1. MANDIBULAR MOVEMENTS
Dr Rohan Bhoil

2. CONTENTS
Introduction
Methods of studying mandibular movements
Importance
Factors which regulate jaw motion
Mandibular positions
The clinical understanding
Conclusion

3. INTRODUCTION
Mandibular
movements are
complex.

4. METHODS OF STUDYING MANDIBULAR
MOVEMENTS
Direct Clinical Observation
Sophisticated Electronic
Instrumentation :
Facial Clinometers ,
Roentgen Fluoroscopy ,
Radionucleotide Tracking;
Optical Pantography; Gnathic
Replicator etc

5. SIGNIFICANCE OF UNDERSTANDING
MANDIBULAR MOVEMENTS
•Developing Tooth Forms For Dental
Restorations,
• Understanding Occlusion,
•Arranging Artificial Teeth,
• Treating TMJ Disturbances,
• Preserving Periodontal Health
• And the designing, selection and adjustment
of articulators.

6. FACTORS WHICH REGULATE JAW
MOTION
•The Neuromuscular Role
•Contacts Of Opposing Teeth
•Anatomy And Physiology Of TMJ's
•The Action Of Muscles /Ligaments

7. NEUROMUSCULAR ROLE
Mastication is a
programmed event
residing in a
‘chewing centre’
located within the
brain stem, probably
in reticular
formation of pons.

8. The cerebellum
ensures a
coordinated
response from
muscles during
mandibular
movements, by
acting as a feedback
control mechanism..

9. Loss of
propioceptors, locate
d principally in
periodontal
ligaments, eliminates
an important source
of control in
positioning of
mandible; for the
edentulous patients.

10. INFLUENCE OF OPPOSING TOOTH
CONTACTS
Opposing tooth surface
contacts are related to
• occlusal surfaces of teeth
• muscles
• TMJs’
• and neurophysiological
components.

11. INFLUENCE OF THE
TEMPOROMANDIBULAR JOINTS
Mandibular
movements except
opening and
closing movements
at the terminal
hinge position, are
combinations of
rotation and
translation.

12. ROTATION:
The movement of a rigid body in which the parts move in
circular paths with their centers on a fixed line called the axis
of rotation. The plane of the circle in which the body moves is
perpendicular to the axis of rotation.
TRANSLATION
• The motion of a body at any instant when all points within the
body are moving at the same velocity and in the same
direction.

13. TMJ
Rotation - in the
lower
compartment of
the TMJ.
The translatory or
gliding movements
- in the upper
compartment.

14. • A complex joint.
• GINGLYMOARTHRODIAL JOINT.
• TMJ consists of 4 main structures:-
– Condyle
– Temporal bone (Squamous part)
– Articular disc
– Ligaments

15. THE TEMPORO MANDIBULAR JOINT
Articulating part of TMJ
includes convex head of
mandibular condyle and the
convexoconcave part of the
temporal bone i.e. mandibular
fossa and articular tubercle.
An intrarticular disc made of
fibrous tissue divides joint
cavity into upper and lower
compartments.

16. ARTICULAR DISC
SAGITTAL PLANE ANTERIOR VIEW

17. LIGAMENTS OF TMJ
1. Fibrous capsule
2. Lateral temporomandibular ligament
3. and two accessory ligaments i.e.
sphenomandibular and the stylomandibular
ligaments.

18. TMJ LIGAMENTS

19. ACCESSORY LIGAMENTS
Stylomandibular ligament limits excessive protrusive
movement of mandible.

20. MUSCULAR INVOLVEMENT IN JAW
MOTION

21. ROLE OF MUSCLES
There are four main
muscles of mastication
Masseter, Temporalis and
the Medial and Lateral
Pterygoids.
All these except the lateral
pterygoids act as
ELEVATORS.

22. MASSETER
Functions:-
Elevation
Superficial portion: protrusion
Deep portion : stabilization against articular eminence

23. TEMPORALIS:-
It is a significant positioning
muscle of the mandible
• It has 3 types of fibres
– Anterior fibers – or vertical.
– Middle fibers –run obliquely.
– Posterior fibers – consists of fibers that are aligned almost
horizontally.

24. MEDIAL PTERYGOID
FUNCTION:
• Elevation and protrusion.
• Unilateral contraction –mediotrusive movement

25. LATERAL PTERYGOID

26. Function
Inferior Lateral Pterygoid:-
• Simultaneous contraction:
depression and protrusion
• Unilateral contraction:
mediotrusion & movement
to opposite side.
Superior Lateral Pterygoid
• During opening: remains
inactive.
• Becomes active only in
conjunction with elevator
muscles.
• Active during power stroke
& when teeth held together

27. THE SUPRAHYOID MUSCLES
These depress the
Mandible, if the hyoid
bone remains fixed.
Thus help when the
mouth is opened
wide or against
resistance.

