Amalgam Restoration Flashcards
Unique about amalgam longevity
Seals more over time due to its corrosion
Percent of allergies to amalgam
1%
Contraindications
Aesthetic places, small or medium isolated lesions
Advantages of amalgam
affordable, easy to use and place
Risk of amalgam
not proven
Disadvantages
more complex and technical which leads to less conservation of teeth, non-esthetic, potential for galvanic reactions (dissimilar metals and saliva is conductor), potential for marginal breakdown, poor edge strength, non-insulating, negative perception
Edge strength of amalgam
Poor
Biocompatibility of amalgam
bioinert or mildly irritating
leakage of mercury?
No, corrosion seals well
amalgam tatoo or stain
mercury that moved to gingiva causes gray color but benign/no histo changes
Thermal irritation
possible for amalgam preps placed deep; hot or cold sensativity
Spherical Amalgam
atomize liquid alloy; less condensation pressure; high early st. FINISH
Lathe Cut
milling or cutting alloy, irregular shaped, more condensation P,proximals
Admixed
Properties of both; more P, easier for interproximals, longer working time slower set
Amalgam capsules
Upper-liquid mercury
Middle-septum
Lower-alloy powder-contains pestle for mixing
Alloy powder contains
Silver, Tin, Copper, some have zinc
Tin in powder
highest affinity for mercury
highest affinity to mercury
Tin
Reduces oxide formation over time
Zinc
Problem of zinc
can have delayed expansion in presence of moisture during prep
Conventional Setting Reaction
3 phase outcome; finish
dimensional change
impacts final adaptation-initial contraction as Hg reacts with alloy and then expansion as setting progresses
increase expansion of amalgam
moisture during placement and under trituration
reduce expansion
inc. trituration time, more P when condensing, use material with reduced mg/alloy ratio
Factors affecting material strength
trituration, high condensation, no porosity (porosity reduces), sufficient mercury content, excess mercury –> increased gamma 2 phase, hardening rate
excess mercury
increased gamma 2 phase
Sweet spot values for Hg concentration by weight % vary by alloy but normally about
50%
ADA spec for amalgam hardening
amalgam reaches 80 MPa within 1 hour
Most amalgam fractures happen when
within the first few hours
Set in 20 min of almagam
only 6%-don’t eat crunchy stuff
amalgam reaches 70% by?
first 8 hours
MArquette type hardening rate
187 MPa in 1 hour, 431 by 7 days; dispersalloy admixed
survival of amalgam
7-15 years on median, larger more complex to the low end, in controlled studies 55-70yrs
Amalgam condensation
compact the alloy (inc. density and remove voids-excess Hg and water), adaptation to walls, reduce excess mercury
Condenser size
Small condenser needs less P for larger F while larger needs more P; INVERSE RELATIONSHIP
F needed for condensing
6-10lbs of force
critical factor in amalgam placement
condensation
Condensation technique
- overlap and orderly-use small condenser first
- overfilling/overpacking-remove with carving
- Time (too long=increased voids)
When condensing class II
condense deepest parts first!!
Size condenser to use first
Small then large once more full
1 min beyond manufacturers recommendation results in ____
> 30% increase in residual Hg
Goal of amalgam carving
reproduce anatomy that results in proper form and function
Flash
extension of the restorative material beyond the prep margins (prone to fracture)
first instrument for carving
some kind of burnisher
When carving should be initiated
before the amalgam has reached its initial set
Carve _____ to margins
Parallel- want instrument to have support to avoid ditching
Grooves are too deep
thin amalgam = prone to fracture, the potential for exposure of prep walls, difficult to finish or polish
over carving effects
soft tissue problems when convexity is lost
Smooth at end with
Cotton roll
dispersalloy regular set (tituration speed, condensation time, set time)
tituration speed: turtle, 11-17 seconds
Condensation time: 3:30
Set time: 4:30
Brittle consideration of amalgam
material is brittle so keep > 1.5 mm
When done condensing do not forget to
clear the condenser!
discard capsules and pessile where
in clear containers
Amalgam scraps go
into amalgam scrap containers
T/F; amalgams can be polish right away with a rotary instrument?
False; only after 24 hours!!!!
