MANDIBULAR POSITIONS
AND JAW RELATIONS
Specific learning objectives;
• To know about the various mandibular
movements, positions, its importance and
the clinical applications.
• To know about various jaw relations, its
importance and the clinical applications.
INTRODUCTION
• It is important to study
mandibular positions
and movements as it
enables us to plan
arrangement of teeth
& selection of
articulators.
COMPONENTS INVOLVED
MUSCLES &
LIGAMENTS
MAXILLA &
MANDILBLE
TMJ
CLASSIFICATION:I) According to Sharry:a) According to direction - Opening and closing movements
Protrusion and retraction
Lateral gliding movements
b) According to tooth contact - Movements with tooth contact
Movements without tooth contact
c) Limitation by joint structure - Border movements
Intra border movements
d) Functions of masticatory system - Mastication
Deglutition
Speech
Respiration
e) CNS - Innate movements – breathing & swallowing
Learned movements – speech and chewing
Posselt’s
Figure
MUSCLES OF MASTICATION
• PRIMARY MUSCLES OF MASTICATION
– Masseter
– Temporalis
– Medial Pterygoid
– Lateral Pterygoid
• SECONDARY MUSCLES OF MASTICATION
The suprahyoid group of muscles being used as
secondary or supplementary muscles they are
– Digastric
– Mylohyoid
– Geniohyoid
MASSETER:-
Function
ELEVATES
RETRUDE
MEDIAL PTERYGOID
• It is a thick quadrilateral muscle
Functions ;
1.
2.
3.
When fibers contract the mandible is ELEVATED.
Muscle is active in PROTRUDING the mandible.
Unilateral contraction will bring about
MEDIOTRUSIVE movement of the mandible.
TEMPORALIS
ELEVATION OF MANDIBLE
POSTERIOR FIBER DRAWS
MANDIBLE BACKWARDS
LATERAL PTERYGOID
Superior Lateral Pterygoid:Closing,
Retracting
Lateral movement in
ipsilateral direction
• Inferior Lateral Pterygoid:opening
protracting
Lateral movement in
contralateral direction
SIDE TO SIDE GRINDING
MOVEMENT
Medial and lateral pterygoid act together to protrude
the mandible
DIGASTRICS:• Not considered a muscle of mastication, but it does have an
important influence on the function of the mandible.
• Divided into 2 portions:– Posterior belly
– Anterior belly
The combinded efforts of the Digastrics and Lateral
Pterygoids provide for natural jaw opening.
Terminology Related to Mandibular
Position and Tooth Position
Basic Premises:
•
When the mandible closes against the
maxilla:
1. There is an ideal way for the teeth to contact
2. There is an ideal place for the condyle and
disc to be situated.
Terminology Describing Tooth Position:
MAXIMUM INTERCUSPATION
• Centric Occlusion (CO)
• Maximum intercuspation
describes an occlusal
relationship
• Patient finds the most
comfortable position
• Easily achievable, but not
always reproducible, by the
patient
MAXIMUM INTERCUSPATION
What is considered Ideal?
– Angle Class I: 1st Molars and Canines
relationship
– Adequate Overlap
– Simultaneous contact
– Occlusal Forces along long axis of teeth.
Class I
• Class I is normal occlusion defined as
having the mesiobuccal cusp of the
maxillary first molar in occlusion with the
buccal groove of the mandibular first molar
class II
• In the class II occlusion; mandible is
retrusive in relation to the maxilla
(retrognathic). In this case, the buccal
groove of the mandibular first molar will lie
distal to the mesiobuccal cusp of the
maxillary first molar.
class III
• If the mandible is protrusive relative to the
maxilla (prognathic), then class III occlusion
exists. In this case, the buccal groove of the
mandibular first molar will lie mesial to the
mesiobuccal cusp of the maxillary first
molar.
