Posterior restorative materials Flashcards
What is amalgam?
Metal alloy containing mercury, silver, tin, copper and other elements. Combination is necessary because no elements alone have suitable properties
What is the only piece of metal that is a liquid at room temperature?
Mercury
What are the noble metals?
Gold, platinum, Palladium, iridium, rhodium, osmium, ruthenium
What is amalgam used for?
Mainly used in class one and class to restorations as fillings for buccal pits and as build up material
What are the percentages of each metal found an amalgam?
Silver = 40 to 60% Tin= 27% Copper = 13 to 30% Zinc could be less than 1% Mercury based upon weight
How much mercury does the amalgam mixture usually contain my weight?
45 to 50%
Which metal has been found that when increased improves clinical performance and decreases the amount of mercury needed?
Copper
What form is amalgam supplied in?
Produced capsules which are most common and require less handling
Bulk in powder or tablet form
What is alloy?
Combined metals that are mutually soluble in a molten state
Which teeth Is amalgam usually limited to?
Posterior teeth
How are amalgams classified?
According to their shape:
- lathe cut- old type
-spherical type – also used years ago
-admixed Dash used presently and is a mixture of lathe cut and spherical
What is moldability?
When alloys are properly mixed. Will allow us to condense the material into the tooth preparation. Should be placed into the prep in small increments to avoid trapping voids in the bottom
What is used in now to mix amalgams?
A tritrator
What will happen from over trituration/longer trituration?
Slows sitting in the mix is shiny and sticky
What happens from under trituration/short?
Crumbly mixture and looks dull
What will mixed amalgam look like when triturated correctly?
Cohesive and shiny. Incorrectly mixed amalgam cannot be worked with
How long does it take for the amalgamation reaction to finish?
Reaction is continuous for several hours and not complete for a few days. Remind patient to avoid chewing in that area for several hours
How should amalgam capsules be disposed of? And why
Should be placed in an unbreakable tightly sealed container to reduce contamination of the operatory air
What happens when shrinkage occurs?
Causes a small space to occur around the restoration. In that space corrosion buildup but may not be a parent because toothbrushing removes it it
What is creep?
Dimensional change that could affect the margins. Slow progressing, permanent deformation that as a result of study force or stress acting on the material
What can moisture contamination do?
Because delayed expansion of the material, weaker restoration and other issues
What is corrosion?
When acids, salts etc. caused the material to have microscopic pores that fill with corrosive product which will weaken the material and cause it to look darker
What are the major causes for amalgam failure?
Secondary decay
Marginal breakdown
Fracture
Cusp fracture (weakened tooth wall)
What is the purpose of adhesives?
Help to seal Dentin tubules, helps tooth be more resistant fractures and less marginal break down