28. MOVEMENTS

29. OPENING &
CLOSING
Lateral Pterygoid is the main
muscle responsible for opening.
Opening of mouth is limited by
the superior lamina of the
articular disc.

30. PROTRUSION AND RETRACTION
Protrusion is brought about
by simultaneous
contraction of the lateral
and medial pterygoids of
both sides
While
Retraction is mainly due to
contraction of the posterior
horizontal fibres of
temporalis muscle

31. CHEWING
Chewing or
side to side
movements
occur due to
alternate
contraction of
muscles of
both sides.

32. CERTAIN BASICS : JAW MOTION

33. MANDIBULAR ROTATION
In opening and
closing and
lateral
movements.

34. AXES OF MANDIBULAR ROTATION
Rotation occurs around three
axes: transverse, vertical and
sagittal, that move constantly
during normal jaw function.

35. MOVEMENT ABOUT A
HORIZONTAL AXIS, AS SEEN IN A
HINGE AXIS OPENING.

36. MOVEMENT OCCURS AROUND
A VERTICAL AXIS DURING A
LATERAL EXCURSION.

37. THE MANDIBLE ALSO ROTATES
AROUND A SAGITTAL AXIS
WHEN ONE SIDE DROPS DOWN
DURING A LATERAL EXCURSION

38. BASIC JAW POSITIONS
Centric Occlusion
it is defined as maximum intercuspation of teeth.
Centric Relation
the most posterior relation of the upper to the
lower jaw from which lateral movements can be made
at a given vertical dimension. {Boucher}

39. • CENTRIC RELATION (GPT-8) :
the maxillomandibular relationship in which the condyles
articulate with the thinnest avascular portion of their
respective disks with the complex in the antero-superior
position against the slopes of articular eminences. This
position is independent of tooth contact. This position is
clinically discernible when the mandible is directed superiorly
and anteriorly.

40. BASIC JAW POSITIONS….
Centric relation is used to transfer position
of mandible in relation to maxilla, to an
articulator.
The centric occlusion is a tooth determined
position, whereas the centric relation is a
jaw to jaw relation determined by the
condyles in the fossae.

41. TERMINAL HINGE AXIS
When the condyles are in their most superior position in the
articular fossae and the mouth is purely rotated open, the axis
around which movement occurs is called the ‘Terminal Hinge
Axis’.

42. Condylar guidance – “Mandibular guidance
generated by the condyle and articular disc
traversing the contour of the glenoid fossa”
Incisal guidance – “ The influence of the contacting
surfaces of the mandibular and maxillary anterior
teeth during mandibular movements”

43. Retruded Contact
Position
- guided occlusal
relationship occurring at
the most retruded
position of the condyles
in the joint cavity.

44. MANDIBULAR MOVEMENTS
Mandible performs
habitual and border movements
opening and closing movements
protrusive and lateral movements
And stopping positions along these movements
centric occlusion,
centric relation,
protrusive border position,
right and left lateral border positions
and a rest position.

45. THE CLINICAL UNDERSTANDING OF
MANDIBULAR MOVEMENT
PARALLELOGRAM OF FORCES.
Factor of muscle pull related to positioning of
mandible after loss of teeth.
Direction of forces is affected by occlusal vertical
dimension.
Mainly two parallelograms.
In edentulous, occlusal plane is made parallel to
ala-tragus line.

46. THE ENVELOPE OF MOTION.
Defining the limits of
possible mandibular motion
and certain mandibular
reference positions.
Records made in sagittal and
frontal planes.

47. Envelope of motion in
the sagittal plane.
•CO, Centric occlusion;
•CR, centric relation;
•MHO, maximum hinge-opening
position
• MO, point of maximum
opening of the jaws
•P, most protruded position of
the mandible with the teeth in
contact
•Rest, postural rest position

48. SAGITTAL PLANE BORDER &
FUNCTIONAL MOVEMENTS:-1. Posterior opening border.
2. Anterior opening border.
3. Superior contact border.
4. Functional.

49. Posterior Opening Border Movements:-
1st STAGE
• Condyles: terminal hinge
position
• Pure rotational movement
2ND STAGE
• Axis of rotation shifts to bodies of
rami.

50. 1st STAGE
• Opening range: 20-25mm
• The movements are the
only repeatable hinge axis
movement of mandible.
2ND STAGE
• Condyles: anteriorly &
inferiorly.
• Mandible: posteriorly &
inferiorly.
• Max opening: 40-60mm.

