Occlusion in Fixed Prosthodontic Practice Dr Wael AL-Omari

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Occlusion in Fixed Prosthodontic Practice

• Dr Wael AL-Omari
• BDS MDentSci PhD.

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Static Occlusion

• Centric occlusion (CO) the occlusion the patient
  makes when they fit their teeth together in
  maximum intercuspation
• CO is also called
• Inter-cuspal position (ICP)
• Bite of convenience
• Habitual bite
• Significance
• Occlusal forces directed axially.
• End point f chewing cycle
• The position in which simple restorations are
  made

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Dynamic Occlusion

• Dynamic occlusion describe occlusal contacts
  when the mandible is moving relative to the
  maxilla
• Guidance from the teeth
• Determined by the shapes of teeth and TMJ
• Canine guidance vs. group function
• Protrusive guidance

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Canine guided occlusion
Group function occlusion
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Significance of Guidance Teeth

• Non-axial loading
• Heavily restored teeth at risk of fracture or
  decementation
• other manifestations wear, mobility,
  fracture, migration,
• TMJ dysfunction.
• Identify guidance teeth before preparation
• If guidance is satisfactory, re-establish the
  same guidance
• pattern in the new restoration.
• If guidance tooth is weak, transfer guidance
  contacts to the
• adjacent stronger teeth
• Provide clearance during preparation in
  excursive positions
• Select appropriate material to restore the
  guidance tooth

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Interferences

• Interference Any tooth to tooth contact which
  hamper or hinder
• smooth guidance in excursions or closure into
  centric occlusion
• Working side interference An interference on
  the side to
• which the mandible is moving
• Non-working side interference (NWSI) or
  balancing side
• interference An interference on the side
  from which the
• mandible is moving.
• NWSI acts as a cross arch pivot, disrupting the
  smooth
• movement and separating guidance teeth on the
  working side.
• NWS contact excursions are guided equally by
  working and
• non-working tooth contacts as an ideal
  complete denture
• occlusion.

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Clinical Significance of Identifying Interferences

• Most NWSIs are on molars that are subjected to
• excessive oblique damaging forces that
  predispose to
• fracture or decementation.
• If inference on a tooth to be prepared, it is
• recommended that interference is removed
  before
• starting tooth preparation.
• Remove interference at a separate appointment
  prior to
• preparation to allow adaptation to the new
  guidance
• pattern.

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Clinical Significance of Identifying Interferences

• Identify a suitable tooth on the working side to
  
• take over the guidance
• Removal of interferences located on teeth are
• not to be prepared is not mandatory.
• Removal of interferences is not advocated as a
• public health measure, especially if
  asymptomatic.
• To avoid introducing interferences on new
• restorations tooth preparation clearance
  should be
• adequate in ICP and lateral and protrusive
• excursions

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NWSI During a right lateral excursion (see
black arrow) the left first molars act as a
cross-arch pivot lifting the teeth out of contact
on the working side .
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Clearance between the preparation and opposing
teeth is inadequate which may cause problems with
the provisional restoration and excessive
adjustment on final restoration.
You can avoid these problems by removing the
non-working side contact prior to tooth
preparation (blue line represents tooth
recontoured in this way)
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Non-working Side Occulsal Interferences
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Retruded Contact Position (RCP) or Centric
Relation (CR)

• Definition Position of the mandible when first
  contact
• between opposing takes place, during
  closure on its
• hinge axis, that is with the condyles
  maximally seated in
• their fossa and the muscles are at their
  most relaxed and
• least strained position.
• Examine RCP preoperatively
• Articulate casts on semi-adjustable articulator
  in RCP for
• adjustment and trial preparation

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Sliding from RCP to ICP
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Significance of CR record 1- It is reproducible
position with or without teeth present 2- If CR
involves tooth to be prepared, better remove
deflective contacts prior to preparation 3-
When re-organizing occlusion at new vertical
dimension 4- To distalize mandible to create
space lingually for anterior crowns 5- If
restoring anterior teeth and CR contact results
in strong anterior thrust against teeth to
be prepared
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Occlusal Examination for Crown/bridge planning

• Check ICP contacts on teeth to be restored
• Check RCP Identify deflective contacts
• Check lateral and protrusive relationship
• Identify the guidance contacts and
  interferences
• on the teeth to be restored
• TMJ examination
• Check wear facets, fremitus, mobility and
• drifting

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Three Dimensional Records for Planning
Crown/Bridge

• Hand-Held Study Casts
• Articulated Study Casts
• Diagnostic Wax-up

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Hand-Held Study Casts

• Advantages
• Provide an unimpeded view of ICP
• Assess the ease of articulation, and the need or
  not for
• iner-occlusal record
• Evaluation of crown height
• Evaluation of inter-occlusal space
• Hand-located models should be sufficiently
  accurate
• Should be used as a diagnostic tool only
• They dont provide information about excursive
  tooth
• contacts or RCP.

