Fixed Prosthodontics – Pontic Design

 

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Pontic Fabrication

Pontics can be made with the metal-ceramic technique, which provides the best solution to the biologic, mechanical, and esthetic challenges encountered in pontic design. Their fabrication, however, differs slightly from the fabrication of individual crowns.

A well-designed metal-ceramic pontic provides easy plaque removal, strength, wear resistance, and esthetics.

 

Anatomic Contour Waxing

For strength and esthetics, an accurately controlled thickness of porcelain is needed in the finished restoration.

To ensure this, a wax pattern is made nearly to the final anatomic contour and then cut it back.

This also permits an assessment of connector design adequacy.

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Armamentarium

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  • Bunsen burner
  • Inlay wax
  • Sticky wax
  • Waxing instruments
  • Cotton cleaning cloth
  • Die-wax separating liquid
  • Zinc stearate or powdered wax
  • Double-ended brushes
  • Cotton balls
  • Fine-mesh nylon hose

 

Step-by-step Procedure

  1. Wax the internal, proximal, and axial surfaces of the retainers.
  2. Soften the inlay wax, mold it to the approximate desired pontic shape, and adapt it to the ridge.

(Prefabricated pontic shapes are also available as a starting point.)

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Prefabricated pontic shapes
  1. Lute the pontic to the retainers and, for additional stability, connect its cervical aspect directly to the master cast with sticky wax. Then wax the pontic to proper axial and occlusal (or incisal) contour.
  2. Complete the retainers and contour the proximal and tissue surfaces of the pontic for the desired tissue contact. The pontic is now ready for evaluation before cut-back.

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Evaluation
The form of the wax pattern is evaluated and any deficiencies are corrected.

Particular attention is given to the connectors, which should have the correct shape and size.

The connectors provide firm attachment for the pontic so it does not separate from the retainers during the subsequent cut-back procedure.

 

CUT-BACK PROCEDURE

  1. Use a sharp explorer to outline the area that will be veneered with porcelain. The porcelain-metal junction must be placed sufficiently lingual to ensure good esthetics.
  2. Complete the cut-back as far as access will allow with the units connected and on the mastercast.
  1. Section one wax connector with a thin ribbon saw (sewing thread is a suitable alternative) and remove the isolated retainer from the master cast.
  2. Refine the pontic cut-back where access is improved by removal of the first retainer.
  3. Reseat the first retainer, reattach it to the pontic, section the other connector, and repeat the process.
  4. Sprue the units and do any final reshaping as needed.
  5. Invest and cast

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The metal coping on the gingival aspect of the pontic follows the same contours that the porcelain will, rather than being just a straight bar of a metal between the retainer copings.
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Evaluation of the metal substructure

The porcelain must cover the labial surface, the incisal portion of the lingual surface, and the entire area adjacent to or contacting the ridge.

About 1 mm of porcelain thickness is needed on the gingival surface.

Porcelain tissue contact allows for better esthetics and removes the potentially rough porcelain –metal junction from contact with the tissue where it could cause irritation.

The tissue contact of the porcelain should be a modified ridge-lap.

There must be no saddle contact.

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Porcelain Application

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Apply a porcelain separating liquid to the stone ridge so that the additional gingival porcelain can be lifted directly from the cast.

Mark the desired tissue contact and contour the gingival surface to provide as convex a surface as possible.

The porcelain on the tissue surface of the pontic should be as smooth as possible. Pits and defects will make plaque control difficult and promote calculus formation.

The metal framework must be highly polished, with special care directed to the gingival embrasures (where access for plaque removal is more difficult).

 

Connector Design

The size, shape, and position of connectors all influence the success of the prosthesis.

Connectors must be sufficiently large to prevent distortion or fracture during function but not too large; otherwise, they will interfere with effective plaque control and contribute to periodontal breakdown over time.

Adequate access (i.e., embrasure space) must be available for oral hygiene aids cervical to the connector.

If a connector is too large inciso-cervically, hygiene is impeded, and over time periodontal failure will occur.

For ease of plaque control, the connectors should occupy the normal anatomic interproximal contact areas because encroaching on the buccal, gingival, or lingual embrasure restricts access.

In addition to being highly polished, the tissue surface of connectors is curved facio-lingually to facilitate cleansing. Mesio-distally, it is shaped to create a smooth transition from one FPD component to the next.

In a facio-lingual cross section, most connectors have a somewhat elliptical shape.

Do not close embrasure spaces. Tissue surface is Curved.

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However, to improve appearance without significantly affecting plaque control, anterior connectors are normally placed toward the lingual.

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Most recommend vertical height for the connectors is 3 to 4 mm.

 

Rigid Connectors

Rigid connectors must be shaped and incorporated into the wax pattern after the individual retainers and pontics have been completed to final contour.

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