Optimal occlusion and muscles of mastication (2) /certified fixed orthodontic courses by Indian dental academy

OptimalOptimal
OcclusionOcclusion
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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RequiredRequired Reading
• Okeson, JP. Management of Temporomandibular Disorders and
Occlusion , 5th ed., (2003), Mosby. Chapter 5.

Criteria for Optimal OcclusionCriteria for Optimal Occlusion
• What is the ideal
functional
relationship of
teeth?
• What is an ideal
occlusion?
• Several concepts
have developed
over time
Esthetic smile BMC 59.1

Concepts of OcclusionConcepts of Occlusion
• Balanced Occlusion
• Gnathology
• Dynamic Individual
Occlusion

Concepts of OcclusionConcepts of Occlusion BalancedBalanced
OcclusionOcclusion
• Bilateral and balancing
contacts through all
excursive movements
• Protrusive
• Laterotrusive
• Developed for complete
dentures
• Rationale was thought to
provide stability to
dentures through all
excursive movements
• Carried over to dentate
patients

Concepts of OcclusionConcepts of Occlusion GnathologyGnathology
• Unilateral laterotrusive
(working side) contacts
• Anterior tooth contact in
protrusive movements
• Developed as desirability of a
balanced occlusion for a
dentate patient was
questioned
• Science of mandibular
movement and tooth contacts
• Used in restoring the dentate
patient and in eliminating
occlusal problems
• All patients with any deviation
from the ideal occlusion were
treated

Concepts of OcclusionConcepts of Occlusion DynamicDynamic
Individual OcclusionIndividual Occlusion
• Concept is based on function
and health rather than any
ideal occlusal arrangement
• In the absence of pathology,
no treatment to change a
patient’s occlusion would be
necessary
• Developed in the late 1970’s

Optimal OcclusionOptimal Occlusion
• Masticatory system is
extremely complex
• Contraction of the elevator
muscles produces
• Tooth contacts
• Forces on each TM joint
• Forces are significant
• Potential for damage is
present
• What is the optimal orthopedic
relationship of the TM joints
and teeth that will
• Minimize damage?
• Prevent damage?
• Eliminate damage?

Optimal Orthopedic JointOptimal Orthopedic Joint
PositionPosition
• The position of the joints where
the a stable orthopedic position is
achieved is called Centric
Relation
• Early definitions described it as
the most retruded position of the
condyles
• Called a ligamentous position
• Important in fabricating complete
dentures
• Reproducible maxillomandibular
position
• Determines position of teeth in
maximum intercuspation

PositionPosition
• Definition of Centric Relation has
changed
• Condyle is in the most retruded
position in the fossa
• Condyle is in the most superior
• Condyles should be positioned
downward and forward on the
eminencia
• Clinically, it is a necessary position
to determine for both dentate and
edentulous patients

PositionPosition Articular DiscArticular Disc
• Dense fibrous connective tissue
• Lacks blood vessels and nerves
• Able to tolerate forces without
damage or pain being produced
• Provides protection to condyle and
fossa during movements
• Articular disc doesn’t determine
position of joint stability

PositionPosition MusclesMuscles
• Determine positional stability of
the joint
• Direction of the forces of the
muscles determine the
orthopedically stable joint position
• Primary TM joints stabilizers
• Masseter (anterosuperior)
• Medial pterygoid (anterosuperior)
• Temporalis (superior)
• Contributors to TM joint
stabilization
• Lateral pterygoid (anterior)
Elevator muscle directional
force in stabilizing the TM
joint Okeson Fig. 5-2

• Most stable orthopedic position
• Condyles in the most
anterosuperior position in the fossa
• This position is without occlusal
interferences
• Called the musculoskeletal stable (MS)
position of the mandible
• This direction of forces is consistent
with the regions of the fossa able to
withstand loading forces
• Anterior and superior roof of fossa
has thick bone
Elevator muscle directional
force in stabilizing the TM
joint Okeson Fig. 5-2

