chapter 11 and 12: amalgam, metal, and alloys

what is an allow?

a mixture of 2+ metals

what is an amalgam alloy?

metal = silver + tin + copper

what is a dental amalgam?

metal alloy with mercury 

what are dental amalgams made of?

equal parts powder and mercury

what is amalgamation?

the process of mixture of metallic compounds beginning to crystallize in mercury

what is trituration/amalgamation-reaction?

when no more metal can dissolve into mercury, amalgamation occurs and continues until the liquid mercury is used up 

what is working time?

the amount of time needed before reaching initial set

what is retention?

mechanically retained direct restorative material

what is the initial setting time?

when the amalgam reaches a pre-defined firmness

what is the final setting time?

the time when the setting reaction is completed 

when does the final set usually occur?

12-24 hours after trituration

what are the 2 methods of forming amalgam alloy particles?

lathe-cut alloys or spherical alloys

what are lathe-cut alloys?

shaving particles off a heat-treated ingot of the allow with a lathe

what is a lathe?

a cutting machine 

what happens to the particles from lathe-cut alloys after getting shaved off?

gets sifted to separate into fine or ultra-fine particles

how are spherical alloys produced?

1. by atomizing a mist of molten alloys into an inert gas 

2. spherical particles form as atomized droplets cool

3. spherical particles get heated and washed in acids

what does admixed mean?

combination of lathe-cut and spherical alloys

what are the advantages of amalgam alloys?

1. durability

2. margins are sealed

3. least technique sensitive restorative material

how long can class I amalgam alloys last?

15-18 years

how long can class II amalgam alloys last?

12-15 years 

what can affect amalgam longevity?

patient diet and hygiene

what are amalgam alloys mainly made of?

silver and tin

what are the minor components of amalgam alloys?

1. copper

2. zinc

3. indium

4. palladium

what happens with overtrituration?

1. mix is too wet

2. has low resistance to condensation

3. sets too quick

4. weaker restoration

what happens with undertrituration?

1. dry

2. crumbles

3. difficult to condense

4. shortened working time

5. sets too quickly

6. weaker restoration from components not being thoroughly mixed 

what reduces mercury content?

proper trituration and condensation

what does minimizing mercury content do?

improves strength

what are the 3 setting phases of amalgams?

g, g1, g2

what is g phase?

gamma phase (Ag-Sn alloy)

what is Ag?

silver

what is Sn?

tin

what is Hg?

mercury

what controls the rate of the set?

Sn

what is g1 phase?

gamma one (Ag-Hg) phase

what is g2 phase?

gamma two (Sn-Hg) phase

why are higher copper amalgams good?

1. reduced corrosion

2. high compressive strength

3. less dimensional change

what is creep?

the gradual change in shape of restoration from compression of teeth

what is tarnish?

oxidation that attacks the surface of the amalgam and slightly below the surface

is tarnishing harmful to the restoration?

no

is tarnishing easily removable?

yes

when does galvanic reaction occur?

when a newly placed amalgam contacts another metal restoration 

what is the thermal conductivity of amalgams?

hot and cold

what is the dimensional change of amalgam?

no change should occur

what is a matrix system?

replaces a mixing wall of the tooth 

what are the 3 parts of the matrix system?

1. flexible metal band

2. device that holds the band in place

3. wooden/plastic wedge to secure the band around tooth

what does the wedge do?

adapts the matrix against gingiva of restoration 

what does the wedge stop?

amalgam from seeping out below the band and prevent overhang

what are other types of matrix systems?

1. retainerless matrix systems

2. sectional bands

what must be added before placing the amalgam?

cavity sealer 

what is the cavity sealer?

copal resin varnish

what is calcium hydroxide used for?

to stimulate production of secondary dentin/reparative dentin/acts as thermal insulator 

what is an amalgam separator?

collection devices that captures the scraps that might get into waste water

what are pure metals?

small interlocking crystals/grains that form a lattice

what are indirect restorations?

made outside of the mouth in the lab 

what is intracoronal?

restoration is placed within the crown of the tooth (inlay)

what is extracoronal?

restoration is placed within the crown of the tooth (onlay)

how are noble metal dental casting alloys classified?

by use or by the type of metal used

what are the different types of noble metal dental casting alloys?

1. noble metal

2. pure gold

3. high noble, noble, base noble

4. burnish

5. other noble metals

what is an example of noble metals?

gold

what is an example of other noble metals?

platinum and palladium 

what are the ADA classifications?

high noble, noble, base metal

what does high noble classification mean?

must contain at least 60% noble elements (40% of which is gold)

what does noble classification mean?

contains at least 25% noble elements and remaining 75% of base metals

what does base metals classification mean?

less than 25% of noble metals 

what is elastic modulus?

measure of stiffness of the alloy

what does a high elastic modulus mean?

stiffer the alloy

what does a low elastic modulus mean?

less stiff alloy

what is thermal expansion?

small increase in length, width, and volume from metal getting heated 

what is thermal conductivity?

conducting heat

what is electrical conductivity?

conducts electricity

how do electrons move in thermal and electrical conductivity?

charged free electrons flow quickly from one another throughout the lattice of the metal

what is the most dense/hardest casting metal?

gold and platinum

what is strength?

the ability to resist fracture or distortion

what is yield strength?

the maximum stress the alloy can withstand before getting permanently distorted 

what is hardness?

resistance to penetration

what is crystal formation?

grains that form when the metal is cooling 

what is annealing?

controlled reheating of gold based alloys

which metals are more resistant to tarnish/corrosion?

noble metals

which metals are more likely to tarnish/corrode?

base metals

what is malleability?

ability to be shaped 

what is ductility?

ability to be elongated (by stretching/pulling)

what are precious metals?

noble metals, gold, palladium, and platinum

what are non-precious metals?

low cost base metals (no gold) 

what are examples of non-precious metals?

copper, nickel, silver, zinc, tin, titanium

what is titanium used for in dentistry?

1. implant fixtures

2. partial denture frameworks

3. all metal/metal ceramic crowns and bridges

what is more biocompatible?

noble metals 

what is a common allergy in dental work?

nickel and beryllium

what do porcelain bonding alloys need to be?

1. compatible with porcelain fused to metal restoration

2. able to withstand high heat without melting or distorting

what does PFM stand for?

porcelain bonded to metal restorations

what must be compatible to prevent PFM failures?

porcelain and metal 

what is degassing?

metal substructure is heated at high heat to form oxides on the metal surface

what does degassing help with?

porcelain bonding to the metal

what is soldering?

joining metals together 

what are the 3 processes to join metals together?

soldering, brazing, and welding

what temperatures is soldering performed at?

450 degrees C - 1100 degrees C

what temperature is brazing performed at?

below 450 degrees C

what is welding?

use of high heat to fuse 2 metals together where they touch

what do gold solders do?

join metals together and repair cast restorations

what is flux?

chemical compound in paste/powder form applied to the alloy surfaces to be soldered 

what is silver soldering mostly used in?

orthodontics and pediatric space maintainers