The question pertains to the correct procedure for finishing and polishing ceramic restorations in prosthodontics. To arrive at the correct answer, let's consider the sequence and importance of each step in the ceramic restoration process:
- **Contouring and Finishing:** During this phase, the ceramic restoration is shaped and smoothed to achieve the desired anatomical form. Contouring helps in replicating the natural shape while finishing ensures smooth surfaces suitable for polishing.
- **Polishing:** This step involves the use of finer abrasives to enhance the surface smoothness and give it a shine. Proper polishing is essential as it reduces surface roughness and minimizes plaque accumulation.
- **Glazing:** Applying glaze or natural glaze is done as the final step. It provides a glassy finish that protects the ceramic and matches the natural shine of teeth. It also helps in sealing the pores of the ceramic, which improves aesthetics and reduces plaque buildup.
Based on this procedure, we can conclude:
- Apply overglaze or natural glaze before contouring and finishing is incorrect because glazing is intended as a final step, not at the beginning of the process.
- Apply overglaze or natural glaze before contouring, finishing and polishing is incorrect for the same reason: glazing occurs after these preparatory steps.
- Apply overglaze or natural glaze after contouring, finishing and polishing is correct. This is because glazing is intended to be a final seal that enhances sheen and aesthetics once the restoration is fully contoured and polished.
- Apply overglaze on natural glaze after contouring is not entirely correct because it suggests a sequence where glazing occurs before finishing and polishing, which is not the standard practice.
Therefore, the correct answer is: Apply overglaze or natural glaze after contouring, finishing and polishing.