Amalgam Flashcards
advantage of dental amalgam?
IDK
disadvantage of dental amalgam?
- poor esthetics compared to resin composite
- weakening of tooth from removal of tooth structure
- recurrent carries
- no adhesive bonding, unless bonded restoration
- sensitivity of properties to manipulation
- brittle nature of material
- biocompatibility
- wastewater pollution w/ mercury
general setting reaction of amalgam?
alloy + Hg -> amalgam
Mercury/alloy ratio in dental amalgam
0.5
mercury/alloy ratio range in commercial products
IDK
List the aspects of the alloy for dental amalgam particles that control the setting process
composition
shape
size of alloy particles
List the requirements for starting alloy particle composition and properties of the resulting dental amalgam that are given in American Dental Association Standard 1.
starting alloy particle:
-The total concentration of other elements cannot exceed 0.1 wt %, unless the manufacturer provides evidence of biocompatibility
resulting alloy properties:
creep 1.0 % maximum, dimensional change between -0.15 and +0.20 %, and compressive strength minimum of 80 MPa after 1 hour and 300 MPa after 24 hours
State the two elements in greatest amount in the alloy for dental amalgam, along with other elements that are found in commercial products
2 primary elements:
Ag (primary) + Sn (secondary)
Also: 2-30% Cu and 0-1%Zn
May include: In and Pd
Comment on whether the alloy particles mixed with mercury are single-phase or contain multiple phases
3 phases
gamma (Ag3Sn)
beta (Ag-Sn)
epsilon (Cu3Sn)
how are dental amalgams classified?
2 ways:
- Method of making Particles
- Filing or lathe-cut
- spherical - composition of particles
- all particles w/ same composition
- different composition
Describe the size range of the particles and the importance of this size range for condensation
of the dental amalgam mix
range:
- spherical particles range from 50micrometer diameter to over an order of magnitude smaller
- lathe-cut: wide range in sizes
intentionally done by manufacurer for optimum condensation
Explain the difference in mercury to alloy ratio that is needed for spherical alloy particles vs. lathe cut alloy particles.
spherical particles have lower mercury/alloy ratio than lathe cut
which one resists more force of condensation, spherical or lathe-cut?
lathe-cut
amalgam classification based on composition of particles?
- high copper vs low copper
2. zinc containing vs zinc free
high copper vs low copper, which one is better, why?
high copper bcz:
greater longevity
lower creep
zinc containing vs zinc free, which one is better? why?
either:
- zinc improves corrosion resistance
- if zinc, then less plastic amalgam mix
what’s used in OSU?
60% spherical (50Ag, 30Sn, 20Cu, 0.5Pd)
40% lathe-cut (57Ag, 30Sn, 14Cu)
the product is classified as: fast, regular and slow setting time and ECT.
relation btwn setting time and mercury/alloy ratio
slower setting times correspond to higher mercury/alloy ratio
why proprietary heat treatment?
- eliminate compositional nonuniformaty
- relieves stresses in alloy particles
- provide manufacturer control of setting time (IMPORTANT)
General form of setting rxn
gamma (starting alloy particles) + Hg (liquid) -> rxn phases (matrix) + unreacted particles (core)
rxn of low copper amalgam
alloy (gamma) + Hg -> gamma 1 + gamma 2 + unreacted alloy particles
rxn of high copper amalgam
alloy (gamma) + Hg –> gamma 1 + n’ + unreacted alloy particles
what’s present in both high copper and low copper amalgam?
gamma 1
No free mercury after _____
No free mercury after setting reaction
stages of setting rxn
step one: both gamma 1 and gamma 2 form initially
step two: disappearance of gamma 2 and formation of n’
what clinical problems would occur with an excessive setting expansion or contraction?
if expansion: loss of anatomy and postoperative pain
if contraction: microleakage
general time period for the setting of a condensed dental amalgam?
