Biomaterials Lecture 2

Front 1

What are the requirements of dental materials?

Back 1

-esthetics (match remaining dentition)
-accurate (margin/occlusion)
-function/strength (chewing forces
-biocompatible
-reproducible (ease of use)

Front 2

What are the components of dental amalgam?

Back 2

Metal alloy
-liquid mercury (Hg)
-solid metal powder

Front 3

1) What is an alloy?
2) miscible

Back 3

1) combo of 2 or more metals- must be able to mix completely
2) liquids completely mix

Front 4

Describe the 3 classifications of amalgam

Back 4

solid solution; intermetallic compound; eutetic mixture (mixed with other chemicals to make it more stronger, and have a longer lifetime than original composition)

Front 5

In a solid solution, what is the structure of amalgam like?

Back 5

single phase - has a range of compositions; random arrangement.
Ex. Gold crowns

-usually seen as a repeating order in space but in a solid solution, its more of a random arrangement.

Front 6

Describe structure of intermetallic compound.

Back 6

Single phase with a specific composition, ordered arragement of atoms, and stronger but more brittle.
-good for bridges - will be more stiff, resist stresses in mouth.

Front 7

Describe structure of the eutectic mixture

Back 7

its immiscible in solid state; has alternating layers of the composition.
-silver and copper mixture to create stronger amalgam

Front 8

What was the composition of amalgam duirng GV Black's age?

Back 8

65% silver, 29% tin, 6% copper. hasn't really changed much over time

Front 9

Advantages of amalgam; disadvantages

Back 9

inexpensive; easy to use; long service, relatively quick to set

disadvantages: esthetics, brittle, no bonding, marginal breakdown. Can set the tooth up for fracture if you create an undercut.

Front 10

Describe the handling of dental amalgam

Back 10

Trituration - mixing of the mercury w/ metal powder. shouldn't be problems w/ spils, tc.

2) condenstation - amalgam is packed into cavity prep. Must check density, and any excess mercury. can move or creep over time.

Front 11

ADA specifications for amalgam?

Back 11

- No exact amts required.
- must be mostly silver and tin
-lesser amts of Cu, Zn, Au, Pd, In, Hg.

Front 12

How are amalgam types classified?

Back 12

-Copper content
low Cu (< 5%) may have issues with retention. higher Cu (30%) not as many issues
-zinc content
- powder particles - shape, mixture ratio.
Ex. spherical, lathe cut
In lathe cut, first form the cast ingot. then use lathe mill; finally treat with heat.

Spherical: molten metal, high pressure. tend to give you stronger at the end, but its harder to pack.

Admixed - combination of the spherical and lathe cut.

Front 13

What is the basic chemcial composition of the alloy powder?

Back 13

Ag-Sn mostly (Ag3Sn = type of molecule that works well with amalgam). <26% wt Sn; beta phase; weaker amalgam.

Front 14

What are the other components added to amalgam? What purpose does this serve?

Back 14

Copper - mechanical properties
palladium - corrosion resistance
Zinc - reducing agent (make alloy flow better) - take oxygen out of alloy.

Front 15

What is the amalgamation reaction?
For low copper alloy

Back 15

Low Cu allows

Ag3Sn (y)
+ Hg (l) yields Ag2Hg3(y1) + Sn 7-8Hg(y2) + Ag3Sn(y)

Front 16

What happens when you have an amalgam settin rxn/

Back 16

Usually have some unreactive power in subtypes.
Ag2H3(y1) dominant phase (50-60%)
-Ag3Yn(y) 27-35%
Sn(7-8)Hg(y2) 11 - 13% (this is weak, and corrodable)

check again

Front 17

What forms the matrix of the set amalgam?

Back 17

Gamma 1 material

Front 18

Describe the high Cu allows? What are the 2 reactions invovled in admixed

Back 18

Add Cu and elminated Sn7-8 Hg (y2);

High Cu: admixed
-2 different particles
2 reactions Ag3(Sn(y)) + Ag-Cu(etectic) + Hg(l) yields Ag2(H3)Y1) = Sny-8Hg(hg)Y2 + Ag3(Sn(y)).

2ndary reaction: Cu6 Sn5 (n1) + Ag2Hg3(y1) final products

-significant improement low Cu amalgam

Front 19

Amalgamation rxn: unicompositional with high Cu

Back 19

single powder; multiple phase
Ag3Sn (y) = Cu3(Sn(E))(Ag/Sn/Cu) + Hg(1) yields Cu6(Sn5)(n') + Ag2Hg3(y1)

higher properties than admixed.

