CDC Prosthetics Design & Fabrication 3 — Questions and Answers
Question 1: Which type of pontic design provides the BEST esthetics for anterior fixed partial dentures while still allowing adequate cleaning?
- Sanitary (hygienic) pontic
- Conical pontic
- Ovate pontic (Correct answer)
- Ridge lap pontic
Correct answer: Ovate pontic
The ovate pontic fits into a prepared tissue depression, creating natural-looking emergence and allowing cleaning with floss.
Question 2: Internal porosity in a cast metal framework is MOST commonly caused by:
- Using too much flux during casting
- Shrinkage porosity from rapid metal solidification without sufficient reservoir (Correct answer)
- Inadequate surface finishing
- Over-investing the wax pattern
Correct answer: Shrinkage porosity from rapid metal solidification without sufficient reservoir
Shrinkage porosity occurs when the metal solidifies too quickly without an adequate sprue/reservoir to feed molten metal into the shrinking casting.
Question 3: A ceramist is layering feldspathic porcelain onto a lithium disilicate coping. Which step is critical before applying body porcelain?
- Applying opaque porcelain to block the glass-ceramic color
- Sandblasting, cleaning, and applying appropriate ceramic adhesion liner per manufacturer instructions (Correct answer)
- Glazing the coping surface prior to layering
- Acid-etching the internal surface of the coping
Correct answer: Sandblasting, cleaning, and applying appropriate ceramic adhesion liner per manufacturer instructions
Lithium disilicate copings require surface preparation and often a liner/wash firing to promote porcelain adhesion and achieve desired final shade.
Question 4: When evaluating occlusal contacts on a finished prosthesis, a 'shimstock' (8 µm foil) is used to:
- Measure the vertical dimension of occlusion
- Detect the presence and holding force of occlusal contacts (Correct answer)
- Record centric relation
- Trim ceramic margins
Correct answer: Detect the presence and holding force of occlusal contacts
Shimstock held between opposing teeth and tugged indicates whether a contact is present and whether it is light or heavy based on resistance to removal.
Question 5: The dental term 'emergence profile' in prosthetic design refers to:
- The angle of the preparation taper
- The contour of a restoration from the gingival sulcus to the height of contour (Correct answer)
- The occlusal cusp anatomy of a crown
- The cross-sectional shape of the connector
Correct answer: The contour of a restoration from the gingival sulcus to the height of contour
Emergence profile describes the three-dimensional contour of a restoration as it exits the gingival sulcus, influencing tissue health and esthetics.
Question 6: Which alloy classification is MOST appropriate for use with PFM restorations due to its high fusion temperature and biocompatibility?
- Type III gold alloy
- Base metal alloy (nickel-chromium or cobalt-chromium) (Correct answer)
- Amalgam alloy
- Type II gold alloy
Correct answer: Base metal alloy (nickel-chromium or cobalt-chromium)
Base metal alloys (Ni-Cr or Co-Cr) have high melting ranges compatible with PFM porcelain firing temperatures and provide adequate stiffness for thin metal copings.
Question 7: A laboratory remount procedure after glazing a full-arch ceramic restoration is performed primarily to:
- Verify shade accuracy under different lighting
- Refine and equilibrate occlusal contacts that may have shifted after ceramic firing (Correct answer)
- Check internal fit using pressure-indicator paste
- Polish the tissue surface of the prosthesis
Correct answer: Refine and equilibrate occlusal contacts that may have shifted after ceramic firing
Firing cycles can cause minor ceramic deformation, so a laboratory remount allows the ceramist to verify and adjust occlusion on the articulator before delivery.
CDC Prosthetics Design & Fabrication 3
Which type of pontic design provides the BEST esthetics for anterior fixed partial dentures while still allowing adequate cleaning?