divergent joints.
• The inferior TM joint is formed by the
mandibular condyle and the inferior surface of
the disc and functions as a simple hinge joint.
• The superior TM joint is larger than the inferior
joint and is formed by the articular eminence of
the temporal bone and the superior surface of
the disc; it functions as a gliding joint.

10. • The thickness of the articular disc varies from 2
mm anteriorly to 1 mm in the middle to 3 mm
posteriorly.
• The purpose of the disc is to allow the convex
surfaces of the articular eminence and the
mandibular condyle to remain congruent
throughout the range of motion of the TM joint
in all planes.
• It increases stability, minimizes loss of mobility,
reduces friction, and decreases biomechanical
stress on the TM joint.

11. • The disc within each TM joint has a complex
set of attachments. The disc is firmly attached
to the medial and lateral poles of the condyle of
the mandible, but it is not attached to the TM
joint capsule medially or laterally.
• These attachments allow the condyle to rotate
freely on the disc in an anteroposterior
direction. The disc is attached to the joint
capsule anteriorly, as well as to the tendon of
the lateral pterygoid muscle.
• The anterior attachments restrict posterior
translation of the disc. Posteriorly, the disc is
attached to a complex structure, collectively
called the bilaminar retrodiscal pad.

12. • The two bands (or laminae) of the bilaminar
retrodiscal pad are both attached to the disc.
• The superior lamina is attached posteriorly to
the tympanic plate (at the posterior mandibular
fossa).
• The superior lamina consists of elastic fibers
that allow the superior band to stretch. The
superior lamina allows the disc to translate
anteriorly along the articular eminence during
mandibular depression; its elastic properties
assist in repositioning the disc posteriorly
during mandibular closing.

14. • The inferior lamina is attached to the neck of
the condyle and is inelastic. The inferior lamina
serves as a tether on the disc, limiting forward
translation, but does not assist with
repositioning the disc during mandibular
closing.
• Neither of the laminae of the retrodiscal pad is
under tension when the TM joint is at rest.
• Loose areolar connective tissue rich in arterial
and neural supply is located between the two
laminae

15. Capsule and Ligaments
• The elasticity of the joint capsule and ligaments
determines the available motion at the TM joint
in all planes.
• Motion can be enhanced or restricted
depending on the flexibility of these structures.
The portion of the capsule superior to the disc
is quite lax, whereas the portion of the capsule
inferior to the disc is taut.
• Consequently, the disc is more firmly attached
to the condyle below and freer to move on the
articular eminence above.

16. • The capsule is thin and loose in its anterior,
medial, and posterior aspects, but the lateral
aspect is stronger and reinforced with long
fibers (temporal bone to condyle).
• The lack of strength of the capsule anteriorly
and the incongruence of the bony articular
surfaces predisposes the joint to anterior
dislocation of the mandibular condyle.
• The capsule is highly vascularized and
innervated, which allows it to provide a great
deal of information about position and
movement of the TM joint.

17. • The primary ligaments of the TM joint are the
TM ligament, the stylomandibular ligament,
and the sphenomandibular ligament.
• The TM ligament bis a strong ligament
composed of two parts, an outer oblique
element and an inner horizontal element.
• The outer oblique element attaches to the neck
of the condyle and the articular eminence. It
serves as a suspensory ligament and limits
downward and posterior motion of the mandible,
as well as limiting rotation of the condyle during
mandibular depression.

19. • The inner horizontal component of the ligament
is attached to the lateral pole of the condyle
and posterior portion of the disc and to the
articular eminence. Its fibers are aligned
horizontally to resist posterior motion of the
condyle.
• Limiting the posterior translation of the condyle
protects the retrodiscal pad. The primary
function of the TM ligament is to stabilize the
lateral portion of the capsule.
• Neither band of the TM ligament limits forward
translation of the condyle or disc, but they do
limit lateral displacement.

20. • The stylomandibular ligament is the weakest of
the three ligaments and is considered a
thickened part of the parotid sheath joining the
styloid process to the angle of the mandible.
• Some investigators have identified the function
of this ligament as limiting the protrusion of the
mandible, but others have stated that it has no
known function.
• The sphenomandibular ligament is described
as the “strong” ligament that is the “swinging
hinge” from which the mandible is suspended.