• Most stable orthopedic position
• Condyles in the most anterosuperior
• This position is without occlusal
interferences
• Called the musculoskeletal stable (MS)
position of the mandible
• This direction of forces is consistent with
the regions of the fossa able to withstand
loading forces
• Anterior and superior roof of fossa has
thick bone
• Posterior condylar position is not the most
stable
• Bone of posterior fossa is thin
• Retrodiscal tissue has sensory innervation
and is highly vascular
• Not designed to withstand heavy forces
Most anterosuperior position
of the joint (solid)
Posterosuperior joint position
(dotted line) Okeson Fig. 5-3

PositionPosition LigamentsLigaments
• Not active in joint function
• Function to limit joint
movement
• Ligamentous position is a
border position
• Not an ideal position for an
optimal orthopedic position
for the TM (or any other) joint

PositionPosition
• MS (musculoskeletal)
position and CR (centric
relation) are the same
• Most stable TM joint position
is with the condyles in an
anterosuperior position in the
fossa

PositionPosition
• Is there an anteroposterior
range while the condyle is in
its most superior position?
• PK Dawson says no
• True for a healthy, young joint
• Okeson says possible if TM
ligament is loose and posterior
movement can occur
• A healthy joint permits very
little posterior movement from
the MS position Most anterosuperior position

PositionPosition
• In a chewing cycle, the
working condyle moves
posterior to the ICP during
closure
• Therefore some posterior
movement (1mm) is normal
during function
• This can increase if
• the TM ligaments are elongated
• there is a joint disorder

Other Joint Position ConceptsOther Joint Position Concepts
• A concept by Gelb* suggests that there
is another optimal condyle position
• Condyles are in an optimal position
when they are slightly translated
• Forces are dissipated where bone is
thickest
• Actually a protrusive mandibular
movement
• Inferior lateral pterygoid muscles are
contracting with the elevators
• Inferior lateral pterygoids would be in a
constant state of contraction
• Not a MS (musculoskeletal) position
• Represents a muscle stabilized position
• Not compatible with resting
musculature
*Gelb H. Clinical management of head, neck and TMJ pain and
dysfunction, Philadelphia, WB Saunders (1977).
Anterior and inferior
movement of condyle
Okeson Fig. 5-5

• As muscle pain is common in
masticatory disorders, a joint position
that has increased muscle activity
would seem to be contraindicated.
• Not a position consistent with a
• Muscular rest position
• Physiologic position
movement of condyle
Okeson Fig. 5-5

• Relaxed muscle position concept
• Using electrical stimulation and
relaxation of the elevator muscles, the
lowest EMG activity can be determined
• This places the condyles in an anterior
and inferior position to the MS or CR
anterosuperior position
• This rest position is at about 7-8mm of
opening
If the patient’s occlusion were built
with the condyles anterior and
inferior, what teeth would be in
contact if the elevators contract and
the inferior lateral pterygoid muscles
are relaxed?
movement of condyle
Okeson Fig. 5-5

Optimal Tooth ContactsOptimal Tooth Contacts
• Occlusal contacts influence the
muscular control of the position of
the mandible
• Occlusal contacts result in
neuromuscular feedback to find a
stable occlusal position
• Muscles can generate forces much
greater than are required for
function
• Occlusal relationships should be
developed to minimize possibility of
damage to
• Teeth
• Peridontium
• Muscles
• TM joints

• Unilateral contact with two molars
(2 teeth)
• Assume that 40 pounds of force is
applied during function
• Right molars provide a fulcrum
• Results in increased vertical force
in the left TM joint
• Results in decreased vertical force
in the right TM joint
• Mandibular position is not stable
• Overclosure occurs on the left side
• Heavy forces can result in damage
to the
• TM joints
• Teeth
• Peridontium
Muscle activity and
mandibular movement with
two molars present Okeson
Fig. 5-6

