Metals and alloys

Question 1

Examples of metals and alloys in dentistry

Answer 1

Amalgam - restorations
Cobalt chromium - dentures
Stainless steel - braces
Gold - restorations
Titanium -  implants

Question 2

Metals in amalgams

Answer 2

Ag/Sn/Cu alloy and Hg

Question 3

Metals in inlays/ onlays

Answer 3

Au alloys, Pd alloys

Question 4

Metals in crowns

Answer 4

Stainless steel, Au alloys, Pd alloys, Ni/Cr alloys

Question 5

Metals in bridges

Answer 5

Au allots, Pd alloys, Ni/Cr alloys

Question 6

Metals in dentures

Answer 6

Co/Cr alloys, stainless steel

Question 7

Metals in dental impants

Answer 7

Titanium

Question 8

What is a metal?

Answer 8

A crystalline material held together by metallic bonds (free electrons and cation)

Question 9

Compare crystal structures

Answer 9

Face centred cubic (packing factor 0.74)

Body centred cubic (packing factor 0.6)

Question 10

Metal microstructure

Answer 10

(Usually) polycrystalline structure consisting of grains and grain boundaries

• Must polish and etch to see this, creates contrast
• Liquid: nuclei of crystallisation
• Solid: grain and grain boundaries (frozen)

Question 11

Which metal are used in their pure form in dentistry

Answer 11

Gold, platinum and titanium

Question 12

Types of alloys

Answer 12

• Substitutional solid solutions
• Interstitial solid solutions
• Intermetallic compounds

Question 13

Subsitutional solid solutions

Answer 13

• diff atoms have same valency with same crystal structure
• atomic size within 15%
  e. g. Au and Cu

Question 14

Interstitial solid solutions

Answer 14

• solute atom ≤ solvent atom
• solute atoms occupy space between solvent atoms
• distortion of lattice occurs to accomodate extra atoms
• e.g. Fe and C

Question 15

Intermetallic compounds

Answer 15

• Formed when 2 or more metals combine with discrete composition/ stochiometric ratio
• e.g. amalgam: contains silver/tin compound (Ag3Sn) and copper/ tin compound (Cu6Sn5)

Question 16

What is a phase?

Answer 16

A homogenous physically distinct part of a system that is separated from other parts by definite physical boundary
-alloys can be single or multiple phase

Question 17

Bonds in metals

Answer 17

Metallic bonds can be weak (e.g. Hg) or strong (e.g. Ni)

Question 18

What is a phase diagram?

Answer 18

Means of presenting phases in an allot graphically, depending on composition and T

Question 19

Difference in cooling curve for pure metal and alloy

Answer 19

Alloy has phase of liquid + solid

Pure metal goes from liquid straight to solid

Question 20

Creation of phase diagram

Answer 20

100% metal A + melting T (Tm)
Metal A and B + liquid and solid zone
100% metal B + Tm
Join up dots

Question 21

What is the eutectic point?

Answer 21

The one T where the alloy acts like a pure metal (changes from solid to liquid)

Question 22

Learn phase diagrams in word doc

Answer 22

LEARN PHASE DIAGRAMS IN WORD DOC