Quiz 5 Flashcards
Why is the cavity preparation slightly overfilled during the placement and condensation of amalgam?
Allows enough material to carve to contours and remove excess mercury that has been forced to the surface during the condensation process.
If excess mercury is left, the physical properties will be poorer.
Why is tin added to solders used in dentistry?
Lower the melting point.
Tin is often added to the solder to lower the melting range and improve the flow of the molten metal.
Why is flux used when gold castings are soldered?
Remove surface oxides so that the solder will flow freely.
Flux is used to remove surface oxides so that the solder will flow freely and wet the alloy surfaces as it melts.
Creep is a phenomenon associated with which phase seen with low-copper amalgam alloys?
Gamma-2 phase.
Creep refers to the gradual change in shape of the restoration from compression by the opposing dentition during chewing.
What is true of the preparation of the metal substructure for porcelain-bonded-to-metal crowns?
These crowns require greater reduction of the tooth than all-metal crowns.
The metal substructure must be at least 0.3 mm thick to prevent distortion at high temperatures.
What is the correct order for application of the porcelain layers during the creation of a porcelain-bonded-to-metal crown?
2, 3, 1.
The correct order is opaque porcelain, body porcelain, and then incisal porcelain.
Why would zinc be added to a base-metal mixture?
Reduces oxidation.
Zinc is added to reduce oxidation when the alloy is cast.
Which metal is used to control the rate of set of the amalgam?
Tin.
Tin is used to control the rate of set of the amalgam.
How is the arch wire held to the orthodontic bracket?
Ligature wire or elastics.
The arch wire is secured by ligature wire or elastics.
Modern dental amalgams are considered to be high in what content compared with their predecessors?
Copper content.
Modern dental amalgams contain 13% to 30% copper compared to 2% to 4% in predecessors.
What is true concerning nickel allergy?
Some responses to nickel cause a skin reaction rather than a response in the mouth.
The overall rate of allergy to nickel for the general population is about 9% to 12%.
What is true concerning endodontic posts?
Parallel posts have been shown to transmit less stress to the root than tapered posts.
The purpose of a post is to retain the core buildup over which the final restoration is placed.
Which of the following would not be hygienic when amalgam material is used?
The floor is carpeted.
Carpets tend to trap amalgam particles and mercury droplets.
Why is flux used with solder?
Remove oxidation.
The flux removes surface oxides so that the solder will flow freely.
What is true of high-copper amalgams in contrast to low-copper amalgams?
High-copper amalgams are more durable than low-copper amalgams.
High-copper alloys have less deterioration at the margins and greater strength.
What is true concerning mercury safety procedures in the dental office?
Studies have shown mercury levels in most dental offices to be far below OSHA’s recommended minimum.
The elemental mercury used in amalgam is less toxic than organic mercury.
After the substructure for a porcelain-bonded-to-metal crown is cast in metal, why is it heated at high temperature?
Form oxides on the surface of the metal.
This process is called degassing.
During conventional root canal therapy, what seals the root canal space?
Gutta percha.
Gutta percha is used to prevent bacteria from growing in the space.
What may happen if a newly placed amalgam contracts excessively?
It will open gaps at the margins, contribute to leakage of fluids and bacteria, and cause sensitivity.
Excessive contraction can lead to various complications.
Spherical alloys require what amount of mercury to wet the particles?
Less mercury and generally set more quickly than lathe-cut particles.
Spherical alloys set more quickly than lathe-cut particles.
