Download Mandibular Movement II

Mandibular Movement II
RSD 811: Session 15
Lina Sharab, DDS,MS.,MSc.
Copyright
• Most of images in this presentation come
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Management of Temporomandibular
Disorders and Occlusion
Jeffrey P. Okeson
Elsevier, 7th edition, 2013
St Louis, Missouri
Special thanks to Dr. Selwitz and Dr.
Haubenreich, Dr.Casky for compiling this
material
Review Topics
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TMJ Anatomy
Centric Relation
Protrusive and Lateral Movements
Mutually Protected Occlusion
The Articulator
Occlusal Interferences
Review and Elaboration
TMJ ANATOMY
The Temporomandibular Joint
• All occlusal analysis starts at the temporomandibular joints
(TMJs).
• The first requirement for successful occlusal treatment is stable,
comfortable TMJs.
Sagittal View
Definition of Occlusal Analysis
A study of the relationships of the occlusal surfaces of opposing
teeth, including the effect these relationships have on related
structures. Also called bite analysis.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published
by Houghton Mifflin Company. All rights reserved
The Temporomandibular Joint
• Through understanding of what is normal, healthy TMJ functions
is required to be able to diagnose what is abnormal.
Sagittal View
Where is the Axis of Rotation?
• The medial poles of the condyles are the only rotation points
that would permit a fixed axis of rotation b/c the condyles are
not parallel to the horizontal axis.
Midmost, Uppermost Position
• The condyle-disk assemblies are braced at the midmost, uppermost
position by compression of the medial third of the assembly
against the medial apex of each condylar fossa.
Coronal View
Medial Pole Bracing
• Medial pole bracing
consistently reinforces
the midmost, uppermost
position.
– For future reference: It
also explains why an
immediate side shift is not
possible from the fully
seated position of the
condyles (CR).
Midmost, Uppermost Position
• Note the anatomy of the
condylar fossa:
– It is “V-shaped”
– A horizontal axis through any
part of the condyle other
than the medial pole would
result in translatory
movements of the medial
pole during a fixed rotational
axis, which would be
incompatible with the Vshape of the fossa.
Looking up at the fossa from below
Mandibular movements
Gothic arch tracing
https://www.youtube.com/watch?v=6qbq3W7Cin8
MUSCLE CONTROL OF DISK
ALIGNMENT
Opening
• As the inferior lateral
pterygoid muscle (+)
starts to pull the
condyle forward, the
superior lateral
pterygoid muscle (-)
releases contraction to
allow the elastic fibers
to start pulling the disk
more to the top of the
condyle.
Maximum Opening
• When the condyle
reaches the crest of the
eminence, the disk
should be directly on
top of the condyle.
– At this point, the elastic
fibers have rotated the
disk back since the
superior lateral
pterygoid muscles are in
a controlled release.
Closing
• As the jaw closes, the
condyle starts to move
back & up the steeper
slope of the articular
eminence.
– To accomplish this, the
superior lateral pterygoid
muscle (+) starts its
contraction as the inferior
lateral pterygoid muscle (-)
releases the condyle to the
elevator muscles that pull
it back.
KEYS TO MANDIBULAR MOVEMENT
Orthopedically stable
joint position
Musculoskeletal
stable position
Directional pull of the
muscles applies
interarticular pressure
to the disc
Thick strong bone
Thin squamotympanic plate
Retrodiscal tissues
Articular Eminence
• Angle compared to horizontal (in Degrees)
• aka Articular Incline, Condylar Inclination
• Steeper incline = Quicker disarticulation of the
posterior teeth in eccentric movements
45º
60º
Angle in
degrees
A steeper (↑º)
articular eminence
will cause the
posterior teeth to
separate More
quickly when the
mandible is moved
forward.
Articular Disc
• Bi-concave - Aids in positioning during
movements
• Dense fibrous tissue
• Few blood vessels or nerves
- Weeping lubrication / nutrient exchange
• Divides the joint into upper (superior) & lower
(inferior) synovial cavities
Inferior Synovial Cavity
• Disc and condyle are tightly joined by lateral
and medial discal ligaments
• Rotational movement
Superior Synovial Cavity
• Articular Disc / Articular Eminence of the
temporal bone
• Translational movement
Superior Retrodiscal Lamina
• Contains elastic fibers
• Retracts the disc posteriorly - the only
structure in the joint capable of doing so
• Ligaments once stretched do not return to
their original length
Superior retrodiscal lamina is stretched
when the condyle is fully translated
Lateral Pterygoid
• Inferior LP - pulls condyle forward, is active
during the opening cycle
• Superior LP - attached to condyle and the disc
– could pull the disc forward or at least apply
tension to it, but it does not. This muscle is active
during the closing cycle.
Closing
Opening
What role do the following two structures play in
translation of the mandible?
1. Temporomandibular ligament – outer
oblique portion
2. Inferior lateral pterygoid
The OOP restricts posterior movement of the neck of the
condyle and acts as a mechanical initiator of translation of
the condyle.
Outer Oblique Portion of the
Temporomandibular Ligament
Contraction of the inferior lateral pterygoid pulls the
condyle forward; this is a muscular component of
translation.
Bi-lateral
contraction =
Protrusion or
opening of the
mandible.
Inferior lateral pterygoid
Unilateral
contraction =
lateral movement
to the opposite
side.
Optimum Orthopedically Stable Joint Position
CENTRIC RELATION
Definitions of Centric Relation
• Old Definition
– Most posterior (retruded) position of the
condyles
– Denture patients – it was reproducible
– Anatomy of the joint had not been examined
• New Definition
– Most anterior superior position of the condyles
in the mandibular fossa with the disc properly
interposed.
Centric Relation
The Glossary of Prosthodontic Terms
“The 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
slopes of the articular eminences.”
