Amalgam Flashcards
Why use amalgam
Inexpensive Easy to use >100 yr history Familiarity Resin free this less allergies
What are the basic constituents of amalgam
Silver
Tin
Copper
Mercury
How does silver affect amalgam
Increases strength and expansion
How does tin affect amalgam
Decreases expansion, strength
Increases setting time
How does addition of copper affect amalgam
Ties up tin Decreases gamma 2 Increases strength Reduces tarnish and erosion Reduces creep (marginal deterioration)
What does mercury do for amalgam
- activates reaction
- liquid at room temp
do spherical alloys require more or less mercury than admixed
spherical less (45 vs 50%) because they have smaller surface area and are easier to wet
Why is zinc sometimes used in amalgam
Decreases oxidation of other elements and less marginal breakdown
Palladium does what to amalgam
reduce corrosion
greater luster
What amalgam that we use has palladium
Valiant PhD
How much mercury is mixed with alloy
50/50
What are the three particle shapes for amalgam
lathe cut, spherical, admix
Tytin have what particle shapes
spherical
Dispersalloy, Original D, and Valiant PhD has what type of particle shape
admix
In amalgam equations what is gamma
the unreacted Alloy
forms 30% of volume of set amalgam
What is gamma 1
2nd strongest
60% of volume
Ag2Hg3
creates matrix around unreacted alloy
gamma 2
weakest and softestphase
Sn8Hg
as corrodes over time Hg is released which reacts with the alloy so volume of gamma 2 decreases over time
Describe admix alloy componets
2 types of particles spherical and lathe cut spherical Ag-Cu lathe cut AG SN The copper ties up the tin
How do single composition high copper alloys differ
the gamma spheres have a copper tin coating that reduce creep and prevents gamma 2 formation
What dimensional change do high copper amalgams undergo
net contraction
.3% shrinkage
contraction leaves marginal gap but is reduced overtime with corrosion
What factors affect amalgam contraction
type of alloy:spherical have more due to less hg
condensation+more condensation + greater contraction
trituration time
more trituration causes higher contraction
Amalgam strength variables
Time: at 1 hr 40-60% at 24 hrs 90%
Spherical alloys strengthen faster
need bulk for strength. Brittle at thinner sections
How does corrosion affect amalgam restorations
Reduces strength
acts to seal margins
low copper 6months
high copper up to 24 months
Which kinds of Am have been shown to last longest? Shortest
Shortest
low copper zinc free
longest
high copper with zinc
Describe an overtrituated mix
hot
decreased setting time
increased contraction
Describe an undertriturated mix
grainy and crumbly
What kind of condensation forces do you use on lathe cut
small condensers with high force
what kind of condensing do you use for spherical
large condensers using vertical/lateral vibratory motion
how do you condense admix
intermediate between spherical and lathe cut
Why should you burnish amalgams and when should you
pre carve to remove excess Hg and improve margin
post car to improve smoothness
doing both gives less leakage
Does polishing improve marginal integrity
Collins J Dent 92 say no
What are the advantages of spherical alloys
Easier to condense
hardens rapidly
smoother polish
what are the disadvantages of spherical alloy
hardens rapidly
hard to get tight proximal contacts
higher tendency for overhang
higher shrinkage
what are the advantages of admixed
easy to achieve tight contacts
good polish
hardens slowly
What are the disadvantages of admix
hardens slowly with lower early strength
Should we bond amalgam?
Cochrane: No difference in Am survival or post op sensitivity
summit 2004: bonded complex am were as retentive as using pins
conclusion: Probably only use for complex
whats the avg daily dose from 8-10 Am surfaces of mercury
1-2 micrograms
What are the threshold mercury levels for pre clinical effects and dangerous effects
preclinical 30micrograms
dangerous 80 micrograms
what is the biologic activity of mercury
binds to sulfhydryl groups
no carcinogenicity but can cause birth defects
what form of mercury is most toxic
alylmethyl
minimal bay japan posoning
when removing Am how does the Hg vapor release compare to the established exposure level threshold
far below, < 5%
any evidence to link Am to diseases
nope
what is the exa ruling on Am
install am separators to reduce Am entering sewer
prohibit use of oxidizing agents for flushing of vacuum systems
prohibit rinsing or flushing of Am waste down a drain
Whats the minimata convention
Global agreement to protect human health from releases of Hg. Phase down use of Am
What does the ban on Am do to Dental Economics
Increase res price ~19%
decrease number of res placed
increase in untreated car
