The temporomandibular joint (TMJ) is structurally unique, with the mandible articulating with the temporal bone at each end. Each TMJ contains an articular disk that separates it into an upper and lower joint. The lower joint functions as a hinge joint while the upper joint functions as a gliding joint. The TMJ is involved in important functions like chewing, swallowing, and speech. Dysfunctions can be caused by trauma, poor posture, or oral habits and include conditions like inflammation, disk displacement, and degeneration. Proper cervical posture and dentition are important for optimal TMJ function.

1. BIOMECHANICS OF TM JOINT
D R . C A M Y B H A G AT ( P T )
M U S C U L O S K E L E TA L C O N D I T I O N S W I T H S P O R T S

2. INTRODUCTION
• TM joint is unique within the body both structurally
and functionally.
• Structurally, the mandible is a horseshoe-shaped
that articulates with the temporal bone at each end;
thus, the mandible has two different but connected
articulations
• Each TM joint also has a disk that separates the
articulation into discrete upper and lower joints that
each function slightly differently.

3. INTRODUCTION

4. INTRODUCTION
• Each TM joint is formed by the condyle (or head) of
the mandible inferiorly and the articular eminence
the temporal bone superiorly with an interposed
articular disk

5. INTRODUCTION
• The lower joint formed by the mandibular condyle and
the inferior surface of the disk is a simple hinge joint.
• The upper joint formed by the articular eminence and
the superior surface of the disk is a plane or gliding
joint.

6. INTRODUCTION
• TM joint is classified as a synovial joint, although no
hyaline cartilage covers the articular surfaces.
• The disk increases stability while minimizing loss of
mobility. The articular disk is necessary to reduce
friction and avoid biomechanical stress on the joint
• Mandibular motion plays a role in phonation, facial
expression, mastication, and swallowing.

7. STRUCTURE
Articular Surfaces
• Above: Mandibular fossa and articular tubercle
• Below: Head of Mandible
Articular Disc
• Biconcave
• Anterior and Posterior portion of disc is Vascular and
innervated
• Middle Portion is Avascular and Not innervated

8. ARTICULAR DISC

9. CAPSULE AND LIGAMENTS
• Short capsular fibers running from temporal bone to
disc and disc to neck of condyle.
• Capsule is highly vascularized and innervated, which
provide information about position and movements.
• Ligaments: Temporomandibular ligament,
Stylomandibular Ligament and sphenomandibular
ligament

11. UPPER AND LOWER
TEMPOROMANDIBULAR JOINTS
• The TM disk divides the TM joint into two separate
joint spaces, each with its own synovial lining.
• Synovial fluid supplies the nutritional demands of the
fibrocartilage covering the joint surfaces and the
avascular middle portion of the disk.
• The lower joint of the TM articulation functions
effectively as a hinge joint. Allows free rotation and
little Translatory movement

12. UPPER AND LOWER
TEMPOROMANDIBULAR JOINTS
• The upper joint of the TM articulation functions as a
plane joint, with the loose attachment of the disk to
the temporal bone allowing Translatory movement
between the disk and articular eminence.

13. FUNCTIONS
• The TM joint is one of the most frequently used joints
in the body.
• It is involved in talking, chewing, and swallowing.
• Most TM joint movements are empty-mouth
movements (e.g., talking); that is, they occur with no
resistance from food or contact between the upper
and lower teeth.
• Speech requires fine control of the jaw, and the ability
to chew requires great strength.

14. MANDIBULAR MOTIONS
• The motions of the TM joint are mouth opening
(mandibular depression), mouth closing
(mandibular elevation), jutting the chin forward
(mandibular protrusion),sliding the teeth backward
(mandibular retrusion),and sliding the teeth to either
side (lateral deviation of the mandible).

15. MANDIBULAR ELEVATION
AND DEPRESSION
• mouth opening can be found in two sequential
phases: rotation and glide.
• In the rotation phase of mouth opening, there is pure
anterior rotation (spin) of the condyle on the disk in
the lower joint . This has also been described as
posterior rotation of the disk on the condyle.
• Second phase involves translation of the disk-condyle
unit anteriorly and inferiorly along the articular
eminence.
• This motion occurs in the upper joint between the disk

16. MANDIBULAR ELEVATION
AND DEPRESSION
• Normal mouth opening is considered to be 40 to 50
mm.
• Of that motion, between 11 mm and 25 mm is gained
from rotation of the condyle in the disk, whereas the
remainder is from translation of the disk and condyle
along the articular eminence.
• fit of three PIP joints is considered normal

17. MANDIBULAR ELEVATION
AND DEPRESSION
• Mandibular elevation (mouth closing) is the reverse of
depression.
• It consists of translation of the disk-condyle unit
posteriorly and superiorly and of posterior rotation of
the condyle on the disk.