– This position is independent of tooth contacts.
– This position is clinically discernible when the
mandible is directed superiorly and anteriorly.
– It is restricted to a purely rotary movement about the
transverse horizontal axis.”
Centric Relation
Additional Clarifications
• At the most anterior-superior position the
condyle-disk assemblies are braced medially,
thus centric relation is also the midmost
position.
• A properly aligned condyle-disk assembly in
centric relation can resist maximum loading by
the elevator muscles with no sign of
discomfort.
Diagnostic Casts
– Remember, the purpose of the mounted casts in
the treatment planning phase is to see how the
mandibular teeth relate to the maxillary teeth
when the condyles are in CR.
– Mounted casts make it possible to determine the
best treatment approach for bringing the teeth
into harmony with the correct maxillo-mandibular
relationship.
Diagnostic Casts
Ignoring the position of the
TMJs when examining the
occlusion is not acceptable.
It does not show what must
be done to achieve
harmony between the
occlusion and the TMJs.
Unmounted casts are
responsible for many
mistakes in restorative
treatment.
Diagnostic Casts
Analysis of the mandible-tomaxilla relationship when
the condyles are in CR
presents a completely
different picture from MI
(ICP).
Protrusive and Lateral
Movements
Movement of the Condyles
• Activity in the right and left TMJ’s is relatively
equal in opening, closing and protrusive
movements
• Right and left joints are acting independently
and differently in all other eccentric
movements
Protrusive Movement
• Mandible moves forward
• Condyles slide downward on condylar incline
(eminence)
• Anterior teeth should separate the posterior
teeth, therefore only incisors and canines
should touch in a protrusive movement
Protrusive Movement
1.Articular
eminence
2.Anterior
guidance
Lateral Movements of the Mandible
Working Side
Laterotrusive side
Side that moves away from
the midline or mid-palatal
suture of the maxilla
Tooth contacts should be
on this side, preferably on
the canine only
Non-Working Side
Mediotrusive Side
Side that moves toward
the mid-palatal suture of
the maxilla
Teeth should NOT contact
on this side
Left Laterotrusive
Nonworking side (right)
• Immediate side shift
• Translates
• “Travels” downward,
forward & inward
• Downward = condylar
inclination
• Inward = Bennett Angle (or
progressive side shift)
Working side (left)
• ISS
• rotate around vertical axis
(mostly) & sagittal axis
(some)
• Relatively fixed in position
Immediate Side Shift
• “Mandibular lateral translation”- Okeson
• The bodily shift of the mandible in the
direction of the working side occurring in the
initial phase of the movement.
• Can be programmed into fully adjustable
articulator.
Bennett angle
Definition: The angle in the horizontal plane between the
condylar path and the sagittal plane.
Related terms: Bennett Movement
R
L
Bennett Angle
22º
The distance the translating (NW) condyle moves
inward or medially – measured in degrees compared
to a straight forward path.
Movement of the Translating Condyle
Downward
(inferiorly)
Down the
articular
eminence
Movement of the Translating Condyle
Forward
Translation
Movement of the Translating Condyle
Inward
Movement of a
fixed radius
around the
rotating condyle
Occlusal Interferences
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•
•
•
Centric
Working (Laterotrusive)
Nonworking (Mediotrusive)
Protrusive
Occlusal Interferences:
Definition
Tooth contacts in eccentric
movements other than the anterior
guidance on canines or incisors.
Vertical force:
along the long axis
Lateral or
horizontal
force: at an
angle to
the long
axis X
Why would we like to avoid having eccentric
contacts on posterior teeth?
• Posterior teeth do not tolerate lateral forces
as well as anterior teeth
1. Root morphology & bone density
2. Proximity to fulcrum
3. Reflexes / proprioception
Posterior teeth don’t tolerate lateral forces as
well as anterior teeth – Why Not?
1. Root morphology & bone density
- Canines have the longest, largest root in the
arch
- Canines and incisors are anchored in dense
cortical bone
- Molars have smaller, shorter, divergent roots
- Anchored in less dense medullary bone
Premolars
• From a morphology standpoint, premolars are
transitional between the canines and the molars
1) Occlusal surface alignment similar to molars allow
axial loading
2) Root form similarities to anterior teeth that allow
them to share in lateral guidance (group function)
Classification of Levers
Class 3 - The fulcrum is at one end, the load at the
other end and the effort lies between the load and
the fulcrum
#2) Why would we like to avoid having
eccentric contacts on posterior teeth?
2. Closer proximity to the fulcrum = ↑ forces
#3) Why would we like to avoid having eccentric
contacts on posterior teeth?
3. Proprioception or sensory feedback to the muscles
- Canine to canine contact in eccentric movement:
results in less activity or contractive force in the
closing muscles
- Posterior teeth contacting in eccentric movement:
results in more activity or contractive force in the
closing muscles
With the condyles in the centric relation position – close
together – the teeth that contact are centric
interferences. If all teeth contact perfectly, then MI = CR.
Working or Laterotrusive
Interference
• A contact on the working side other than
canines or group function
“Similar” cusps
will contact:
Lingual / Lingual
or
Buccal / Buccal
Non-working or Mediotrusive
Interference
• Any contact on the non-working side
“Dissimilar” cusps
will contact:
Lingual / Buccal
Protrusive Interference
• Any posterior tooth contact during
protrusion
Role of Stress in TMJ Disorders
• Increase in stress can lower an individual’s
ability to accommodate occlusal interferences
• If stress cannot be relieved there may be a
need to alter or refine the occlusion via
occlusal adjustment, bite guard therapy or
restoration of the teeth
Today in Lab
• Start # 12 Full Crown for Practical
• Finish 29 if possible.
• Turn in Module 3 Sign-Off Sheet if possible