stainless steel

Question 1

main uses

Answer 1

ortho appliance
denture base material

Question 2

what is wrought alloy?

Answer 2

It’s an alloy which can be manipulated/ shaped by cold working.
So it can be drawn into a wire.

wires
p-/ denture clasps

Question 3

steel composition

Answer 3

Iron
Carbon
Manganese
Phosphorus
Sulfur
Silicon
Chromium
Nickel
Molybdenum

has many uses including medical instruments

Question 4

iron in steel

Answer 4

its ALLOTROPIC.
So, in a solid state, it can exist in TWO crystalline forms – two phases – depending on its temperature.
Below 900C or above 1400C it has a BODY CENTRED CUBIC crystalline structure.
In between it forms a FACE CENTRED CUBIC lattice structure.

Question 5

definition solid solution

Answer 5

TWO metals that form a COMMON LATTICE structure are – by definition - SOLUBLE in one another.

That means they form a SOLID SOLUTION

Question 6

types of solid solution

Answer 6

RANDOM one – where both types of atoms in the lattice structure – are arranged in random fashion.

SUBSTITUTIONAL type is the ORDERED solid solution.
Here we can predict the type of atom based on its location.

INTERSTITIAL one.
IRON occupies all the lattice sites – and the CARBON fits in the spaces, in random fashion.

Question 7

martensite uses

Answer 7

is very useful – in non-dental applications.
It can be used to produce materials that are soft or hard – or somewhere in between.
And that’s achieved by TEMPERING the material.

Question 8

steel is regarded as stainless only

Answer 8

if there’s at least 12%

Question 9

s/steel key facts

Answer 9

corrosion resistance

CRUCIALLY S/Steel forms a chromium oxide layer on its surface, which protects it from corrosion
nickel provides this

comes in two forms
Austenitic and Martensitic

Question 10

martensitic s/steel

Answer 10

12% Cr

it can be tempered to produce very hard materials
used to make dental instruments.

Question 11

austenitic s/steel uses

Answer 11

dental instruments - withstands the autoclave process

wire for ortho

denture base = needs to be swaged

Question 12

18-8 stainless steel composition

Answer 12

Iron 72%
Chromium 18%
Nickel 8%
Titanium - 1.7%
Carbon - 0.3 %

there is a range of grades from soft to hard = spring temper

Question 13

working in s/steel

Answer 13

work done on metal/alloy at LOW TEMPERATURE - below recrystallisation temperature. Work done could be:- bending, rolling, swaging.
These processes cause SLIP – that is defects/dislocations in a grain being moved along to the grain boundaries; where they stay, they can’t jump to another grain
As a consequence of this, the alloy has fewer defects within the lattice structure making up each grain – this makes the alloy a stronger, harder material.

Question 14

springiness

Answer 14

SPRINGBACK ABILITY

ability of a material to undergo large deflections (so as to form an arc) without permanent deformation – that is, the material will subsequently return to its original shape.

SPRINGINESS is calculated as the ratio ( EL / YM).

Question 15

stiffness of wire

Answer 15

• Depending on the required force for tooth movement, you need an alloy with an appropriate rigidity.
• Ideally thewire should have a high level of ductility – so that when a large stress is applied the wire is able to undergo some permanent deformation before it fractures. This allows the wire to be manipulated to the desired configuration.

Question 16

benefits of S/steel as a denture base material

Answer 16

it’s thin – less than one tenth the thickness of acrylic resin
Its Light
Fracture resistant and Corrosion resistant

can be polished to a smooth surface, that conducts heat
withstands large impact forces

disadvantages -
sources of inaccuracy and the risk of damage due to the high pressures during swaging.