What is the most widely used material in restorative and corrective dentistry?
metal
an alloy of mercury
amalgam
What 5 metals make up the amalgam alloy in dentistry?
mercury
silver
copper
tin
zinc
true or false. silver is susceptible to corrosion
true
why is copper added to amalgam?
to minimize corrosion (eliminate gamma-2 phase)
Why was less microleakage and marginal recurrent decay seen in old amalgam alloys?
due to higher levels of corrosion - the biproducts of it block dentinal tubules
What are 3 desireable features of amalgam?
durable
similar compressive strength to enamel
relatively inexpensive
What are 6 undesireable features of amalgam?
unattractive
high thermal conductivity
dimensionally unstable (creep)
delayed expansion if contaminated with saliva
requires tooth support
fracturable by excessive occlusion
true or false. When polishing amalgam, you should move from coarse to fine agents. What are 3 agents that can be used?
true
bur
pumice
tin oxide
_______ amalgam is to remove surface tarnish, stains, flash, and roughness
polishing
How does polishing reduce the rate of corrosion?
causes less surface area for it to happen
what is the final polish of amalgam in the mouth?
tin oxide
What are 2 ways to avoid amalgam overhangs?
use properly placed band and wedge
detect overhangs with explorer
How much has the use of dental amalgams reduced in the last 15 years?
by 40%
What are 2 main disadvantages of using dental amalgams?
lack of aesthetics
pts fear of mercury being unsafe
true or false. testing shows that amalgam is safe
true
Amalgam composition contains what 4 main metals?
silver
copper
tin
mercury
The addition of mercury to dental amalgams causes a reaction called what?
amalgamation
What percent of MODERN AMALGAM is made up of copper?
10-30%
What is the purpose of HIGH COPPER (modern amalgams)?
increase longetivity
50% strength in one hour
sets completely in 24 hrs
In what type of amalgam does expansion occur if moisture contamination occurs during placement?
low copper amalgam
In spherical alloy amalgams, _______ mercury is required, and sets ______ than lathe-cut
less
faster
Mercury makes up what percent of amalgam (BY WEIGHT)?
43-50%
What metam material in amalgam inhibits corrosion by reducing oxidation of other metals?
zinc (0.01%-2%)
In ____-_____ amalgams, _______ was responsible for gradual expansion of the amalgam over time (delayed expansion) when moisture contamination was present during placement
low-copper
zinc
What type of reaction is the setting transformation of amalgam?
CHEMICAL reaction of powder alloy mixed with liquid mercury
How long does it take for most amalgams to completely set?
24 hours
What are the 3 different phases of the chemical reactions of amalgam?
gamma phase
gamma-1 phase
gamma-2 phase
Which phase of the chemical setting reaction of amalgam is the silver alloy phase, strongest phase, and has the least corrosion?
gamma phase
which phase of the chemical setting reaction of amalgam is when mercury reacts with silver, it is strong, and corrosion resistant?
gamma-1 phase
Which phase of the chemical setting reaction of amalgam is when mercury racts with tin, it is the weakest phase, and corrodes easily?
gamma-2 phase
What metal is used to control the rate of set of amalgam?
TIN
which type of amalgams have NO gamma-2 phase? And why does this happen?
high-copper amalgams
the copper reacts with the tin so tin is not availabled for mercury to react with it
Oxidation on amalgam surface and slightly below; from contact with OXYGEN, CHLORIDES and SULFIDES in the mouth
tarnish
What type of oxidation of amalgams is not very destructive, rougher the surface the more of it occurs, palladium is added to reduce it, and polishing reduces it?
tarnish
true or false. higher copper amalgams tarnigh less
true
chemical reaction between amalgam and substances in saliva or food resulting in oxidation of amalgam; can occur from two dissimilar metals in electrolyte solution (including saliva)
corrosion of amalgam
What is the electric current generated when two dissimilar metals in electrolyte solution (saliva) come in contact called? What process causes this event?
galvanism
one metal oxidizes
________ is responisble for the corrosion of amalgam
oxidation
What are 3 interactions within amalgam between different metals?
weakens amalgam
stains tooth structure (corrons enters dentinal tubules and stains dentin)
marginal deterioration
What type of amalgam alloy makes up most amalgams now?
high-copper
What are 4 main benefits of high-copper alloys?