24 hours
core and matrix in terms of bricks and mortar
bricks = alloy = core mortar = rxn phases = matrix
weakest microstructural phase ?
gamma 2 in low-copper amalgam
which one corrodes? gamma 1 or 2
gamma 2
what’s the strongest microstructural phase?
incompletely consumed starting alloy particles (gamma)
what’s the major phase found in both low and high copper amalgam?
gamma 1
amalgam: brittle or ductile?
brittle
rate amalgam based on:
- compressive loading vs. tensile loading
- bending
compressive > tensile
cannot bend
mechanical properties of amalgam after 1 hr, 1 day, and 1 wk
greater difference in strength after 1 hr compared to 1 day
final compressive strength = 1 wk (about the same as after 1 day)
which amalgam sets most rapidly?
HCSS
how is creep measured in lab?
cylindrical specimen
stored for 1 wk
compressed at 36 MPa
change in length measured from 1-4 hr
which one has higher creep? low/high copper amalgam
low copper amalgam
why is creep related to low copper amalgam?
creep mechanism is grain boundary sliding of gamma 1 phase (which is blocked by n’ in high copper amalgam)
compare the compressive strength of LC, HCSS, and HCB
compressive strength:
HCSS > HCB > LC
compare the tensile strength of LC, HCSS, and HCB
tensile strength:
HCSS > LC > HCB
compare the creep of LC, HCSS, and HCB
creep (%)
LC > HCB > HCSS
(so LC sucks)
compare tensile strength of amalgam, resin, alloy gold
tensile strength:
Gold alloy»_space;> amalgam > resin
what happens if you have too much mercury?
formation of greater amount of rxn phases
- increases setting expansion
- decreases strength
why trituration?
decrease setting expansion
increase strength
why condensation?
-adapt restoration to cavity walls
-minimize porosity
-control final mercury content
(also, decrease setting expansion and increase strength)
what happen when we overtriturate?
makes mixed material hot
reduces working time
increases creep
what’s the effect of small increase of condensation pressure?
-decrease setting expansion
-increase strength
(same reasons as the trituration reasons)
problems of moisture contamination of Zinc-containing amalgam
-and what’s the mechanism for it?
- excessive setting expansion
- decreases strength
H2 released from Zn reduction of water
Zn sucks, so why we may find it amalgam?
not economically feasible for manufacturer to eliminate Zn
-also, Zn eliminates corrosion
types of corrosion and their possible location on the restoration
- Galvanic corrosion: at interproximal contacts w/ gold alloys
- electrochemical corrosion: b/c multiple phases
- crevice corrosion at margins
- chemical corrosion at occlusal (bcz of rxn w/ sulfide ions)
slide 35
why do we prevent corrosion?
to reduce microleakage
to eliminiate decrease in strength
what phases in low copper and high copper amalgams undergo corrosion?
low copper: gamma 2
high copper: n’
why greater potential w/ low copper compared to high copper amalgam?
low copper has gamma 2 which results in bulk corrosion
high copper has n’ (n’ is not interconnected, so n’ corrosion only happens at the margin, w/o bulk corrosion)
why polishing amalgam restoration would reduce corrosion?
bcz unpolished scratches or secondary anatomy = lower pH and O2 concentration of saliva = plaque = corrosion
Zn containing amalgam vs. corrosion
Zn-containing amalgams have superior marginal integrity and longetivity
-preferential Zn corrosion may occur
what are the routes of mercury exposure for dental office personnel and patients?
skin
inhalation of vapor
airborne droplets
what’s the threshold limit value for mercury exposure?
0.05 mg Hg/m3
what is recommended to do when placing amalgam?
- use single use capsule
- use a no-touch technique
- clean up
- discard any old or damaged mixing capsules
- store amalgam scrap in cool space
- store amalgam scrap in a jar of water and SULFUR
- avoid baseboard heating in operatories where dental amalgam is used
- use face mask and water spray with high vacuum evacuation
- do not use ultrasonic condensers
- office personnels should have their mercury levels checked by urinalysis
