Transcript Criteria for Optimum Functional Occlusion

Criteria for Optimum
Functional Occlusion
Dr. Pauline Hayes Garrett
Dr. Patricia W. Kiln
Department of Endodontics,
Prosthodontics and Operative Dentistry
University of Maryland, Baltimore
This material is taken from:
Okeson, J.P. (2003). Management of
Temporomandibular Disorders and Occlusion
6th Ed. , St. Louis, MO: Mosby, Chapter 5
Wheeler’s Dental Anatomy, Physiology and
Occlusion, Ash, Eighth Edition, Saunders, 2003,
Chapter15,
pgs. 421-433
Objectives!
• Explain and describe the criteria
for optimum function of the
masticatory system.
• Identify and explain optimum
occlusal contacts and function in
the absence of pathology.
The masticatory system
consists of an extremely
complex and interrelated
group of muscles, bones,
ligaments, teeth and nerves
Illustration Reprinted from: Okeson, J.P. (2003).
Management of Temporomandibular Disorders and
Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter
3.with permission from Elsevier. Pg.31
The mandible is a bone suspended from the skull by ligaments
and a muscular sling. The elevator muscles (masseter, medial
pterygoid, and temporalis) raise the mandible. When force is
applied, contact is made in three places…the two TMJs and the
dentition. These forces are potentially quite heavy so damage
could occur at all three sites.
Anatomic structures of the
TMJ (temporomandibular
joint):
Articular disc –
dense fibrous connective
tissue; no nerves or blood
vessels so it can endure
heavy forces without
damage or pain.
Illustrations Reprinted from: Okeson, J.P. (2003).
Management of Temporomandibular Disorders and
Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter
3.with permission from Elsevier. Pg.113
The articular disc separates, protects and stabilizes the condyle
in the mandibular fossa during functional movements.
Fibers from the upper head of the Lateral Pterygoid pull the disk
down and forward.
ARTICULAR DISC - SHAPE ,
ATTACHMENTS AND FUNCTION
Peripherally the disc is attached to the
fibrous capsule and the superior head of
lateral pterygoid (anteriorly). Fig. A
Medially and laterally the disc is tightly attached
to the head of the condyle by the medial and
lateral collateral (discal) ligaments. (figure
B) They are composed of collagenous connective
tissue.
These ligaments function to restrict the disc
from moving away from the condyle and permit
the disc to move anteriorly and posteriorly
together with the condyle (as a condyle-disc
unit) during translation. They also function
during the rotation of the TMJ.
Illustrations Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and
Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. (Fig. A ,pg 113),( Fig B,
Pg.14)
Positional stability of TMJ
• Determined by
muscles pulling across
the joint to prevent
dislocation
• Major stabilizing
muscles
– Masseter
– Medial pterygoid
– Temporalis
– Superior head of
the lateral
pterygoid
CENTRIC RELATION:
Most musculoskeletally stable position of the TMJ
Optimum functional tooth contacts:
Maximum Intercuspation
• When closing in
Centric Relation
results in a cusp tip to
cusp tip occlusal
position.
• The neuromuscular
system can possibly
slide the condylar
position (via a Centric
Slide) so that a cusp
tip to fossa
relationship was
attained.
Optimum functional tooth
contacts
• To be in harmony,
all must be stable
• Stable occlusion
leads to both
effective
functioning AND
minimal damage
to all components
Optimum functional tooth
contacts
• The musculoskeletal
system is capable of
applying much more
force than necessary
for effective function
…so…
• It’s important to
establish occlusal
conditions to accept
heavy forces without
damage while still
being efficient
Optimum functional tooth
contacts
• Optimum occlusal
conditions, then,
require even and
simultaneous contact
of all possible teeth.
• This maximizes the
stability of the
mandible…and
• Minimizes the
amount of force on
each tooth
With only two posterior
contacts, all force is
loaded on that side
causing
the muscle system to pull
the condyle on the
unopposed side further
into the mandibular
fossa. This causes an
unnatural shift and
possible damage to one
or both sides of the TMJ.