ELIMINATES gamma-2 reaction that weakens the alloy
MORE durable
LESS deterioration of margins (better marginal integrity)
LESS corrosion
What are 3 main affects of amalgam corrosion?
weakens over time
stains surrounding tooth
breaks down at margin
gradual change in shape from compression of opposing dentition from chewing (opposing teeth) or pressure (adjacent teeth)
CREEP of amalgam
true or false. Creep of amalgam is occureing less now that most amalgams are high-copper
true
Creep is a phenomenon associated with ______ phase in ___-_______ amalgam alloys
gamma-2
low-copper
true or false. All amalgams expand and contract on setting
true
Which type of dimensional change of amalgam will put pressure on cusps causing biting pain/cusp fracture?
EXPANDS too much
Which dimensional change of amalgam will result in open gaps which=marginal leakage and hypersensitivity?
CONTRACTS too much
Amalgam restorations are ________ in compression than compsite or glass ionomer.
STRONGER
Amalgam restorations are ______ in tension and shear pressure
WEAK
What is needed for amalgam restorations to resist breaking from tension and shear pressures?
bulk
higher copper amalgams have high ___________ compressive strength; and sets in less than _______ hrs (which is late compressibe strength)
EARLY
24 hours
Which type of high-copper alloy establishes contact easily, uses more mercury (50% by weight), and has a longer working time?
admix (both spherical and lathe-cut)
Which type of high-copper alloy uses less condensation pressure-little resistance, uses both vertical and lateral condensation, must use heavier wedging to get contact, has high early compressive strength (1 and 24 hours), uses 10% less mercury, and has a faster set?
spherical
How will the alloy appear if it has been properly triturated?
satin appearance
How will the alloy appear if it has been UNDER triturated?
dry, crumbly, and sets too quick which=a weak filling
How will the alloy appear if it has been OVER triturated?
too wet, sets too quickly also which=a weak filling
Why must you use larger condensers for the condensation of high copper alloys?
What is a good analagy to remember this concept?
it has less resistance to condensation pressure
"high-heel" shoe - more pressure per square inch on smaller condensers
What is the purpose of oerfilling the cavity preparation?
to have enough to carve the tooth contours
It is important to remove excess mercury from condensation, what results if it is not removed?
physical properties are poorer
Carving amalgams after the set starts will do what?
damage the margins
How long should the pt wait before eating on amalgam restorations? Why
8 hours
the restoration will be at 80% strength at that point
Which type of alloys are shiny, so no polish is needed?
modern, high-copper alloys
When is it appropriate to polish amalgam restorations?
no earlier than 24 HOURS after placement; once the crystallization of amalgam is complete
Polishing is done with ______ as a coolant, and a _______ touch
water
light
What happens if amalgams are heated more than 140*? Which is the reason water is used to cool while polishing.
mercury is released
Why must you use a light touch when polishing amalgams?
heavy touch creates friction, which creates heat
true or false. Heat from the friction of polishing can injur pulp tissue
true
amalgams are retained in the cavity preparation by what 3 things?
parallel walls
undercut walls
irregularities in tooth wall
what are 3 features of bonded amalgams?
etched with phosphoric acid
one or two bonding resins
amalgam is applied to WET bonding agent which is chemically cured resin
Why is amalgam applied to wet chemical cured resin?
wet resin mechanically intermixes with amalgam during condensation
What are two tools that can be used to help minimize swallowing amalgam particles or inhaling released amalgam vapors (from drilling out amalgam>heat)
rubber dam
high-volume evacuation
true or false. Most dental offices are far below the recommended levels of mercury exposure levels accepted by OSHA
true
Where should scrap mercury be stored?
in an airtight container underwater
true or false. dental offices should NOT have carpet or tile floors, because it is hard to clean mercury or amalgam spills
true
true or false. mercury free amalgams are no longer used in the U.S.