21. • Some investigators have stated that it serves
to protect the mandible from excessive anterior
translation.
• Others have stated that this ligament has no
function.
• The sphenomandibular ligament attaches to
the spine of the sphenoid bone and to the
middle surface of the ramus of the mandible.
• Abe and colleagues stated that the
sphenomandibular ligament also has continuity
with the disc medially

22. • Loughner and colleagues examined the
structures surrounding the TM joint in 14
cadaver heads and found that the
sphenomandibular ligament is not continuous
with the medial capsule; rather, it is
immediately adjacent to the capsule.
• These investigators concluded that since the
sphenomandibular ligament does not attach to
the medial joint capsule, this ligament has no
functional significance for the biomechanics of
the TM joint.
• However, they suggested that the
sphenomandibular ligament serves as an
accessory ligament and, in concert with the TM
ligament, provides structural support for the TM

23. JOINT FUNCTION
Joint Kinematics
• The TM joint is one of the most frequently used
and mobile joints in the body. It is engaged
during mastication, swallowing, and speaking.
• Most of the time, the TM joint movements
occur without resistance from chewing or
contact between the upper and lower teeth.
• However, as a third-class lever, the TM joint is
designed to maintain its structure in spite of
significant forces acting on it.
• As previously noted, the articular surfaces are
covered with a pseudofibro cartilage that has
the ability to remodel and repair and thus is
able to tolerate repeated, high-level stress.

24. • Mastication requires tremendous power, while
speaking requires intricate fine motor control.
The musculature is designed to accomplish
both these tasks.
• Both osteokinematic and arthrokinematic
movements are required for normal function of
the TM joint.
• Osteokinematic motions include mandibular
depression, elevation, protrusion, retrusion,
and left and right lateral excursions.
• Arthrokinematic movements involve rolling,
anterior glide, distraction, and lateral glide.

25. Mandibular Depression and Elevation
• Mandibular depression and elevation are
fundamental components of mastication.
• Under normal circumstances, the motions of
mandibular depression and elevation are
relatively symmetrical, with each TM joint
following a similar pattern.
• To accomplish mandibular depression and
elevation, the mandibular condyle must roll and
glide.
• The literature is contradictory as to whether the
rolling and gliding occur sequentially or
concurrently. However, the literature is
consistent in what rolling and gliding occur.

26. • During rotation, the mandibular condyle spins
relative to the inferior surface of the disc in the
lower joint.
• During translation, the mandibular condyle and
disc glide together as a condyle-disc complex
along the articular eminence. Translation
occurs in the upper joint between the disc and
the articular eminence

29. • Normal mandibular depression range of motion
is 40 to 50 mm when measured between the
incisal edges of the upper and lower front
teeth. Mastication requires approximately 18
mm of mandibular depression.
• Rolling occurs predominantly during the initial
phase of mandibular depression with as little
as 11 mm or as much as 25 mm, resulting from
rotation of the condyle on the disc.
• The remaining motion results primarily from
anterior translation of the condyle-disc complex
along the articular eminence.
• The shape of the condylar head and the
steepness of the articular eminence positively
correlate with the amount of rotation.

30. • Both the shape of the condylar head and the
steepness of the articular eminence can be
asymmetrical from one TM joint to the other,
thus affecting the symmetry of motion.
• As a quick screen, the clinician may use the
adult knuckles (proximal interphalangeal joints)
to assess the degree of mandibular
depression.
• Two knuckles placed between the upper and
lower incisors is considered functional, while
three knuckles is considered normal.
• Gravity assists with mandibular depression.

33. • The mandibular elevators are thought to
provide eccentric control of mandibular
depression, although their contribution is
unclear.
• Mandibular elevation is the reverse of
mandibular depression.
• The mandibular condyle rotates posteriorly on
the disc in the lower joint, and the condyle-disc
complex translates posteriorly in the upper joint

34. Control of the Disc During Mandibular
Elevation and Depression
• Active and passive control is exerted on the
articular disc during mandibular depression
and elevation. Passive control occurs through
the capsuloligamentous attachments of the
disc to the condyle.
• The lateral pterygoid muscle attaches to the
anterior portion of the disc, producing active
control, although evidence suggests that this
attachment may not be consistently present.
• Bell proposed two other muscle segments that
may assist with maintaining disc position
during active movement.

37. • During mandibular depression, the medial and
lateral attachments of the disc to the condyle
limit the motion between the disc and condyle
to rotation.
• As the condyle translates, the biconcave shape
of the disc causes it to track with the condyle
without any additional active or passive
assistance.
• However, the inferior retrodiscal lamina limits
forward excursion of the disc.
• The superior portion of the lateral pterygoid
muscle attaches to the disc and appears to be
positioned to assist with anterior translation;
however, no activity is noted during mandibular
depression

38. • During mandibular elevation, the elastic
character of the superior retrodiscal lamina
applies a posterior distractive force on the disc.
• In addition, the superior portion of the lateral
pterygoid demonstrates activity that is
assumed to eccentrically control the posterior
movement of the disc, while maintaining the
disc in an anterior position until the mandibular
condyle completes posterior rotation to the
normal resting position.
• Abe and colleagues suggested that the
sphenomandibular ligament also assists this
action.
• Again, the medial and lateral attachments of
the disc to the condyle limit the motion to
rotation of the disc around the condyle

39. Mandibular Protrusion and Retrusion
• Mandibular protrusion and retrusion occur in
the upper TM joint.
• The condyle-disc complex translates in an
anterior inferior direction, following the
downward slope of the articular eminence,
during protrusion and returns along a posterior
superior path.
• Rotation is not present during protrusion and
retrusion. The teeth are separated during these
motions.
• Ideally, the lower teeth should surpass the
upper teeth several millimeters; however,
protrusion is considered adequate when the
upper and lower front incisal edges touch.