With two posterior
contacts on each side,
the same load is more
equally distributed and
the mandible is more
stable and balanced.
As the number
of occluding teeth
increases,
the force to each
tooth decreases
since the load is
distributed over
a greater area.
This new information allows us to redefine the
criteria for optimum functional occlusion:
This new information allows us to redefine
the criteria for optimum functional occlusion:
Centric Relation coincides with maximum
intercuspation = optimum functional occlusion =
Centric Occlusion.
Centric Occlusion may or may not =
Maximum intercuspation
• The first Tooth Position when the condyles are in centric
relation = Centric Occlusion
– The occlusion of opposing teeth when the mandible is in
centric relation. This may or may not coincide with the
maximal intercuspal position.
Direction of force placed
on teeth
• Osseous tissue does not
tolerate pressure forces
• Pressure forces exerted on
bone, cause bone to
resorb (go away)
• The periodontal ligament
helps control these forces
and provide stimulation
– Pressure = bad
– Tension = good
• The periodontal ligament
converts a destructive
force (pressure) into an
acceptable force (tension).
Periodontal
Ligament
Bone
Periodontal ligament accepts various
directions of occlusal force
• Cusp tip or fossa
contact
– Force is directed
vertically through
the long axis
– Force is well
accepted due to
the alignment of
the periodontal
ligament fibers
Periodontal ligament accepts various
directions of occlusal force
• Contacts on inclines
– A horizontal
component causes
tipping
– Some areas of the
periodontal ligament
(PL) are compressed
while others are
elongated
– Forces are not
effectively dissipated
to the bone
Criteria for optimum functional
occlusion…
• The definition must
now include the
concept that each
tooth should contact
in such a manner that
the forces of closure
are directed through
the long axis of the
tooth
– This is also know
as Axial Loading
Forces applied along the long axes
of teeth are generally well tolerated
• Axial Loading:
the process of directing
occlusal forces through
the long axis of the tooth
• Compare to pounding the
top of a fencepost
• With proper contact,
posterior teeth receive
force along the vertical or
long axis in MI
Forces applied at an angle to the long
axis have potential to cause harm
• Compare to forces
used to remove a
fence post
• May cause mobility,
wear, or fracture
Axial loading accomplished
in two ways:
• Development of tooth contacts
on cusp tips or flat surfaces,
perpendicular to the long axis
of the tooth (marginal ridges,
bottom of fossae).
• Tripodization – each cusp
contacting a fossa in such a
way that three contacts points
are made
• Both of these methods
eliminate off-axis forces,
allowing the PL to reduce forces
to the bone
Which teeth can best
accept horizontal forces?
• Damaging horizontal forces of eccentric
movement must be directed to the anterior
teeth, positioned furthest from the fulcrum
• Examining all anterior teeth, it is apparent
that the canines are best suited to accept
these forces. [WHY?]
Cuspids are best suited to accept
horizontal forces of Occlusion
• Long, thick roots
• Better crown/root ratio
• Surrounded by dense bone
• Extensive periodontal ligament
• Most proprioceptively sensitive
tooth in the mouth
Posterior
disocclusion
Guidance Canine
Canines disocclude the posterior teeth in lateral
excursions. When
this condition exists, it is called canine guidance.
Scheme of Occlusion:
Canine Guidance
Scheme of Occlusion:
Canine Guidance
To restart movie, click on
image!
IF canines not positioned well (or
absent)
• When restoring this occlusal scheme the best
alternative is group function
– Group function is when several posterior
teeth on the working side contact during
excursions
– No contact on non-working side during
excursions
– No posterior contact during protrusive
movements
– Most desirable is canine plus premolars and
the MB cusp of the first molar
– More posterior than the MB cusp of first
molar not desirable because of increased
force that can be generated closer to the
fulcrum (TMJ) and force vectors (muscles).
