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Occlusion in Fixed Prosthodontic Practice
Dr Wael AL-OmariBDS; MDentSci; PhD.
Static OcclusionCentric 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
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
Canine guided occlusion
Group function occlusion
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
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.
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.
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
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 .
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)
Non-working Side Occulsal Interferences
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
Sliding from RCP to ICP
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
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
Three Dimensional Records for Planning Crown/Bridge
Hand-Held Study Casts Articulated Study Casts Diagnostic Wax-up
Hand-Held Study Casts
Advantages: Provide an unimpeded view of ICP Assess the ease of articulation, and the need or not for iner-occlusal recordEvaluation of crown height Evaluation of inter-occlusal space
Hand-located models should be sufficiently accurate Should be used as a diagnostic tool only They don’t provide information about excursive tooth contacts or RCP.
Articulated Study Casts
Simple hinge or non-anatomical articulators: Limited accuracy, can’t 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
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
Diagnostic wax-up
Records for Making Crown/Bridge Work
The Articulator Opposing Casts Interocclusal Records (IOR) Copying Tooth Guidance
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
Simple hinge articulator
Semi-adjustable articulator
Fully adjustable articulator
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.
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
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 patient’s mouth.
Opposing impression can be ideally taken
with addition silicone, though alginate is
satisfactory
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.
Interocclusal Records (IOR)
An IOR should:
1- Record the tips of cusps or preparation2- 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.
Trimmed IOR restricted ton area of toot preparation (Steele et al, BDJ, 2002)
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)
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
Loss of all guiding surface after teeth preparation
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.
Replica of temporary crowns after adjustment in the mouth
Autopolymerizing acrylic
Custom incisal guide table made in autopolymerized acrylic utilizing all excusive movements
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
Thank You