Temporomandibular joint biomechanics are important to understand the TMJ pain and dysfunction.
This text discusses the relevant anatomy and biomechanics of TMJ.
2. INTRODUCTION
Temporomandibular joint is unique in both structure and
function.
Structurally, mandible is horse-shoe shaped bone which
articulates with temporal bone.
The most important functions of this joint is speech and
mastication.
Type of joint: synovial (condylar joint).
3. Articulation: mandible and temporal bone
Lower teeth articulate with mandible and can guide or
restrict the movement
Temporal bone: lateral wall of the cranium
Styloid process: projects inferiorly
Stylomastoid foramen: exit of facial nerve
Mandible:
2 ramus
Angle of ramus
Easily palpable
RELEVANT ANATOMY
4. Articular surfaces:-
Superior(Temporal bone)
- Articular tubercle
- Mandibular fossa
- Tympanic plate
Inferior(Mandible)
- head of mandible
Main point of contact: articular eminence
Fig. 1
5. Articular surfaces of synovial joint are generally covered with
hyaline cartilage but in TMJ the surface is covered with
fibrocartilage so it allows static and dynamic loading.
7. ARTICULAR DISC
Fibrous plate
Divides the joint cavity in 2
parts
Function:
• Increase stability
• Decrease loss of mobility
• Reduce friction
• Reduce biomechanical
stress
8. Superior TMJ:-
- Larger
- Consists of articular eminence of temporal bone and superior surface of
disc
- Functions as gliding joint
Inferior TMJ:-
- Consists of mandibular condyle and inferior surface of condyle
- Function as hinge joint
9. Retrodiscal tissue:
vascular and highly innervated
Could lead to pain in TMJ
disorder when there is
inflammation and
compression
10. MOVEMENTS AT TMJ
1. Depression (open mouth)
2. Elevation ( closing mouth)
3. Protrusion (protraction of chin)
4. Retrusion ( retraction)
5. Lateral movement ( side to side movement)
13. MANDIBULAR DEPRESSION AND
ELEVATION
DEPRESSION:
Normal ROM: 35 to 55 mm
Early stage: rolling/ rotatory movement (0 to 11- 25
mm)
- Mandibular condyle spins relative to inferior surface
in inferior joint
Late stage: translatory movement - mandibular and disc
glide together as a complex along articular eminence in
superior joint
Control of disc:
- med. And lat. Disc attachment of disc limit rotation
- Inf. Retrodiscal lamina limit forward excursion
14. ELEVATION
Condyles rotated posteriorly on disc in lower
joint
Condyle disc complex translates posteriorly in
upper joint.
Control of disc
Sup. Retrodiscal lamina apply post. Distractive
forced
Eccentric control of sup. Lateral pterygoid
muscle
15. MANDIBULAR PROTRUSION AND
RETRUSION
During protrusion: (ROM: 3- 6mm) Condyle disc translates in anterior
inferior direction following downward slope of articular eminence.
During retrusion: (ROM: 3- 4mm) returns posterior superior path.
16. Control of disc
During protrusion: retrodiscal tissue stretch upto 6 to 9mm to
complete the motion
During retrusion: limited by temporomandibular ligament and
compression of retrodiscal tissue
17. MANDIBULAR LATERAL EXCURSION
Normal ROM: 0 to 10- 15mm
Ipsilateral mandibular condyle spins
around a vertical axis within
mandibular fossa, while contralateral
mandibular condyle translates
anteriorly along the articular
eminence.
19. ASSYMETRICAL MOVEMENTS
Rotating one condyle around anterior posterior axis while the other
condyle depresses
It takes place in frontal plane with chin moving downwards and deviating
from midline and towards the condyle which is spinning
Ex. Chewing and grinding movements
20. MUSCLES
I. PRIMARY MUSCLES
Temporalis:
- Origin : Temporal fossa
- Insertion : coronoid process
- Action: Elevation, lateral excursion,
post. Fibers retraction of
protruded mandible
21. Masseter:
- origin: Zygomatic arch and
zygomatic bone
- Insertion: external surface of
ramus of mandible
- Action: elevation (close mouth to
bite), Superficial fibers
protrusion
22. Lateral pterygoid:
- origin: i) upper head: intra-temporal
surface and sphenoid bone
ii) Lower head: pterygoid plate
- Insertion: pterygoid fossa (neck of
mandible)
- Action: depresses mandible (open
mouth), protrude mandible, grinding
movement
23. Medial pterygoid:
- Origin: maxilla
- Insertion: Internal surface of ramus
near angle of mandible
- Action: side excursion, elevation
24. II. SECONDARY MUSCLES:
Suprahyoid muscles:
i. Digastric
ii. Geniohyoid
iii. Mylohyoid
iv. Stylohyoid
Function: mandibular
depression
25. Infrahyoid muscles:
i. Omohyoid
ii. Sternohyoid
iii. Sternothyroid
iv. thyrohyoid
Function: stabilizing
hyoid
27. REFERENCES
B. D. Chourasia, Human anatomy, head-neck-brain; vol.3, 6th edition.
K. L. Pamela, C. Norkins, Joint structure and function; 5th edition.
C. Kisner, L. A. Colby, Therapeutic Exercise, 6th edition.
C. A. Oatis, Kinesiology: The mechanics and pathomechanics of human
movements, 3rd edition.