Fall Lecture 1: Dental Amalgam: Physical and Mechanical Properties, Composition, and Handling Flashcards
Alloy:
2 or more metals to give greater strength or resistance to corrosion, 2 or more metals with non-metals
2 examples of alloys:
bronze, brass
Bronze:
copper, tin, and other metals (aluminium, etc.) and non-metals such as arsenic, phosphorus, or silicon
Brass:
copper, zinc
Dental amalgam alloy:
silver, tin, copper, zinc
Which metal is kept separate from the rest in the amalgam capsules?
mercury
Dental amalgam alloy:
silver, tin, copper, mercury (may also contain: zinc, palidium)
When does dental amalgam become an amalgam?
when it mixes with mercury
3 types of dental amalgam alloy:
Conventional lathe-cut alloy, spherical alloy, admix alloy (mixture of lathe-cut and spherical particles)
Formulation of alloy we use is based on:
what G.V. Black Presented in 1885
How did dental alloys change in the 60’s?
high copper content and spherical particles
Lathe-cut alloys:
irregularly shaped particles produced by milling or lathe cutting of cast of _?___ amalgam alloy
Spherical alloys:
made in a gas chamber, less mercury than lathe cut = better props, low mercury helps the spherical powder, smaller volume ratio than lathe powder
Alloys w buttery/soft consistency:
spherical
Issue with filing Class 2 resto with spherical alloy:
buttery, soft, very plastic, good proximal (Class 2) contact can be tough to get, need great clinical technique
Why can spherical be used for core build up material?
high early strength, strong after 10-15m
Which have higher final strength, admix alloys or spherical alloys?
spherical, core build up must be strong
Benefit of admix:
denser final amalgam
Most common material in dental amalgam:
admix alloy
Admix alloy requires:
more force, better for proximal contacts, stregnth is time dependent, initially relatively weak, delay final polishing at least 24h
These alloys have low copper:
lathe-cut and spherical
These alloys have high copper:
admix and spherical
Does spherical have low or high copper?
can be either
Silver provides:
strength
Fxn of tin in amalgam:
dec expansion
Composition of dental amalgam, high to low:
Ag, Sn, Cu, Zn (STCZ)
TF? It is important that the amalgam expand after it is set.
F. should not expand (tin)
Copper fxn:
strength, (low to high range)
Low copper percentage:
3%
High copper
up to 30%
Copper decreases corrosion by:
decreasing gamma 2 phase
What eliminates the gamma 2 phase?
copper
Zinc fxn:
scavenger, deoxidizer during melting, inc plasticity, more susceptible to moisture contamination, delayed expansion
TF? Zn free amalgam is better, than with Zn.
F.
These alloys are brittle and difficult to blend uniformly
sliver/tin alloys (copper replaces the silver to increase strength)
First silver/copper alloy was made in:
early 60’s
Silver/ copper alloy is aka:
dispersed phase or admix high-copper alloy
Amalgam we use:
Valiant PHD XT, phase dispersed (Ivoclar Vivadent), low mercury, high copper, extended stetting time (7-10min)
State of the art amalgam:
high copper amalgam
% Cu required to be a high copper amalgam:
9-30%
Benefits of high copper amalgam:
inc strength and marginal integrity, elimination of gamma 2 phase
Is an 8% copper amalgam considered a ‘high copper’ amalgam?
no
Why does high copper amalgam perform the best in clinic?
elimination of gamma 2 phase
Gamma phase:
unreacted particles (sliver, tin particles, strong, suspended in matrix of gamma 1 phase, reaction product of silver and mercury, less strong and more corrosion susceptible (?)
Which amalgam reaction has a gamma 2 phase?
conventional or low copper amalgam reaction, weakest, most corrosion susceptible phase
Phases, strong to weak:
gamma, 1, then 2
If a tin/mercury compound is present is this low copper or high copper reaction?
low copper
What compound is eliminated with the elimination of the gamma 2 phase?
Sn7Hg (weakest compound eliminated, high copper reaction stronger)
Low copper amalgam development:
dissolution, precipitation of g1 crystals, Hg consumption and growth of g1 and g2, final set
Greater unconsumed silver tin will lead to greater/decreased strength:
greater
Creep:
low creep, better restoration, time dependent deformation due to stress on material (high Cu amalgam: improved marginal integrity, decreased breakdown in margin, less creep)
Amalgams w delayed expansion after moisture contamination:
zinc-containing amalgams, tin helps to reduce expansion (wks to mths)
___ gas causes the restoration to expand after wks to mths
hydrogen
When to use zinc-free amalgam?
moisture control difficult
compressive strength of amalgam, high or low?:
very high
tensile and shear strength of amalgam are higher/lower than its compressive:
lower
Tarnish:
amalgam surface is dulled or discolored, formation of oxide layers
Corrosion
actual deterioration of a metal, chemical rxn bw metal and env (H20, air, saliva) forming metal compounds or corrosion products
Zinc works as:
scavenger, deoxidizes
increase tin:
increase tarnish and corrosion
Increased copper
decrease tarnish and corrosion
percolation of amalgam:
influx of salivary fluid bw microscopic gap bw resto and tooth
High copper amalgams have fast/slow rate of percolation:
slow, no g2 phase in high copper amalgam
this phase corrodes the most
g2 phase
Percolation takes (this long) in high copper amalgams:
6 mo
These metals have all the opposite effects as each other:
Sn and Cu
Effects of Sn:
dec strength, dec setting expansion, inc creep, inc flow, dec compressive strength, inc tarnish and corrosion
Which metal has all the same properties as Cu except for tarnish and corrosion?
Ag
Which amalgam has more copper?
admix
What causes the delayed expansion?
zinc
What reduces the oxide layer?
zinc
__ increases corrosion, while __ decreases corrosion:
tin, copper
This helps to create self sealing:
percolation
This is (basically) the corrosive phase:
g2 phase
