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Criteria for Optimum Functional Occlusion

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					  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       Periodontal
  – Pressure = bad              Ligament

  – Tension = good
• The periodontal ligament
  converts a destructive
  force (pressure) into an
  acceptable force (tension).                 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                • Mediotrusive
  (working)                      (non-working)
  contacts must                  contacts can be
  provide                        destructive due
  adequate                       to the amount
  guidance to                    and direction of
  disocclude                     forces applied
  teeth on the                   to the joint and
  opposite side of               dental
  the arch                       structures
                                 (horizontal =
  immediately…                   bad)
  BECAUSE
                                          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           Anterior guiding
Disocclusion        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         Figures reprinted from:
                         Evaluation, Diagnosis, and
     • Protection        Treatment of Occlusal Problems,
                         2nd ed., Peter Dawson,
                         Mosby,1989. pg.438-439, with
                         permission from Elsevier.
     Deflective Occlusal Contacts
                                   Arc of closure interferences
Centric Interferences

In these slides, the
  “red” areas
  indicate
  interferences. The
  indicated
  treatment is an
  occlusal
  adjustment to                   Line of closure interferences
  remove the            Figures reprinted from: Evaluation, Diagnosis, and Treatment of
  interference.         Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg.438-
                        439, 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 (non-
  working) 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.

				
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