Question 1

During conventional root canal therapy,the root canal space is sealed with _____ so that bacteria cannot grow in the space.

Accepted Answer

During conventional root canal therapy,the root canal space is sealed with gutta percha so that bacteria cannot grow in the space.Conventional root canal therapy generally entails making an access preparation through the crown of the tooth to the pulp chamber,removing the diseased pulpal tissue from within the root canal with a series of fine files,and sealing with gutta percha.

Question 2

Which of the following is the most esthetic margin for a ceramic-metal crown?

Accepted Answer

The porcelain facial margin is the most esthetic margin.This is achieved by not extending the metal substructure all the way to the margin and leaving room to place porcelain to complete the margin.The metal at the margin of a disappearing metal margin crown has been ground to a thin knife-edge where it extends to the edge of the preparation margin.The all-metal margin is used only when it is not in an esthetic zone.

Question 3

Which of the following is true concerning grain formation in dental casting alloys?

Accepted Answer

Iridium or ruthenium is added to gold-base alloys to keep the crystals from growing too large.Small crystals produce more desirable properties in the metal alloy than large crystals do.Reheating gold-based alloys (called annealing)can improve some of the properties.However,with base-metal alloys,reheating will degrade the physical properties.

Question 4

Dental wrought wire is primarily used for what purpose?

Accepted Answer

Dental wrought wire is used primarily for clasps for removable prosthetic appliances.It can be a base metal such as stainless steel or a high-noble alloy composed of platinum-gold-palladium (called PGP wire).Additional examples of wrought wire used in dentistry include arch wires and ligature wires used in orthodontics and arch bars and ligature wires used in oral surgery for stabilization of a jaw fracture.

Question 5

Why are silver-based solders used primarily in dentistry?

Accepted Answer

Silver-based solders are used primarily in dentistry to solder fixed-space maintainer components and to solder wire components to removable orthodontic appliances.Gold-based solders are used to join together units of a bridge,add contacts,close holes ground into the occlusal surface by adjusting the bite,or correct small marginal deficiencies on onlays and crowns when they are found to be deficient at the try-in appointment.Stainless steel alloys are used to create wires,brackets,and bands used in orthodontics,as well as fixed-space maintainers and stainless steel crowns used in pediatric dentistry.

Question 6

Which of the following statements is true of noble dental casting alloys?

Accepted Answer

Noble dental casting alloys do not require any gold but must contain at least 25% noble metals by weight.High-noble alloys must contain at least 60% by weight of noble alloys,of which gold must account for at least 40% by weight.Base-metal alloys do not require gold and require less than 25% by weight of noble metals.

Question 7

Which of the following is a noble metal used for dental casting alloys?

Accepted Answer

Platinum,palladium,and gold are noble metals used for dental casting alloys.The primary base metals used in casting alloys are copper,nickel,silver,zinc,tin,and titanium.Copper and silver are often added to gold alloys to increase their hardness.Zinc is added to reduce oxidation when the alloy is cast.Because of their low cost,base metals have also been called nonprecious metals.Although they are not considered to be as good as the noble metals,the base metals are essential for many applications in dentistry.

Question 8

Which of the following metals is added to both gold and silver solders to lower the melting range?

Accepted Answer

Tin is added to both gold and silver solders to lower the melting range.Gold solders generally contain gold,silver,and copper,with small portions of tin and zinc.Silver solders contain varying amounts of silver,copper,and zinc and small amounts of tin.

Question 9

How is the arch wire held to the orthodontic bracket?

Accepted Answer

The arch wire is held to the orthodontic bracket by ligature wire or elastics.The edgewise bracket is the most common type and has a horizontal slot between four wings.The slot is where the arch wire is placed,and the wings are used to hold the elastics or ligature wire that secures the arch wire.

Question 10

Which description is correct regarding palladium?

Accepted Answer

Palladium increases the hardness of the alloy.It is widely used because it has good corrosion resistance and is less expensive than gold.Platinum and palladium are noble metals that are sometimes referred to as precious metals because of their high monetary value.Although silver is considered to be a precious metal,it is not considered noble because of its corrosion in the oral cavity.

Question 11

Which of the following is true concerning the use of endodontic files and reamers in dentistry?

