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9. TMJ
OTHER SYNOVIAL
JOINTS
2 BLASTEMA
-Temporal
-Condylar
Cavity formation within a
single blastema
Fibrous cartilage at the
articular surfaces
Hyaline cartilage at the
articular surfaces.
Cartilage acts as growth Does not
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centre
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10. Temporomandibular joint
Types of joints
Embryology
Functional anatomy
Muscles of mastication
Biomechanics of TMJ
Evolution
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11. Embryology
Primary Jaw joint
Homologous reptiles.
-maeckels cartilage
functions as the primary
joint.mouth opening
begins
Persists till 4 months IUL
6 weeks iu.-Membranous
bone forms lateral to
meckels cartilage at-body
and ramus
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12. Embryology
10th week-the joint forms
both malleo- incudal and
Definite jaw joint move
together in synchrony for 8
weeks in fetal life. The
accessory mandibular
condylar cartilage develops
as 1st blastema..
Grows towards the later
developing temporal
blastema.
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13. Embryology
-Lateral pterygoid develops medial to future
condyle and causes movement at through the
primary meckelian joint.
Fossa
Interposed connective tissue becomes thinner.
Two clefts develop in the fibrous connective
tissue forming two joint cavities.
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14. Embryology
1st
inferior compartment
2nd superior compartment.
Invading synovial membrane compartment.
Cavitation.
Early immobilization
Early functional activity
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25. ARTICULAR DISC
Devoid of blood vessels and nerve
Flexible and adaptable to functional
demands
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26. Attachments of the articular discRetrodiscal tissue
Loose connective tissue
Rich blood and nerve
supply
Bilaminar zone
Superior retrodiscal
lamina(elastic fibres)
Inferior retrodiscal
lamina(collagenous fibres)
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27. Attachments of the articular disc -
Temporal bone
Retrodiscal
tissue
Capsular
ligament +
superior
LPM
condyle
Medially + laterally attached to the capsule which divides
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joint cavity
37. Stylomandibular ligament
Extends from the
styloid process to
the angle + post
border of ramus
Limits excessive
protrusive
movement
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38. Temporomandibular joint
Types of joints
Embryology
Functional anatomy
Muscles of mastication
Biomechanics of TMJ
Evolution
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42. The medial pterygoid
Function
Origin & insertion
elevation
Protrusion
Muscle sling with Masseter
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U/l - mediotrusive
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43. The lateral pterygoid- inferior
portion
Function-protrusion
Origin & insertion
U/l – mediotrusive
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With depressors – downward+forward
44. The lateral pterygoid- superior
portion
Infratemporal surface
Active during
of greater wing of
power stroke
sphenoid – capsule
Closure with
,disc ,neck
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elevators
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46. The digastricus
Function– b/L contraction depression of mandible
with fixed hyoid bone
Raises hyoid –swallowingwhen mandible is fixed
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49. Temporomandibular joint
Types of joints
Embryology
Functional anatomy
Muscles of mastication
Biomechanics of TMJ
Evolution
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50. Biomechanics of TMJ
•
Based on structure and function can be divided
into 2 systems
First joint system
-Inferior joint cavity
Second joint system
-Superior joint cavity
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51. Biomechanics of TMJ
Articular disc as meniscus
1.
Not a determinant of joint movement
Attached on one side and unattached on
the other.
Freely extends into the joint space
2.
3.
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52. Biomechanics of TMJ
TMJ - no attachment
Yet stable due to muscles
Resting stage – tonus
Increase muscle activity - increase
interarticular pressure
Absence of pressure - dislocate
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53. Biomechanics of TMJ
Disc space varies with
pressure
Increased – disc space
narrows
Decreased – space widens
Condyle on anterior /
posterior zone
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54. Biomechanics of TMJ
Mandibular opening and closing
SRL –retract the
disc
Closed joint
position – relaxed
Stretched – during
opening
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55. Biomechanics of TMJ
Mandibular opening and closing
SLP – protractor of the
disc
ILP – protractor of
condyle
So forward movement
– articular cartilage –
disc morphology.
opening
closing
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56.
Biomechanics of TMJ
closed mouth resting
position
SLP - tonus
SLP > SRL
Resting position-interarticular pressure
reduced,disc space wide. Disc rotated anteriorly
Condyle contacts intermediate & post zone
Open mouth –SRL stretches , SRL > SLP Disc
rotated posteriorly
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58. Biomechanics of TMJ
Power stroke / chewing
pressure reduced on biting side
Fulcrum around food
Pressure increased on contralateral side
Same side – separation – dislocation
SLP - active ,positions disc anteriorly on condyle
Stabilizes joint
Teeth approach intercuspation –pressure increases
Mechanical post rotation – intermediate zoneresting positionwww.indiandentalacademy.com
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59. Biomechanics of TMJ
Points to remember
1.