18. CONTROL OF THE DISK DURING MANDIBULAR
ELEVATION AND DEPRESSION
• The articular disk is controlled both actively and
passively during mouth opening and closing.
• The passive control is exerted by the
capsuloligamentous attachments of the disk to the
condyle.
• Active control of the disk may be exerted through the
disk’s attachment anteriorly to the superior portion of
the lateral pterygoid muscle

19. CONTROL OF THE DISK DURING
MANDIBULAR
ELEVATION AND DEPRESSION
• During mouth closing, the elastic character of the
superior retrodiskal lamina applies a posterior
distractive force on the disk.
• The activity of the superior lateral pterygoid allows the
disk-condyle complex to translate upward and
posteriorly during mouth closing and then maintains
the disk in a forward position until the condyle has
completed its posterior rotation on the disk or until
the disk has rotated anteriorly on the condyle.

20. MANDIBULAR PROTRUSION
AND RETRUSION
• This motion occurs when all points of the mandible
move forward the same amount.
• The condyle and disk together translate anteriorly and
inferiorly along the articular eminence.
• No rotation occurs in the TM joint during protrusion.
• The motion is all translation and occurs in the upper
joint alone.

21. MANDIBULAR PROTRUSION
AND RETRUSION
• Retrusion occurs when all points of the mandible
move posteriorly the same amount.
• Tension in the temporomandibular ligament limits this
motion,

23. MANDIBULAR LATERAL
DEVIATION
• In lateral deviation of the mandible (chin) to one side,
one condyle spins around a vertical axis and the other
condyle translates forward.
• For example, deviation to the right would involve the
right condyle spinning and the left condyle translating
or gliding forward

24. MUSCULAR CONTROL OF THE
TEMPOROMANDIBULAR JOINT

25. MUSCULAR CONTROL OF THE
TEMPOROMANDIBULAR JOINT
• The primary muscle responsible for mandibular depression is the
digastric muscle
• The posterior portion of the digastric muscle arises from the
mastoid notch, and the anterior portion arises from the inferior
mandible.
• The tendon that joins the anterior and posterior portions is
connected by a fibrous loop to the hyoid bone in the neck.

26. MANDIBULAR DEPRESSOR
• The lateral pterygoid muscles are considered to be mandibular
depressors.
• Gravity is also a mandibular depressor.

27. MANDIBULAR ELEVATOR
• The temporalis muscle attaches to the inside of the coronoid
process .
• The masseter muscle is attached to the outer surface of the
angle and ramus of the mandible.
• The medial pterygoid muscle is attached to the inner surface of
the angle and ramus of the mandible
• the superior portion of the lateral pterygoid is also active
during mouth closing assumed to be eccentric control of the disk

28. SUMMARY: MANDIBULAR
ELEVATION AND DEPRESSION
• Mouth opening (mandibular depression) is initiated by
concentric action of the digastric muscles bilaterally,
and by the inferior portion of the lateral pterygoid
muscles.
• Mouth closing (mandibular elevation) is produced by
the collective concentric action of the masseter,
temporalis, and medial pterygoid muscles, with
eccentric control of the TM disks by the superior
lateral pterygoid muscles

29. PROTRUSION, RETRUSION
AND LATERAL DEVIATION
• Mandibular protrusion is produced by bilateral action
of the masseter, medial pterygoid and lateral
pterygoid muscles.
• Retrusion is produced through the bilateral action of
the posterior fibers of the temporalis muscles with
assistance from the anterior portion of the digastric
muscle.

30. PROTRUSION, RETRUSION
AND LATERAL DEVIATION
• Lateral deviation of the mandible is caused by
unilateral action of a selected set of these muscles.
• 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.

31. RELATIONSHIP WITH THE
CERVICAL SPINE
• The cervical spine and the TM joint are intimately
connected.
• muscles that attach to the mandible also have
attachments to the head (cranium), to the hyoid bone,
and to the clavicle, atlanto-occipital joint and Cervical.
• Head and neck position, too, may affect the tension in
cervical muscles that, in turn, may affect the position
or function of the mandible.

32. RELATIONSHIP WITH THE
CERVICAL SPINE
• Proper posture minimizes the force produced by the cervical
extensors and other cervical muscles necessary to support the
weight of the head.
• Poor cervical posture over time may lead to adaptive shortening
or lengthening in muscles around the head and cervical spine,
affecting range of motion, muscular force production
capacity, and joint morphology in the involved region.

33. TM/CERVICAL
JOINT INTERRELATIONSHIPS
• A forward head posture frequently involves extension of the
occiput and the upper cervical spine, leading to compensatory
flattening of the lower cervical spine and upper thoracic spine to
achieve a level head position.
• With the occiput extended on the atlas (C1), the suboccipital
tissues adapt and shorten.
• The suboccipital tissues include the anterior atlantoaxial and
atlanto-occipital ligaments (cephalad continuations of the
ligamentum flavum), the posterior belly of the digastric muscles,
the stylohyoid muscles, and the upper fibers of the upper
trapezius, semispinalis capitis, and splenius capitis muscles.

