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