Ligaments do not actively participate in
function of TMJ
Ligaments do not stretch
Articular surfaces must maintain constant
contact
2.
3.
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60. Temporomandibular joint
Types of joints
Embryology
Functional anatomy
Muscles of mastication
Biomechanics of TMJ
Evolution
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62. EVOLUTION OF T.M.J
Primitive vertebrates
Collection of food led to dev of jaws along
with fins
Amphibians and reptiles
Greater demand on jaw mechanics to adjust
to new habitat
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63. Mammals
Greater benefit from food source
Modification in jaws, joint, dentition
Humans
Upright posture
Bipedal locomotion
Shrinkage of human face
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64. Earliest functional activity of
TMJ
1.Prehension
2.Control size of mass of food entering
alimentary tract
-sharp cusps
-force in a direction effective
-sharp cutting edges
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65. Jaw joint has been classified into1.Primitive
jaw
jointreptilian
jointquadrate-articular occlusion
jaw
2.Mamalian type of jaw jointdentary
squamosal articulationearly TMJ
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67. Most primitive jaw
Flexible plate of fibrocartilage connects the
upper and lower cartilagenous jaws(shark)
-1st arch no longer forms the gill and grows
under the brain as palatoquadrate bar.It extends
front to back under the base of the skull to join
the lower jaw(maeckels cartilage )at the
epiceratobranchial joint.
The second arch modified to support the first
arch in its function-hyomandibular cartilage.
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68. Relationship of primitive jaw and
cranial base
AMPHISTYLIC SUSPENSION
Upper jaw connected to cranium-2 places
Behind
eye
Hyomandibular cartilage attached to
cranium
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69. Relationship of primitive jaw and
cranial base
HYOSTYLIC SUSPENSION
. Hyomandibular element was the only
articulation between the jaws and the
cranial base
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70. Relationship of primitive jaw and
cranial base
Autostylic suspension
Upper jaws are firmly fused to the cranial base.eg
chimera
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71. Relationship of primitive jaw and
cranial base
STREPTOSTYLIC SUSPENSION
Great degree of movement between jaws
and cranial base
Assists in swallowing
Reptiles and modern snakes
The pterygopalatine component can remain
clamped onto the animal while other parts
shifted their grip
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72. Mobility of upper and lower jaws
Amphibians and higher vertibrates
Maxillary palatine , pterygoid elements
attached to the cranium,but hyomandibular
(stapes) ,quadrate (incus) and articulare
(malleus) continued to form movable joint.
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73. Bones dentine and enamel
Bones dentine and enamel first appeared in
fossil records as-dermal plates of primitive
creatures.
In primitive sharks the denticles extend into
the jaws to give rise to teeth. The dermal
bones sank into the skin . They gained
attachment to muscles.
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74. `
The bones at the margin of upper jaw
Pre maxillae-with ant teeth
Maxillae – with marginal teeth
Jugal bone-lower orbit
Quadrato-jugal
Quadrate
Squamosal bone
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75. Lower jaw
Maeckels cartilage(core of the lower
jaw)became invested in 8 separate dermal
bony plates.
Dentary(with marginal row of teeth)
2 spenials
Angular
Surangular
Prearticular
2 coronoid bones
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76. Development of muscles
Advanced reptiles – capitii
mandibularis and
pterygoid muscles.
Well divided muscles
Increased functional
activity
Size of dentary
bone,heterodont dentition
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78. Development of inter-articular
disc
Primitive joint did not have any cartilage.
Lateral part of the muscle that extended
from the pterygoid region to the maeckels
cartilage gives rise to the cartilage.
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79. Functional activity of the
mamalian TMJ
Prehension
Tearing
Crushing
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84. Slicing in carnivore
Well dev canines
Condyle encircled in fossa
at level of occlusal surface
of mandibular teeth
Coronoid – large
Disc present
Right and left halves are
not united at the
symphysis.
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85. Slicing in carnivore
Masseter +temporalis
–well dev
Zygomatic arch-strong
No forward
Minimum lateral
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86. Rodent - gnawing
Incisors chisel shaped
Continuous erruption
Differential wear
Ant –post oriented
glenoid fossa
No side to side
movement
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87. Herbivore - grinding
Well dev molars
Ascending ramus increased
height
Condyle oval
No articular eminence
Slight post glenoid process
Capsule is present.
Anisognathous-do not
occlude simultaneously.
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88. Herbivore - grinding
Disc & capsule present
Masseter + temporalis well dev
but not as much as the
carnivores.
Lat pterygoid
Lateral movements prominent
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