34. TM/CERVICAL
JOINT INTERRELATIONSHIPS
• The forces necessary to maintain the head against
gravity with a poor cervical posture and forward head
result in muscle imbalance and altered movement
patterns.
• Increased tension from shortening of the
tissues may lead to headaches that originate in the
suboccipital area, limitation in active range of motion
of the upper cervical spine, and TM joint dysfunction.
• Furthermore, pain in the TM region may be referred
from the cervical region.

35. TM/RESPIRATORY/
CERVICAL DYSFUNCTION
• a child with allergies who has difficulty breathing
through the nose will often hyperextend the upper
cervical spine to more fully open the upper respiratory
tract.
• Such a cervical posture places the upper and lower
teeth in contact with each other and may affect the
resting position of the TM joint.
• muscles surrounding the TM joint complex expend
greater energy to maintain this posture and have
more difficulty resting and repair.

36. TM/RESPIRATORY/
CERVICAL DYSFUNCTION
• Resistance to inspiration may also lead to use of
accessory muscles of respiration (scalene and
sternocleidomastoid muscles) to assist with breathing.
• Use of these accessory muscles may lead to a forward
head posture.
• Such a posture contributes over time to a cycle of
increasing musculoskeletal dysfunction, including
repeated episodes of TM inflammation that can result
in fibrosis of the TM joint capsule.

37. DENTITION
• Occlusion, or contact of the teeth, is intimately
involved in the function of the TM joint.
• When the central incisors are in firm approximation,
the position is called maximal intercuspation or the
occlusal position.
• This is not, however, the normal resting position of the
mandible. Rather, 1.5 to 5.0 mm of “freeway” space
between the upper and lower incisors is normally
maintained
• By maintaining this space, the intra-articular pressure
within the TM joint is decreased, the stress on the
articular structures is reduced, and the tissues of the
area are able to rest and repair.

38. AGE-RELATED CHANGES IN THE
TEMPOROMANDIBULAR JOINT
• tissues are likely to become less supple, less elastic,
and less able to withstand maximal forces with aging,
leading to biomechanical changes in musculoskeletal
tissues as one progresses through the life span.

39. DYSFUNCTIONS
• dysfunctions are caused by direct trauma such as
motor vehicle accidents or falls.
• Others are the result of years of poor postural or oral
habits such as forward head posture or bruxism
(grinding of the teeth).
• most common forms of TM joint complex dysfunction:
inflammatory conditions, capsular fibrosis, osseous
mobility conditions, articular disk displacement, and
degenerative conditions.

40. INFLAMMATORY
CONDITIONS
• Inflammatory conditions of the TM joint include
capsulitis and synovitis.
• Individuals with inflammatory conditions may
experience diminished mandibular depression as a
result of pain and inflammation within the joint
complex.
• Inflammation can lead to adhesions that restrict the
movement of the disk and limit the function of the TM
joint

41. OSSEOUS MOBILITY
CONDITIONS
• Osseous mobility disorders of the TM joint complex
include joint hypermobility and dislocation.
• The hypermobility is a result of laxity of the joint
capsules, tendons, and ligaments.
• Joint noises occur at the end of mandibular
depression and at the beginning of mandibular
closing.
• Hypermobility of one TM joint results in deflection of
the mandible toward the contralateral side with mouth
opening.

42. ARTICULAR DISK
DISPLACEMENT
• The articular disk of the TM joint may sublux,
contributing to dysfunction in this joint.
• Articular disk displacement conditions include disk
displacement with reduction and disk displacement
without reduction.
• Individuals exhibiting disk displacement with
reduction experience “joint noise” at two intervals:
during mandibular opening and mandibular closing.
• This joint noise is known as a reciprocal click and is a
key sign in diagnosing disk displacement with

43. ARTICULAR DISK
DISPLACEMENT
• Individuals with disk displacement without reduction
typically describe an inability to fully depress the
mandible, as well as difficulty performing functional
movements involving the jaw such as chewing, talking,
or yawning.
• The abnormalities of the lateral pterygoid muscle
noted included hypertrophy, contracture, and
atrophy of the superior and inferior bellies of the
lateral pterygoid muscles of the involved TM joint.
• Hypertrophy of this muscle indicates overactivity,
which thus possibly leads to the excessive anterior

44. DEGENERATIVE CONDITIONS
• Primarily two conditions affect the TM joint:
osteoarthritis and rheumatoid arthritis
• degenerative changes in the TM joint, including joint
space narrowing, erosions, osteophyte formation,
sclerosis, and remodelling.
• Loss of posterior teeth may also contribute to
degenerative changes because simple occlusion of the
remaining teeth alters the forces that occur between
the TM joint forces