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Articulated Study Casts

• Simple hinge or non-anatomical articulators
• Limited accuracy, cant replicate jaw movements
  .
• Semi-adjustable articulator combined with
• facebow and interocclusal records
• Reproduce the jaw movements
• The quality of the casts are of paramount
  importance

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Diagnostic Wax-up

• The diagnostic wax-up allows you to plan
• 1- The new static occlusal contact and the shape
  of
• guidance teeth.
• 2- The effect of occlusal modification on
  appearance
• 3- Best option for creating interocclusal spaces
  for
• restoration.
• 4- Can be used as a template for the temporary
  and final
• restorations

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Diagnostic wax-up
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Records for Making Crown/Bridge Work

• The Articulator
• Opposing Casts
• Interocclusal Records (IOR)
• Copying Tooth Guidance

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The Articulators

• Non-Adjustable Articulators
• Fixed Average Value Articulators
• Condyler angle is fixed 30-45 bennet
• angle is fixed at 15
• Performs open, close and horizontal movement
  
• Semi-Adjustable Articulators
• Fully Adjustable Articulators

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Simple hinge articulator
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Semi-adjustable articulator
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Fully adjustable articulator
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Articulator

• Small number of crowns not involved in excursive
  contacts
• can be made reasonably on a non-adjustable
  articulator.
• Crowns involved in excursions better made on
  articulator
• with anatomical dimensions. This is more
  important where
• several crowns to be made at the same time.
  Semi or fully
• adjustable articulators can be used for
  this purpose.
• Majority of cases, however, can be managed
  satisfactorily
• using fixed average value articulator in
  combination with a
• facebow.

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Indications of Semi-Adjustable Articulators

• Semi-adjustable articulators should be used at
  the following
• 1-   Ensure good guidance especially when
  multiple crowns involved.
• 2-   Plan to increase vertical dimension.
• 3-   When ICP is lost due to many preparations or
  when reorganizing
• the occlusion based on RCP.
• 4-   Plan to remove occlusal interferences.
• 5-   When providing occlusal splint either before
  or after treatment.
• 6- Semi-adjustable articulators should be used
  for adhesive ceramic
• restorations, because adjustment in the
  mouth prior to
• cementation may damage the restoration

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Opposing casts

• Casts with stone blebs never fit into ICP and
• results in perfect fitting of crown on the
  cast
• but very high in the ICP in the patients
  mouth.
• Opposing impression can be ideally taken
• with addition silicone, though alginate is
• satisfactory

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Interocclusal Records (IOR)

• IOR designed to improve the accuracy of
• mounting, though the opposite may result.
• IOR may make locating working and opposing casts
  in ICP more
• difficult and may introduce further
  inaccuracies.
• Try to locate casts by hand before IOR is taken.
• IOR is required to stabilize casts.
• Occlusal fissures reproduced accurately in IOR
  may well not be
• reproduced to the same extent in the casts,
  preventing full seating
• of casts in the record. The same may happen
  if IOR reproduced
• soft tissue contacts.

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Interocclusal Records (IOR)

• An IOR should
• 1-    Record the tips of cusps or preparation
• 2-  Avoid capturing fissures patterns as much as
• possible.
• 3- Avoid soft tissue contacts.
• 4-  The ideal is small IOR with trimmed margins
  and
• restricted to the area of preparation.
  Verify the
• ICP using foil shimstock.

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Trimmed IOR restricted ton area of toot
preparation (Steele et al, BDJ, 2002)
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Occlusal silicon record capturing excessive
details
A very detailed record could not fully seat a
less detailed stone cast (arrow)
(Steele et al, BDJ, 2002)
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Copying Tooth Guidance

• Palatal surfaces of maxillary anterior teeth are
  involved in protrusive guidance contacts and in
  speech formation
• If several teeth are to be prepared there may be
  no existing guidance surface left intact after
  preparation, So the guidance will be lost

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Loss of all guiding surface after teeth
preparation
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Copying Tooth Guidance

• The most effective methods to address this
  problem necessitate
• the use of a facebow and semi-adjustable
  articulator to allow Anatomical movement in
  excursions.they are
• 1. The crown about methods
• Alternate teeth are restored, thus
  maintaining the shape of functional surface,
  which continue to provide guidance for the
  articulated cast.
• 2. The custom incisal guide table.

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Replica of temporary crowns after adjustment in
the mouth
Autopolymerizing acrylic
Custom incisal guide table made in
autopolymerized acrylic utilizing all excusive
movements
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The guidance table is used to copy the teeth
guidance in all excursive relationships to
fabricate the final crowns
The guidance table also assists in determine the
crowns lengths (canine) and contacts
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Thank You