Finishing of Cast Structures in Fixed Prostheses and their Adaptation in the Patient’s Mouth

I.Laboratory Procedures: The inner surface of the cast should be examined for nodules and bubbles. If present, nodules, roughness, and bumps should be removed with a tungsten bur. The cast is carefully placed on the die and then removed to inspect the die for any scratches and irregularities. Surfaces corresponding...
Man getting his teeth fixed at dental clinic
Finishing of Cast Structures in Fixed Prostheses and their Adaptation in the Patient’s Mouth
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I.Laboratory Procedures:

  • The inner surface of the cast should be examined for nodules and bubbles.
  • If present, nodules, roughness, and bumps should be removed with a tungsten bur.
  • The cast is carefully placed on the die and then removed to inspect the die for any scratches and irregularities.
  • Surfaces corresponding to these imperfections in the cast should be checked.
  • Areas with residual plaster or die spacer on the cast should be relieved with a tungsten bur.
  • Ideally, the cast should only contact the die at the restoration’s marginal areas.
  • There should be a thin gap across the entire inner surface of the cast for the cement to be used.
  • If enough space is not provided in the laboratory, a gap can be created using chemical or electrolytic roughening methods.
  • The sprue is cut from the casting at the closest point, and the roughness created is smoothed with coarse and then fine-grit rubber discs.
  • The restoration is fitted onto the working model. If necessary, fit is adjusted using coarse discs and stones.
  • On the articulator, eccentric and centric early contact points are identified using articulating paper and green stones, and adjustments are made using finishing burs and rubber discs.

Final polishing is done with polishing discs, and the inner surface of the restoration is sandblasted.

II. Clinical Procedures: The in-mouth evaluation of a restoration should be performed in the following order:

  1. Proximal contacts
  2. Restoration margins (marginal fit)
  3. Occlusion
  4. Contours
  5. Esthetics

Covers the detailed processes involved in finishing and fitting cast structures for fixed prostheses, both in the laboratory and clinically. These steps are crucial to ensure the best fit, function, and aesthetics of the prosthetic restoration.

Proximal Contacts:

The proximal contacts of a restoration should resemble natural teeth in terms of location, size, and tightness.

If proximal contacts are too tight, they can hinder proper seating of the restoration, causing discomfort and making it difficult for the patient to floss. Open proximal contacts can lead to food impaction and discomfort from damaging the gums.

Proximal contacts should be checked with dental floss. Tight contacts can be adjusted with discs, while open contacts may require addition of solder.

Marginal Fit:

  • When a crown is fully seated on a tooth, its edge fit should be checked.
  • The edges of the crown should not be too long, short, or open. If the gap is more than 50 µm (if a probe can enter between the restoration and tooth), it’s generally considered open.
  • If a probe can slide occlusally under the crown’s margin, the margin is too long.
  • If a probe held along the gingival margin encounters a significant bump when passing from crown to root surface, it indicates that the preparation is not fully covered, or the crown is not seated properly or is too short.
  • The crown margin should follow a smooth and straight line along the cervical line.
  • The casting must be evaluated for stability on the prepared tooth. If it rotates or moves under force, any nodules causing the issue must be corrected, or the casting should be redone if it’s distorted.
  • Materials to detect internal gaps: diluted lipstick in chloroform, thinned typewriter correction fluid, dry indicator spray, marking wax, impression-type materials (Fit-Checker).

Contact areas should be relieved with a carbide bur. All marking materials should be removed with chloroform and by sandblasting before cementation to not reduce retention.

Occlusal Adjustment:

  • Static and dynamic criteria should be considered in occlusal relationships. Attention should be paid to the positions of the teeth and the integrity of closure and contact.
  • For occlusal adjustment, the use of two-color articulating paper is recommended for different movements. One color is used to identify centric contacts, while the other facilitates the identification of lateral and protrusive movements. Excessive contacts should be removed with an abrasive stone.
  • Care should be taken not to raise the occlusion excessively. For control, a narrow plastic gelatin strip can be placed on the restoration, asking the patient to bite. The gelatin should show similar resistance when pulled laterally, as with adjacent teeth.

If the restoration is lowered in occlusion, it may need to be added to or replaced.

Contours:

  • Improper contours can damage gum health and deviate from a natural appearance. Over-contoured areas will increase plaque accumulation. Concavities given in furcation areas should also be designed for easy access by a toothbrush.

Aesthetics:

  • The restoration should be observed from a conversational distance, checking its relationship with the patient’s other teeth, and the patient should be asked for their opinion.

Covers the essential aspects of finishing and adapting cast structures in fixed prostheses, including checking proximal contacts, marginal fit, occlusal adjustment, contours, and aesthetics. These steps are crucial for the successful integration of the prosthetic work into the patient’s oral environment.

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