3 - Cobalt Chrome & Stainless Steel

Question 1

co/cr alloys: dental uses?

Answer 1

• connectors for partial dentures
• clasps: retention
• palates in complete denture (sometimes)

Question 2

co/cr: composition?

Answer 2

cobalt 55-65%
chromium 30%
molybdenum 4-5%
carbon (small amnt)

Question 3

co/cr: what happens when there is too much chromium in the composition?
max. amnt of chromium used to improve what?

Answer 3

• alloy becomes too brittle

- max. chromium used to improve corrosion resistance

Question 4

molybdenum: what does it contribute to? x2

Answer 4

• reduce grain size

- improve hardness

Question 5

carbon: what does it contribute to? x3

what happens if there is too much carbon?

Answer 5

• hardness
• strength
• ductility

-too much carbon will make the alloy brittle

Question 6

properties of co/cr? will it be enough for crowns/bridges?

Answer 6

• high casting temperature, 1500-1550deg
• casting shrinkage ~2%
• not accurate enough for crowns/bridges

Question 7

advantages of co/cr? x5

Answer 7

• strong
• can be made thinner than gold for partial denture
• half density of gold
• low corrosion
  high biocompatability, but some alloys contain nickel -> can produce allergic response

Question 8

problems with co/cr?

Answer 8

• difficult to polish
• cannot be burnished
• clasp can fracture

Question 9

stainless steel:
alloy of?
resistant to?

Answer 9

• iron

- resistant to corrosion

Question 10

dental uses of stainless steel?

Answer 10

• dental instruments
• endodontic files
• hand pieces
• partial denture clasps
• mesh for orthodontics

Question 11

stainless steel:
huge variety of properties can be obtained by?
steel is an alloy of?
cast iron has how much carbon?
stainless steel - minimum of how many % chromium?
what is formed in exposed SS?

Answer 11

• by small changes in composition
• carbon (max 2%) and iron
• greater than 2% carbon
• 11% chromium
• a layer of chromium oxide formed

Question 12

types of stainless steel and examples of each?

Answer 12

• austenitic: ortho wires, denture clasps
• ferritic: non-cutting instruments
• martenistic: cutting instruments, burs etc

Question 13

amount of chromium (Cr), nickel (Ni) and carbon (C) in

• ferritic s/s?
• austenitic s/s?
• martenistic s/s?

Answer 13

Ferritic: 11.5-27% Cr
0% Ni
0.2% C

Austenitic: 16-22% Cr
7-22% Ni
0.25% C

Martenistic
11-17% Cr
0.2-5% Ni
0.15-0.25% C