Group function
• Laterotrusive
(working)
contacts must
provide
adequate
guidance to
disocclude
teeth on the
opposite side of
the arch
immediately…
BECAUSE
• Mediotrusive
(non-working)
contacts can be
destructive due
to the amount
and direction of
forces applied
to the joint and
dental
structures
(horizontal =
bad)
Group Function:
Working Side
Note: Shift of midline laterally and slightly anteriorly
Group Function:
Balancing Side
(No Contacts)
Scheme of Occlusion:
Group Function
To restart movie, click on
image!
Anterior Group Function
•
A form of
articulation in which the
canines and incisors
(usually just the lateral
incisors) function
together to disocclude
the posterior teeth
during lateral and lateral
protrusive excursions of
the mandible. In this
scenario the premolar
would probably work in
conjunction with the
lateral incisor to support
the lateral and lateral
protrusive excursions.
Anterior and posterior
teeth function differently
• Posterior teeth accept forces well
during closure of mouth. Because
of their position in the arch, forces
can be directed along the long axis
of the teeth and dissipated
• Posterior teeth function effectively
in stopping the mandible during
closure
ANTERIOR GUIDANCE
Posterior
Disocclusion
Anterior guiding
contacts
Anterior and posterior
teeth function differently
• Anterior teeth are not positioned to
accept heavy forces. Their labial angle
makes it impossible to achieve axial
loading.
• They CAN direct eccentric forces
Illustrations Reprinted and modified from: Okeson, J.P. (2003). Management of
Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby.,
with permission from Elsevier. Pg. 124
• Malocclusion!
– This patient has
an anterior open
bite and will not
have the normal
wear pattern of a
young adult.
– Note: This patient
has no anterior
guidance!
Anterior and posterior
teeth function differently
• Posterior teeth should contact
slightly more heavily than anterior
teeth in centric occlusion. This is
called mutually protected
occlusion.
Interferences
• Three Types:
• Interference to the desired Occlusal
scheme (Canine Guidance/Group
function): excursive interference
– eg. Mediotrusive/Non-working side
interference
• Prematurity (usually a high restoration)
• Deflective Occlusal Contact (centric
interference-usually natural)
Contacts on inclines
(eccentric forces)
• When forces are
NOT effectively
dissipated to the
bone, a
pathologic
response may be
elicited
– Neuromuscular
reflex activity
• Avoidance
• Protection
Figures reprinted from:
Evaluation, Diagnosis, and
Treatment of Occlusal Problems,
2nd ed., Peter Dawson,
Mosby,1989. pg.438-439, with
permission from Elsevier.
Deflective Occlusal Contacts
Centric Interferences
In these slides, the
“red” areas
indicate
interferences. The
indicated
treatment is an
occlusal
adjustment to
remove the
interference.
Arc of closure interferences
Line of closure interferences
Figures reprinted from: Evaluation, Diagnosis, and Treatment of
Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg.438439, with permission from Elsevier.
Summary
• When the mouth closes, the condyles
should be in the most supero-anterior
(musculoskeletally stable) position,
resting on the posterior slopes of the
articular eminences with articular discs
properly interposed. In this position,
there should be even and simultaneous
contact of all posterior teeth. Anterior
teeth contact, but more lightly than
posterior teeth
Summary
• All tooth contacts should provide axial
loading of occlusal forces when
possible.
• When the mandible moves into
laterotrusive position, there should be
adequate tooth-guided contacts on the
laterotrusive side (working) to
disocclude the mediotrusive (nonworking) side immediately. The most
desirable guidance is provided by the
canines (canine guidance)
Summary
• When the mandible moves in protrusive
position, there should be adequate
tooth-guided contacts on the anterior
teeth to disocclude all posterior teeth
immediately= Christensen’s effect
• In the alert feeding position, posterior
tooth contacts should be heavier than
anterior tooth contacts.