Question 1

For what reason have insurance carriers seen a reduction in the use of dental amalgam for posterior restorations by approximately 45% in the past 20 years?

Accepted Answer

Insurance carriers have seen a reduction in the use of dental amalgam for posterior restorations by approximately 45% in the past 20 years,probably because concerns by patients about its safety and its lack of esthetics have prompted many patients to request tooth-colored materials.Still,no other direct restorative material has the durability,ease of handling,and good physical characteristics of amalgam.Its wear resistance and compressive strength are superior to composite resin and glass ionomer cement.A study conducted by the National Institutes of Health (NIH)in 1991-1993 concluded that amalgam is safe for human use.

Question 2

High-copper amalgams do not have a _____ phase and are superior in their clinical performance to low-copper amalgams.

Accepted Answer

High-copper amalgams do not have a gamma-2 phase and are superior in their clinical performance to low-copper amalgams.The gamma phase is the silver alloy phase;it is the strongest phase and has the least corrosion.The gamma-1 phase consists of mercury reacting with the silver.It is strong and corrosion resistant,although not as resistant as the gamma phase.The gamma-2 phase consists of the reaction of mercury with tin.Gamma-2 is weak and corrodes readily.

Question 3

Modern dental amalgams are considered to be high in _____ content compared with their predecessors.

Accepted Answer

Modern dental amalgams are considered to be high in copper content (13% to 30%)compared with their predecessors,which had 2% to 4% copper by weight.They generally contain 40% to 70% silver and 12% to 30% tin.They are mixed with mercury 43% to 50% by weight.

Question 4

Which of the following is true concerning mercury safety procedures in the dental office?

Accepted Answer

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.Although dental offices do not contribute as much mercury to the environment as large companies,their contribution is not insignificant.A "mercury-free" amalgam was developed that had an appearance and handling characteristics similar to amalgam.It used gallium as a substitute for mercury.These products are still used in some countries but not in the United States.

Question 5

Why is the cavity preparation slightly overfilled during the placement and condensation of amalgam?

Accepted Answer

The cavity preparation is slightly overfilled during the placement and condensation of amalgam to allow 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.

Question 6

Spherical alloys require _____ mercury to wet the particles and generally set _____ than lathe-cut particles.

Accepted Answer

Spherical alloys require less mercury to wet the particles and generally set more quickly than lathe-cut particles.

Question 7

It takes up to _____ for most amalgams to gain their maximum strength.

Accepted Answer

It takes up to 24 hours for most amalgams to gain their maximum strength.Many of the high-copper spherical amalgams gain approximately 50% of their compressive strength in the first hour.Once fully set,they are hard,strong,durable restorations.

Question 8

Patients should be advised to avoid chewing on a newly placed amalgam for at least:

Accepted Answer

Patients should be advised to avoid chewing on a newly placed amalgam for at least 8 hours.Most amalgams will gain about 80% of their strength by then.

Question 9

Polishing of amalgam restorations should be:

Accepted Answer

Polishing of amalgam restorations should be wet with a light touch.This will avoid generating heat that can bring mercury to the surface and potentially irritate the pulp.Typically,polishing agents such as Silux or a slurry mix of fine pumice or abrasive-impregnated rubber polishers are used.Care should be taken not to generate heat.Do not polish dry.

Question 10

In the low-copper amalgams,zinc was responsible for the gradual _____ of the amalgam over time if moisture contamination was present during placement.

Accepted Answer

In the low-copper amalgams,zinc was responsible for the gradual expansion of the amalgam over time if moisture contamination was present during placement.Contact of the moisture with zinc caused the formation of hydrogen gas within the amalgam,which caused it to expand.Delayed expansion could cause the restoration to expand beyond the cavity walls and could cause cracking in the adjacent enamel.

Question 11

What mechanical device mixes the dental amalgam alloy and mercury?

Accepted Answer

The dental amalgam alloy and mercury are mixed together in a mechanical device called a triturator.The triturator has settings that allow adjustment in the speed and time of the mixing process.The manufacturer's recommendations should be followed for the selected material.