• Bilateral molar contact (4 teeth)
• Contact is achieved on both sides
on closure
• Even, simultaneous contact on
closure occurs
• Additional teeth decrease the load
• Same 40 pound load is decreased
to 20 pounds on each tooth
• Results in a more stable occlusal
condition than previous example
• Less potential for damage to
• TM joints
• Teeth
• Peridontium
Muscle activity and
bilateral molar contacts
Okeson Fig. 5-7www.indiandentalacademy.comwww.indiandentalacademy.com

• Bilateral molar and second
premolar contact (8 teeth)
• Contact is achieved on both sides
on closure
• Additional teeth decrease the load
• Same 40 pound load is decreased
to 10 pounds on each tooth
• Results in an even more stable
occlusal condition than previous
example
• Less potential for damage to
• TM joints
• Teeth
• Peridontium
Muscle activity and
bilateral molar and premolar
contacts Okeson Fig. 5-8www.indiandentalacademy.comwww.indiandentalacademy.com

Optimal Tooth ContactsOptimal Tooth Contacts SummarySummary
• Contact with all teeth should be of
even magnitude and simultaneous
• Forces on individual teeth are
minimized with this arrangement
• Condyles should be in their most
anterosuperior position in the fossa
(MS position or CR position)
• Therefore ideally, ICP is
coincident with CR (MS)
• This is called orthopedic stability
Muscle activity and
bilateral molar and premolar
contacts Okeson Fig. 5-8www.indiandentalacademy.comwww.indiandentalacademy.com

Optimal Force DirectionOptimal Force Direction
• Bone reacts to pressure force by
resorbing
• Periodontal ligament suspends the
tooth in its socket
• Most PDL fibres run in an oblique
direction
• Pressure force is converted to a
tension force and stimulates bone
formation
• PDL can be considered to be a
shock absorber that protects bone
from occlusal force
Expanded view of periodontal
ligament Okeson Fig. 5-9

• Occlusal forces directed along a
cusp tip or flat surface such as a
fossa or marginal ridge directs the
force through the long axis of the
tooth
• Vertically directed forces are called
axial loading
Expanded view of periodontal
ligament Okeson Fig. 5-9

• Occlusal forces directed along a
cusp tip or flat surface such as a
fossa or marginal ridge directs the
force through the long axis of the
tooth
• Vertically directed forces are called
axial loading
Axially directed forces
Okeson Fig. 5-10

• Axial loading can be achieved in
two ways
• Develop contacts on cusp
tips or flat surfaces (fossa or
marginal ridges)
Axially directed forces
Okeson Fig. 5-12a and b
• Develop three contacts
surrounding a cusp tip as it
contacts a fossa
• Called tripodization

• Both direct forces axially and
eliminate non-axially directed forces
• Non-axially directed forces produce
tipping forces that result in
A compression of the PDL
B expansion of the PDL
• Potential for bone resorbtion
Non-axially directed forces
Okeson Fig. 5-11

Optimal Force MagnitudeOptimal Force Magnitude
• Mandibular movements include
laterotrusive and protrusive
movements
• Allows horizontal forces to be
placed on teeth
• Forces are potentially damaging
Are some teeth better than
others to accept these horizontal
forces?
• Masticatory system is a lever
system
• Similar to a nutcracker
• More force can be generated closer
to the fulcrum
Greater force magnitude can
be produced closer to the
fulcrum (TMJ) Okeson Fig.
5-13

• More force can be generated on
posterior teeth than on anterior
teeth
• Damaging horizontal forces are
best managed by the anterior teeth
Which of the anterior teeth are
best suited to accept horizontal
forces in eccentric movements?
• Central incisors
• Lateral incisors
• Canines
Why?
Greater force magnitude can
be produced closer to the
fulcrum (TMJ) Okeson Fig.
5-13