Accepted Answer

Nickel-titanium files are far more flexible than stainless steel files.Stainless steel files become stiffer as the diameter of the file increases.Reamers are similar to files except that they have fewer twists in the metal and cut faster.Rotary instruments are usually composed of nickel and titanium alloys.

Question 12

Which of the following is true concerning endodontic posts?

Accepted Answer

Parallel posts have been shown to transmit less stress to the root than tapered posts.It once was believed that posts reinforced endodontically treated teeth against fracture;however,it is now clear that the purpose of a post is to retain the core buildup over which the final restoration is placed.Some patients may confuse the post with an implant and need to be educated as to the differences.Cast posts generally are made with the core already attached.Preformed posts generally do not have a core attached by the manufacturer,so one must be added.

Question 13

The metals in porcelain bonding alloys are selected and blended so that they have which of the following properties?

Accepted Answer

With metals in porcelain bonding alloys,small amounts of metals such as indium,iron,tin,or gallium are added to form oxides on the metal surface to which porcelain will bond.They have the ability to withstand the high temperatures at which porcelain is fired without distorting or melting.They have a lower thermal expansion than gold alloys used for all-metal crowns.Titanium and titanium alloys have such high melting temperatures and difficulty in handling that they have limited use for ceramic-metal crowns.

Question 14

After the substructure for a porcelain-bonded-to-metal crown is cast in metal,why is it heated at high temperature?

Accepted Answer

After the substructure for a porcelain-bonded-to-metal crown is cast in metal,it is heated at high temperature to form oxides on the surface of the metal.This process is called degassing,although oxidizing would be a more accurate term.

Question 15

Which of the following represents the correct order for application of the porcelain layers during the creation of a porcelain-bonded-to-metal crown?
1)Incisal porcelain
2)Opaque porcelain
3)Body porcelain

Accepted Answer

The correct order is opaque porcelain,which is the first layer of porcelain applied to the metal,and then body and incisal porcelains,which are built up or stacked to simulate dentin and enamel colors and translucency.After final contouring of the crown,another firing while maintaining the temperature at the fusing temperature for a while will produce a surface glaze.

Question 16

Why is flux used when gold castings are soldered?

Accepted Answer

Flux is used when gold castings are soldered,to remove surface oxides so that the solder will flow freely and wet the alloy surfaces as it melts.The alloys are heated with a torch until they turn red.The solder is added and heated until it melts and flows over the exposed surfaces of the bridge units.

Question 17

Which of the following is true concerning nickel allergy?

Accepted Answer

Some responses to nickel cause a skin reaction rather than a response in the mouth,even though the oral cavity is the source of the nickel.Women have a higher rate of allergy to nickel than do men,by a ratio of 10 to 1.The overall rate of allergy to nickel for the general population is about 9% to 12%.The allergic response is sometimes seen around the free gingival tissues,especially at the margins of base-metal crowns.It is less common with removable partial dentures because the metal often is not in direct contact with the tissues and they are not worn constantly,as are fixed partial dentures or single crowns.

Question 18

The higher the fineness number of a gold solder,the _____ the gold content and the _____ the melting point of the solder.

Accepted Answer

The higher the fineness number of a gold solder,the higher the gold content and the lower the melting point of the solder.Gold solders with different melting ranges (690° C to 870° C)are available,depending on their composition,to accommodate the melting ranges of the gold alloys to which they will be soldered.

Question 19

Which of the following base metals has the highest incidence of allergic response?

Accepted Answer

Nickel has the highest incidence of allergic response.The allergic response is sometimes seen around the free gingival tissues,especially at the margins of base-metal crowns.It is less common for removable partial dentures because the metal often is not in direct contact with the tissues,and they are not worn constantly as with fixed partial dentures or single crowns.Some responses to nickel cause a skin reaction rather than a response in the mouth,even though the oral cavity is the source of the nickel.

Question 20

Which of the following is true of the preparation of the metal substructure for porcelain-bonded-to-metal crowns?

Accepted Answer

To make room for the metal substructure and porcelain,these crowns require greater reduction of the tooth than all-metal crowns.Porcelain-bonded-to-metal crowns have a metal substructure that is covered with layers of porcelain.The metal substructure must be at least 0.3 mm thick to prevent distortion at high temperatures and to be convex in shape with no sharp angles.

Quiz 11: Casting Metals, solders, and Wrought Metal Alloys