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52 terms

properties of amalgam

STUDY
PLAY
the ability to be molded, upon mixing allows us to place it into the cavity preparation with rentetive features while it is moldable, and have it set up hard so it is held in place, like two puzzle parts fitting togeher
plasticity
streght of amalgam to withstand forces that would crush it
compressive forces
is teh strenght of amalgam that resists being pulled apart, such as the proximal box of amalgam being broken off of teh occlusal portion by pulling it apart at the thines area
tensile strenght
narrower portion of a preparation that connects the occlusal portion with a proximal box or extension
isthmus
tensile strenght of amalgam is only about ___of compressive strenght
1/8
amalgam must be well____and not over carved especially in the isthmus in order to maintain excellent bluk, thereby improving properties that would resist being broekn apart
condensed
amalgam is strong when bulky or thin?
bulky
does not bend udner foces, will break easilty when chewe on if is___
brittle
thin layer of excess amalgam that extends beyond the cavosurface margins
flash
Who must removed flash sinc it would break under occlusal forces and result in rough margins that would collect plaque?
EFDA
amalgam undergoase dimensional changes about___and ___times that of a tooth when subjected to changes in temperature, which is clinically tolerable
3 and 1/2 times
the tooth does not change in size to the same extent as the dental amalgam, so an___ and ___of a space between the tooth and filling can suck in and then push out oral fluids into the small space
opening and closing
the process of pulling in and pushing out fluids into this space is called
percolation
this also contributes to tooth sensitivity
percolation
the dimensional changes that occur upon temperature changes can be measured as a number called the
coefficient of thermal expansion
the greater the number of coefficient, the__the amount of dimensional change
greater
the more difference between the coefficient of expanison for the tooth and the coefficient for the filling, the moer likely___and ____ will occur
percolation and subsequent sensitivity will occur
the generally undesirable chemicla breakdown of amalgam similar to the rusting of exposed car metal
corrosion
the difference in oxygen concentrations sets up a condition that is doncutive for what to occur
corrosion
oral fluid found in small, microscopic pit of amalgam have less or more oxygen thatn fluid elsewehre on the amalgam surface
less oxygen
the negative result of corrosion may be______of the amalgam surface, the poorer physical properties resulting in teh need to replace the amalgam
blackening
corrosion products also provide a benefit by___
slowly filling in teh microscopic gap that exists between amalgam and tooth, reducing post operative sensitivity over time
corrosion is reduce when using
high copper alloys
polishing result in a ___surface, thus reducing surface corrosion
smoother surface
this is poor between the tooth and amalgam, which allows fluids and bacteria into and out of the dentinal tubules resulting in irritation
seal at the margin
a thin protective layer of insoluble material called____ is used to protect the tubules when dentinal procteciton is required
copal varnish
amalgam resists _____or wearing away with rubbing froces from opposing teeth or restorations
abrasion , abrasion resistance
a quality of amagalm that is not desirable since hot and cold conducted through the amalgam toward the pump may result in discomfort
thermal conductivity, is a good thermal conductor
thick layer of thermal insulating base may be used in deep preparation under metallic restorations that are lcose to the pulp, what is the thermal insulating base
zinc oxide, eugenol, glass ionomer
under repeated on/off biting foces, amaglam resists this
creep
is a deforming of metal over time when constant forces are placed upon it
creep
when plaed under foce, amalgam deofrms to become thinner and iwder so it appears to ____of the preparation
grow out , creeping out
how can creep be minimized
selecting and using high copper alloys
occurs when dissimilar metal in the mouth are connecte dthrough a lyaer of saliva and act like a battery
galvanism
when the teth with these dissimilar metals come together during fucntion, an electrical current is conducted through _____between two different metal and inot the pulp. resulting in sharp immediate nerve irritation
saliva
when does galvanism occur
newly placed restorations but usually diminishes as teh surface of restorations change chemicall over a few weeks
mixing speed and mixing time affect the characteristics of amalgam, results in cohesive ball of velvety, shiny amalgam
trituration effect
what is the liquid and what is the powder when mixing amalgam with mercury
mercury is the liquid, amalgam is the powder
what will amgalm look if under triturated
will appear dry and grainy not cohesive
porosity will contribute to what other undesirable properties
corrosion and less strength
if over triturated what will happen
the amalgam will be hot, crumbly, quick setting, but properties are not affects as much as undertrition
what is needed to decrease voids between amalgam layers, thus improving all properties, and decreasing corrosion
adequate condesation
lathe cut or admixed amalgams need to be what
adequately condensed
the force applied to eh amagam is related to the_____of the condenser nib
diameter
much more force is given by what size condenser
smaller
burnishing the amgalm, immediately after carving improves ___by reducing ____ ____
surface properties
is critical to obtaining the best amalgam properties
the correct amount of mercury
is too much or too little mercury bad for strenght of amalgam
too much
too much mercurty will exhibit increased___,___and ___
increased setting expansion, increased corrosion, and increased creep
mercury rich layer
plash
tbhis occurs during condensation results in udnersirable delayed expansion of amalgam since zince and water yileds hydrogen gas
mosture contamination
zinc free amalgam reduces
delayed expansion