dental 5 Flashcards
what is an alloy
mixture of metal
amalgam
an allow containing mercury and one other metal
dental amalgam- produced by mixing (L) mercury with (S) particles of an alloy containing silver, tin or copper
requirements of amalgam alloy
it should primarily consist of copper-silver or tin
can contain a small amount of
indium, platinum, platinum, zinc and mercury
classification of alloys
zinc-containing alloys-0.01% or more
low copper alloys- 5% or less
high copper alloys- 13-30%
qualities of high copper alloys
13-30% increase strength corrosion resistance marginal integrity
silver alloy amalgam powder
lathe-cut- irregular shape
spherical (cut)
admixed- (mixture of both spherical and lathe cut)
dimensional changes during the setting of amalgam
initial contraction- 20min - associated with the solution of the alloy particles in mercury
expansion- due to the reaction of silver and copper and the formation of the matrix phase
the final value is at 24hour-
amalgam doesn’t adhere to tooth structure forming an interfacial gap
corrosion
progressive destruction of metal by chemical or electrochemical reaction with the environment
results in loss of strength and marginal integrity
bonding of amalgam
amalgam don’t bond to the tooth structure and therefore does not restore the original strength of the clinical crown. adhesive systems attempt to bond the amalgam to the tooth structure
trituration
mixing of mercury and amalgam particle
amalgam particles + mercury → dental amalgam + unreacted powder
Ag3Sn + Hg → Ag2Hg3 + Sn7Hg + Ag3Sn
what is ammalgamation
outer silver tin particle dissolve into mercury when coming into contact with mercury
dental amalgam
gamma is silver and tin
trituration- mixing of mercury and alloys
silver 65% gamma 1 dissolves first into mercury
tin 29% gamma 2 dissolves second into mercury
after titration gamma 1 and 2 crystals grow and mercury dissolves in the remaining powder (unreacted alloy particles
high copper alloys properties
improves mechanical properties corrosion characteristics are better increase marginal integrity improved performance in clinical trials
2 types of high copper alloy powders
admixed alloy powder
single composition alloy powder
admixed alloy powder
79.1 % silver
28.9% copper
sphericle particle
added to low copper lathe cut amalgam particle
admixed particles usually contain 30-55% copper powder
single composition alloy powder
η phase (Cu6Sn5)
particles made of the same chemical composition
60%silver 27%tin 13-30%coppper
η phase (Cu6Sn5) occurs when tin amlgum reacts with copper in silver copper
a layer of η phase crystals form around the unreacted silver copper alloy particle
resin composite
reinforce polymer system used to restore hard tissue such an enamle and dentin
polymer matrix composite (resin composite)
resin composite used to replace missing toothe structures and modify tooth color and contour thus enhancing easthetic
activated by visible wavelengths
3 components of rein based composites
matrix- plastic resin materials that forms a coniuous phase
filler -reinforcing particles dispersed in the matrix (strengthen resin composite and provides degree of tranlucency)
coupling agent - promotes adhesion between matrix and filler material
hybrid composite
2 types of fillers blended together-
fine particle- size 2 to 4 μm
microfine particle 0.04 to 0.2 μm.
microhybris composites
fine particle - 0.04 to 1 μm.
blended with silica microfine particles
contain 60-70% filler by volume
has good clinical wear resistance, mechanical propoties and suitible for stressing application but lose surface polish with time and become dull
nanofills
contain nanonmeter size particles 1 to 100μm.throughout resin matrix
nanohybrids
consits of large particles 0.4 to 5 μm with added nanometer size particles thus are hybrid materials
surface gradually becomes dull
nanoclusters
synthasized from silica sols
size- 5 to 75nm
