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...
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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