Question 12

Which of the following statements is true of high-copper amalgams in contrast to low-copper amalgams?

Accepted Answer

High-copper amalgams are more durable than low-copper amalgams.The higher copper content of newer alloys eliminates the formation of the gamma-2 reaction product that caused weakening of the amalgam.High-copper alloys have virtually replaced low-copper alloys because high-copper amalgams have less deterioration at the margins,less corrosion,and greater strength.

Question 13

Which of the following is true of tarnish?

Accepted Answer

Tarnish results from contact with oxygen,chlorides,and sulfides in the mouth.It causes a dark,dull appearance,but it is not very destructive to the amalgam.The rougher the surface,the more it tends to tarnish.Polishing of the restoration can reduce the tarnish.

Question 14

Which of the following statements is true regarding the strength of dental amalgam?

Accepted Answer

Amalgams are relatively weak in tension and shear and therefore require adequate bulk to resist breaking.Amalgams are stronger in compression than composites or glass ionomers.Some high-copper amalgams gain approximately 80% of their strength in the first 8 hours.Low- and high-copper amalgams are comparable in compressive strength once they have completely set at about 24 hours.

Question 15

Which of the following may happen if a newly placed amalgam contracts excessively?

Accepted Answer

If it contracts excessively,it will open gaps at the margins,contribute to leakage of fluids and bacteria,and cause sensitivity.If it expands excessively,it can put pressure on the cusps and cause pain with biting pressure,or it may result in fracture of the cusps.Ideally,the dimensions of a newly placed amalgam should not change.Some expansion and contraction occur during the setting reaction of the amalgam.It is the net effect of these two processes that is important.

Question 16

Undertriturated amalgam alloy has a _____ appearance and sets too _____,resulting in a weaker restoration.

Accepted Answer

Undertriturated amalgam alloy has a dry,crumbly appearance and sets too quickly,resulting in a weaker restoration.This occurs because the components have not completely mixed,leaving a higher level of unreacted mercury and alloy particles.Overtriturated alloy is too wet.It also results in an amalgam that sets too quickly because of the heat produced by the prolonged mixing.It results in a weaker restoration that will corrode more readily because it forms too many reaction products.

Question 17

Creep is a phenomenon associated with the gamma-_____ phase seen with _____-copper amalgam alloys.

Accepted Answer

Creep is a phenomenon associated with the gamma-2 phase seen with low-copper amalgam alloys.It refers to the gradual change in shape of the restoration from compression by the opposing dentition during chewing or by pressure from adjacent teeth.High-copper alloys exhibit far less creep and have superior marginal integrity.

Question 18

When spherical high-copper dental amalgam alloys are contrasted with admixed dental amalgam alloys,the spherical alloy:

Accepted Answer

When spherical high-copper dental amalgam alloys are contrasted with admixed dental amalgam alloys,the spherical alloy has very little resistance to condensation into the cavity preparation and feels soft compared with an admixed amalgam.The spherical alloy needs approximately 10% less mercury than the admixed alloy for the amalgamation process.Spherical alloys do not displace a matrix band and keep it in contact with the adjacent tooth in class II preparations as well as admixed amalgams do.Spherical amalgams have higher 1-hour and 24-hour compressive strengths than admixed amalgams do.

Question 19

Which of the following metals is used to control the rate of set of the amalgam?

Accepted Answer

Tin is used to control the rate of set of the amalgam.Both silver and tin dissolve into the liquid mercury until the solution becomes saturated with them;they also absorb mercury.Newly formed particles begin to precipitate out of the mercury until no more mercury is left to react.

Question 20

When the silver-based alloy used to create dental amalgam is mixed with _____,the reaction that occurs is called amalgamation.

Accepted Answer

When the silver-based alloy used to create dental amalgam is mixed with mercury,the reaction that occurs is called amalgamation.The material that is produced is called dental amalgam.

Quiz 10: Dental Amalgam