Front 20

What is the microstructure of the unicompositional amalgam

Back 20

Ag2Hg3(y1) with Cu6Sn5(n').

All have y1 phase

Front 21

What does the elimination of Sn7-8Hg(y2) yield?

Back 21

Lts good things
-increased strength
-decreased corrosion
-improved marginal integrity
-improved dimensional stability

Front 22

What are the ADA specifications regarding the compressive strength?
Dimensional change? and Creep

Back 22

Compressive strength: 1 hour/ 80 Mpa (most important)
dimensional change 24 hrs +/- 20 mm/cm

creep: 3% after 1, 4 hours

Front 23

In regard to the stress strain diagram, what tells you whether you have a brittle or ductile material?

Back 23

ductile: the plasticity curve tends to elongate for a while; line between yield strength and ultimate strength is longer.
brittle: very short line between yield strength and ultimate strength. so it cracks easily

The larger the amalgam restoration, the more stress it will receive.

Front 24

With regard to physical prop of amalgam?

Back 24

Strong in compression
weak in tension, shear
-minimize the forces in restoration
-very brittle

Front 25

Describe the relative strengths of the materials in the different compositions for compressive and tensile strength

Back 25

High Cu unicompositional is stronger than high Cu admixed, is higher than low Cu for compressive strength

For tensile strength, all are equal except early.

Front 26

Describe the dimensional change in Amalgam.
Contamination of water causes?

Back 26

due to zinc , get large expansion, and also production of H2.

Front 27

What is Creep?

Back 27

Creep = dimensional change under stress after setting.
-largest for low Cu lathe cut (6%), lowest for high Cu, unicompositiona
-low y2, means less creep
-less creep = less marginal breakdown

Front 28

What occurs if you have 2 types of materials?

Back 28

Can get corrosion.
ex. smokers can have black amalgam

Electrocurrent flow may happen if you have silver amalgam near a gold amalgam. Get some surface oxidation. Pt may report pain or shock.

Front 29

What are the thermal properties of amalgam?

Back 29

-thermal expansion (2.2X coronal tooth)
thermal conductivity: high sensitivity. good idea to put a base underneath the amalgam (CaoH base or ionomer) will break up conduction of hot and cold.

Front 30

What are the mechanical properties of amalgam effected by?

Back 30

-composition
-manipulation***
esp titruition and mixing

Front 31

What happens if you have over trituration

Back 31

-if you do this, you have reduced working time, comes out almost set
-sets before the placement
-poor adherence
-can get fractures

Front 32

What happens if you have under trituration? Under condenstion?

Back 32

-excess Hg
-weaker
creep
-corrosion
-moves and flows very easily

Under condensation:
-voids
-poor adhesion
**still better to aire on the side of undermixing

Front 33

What occurs w/ moisture contamination?

Back 33

get voids
expansion
amalgam will pit, created by gaps left behind as the water boils off.

Front 34

What can you do to finish the amalgam?

Back 34

Surface finish
-if its rough: corrosion, tarnish
-burnish
-polish

Front 35

What are some physical properties of mercury? What 2 systems are greatly affected by mercury?

Back 35

Freezing pt = -38.87C
high Vapor pressure

toxic: CNS, and kidney

Front 36

What are ways you can get Hg?

Back 36

-Free vs. bound Hg in amalgam
-vapor: passivated surface
-ingestion- esp swordfish.

**fewer dentists are using it.

Front 37

What is an amalgam separator?

Back 37

Machine that will remove the amalgam in the wastewater that is required by EPA.
-reduces the mercury release.

Front 38

What are some alternative alloys to Hg in amalgam?

Back 38

Ga is liquid metal (Ga-Sn-In alloy)
susceptible to corrosion in mouth, not nearly as long lasting. failed within a few years.
2) fine particles of silver - fuse it together in the mouth.
problems seen in layers esp in larger restorations.

Front 39

What occurs when you have fractured amalgam?

Back 39

-mechanical interlock
-strenght is 50% of original
-repeated fractures may occur.

*best thing is to replace it, don't try to repair it.

Front 40

Amalgam bonding types? (2 of them)

Back 40

1) place into mouth and cure it. Still need mechanical retention. may not help on the long term.
2) place into mouth with binding agent w/o curing it.