Which of the anterior teeth are best
suited to accept horizontal forces in
eccentric movements?
• Canines
Why?
• Longest and largest roots
• Best crown:root ratio
• Surrounded by dense compact bone
compared to the medullary bone of
posterior teeth
• Due to sensory input, there is lower
muscle activity when the canines are in
contact
• Therefore, the canines are the best
teeth to be in contact during a
laterotrusive movement
• Arrangement is called canine
guidance or canine rise occlusion
Left laterotrusive movement
illustrating canine guidance
Okeson Fig. 5-14

Which of the anterior teeth are best
suited to accept horizontal forces in
eccentric movements?
• Canines
Why?
• Longest and largest roots
• Best crown:root ratio
• Surrounded by dense compact bone
compared to the medullary bone of
posterior teeth
• Due to sensory input, there is lower
muscle activity when the canines are in
contact
• Therefore, the canines are the best
teeth to be in contact during a
• Arrangement is called canine
guidance or canine rise occlusion
Lingual view of a right
laterotrusive movement with
canine guidance Okeson Fig.
5-14

• Most patients have other teeth in
addition to the canines in contact in a
• If canines plus some other posterior
teeth are in contact in a laterotrusive
movement, it is called a group
function occlusion
• Best arrangement is canines, premolars
and the MB cusp of the first molar
• Additional posterior contacts are
undesirable due to proximity to the
fulcrum (TM joint)
Left laterotrusive movement
illustrating group function
Okeson Fig. 5-15

• Most patients have other teeth in
addition to the canines in contact in a
• If canines plus some other posterior
teeth are in contact in a laterotrusive
movement, it is called a group
function occlusion
• Best arrangement is canines, premolars
and the MB cusp of the first molar
• Additional posterior contacts are
undesirable due to proximity to the
fulcrum (TM joint)
Lingual view of a right
laterotrusive movement with
group function Okeson Fig.
5-15

• Protrusive movements can
generate horizontal forces that
are potentially damaging
• Anterior teeth are best suited
to dissipate these forces
• Distance from the fulcrum
• Anterior teeth should disclude
the posterior teeth because of
the
• Amount of force on posteriors
• Direction of force on posteriors
• In a protrusive movement,
only the anterior teeth
should contact, not the
posterior teeth
Lingual view of a protrusive
movement Okeson Fig. 5-17

Summary
• Anterior teeth cannot tolerate
heavy forces on closure (due
to axial inclination)
• Posterior teeth are best able
to withstand closing forces
• Anterior teeth are best able to
tolerate eccentric forces
• Laterotrusive
• Protrusive
Vestibular view of posterior bite
collapse Okeson Fig. 5-18a

Summary
• Anterior teeth cannot tolerate
heavy forces on closure (due
to axial inclination
• Posterior teeth are best able
to withstand closing forces
• Anterior teeth are best able to
tolerate eccentric forces
• Laterotrusive
• Protrusive
Posterior bite collapse and
heavy anterior forces Okeson
Fig. 5-18a

Effect of Posture on ToothEffect of Posture on Tooth
ContactsContacts
• The postural position is
maintained during periods of
inactivity
• Lips are together and teeth are
apart
• Usually there is a space of 2-4mm
between the teeth
• Posture influences tooth contacts
• If occlusion is established with the
patient reclined, a posteriorly
positioned occlusion will be
established
• With the patient upright, the
mandible will be positioned slightly
forward to this and result in heavy
anterior contact
• Called the anterior envelope of
function
Functional movements during a
chewing stroke Okeson Fig. 4-
19

Summary of Optimal OcclusionSummary of Optimal Occlusion
• The condyles should be in their most anterosuperior position in the
fossa during closure (MS or CR position)
• All teeth should contact evenly
• All teeth should contact simultaneously
• Anterior tooth contact should be lighter than posterior contact in MI
• All tooth contact should provide axial loading
• In a laterotrusive movement, the working side teeth should disclude
the non-working side teeth
• The best working side guidance is canine guidance
• Anterior teeth should provide immediate disclusion of all posterior
teeth in protrusion
• In an upright head position, posterior tooth contacts are heavier than
anterior tooth contacts in MI
• This type of occlusion is called a mutually protected occlusion

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