41. • Protrusion is an important component
necessary for maximal mandibular depression.
• Retrusion is an important component of
mandibular elevation from a maximally
depressed mandible.
Control of the Disc During Mandibular
Protrusion and Retrusion
• During protrusion, the posterior attachments of
the disc (the bilaminar retrodiscal tissue)
stretch 6 to 9 mm to allow completion of the
motion.
• The degree of retrusion is limited by tension in
the TM ligament as well as by compression of
the soft tissue in the retrodiscal area between
the condyle and the posterior glenoid spine.

42. • An estimated 3 mm of translation occurs during
retrusion; however, this motion is rarely
measured
Mandibular Lateral Excursion
• Lateral excursion involves moving the
mandible to the left and to the right.
• The degree of lateral excursion considered
normal for an adult is 8 to 11 mm.
• One functional screen to estimate whether this
motion is normal is to observe whether the
mandible can move the full width of one of the
central incisors in each direction.

45. • Active lateral excursion is described as
contralateral (the opposite side) or ipsilateral
(the same side) relative to the primary muscle
action.
• To accomplish lateral excursion, the ipsilateral
mandibular condyle spins around a vertical
axis within the mandibular fossa, while the
contralateral mandibular condyle translates
anteriorly along the articular eminence.
• A slight degree of spin and lateral glide of the
contralateral mandibular condyle is necessary
to achieve maximal lateral excursion.

46. • Another normal asymmetrical movement of the
TM joint involves rotating one condyle around
an anteroposterior axis while the other condyle
depresses.
• This movement results in a frontal plane
motion of the mandible, with the chin moving
downward and deviating from the midline
toward the condyle that is spinning.
• These motions are generally combined into
one complex motion used for chewing and
grinding food

47. • Deviations and deflections may be noted during
osteokinematic movements of the mandible.
• A deviation is a motion that produces an “S” curve
as the mandible moves away from the midline
during mandibular depression or protrusion and
returns to midline by the end of the movement.
• A deflection is a motion that creates a “C” curve,
with the mandible moving away from midline during
mandibular depression or protrusion but not
returning to midline by the end of the movement.
• Deviations and deflections may result from
mandibular condyle head shapes differing from
right to left. If no other signs or symptoms
accompany these asymmetries, then deviation or
deflection is considered inconsequential.

48. Muscles
Primary Muscles
• The muscles acting on the TM joint are divided
into primary and secondary muscle groups.
The primary muscles include the temporalis,
masseter, lateral pterygoid, and medial
pterygoid.
• The temporalis is a flat, fan-shaped muscle
that is wide at the proximal portion and narrow
at the inferior portion.

49. • The superior fibers attach to the cranium while
the inferior fibers attach to the coronoid
process and the anterior edge and medial
surface of the ramus of the mandible.
• The temporalis fills the concavity of the
temporal fossa and can be palpated easily over
the temporal bone.
• The masseter is a thick, powerful muscle with
its superior attachments on the zygomatic arch
and zygomatic bone and its inferior attachment
on the external surface of the ramus of the
mandible.

50. The lateral pterygoid consists of superior and
inferior segments that travel in a horizontal
direction and combine posteriorly to attach to
the neck of the mandible, the articular disc,
and the joint capsule.
The medial pterygoid parallels
the masseter in line of force and
size. The superior fibers attach to
the medial surface of the lateral
pterygoid plate on the sphenoid
bone, and the inferior attachment
is on the internal surface of the
ramus near the angle of the

51. Secondary Muscles
• The secondary muscles are smaller than the
primary muscles and consist of the
suprahyoid and infrahyoid groups .
• The digastric, geniohyoid, mylohyoid, and
stylohyoid comprise the suprahyoid group.
• The infrahyoid group includes the omohyoid,
sternohyoid, sternothyroid, and thyrohyoid
muscles.
• The suprahyoid muscles assist with mandibular
depression, while the infrahyoid muscles are
responsible for stabilizing the hyoid.

53. • Both the suprahyoid and infrahyoid muscle
groups are involved in speech, tongue
movements, and swallowing.
• The digastric muscle is predominantly
responsible for mandibular depression.
• The hyoid bone has to be stabilized for the
digastric muscle to depress the mandible.
• This stabilization is provided by the infrahyoid
muscles.