Term Describing Mandibular Position
CENTRIC RELATION
• Centric Relation
– A condylar position;
Superior and anterior
position of the mandible
with the disc properly
interposed
– Describes the most
stable position of the
condyle
Terms Describing Mandibular
Position
• Centric Relation
– Why a superior and
anterior position?
The Muscles of
Mastication drive this
process
In an Ideal Occlusion, CR and MI
Occur Simultaneously.
The condyle seats in CR simultaneous with
the teeth occluding in MI. No slide occurs.
Terms for Describing Eccentric
Movements of the Mandible
• Protrusive - anterior
movement of the
mandible
• Retrusive - posterior
movement of the
mandible
• Eccentric - movement
away from a centric
position (CR or MI)
Protrusive
Terms for Describing Eccentric
Movements of the Mandible
Lateral movementsmoving the
mandible to the left
or to the right.
Shown is a “left lateral movement”
Summary of Characteristics of an
Ideal Occlusion
► CR
and MI occur simultaneously
► All teeth contact simultaneously
► All occlusal forces are longitudinal
► Posterior tooth contacts dominate
Jaw relation/maxillomandibular relation
 Types:
1. Orientation relation
2. Vertical relation
3. Horizontal relation
centric relation
eccentric relation—protrusive records
---lateral records.
ORIENTATION RELATIONS
Orientation relations are those that orient the
mandible to the cranium in such a way that when the
mandible is kept in its most posterior unstrained
position, the mandible can rotate in the sagittal plane
around
an
imaginary
transverse
through or near the condyles
axis
passing
Vertical jaw relation
• Amount of separation b/w maxilla & mandible.
• Acc GPT –8.
– Distance b/w two selected points one on a fixed and
one on a movable member
or
– The vertical dimension of face b/w any two arbitrary
selected points located one above and one below the
mouth,usually in the midline.
Classification
1.
2.

Vertical dimension of occlusion
Vertical dimension of rest
Vertical dimension of occlusion: (GPT-8)
The distance b/w two points when the occluding members
are in contact.
OR
It is the relation of the mandible to the maxilla when the
occlusal stops are provided by the teeth/occlusion.
 Vertical dimension of rest:
The distance b/w two selected point measured when the
mandible is in the physiologic rest position.
INTEROCCLUSAL DISTANCE /INTEROCCLUSAL
REST SPACE.
• Difference b/w the resting vertical dimension and
vertical dimension of occlusion.
• First studied by Dr.M E Niswonger
• 2-4mm.
• Vertical dimension of speech:
the distance measured b/w two
selected points on each jaw during
closest proximity during speech.
Horizontal jaw relations
Eccentric relation
Centric relation
Protrusive record
Lateral record
Centric relation: -- GPT -8
Centric relation is defined as a maxillomandibular
relationship in which the condyles articulate with the thinnest
avascular portion of their respective disks with the complex in
the anterior superior position against the shapes of articular
eminences. This position is independent of tooth contact. This
position is discernible when mandible is directed superiorly and
anteriorly and restricted to a purely rotatary movement about a
transverse horizontal axis.
Significance of centric relation
Ideal arch – arch relationship.
Hinge position- only pure
rotation without any tanslation
Reproducible position- reliable
reference
Reference position for occlusal
reconstruction
Two characteristics features of centric relation
Reproducible position
Untranslated hinge position of mandible
Centric relation is the terminal hinge relation
Consequences of incorrect centric relation
recording
Natural dentition– damage to
periodontal structure,
hypersensitivity, excessive attrition,
hypermobility of teeth.
Pain & dysfunction of masticatory
muscle, headache, neck& shoulder
pain.
Dentures- not in centric relation—
premature contact.
TMJ dysfunction— condyle press
upon peripheral vascular &
innervated part of articular disc.
Mucosal irritation & soreness.
Spasm of muscle of mastication
Resorption of residual alveolar
ridges.
CONCLUSION
• “Nature has blessed us with a marvelously
dynamic masticatory system, allowing us
to function and therefore exist.”
• “ You cannot successfully treat dysfunction
unless you understand function.”