occlusal relation

METHODS FOR ESTABLISHING OCCLUSAL RELATIONSHIPSم اسماء عبد السلام عبد القادر

Centric Relationthe most retruded relation of the mandible to the maxillae when the condyles are in the most posterior unstrained position in the glenoid fossae from which lateral movement can be made at any given degree of jaw separation.

Record bases and occlusal rims

Record bases
The record base is fabricated over the saddle area on the denture base minor connector. The most commonly used material is autopolymerizing acrylic resin as it is stable.

Procedure

1. Outline of record base is marked on cast.
2. Undercut on the ridge part of cast is blocked out with modelling clay or baseplate wax.
3. Tin foil substitute or any suitable separating medium is applied on the cast.
4. After the separating medium has dried, the framework is placed on cast.
5. A sprinkle-on method is used to mix the monomer and polymer and a uniform thickness of 2 mm is obtained After polymerization, the base is trimmed and polished.

Occlusal rims

Most commonly used material is medium baseplate wax ,modelling plastic may also be used. They should be so shaped that they represent the lost teeth and supporting structures. It should be centred over the crest of the ridge in cases of lower arch.


Methods for taking maxillo mandibular relation ships for partially edentulous patient

1- Direct Apposition of Casts.

2-Interocclusal Records With Posterior Teeth Remaining.
3- Occlusal Relations Using Occlusion Rims on Record Bases .
4- Jaw Relation Records Made Entirely on Occlusion Rims.
5-Establishing Occlusion by the Recording of Occlusal Pathways.

1- Direct Apposition of Casts

If only few teeth are to be replaced, especially in class III removable partial dentures, hand articulation is sufficient to establish jaw relation.
Methods:
• Occlusal analysis and the correction of any existing occlusal disharmony (if present)should preceded the acceptance of such jaw relation record.
• Apposing casts may be occlude by hand.

• 3.The occluded casts should be held in apposition with rigid supports with sticky wax to the bases until they are securely mounted in the articulator.
• 4.Such a jaw relation record established between the remaining natural teeth.

2-Interocclusal Records With Posterior Teeth Remaining

Indication:
When sufficient natural teeth remain to support the removable partial denture but the relation of opposing natural teeth dose not permit the occluding of cast by hand.
Methods:
• The patient should be instructed for correct closure in the most posterior position(centric occlusion),so that the patient will not hesitated during recording of the relation.
• Uniformly softened wafer of base plate or set up wax is place between two arches and the patient is guided o close in centric relation.
• Wax is then removed and immediately rinsed thoroughly in room temperature water.
• The indentation of the occluded cusps aid us for correct occluding of the casts.

3- Occlusal Relations Using Occlusion Rims on Record Bases

Indications:

• When one or more distal extension areas are present.
• When a tooth supported edentulous space is large.
• When opposing teeth do not meet

Methods:

• Construction of record base (cold cure acrylic) with occlusion rims.

• Checked in patient mouth

• Recording the vertical dimension.
• Adjust the occlusion rim according to vertical dimension.

• Bite registration material

(ZOE paste, Wax, Compound, Silicone)

4- Jaw Relation Records Made Entirely on Occlusion Rims

Indication:
• When an opposing maxillary complete denture is to be made concurrently with a mandibular removable denture.
• Used in those rare situation in which the few remaining teeth do not occlude and will not influence eccentric jaw movements.
The steps of this method are the same as that of complete denture.

5-Establishing Occlusion by the Recording of Occlusal Pathways

This technique records all possible functional movements of the teeth opposing the edentulous span, and the artificial teeth are set accordingly so that they remain in harmony with their antagonist in all times. The pathways are generated by the patient on a wax occlusal rim.

Procedure

1. A hard wax occlusal rim attached to an acrylic resin record base is constructed on the metal framework slightly higher than the normal, approximately 0.5–0.75 mm. The buccolingual width of the rim should be more than that of the opposing tooth.

2. It is then inserted in the patient’s mouth and the patient is instructed to simulate chewing movements for a period of 20–30 min.Alternately, the patient is instructed to take the framework home and wear it continuously for 24 h except when eating and consuming hot or chilled drinks.
3. Whichever method is used, patient will invariably perform all possible jaw movements that will be recorded in the form of indentations and pathways on the wax rim.

4. The wax pattern thus obtained from the patient is then boxed and poured in dental stone. This provides a record of the opposing teeth with the functionally generated pathways.
5. The stone record with the opposing wax pathway on the framework is then mounted on an articulator(in correct vertical dimension) and the artificial teeth are set accordingly.

Articulation:

1. The casts with the jaw relation record is then mounted on an articulator.
2. The simplest articulator to accomplish the desired purpose is selected.
3. A simple hinge or nonadjustable articulator is sufficient for class III arches. For most of the other situations, a semi-adjustable instrument
is indicated.


Arrangement of artificial teeth and occlusion

Anterior teeth arrangement:
It is directly associated with aesthetics of the prosthesis and hence very important. Denture acrylic teeth are the most aesthetic tooth type, available in any shade, size or contour.
The selected teeth should be in harmony with the patient’s features and remaining natural teeth. The opposing and adjacent teeth are also considered.

Shade guide tooth is moistened and selection is made in natural light if possible. Shade should be taken quickly as first impression will be most accurate.
In cases of long standing edentulousness, there is diminished mesiodistal space for setting the teeth due to the mesial migration/tilting of the adjacent natural teeth. To overcome this problem, if narrower teeth are chosen it will produce an artificial appearance. Proximal contouring of the teeth to regain space should be considered during mouth preparation.

As an anterior denture tooth is positioned adjacent to a natural tooth, the proximal surface of the artificial tooth may be recontoured for better and close adaptation with the natural tooth.
The denture base flanges should be contoured and smoothened to give a natural pleasing appearance.

Posterior teeth arrangement

Mould selection
1. The tooth size or mould is dictated by the length of the edentulous span.
2. Posterior denture teeth are selected on the basis of measurement from the distal surface of the canine to the beginning of the upward incline of the ramus of mandible.

• The universal teeth setting principles should be applied to set these teeth if possible. Posterior teeth must not only fit into the available space, they should also be in harmonious occlusion with the opposing teeth.

As a general rule the classic pattern of intercuspation of maxillary and mandibular teeth

should be followed. However, these rules although
cannot be accurately followed because of the
presence of natural opposing teeth. To obtain a
good interocclusal anatomy, it may be necessary to set the teeth around 0.5–0.75 mm higher than the correct vertical dimension. The excessive vertical height can then be corrected by selective grinding to achieve a harmonious occlusion.


Positioning tooth adjacent to the clasp
Artificial tooth adjacent to the clasp has to be in harmony with the opposing teeth, the residual ridge and the clasp. The tooth should be first adjusted in proper occlusion with the opposing teeth and then adapted to the alveolar ridge. A small space, 2 mm should be left between the denture tooth and the adjacent abutment tooth. The minor connector supporting the clasp will occupy this space.

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