51. Anterior Opening Border Movements:-
• Generated when closure
accompanied by contraction
of inferior lateral pterygoid.
• Not a pure hinge movement
due to eccentricity.

52. Superior Contact Border Movements
• Throughout this entire border movement tooth contact
is present.
• It depends on:-
– Amount of variation between centric relation and
maximum intercuspation.
– The steepness of the cuspal inclines of the
posterior teeth.
– Amount of vertical and horizontal overlap of
anterior teeth
– Lingual morphology of maxillary anterior teeth.
– General inter arch relationships of the teeth.

57. Envelope of
motion in the
frontal plane
•CO, Centric
occlusion
•MO, point of
maximum
opening of the
jaws
• Rest, postural
rest position.

58. Left lateral superior movement

59. Left lateral opening movement

60. Right lateral superior border movement

61. Right lateral opening border movement

62. • Maximum movements-
Opening : 50-60 mm
Lateral : 10 to 12 mm
Protrusive : 8 to 11 mm
And retrusive range is
about 1 mm.

63. Functional Movements:-
• Occur during functional activity of mandible.
• Free movements: take place within border movements.
• Occur chiefly around centric.

64. Functional Movements:-
• During chewing, the mandible
drops directly inferiorly until the
desired opening is achieved.
• It then shifts to the side on which
bolus is placed and rises up.
• As it approaches maximum
intercuspation, bolus is broken down
between the opposing teeth.
• In the final closure, the
mandible quickly shifts back to
the intercuspal position.

65. EFFECT OF POSTURE

66. Envelope of Motion
Gives reference positions from where fundamental movements of
mandible occur-
– Helps in making vertical & horizontal jaw relation records
• CR– MHO :represents Posterior terminal hinge movement, which
is used to locate transverse hinge axis for mounting of casts on
articulator.
– The rest position is a guide to
re-establishing the proper vertical
dimension of occlusion.

67. • Multiple restorations and
complete dentures are so
constructed that their occlusion is in harmony with
centric relation, because mastication in dentulous
occurs at CO but in edentulous at CR.
• Except at the occlusal contact position, where
envelope of movement is controlled by teeth, all other
contours are controlled by muscles, joints and soft
tissue forces.
Envelope of Motion

68. The gothic arch or arrow point tracing.
It is a graphic registration of lateral
border movements on a horizontal
plane, which results in an angular
tracing.
The direction of lateral movements is
actively determined by the lateral
pterygoid muscle on nonworking side
and by the deep capsular ligaments of
condyle on working side.

69. WORKING & NONWORKING SIDE
The side toward which the
mandible moves in a lateral
excursion is called Working side
And
The Nonworking side is that side of
mandible that moves toward
median line in a lateral excursion

70. Left lateral border movement

71. Continued left lateral border movement
with protrusion

72. Right lateral border movements
Condyles in CR
Contraction of left inferior
lateral pterygoid
Left condyle moves
anteriorly,medially and
Inferiorly

73. Continued right lateral movement with
protrusion
Contraction of rt. lateral pterygoid
& continued contraction left
inferior pterygoid
Right condyles moves anteriorly
and to left
Mandibular midline coincides with
midline of face

74. BENNETT SHIFT
Described by Dr. Norman Bennett in 1908 , it is the
direct lateral side shift that occurs simultaneously
with a lateral excursion

75. The primary cause :is the contraction of lateral pterygoid
muscle because its origin is located medially to its insertion.
When mandible shifts to the side, its movement occurs in two
segments-
an immediate side shift in which the major direction of
movement is mediolateral
and a progressive side shift, which begins thereafter and
continues with the major direction of movement being anterior.

76. Physiological rest position
• Established by muscles and gravity.
• Is actively determined.
• It is a ‘range of posture’
• Usually 2-4mm below maximum intercuspation
position, but can be upto 10 mm.
• Remains relatively stable for reasonable periods of
time.
• Affected by short and long term intra oral and
general health factors and by position of head.

77. Conclusion
Knowledge of Jaw Movements is Essential for
Successful Treatment of Patients. It is imperative
to learn as much possible about jaw
movement, in order to reproduce those aspects
of its motion, considered necessary for proper
functioning of the occlusion, either natural or
artificial.

78. References
• Complete denture prosthodontics – 3rd
edition, by John J Sharry
• Prosthodontic Treatment for Edentulous
Patients – by Zarb and Bolender, 12th edition.
• An evaluation of mandibular border
movements: Their character and significance -
Harry C. Lundeen

79. Thank you !!!