55. Coordinated Muscle Actions
• Mandibular depression occurs from the
concentric action of the bilateral digastric
muscles in conjunction with the inferior portion
of the lateral pterygoid muscles.
• Mandibular elevation results from the collective
concentric action of the bilateral masseter,
temporalis, and medial pterygoid muscles.
• The bilateral superior lateral pterygoid muscles
eccentrically control the TM discs as the
mandibular condyles relocate into the
mandibular fossa with mandibular elevation.

56. • The other mandibular motions of protrusion,
retrusion, and lateral deviation are produced by
the same muscles that elevate and depress the
mandible, but in different sequences.
• Mandibular protrusion is produced by the
bilateral action of the masseter, medial
pterygoid, and lateral pterygoid muscles.
• Retrusion is generated through the bilateral
action of the posterior fibers of the temporalis
muscles, with assistance from the anterior
portion of the digastric muscle.
• Lateral deviation of the mandible is produced
by the unilateral action of a selected set of
these muscles.

57. • The medial and lateral pterygoid muscles each
deviate the mandible to the opposite side.
• The temporalis muscle can deviate the
mandible to the same side.
• The lateral pterygoid muscle is attached to the
medial pole of the condyle and pulls the
condyle forward.
• The temporalis muscle on the ipsilateral side is
attached to the coronoid process and pulls it
posteriorly.
• Together these muscles effectively spin the
condyle to create deviation of the mandible to
the left.

58. Relationship to the Cervical Spine and
Posture
• The cervical spine and TM joint are intimately
connected.
• A biomechanical relationship exists between
the position of the head, the cervical spine, and
the dentofacial structures.
• The attachments of the primary and secondary
muscles provide strong evidence of the
relationship among the TM joint, cervical spine,
throat, clavicle, and scapula.
• The impact of posture on the TM joint becomes
apparent once the attachments of the
musculature are examined.

59. • Given their attachments, muscles acting on the
mandible may also impact the atlanto-occipital
joint and cervical spine.
• Head and neck position may affect tension in
the cervical muscles, which may in turn
influence the position or function of the
mandible.
• Correct posture minimizes the forces produced
by the cervical spine extensors as well as the
other cervical muscles necessary to support
the weight of the head.
• Over time, improper posture can lead to
adaptive shortening or lengthening of the
muscles around the head, cervical spine, and
upper quarter.

60. COMMON IMPAIRMENTS AND
PATHOLOGIES
• Mechanical stress is the most critical factor in
the multifactorial Etiology. Dysfunction of either
the muscles or the joint structure generally is at
fault.
• Most clients with TM dysfunction will not fit into
a specific category of dysfunction classification,
which creates a clinical challenge.
• Additionally, only 20% to 30% of individuals
with internal derangement of the TM joint
develop symptomatic joints.
• These symptoms may progress or resolve
spontaneously

61. Age-Related Changes in the TM Joint
• The aging process affects the joints of the
human body.
• The TM joint is no exception. However,
degenerative changes are not always the result
of the normal aging process.
• Degenerative changes may occur from a
preexisting dysfunction. Furthermore,
degenerative changes do not necessarily
indicate disability.
Inflammatory Conditions
• Inflammatory conditions of the TM joint include
capsulitis and synovitis. Capsulitis involves
inflammation of the joint capsule, and synovitis
is characterized by fluctuating edema caused
by effusion within the synovial membrane of
the TM joint.

62. • Individuals with inflammatory conditions
experience pain and inflammation within the
joint complex, which may diminish mandibular
depression.
Osseous Mobility Conditions
• Osseous mobility disorders of the TM joint
complex include joint hypermobility and
dislocation.
• Many similarities are noted in the client history
and clinical findings for these two conditions.
• Hypermobility, or excessive motion, of the TM
joint is a common phenomenon found in both
symptomatic and nonsymptomatic populations.

63. Capsular Fibrosis
• Unresolved or chronic inflammation of the TM
joint capsule stimulates overproduction of
fibrous connective tissue, which creates
capsular fibrosis of the TM joint complex.
• The resultant fibrosis causes progressive
damage and loss of tissue function.
Articular Disc Displacement
• Articular disc displacement occurs when the
articular disc subluxes beyond the articular
eminence.
• Two conditions can result: disc displacement
with reduction and disc displacement without
reduction.

64. • Without intervention, disc displacement with
reduction often advances to disc displacement
without reduction.
Degenerative Conditions
• Two degenerative conditions may affect the TM
joint: osteoarthritis and rheumatoid arthritis.
• Hertling and Kessler stated that 80% to 90% of
the population older than 60 years have some
symptoms of osteoarthritis in the TM joint.