Dental Amalgam Flashcards
if a patient is wanting amalgams changed for aesthetic reasons what would you advise the patient?
amalgam fillings are safe
mercury vapour produced on removal
when is amalgam the best choice of filling material?
not good moisture control
large occlusal load
not good supragingival enamel margins
large complex restoration
what happened in 1833
crawcour brothers brought amalgam to the usa, powdered pennies and mercury - expanded on setting
1895?
GVBlack - modern day
67% silver, 27% tin, 5% copper, 1%zinc
what is creep?
when amalgam flows out of restoration and becomes proud
occlusal loading causes fractures
why was copper added?
improves strength of the set material
reduces creep and corrosion
what is the tin mercury phase?
the gamma 2 phase
weakest phase - causes creep
what does copper eliminate?
eliminates the tin mercury phase
no expansion
what does zinc act as in amalgam?
a scavenger
takes up O2 from oxidisation and is easily removed
what happened in the 1960’s?
conventional low copper alloy was lathe cut
= admixture - 1st gen of high copper alloy = spherical AgCu
1970’s
first single composition spherical
1980’s
sim to 1970’s
90’s?
first mercury free alloy - gallium
problems with mercury free alloy?
increased corrosion and excessive post setting expansion
what kind of amalgams are available today?
low copper alloys, admixed high copper alloy, single composition high copper alloy
why is amalgam encapsulated?
reduce hg contamination
what are the benefits of amalgam being resin free?
no allergies
why is saliva control necessary?
water contamination causes expansion on setting
what does carving remove?
weak gamma 2
how can amalgam be manipulated?
trituration, condensation, burnishing, polishing
what happens during overtrituration?
hot mix - sticks to capsule
reduced working and setting time
increase in contraction
what happens during undertrituration?
grainy, crumbly mix produced
what condensers are beneficial for lathe cut? spherical cut?
small
large
what are the benefits of burnishing pre carve?
post carve?
combined?
- removes excess mercury, improves margin adaption
- improves smoothness
- less leakage
when to polish and why?
after 24 hours
increase smoothness, reduce plaque retention, reduce corrosion
when to bond an amalgam?
gives retention when there is no retention form
missing cusp
gives good marginal seal
advantages of bonding?
dont need pins, reduced marginal leakage and post op sensitivity, reinforcement of tooth structure
disadvantages of bonding?
time consuming, expensive, no long term data on efficacy
before using smartchem/rely x what do you apply?
line cavity with vitrebond
where does toxicity from amalgam arise from?
from the mercury
what can happen if the pt has an allergy to amalgam?
contact dermatitis, oral lichen planus
what is the potential threat to pregnant women with amalgam?
mercury can cross the placenta
