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CDT Exam Part 2 Questions & Answers 2024/2025
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CDT Exam Part 2 Questions & Answers 2024/2025 If the metal's surface is sharp or uneven, - ANSWERStensile stresses are created in the porcelain as it cools and may cause the veneer to fail Opaque firing cycle - ANSWERS-Using a #6 sable brush, slightly moisten the casting with fluid and appl...

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  • August 3, 2024
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  • 2024/2025
  • Exam (elaborations)
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CDT Exam Part 2 Questions & Answers
2024/2025

If the metal's surface is sharp or uneven, - ANSWERStensile stresses are created in the porcelain as it
cools and may cause the veneer to fail



Opaque firing cycle - ANSWERS-Using a #6 sable brush, slightly moisten the casting with fluid and apply
opaque, condense

-Fire the casting 600 to 960C and 32C per minute in a vacuum



Removing contamination from a metal die - ANSWERSIf a high-gold content alloy framework has been
finished on a metal die (copper, silver, or amalgam), boil it in nitric acid for 1 minute and then pickle it in
hydrochloric acid



Pretreatment of the metal surface before porcelain application - ANSWERS-Treatment varies with the
base-metal elements, such as tin, indium, and iron, to precipitate on the surface and produce an oxide
film.

-Alloys that contain greater amounts of base-metal elements (notably nonprecious alloys) produce
thicker oxide layers

-in contrast, high-gold content alloys with far lesser amounts of base elements produce fewer surface
oxides

-for this reason bond strength varies greatly depending on the types of alloy and surface pretreatments



Order of procedures for pretreating metal surface/Oxidizing - ANSWERS1. Surface grinding

2. Ultrasonic cleaning with distilled water or steam cleaning

3. heating under vacuum and 1040*C for 2 minutes

*4. Deoxidizing with acids or air abrading with aluminum oxide

*5. Heating at atmospheric pressure at 1040*C for 2 minutes (4 & 5 are only done on nonprecious alloys
that produce an excessive amount of oxides, never do this to high-gold content alloys)

, Surface grinding (pretreating metal) - ANSWERS-normally considered to be the last step of metal
finishing, surface grinding is done to remove defects and make final adjustments

-increases the mechanical bond between the porcelain and metal

-best accomplished by using a carbide bur and grinding in only one direction

-*if you leave the surface rough, it can create stresses within the porcelain veneer

-**From this point on, handle the castings with forceps to prevent contaminating the porcelain-bearing
surfaces with oil and dirt from your fingers



Ultrasonic Cleaning (pretreating metal) - ANSWERS-the purpose is to clean the metal of any abrasive
particles, dirt, and oils that may have attached to the surface during the grinding process

-if oily residue remains on the ground surface, it will bake on the metal surface as a contaminant

-steam cleaning is also effective



Heating Under Vacuum (pretreating metal)/ Oxidizing - ANSWERS-the term "oxidation" describes the
heating process used to produce a controlled oxide layer on the metal's surface and to dispel gases
absorbed by the metal during casting

-if the gasses aren't released before the porcelain is applied, they could cause the opaque to bubble at
the interface between metal and porcelain

-they will migrate to the top and become visible

-the resultant holes can be repaired; but each time the porcelain is fired under vacuum, the risk of
escaping gas increases

-heating the framework under vacuum to 1040*C for 2 minutes will drastically decrease bubbling



Deoxidizing (pretreating metal) - ANSWERS-some metal-ceramic alloys produce excess amount of oxides
that decrease bond strength and darken the metal surface

-air abrading the metal surface will deoxidize the castings and, to some extent, expose "fresh" metal for
re-oxidation

-*** DO NOT deoxidize the castings made from high-gold content alloys. These alloys produce fewer
surface oxides and deoxidation could strip the metal surface of its base-metal atoms



On average, the volume shrinkage of porcelains is between ____ and ___ %

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