Ist Year - Dental Materials

1. Wrought AlloysWrought Alloys
ByBy
Dr.Reham Mohammed Abdallah

2. Production & Uses of wrought alloys
Requirements of wrought wires
Types of wrought alloys
1. Stainless steel alloy‫كله‬
2. Wrought cobalt-chromium-nickel alloy
‫بس‬ ‫كمقارنة‬
3. Wrought Nickel- titanium alloy‫كله‬
4. Beta-Titanium alloy ‫بس‬ ‫كمقارنة‬

3. Production of wrought alloys

4. • Wrought alloys are prepared by altering
the casting alloy mechanically into a
prefabricated shape.
• Wrought alloys have a fibrous grain
structure compared with crystalline
structure of casting alloys.

5. Uses of wrought alloys
1. Orthodontic wires and brackets

10. Requirements of wrought wires usedRequirements of wrought wires used
in dentistryin dentistry
1. Springiness (flexibility); It is the ability of
the wire to undergo large deflection
without permanent deformation.
• Spring back potential =
yield strength/Elastic modulus
• Spring back should be high which results in
an increase in its range of action.
• Spring back is the measure of how far a
wire can be deflected without causing
permanent deformation.

11. Requirements of wrought wires usedRequirements of wrought wires used
in dentistryin dentistry
2. Stiffness;
certain stiffness is required to apply a
suitable force for tooth movement
during orthodontic treatment.
• Clinically, it represents the
magnitude of the force required to
deflect or bend a wire.
3. Least friction at bracket – wire
interface. Otherwise it limits the
tooth movement

12. Requirements of wrought wires usedRequirements of wrought wires used
in dentistryin dentistry
4. Formability (ductility);It is the ability to
be bent without fracture.
5. Corrosion resistance.
6. Ability to be joined by soldering or
welding.
7. Resilience is a property of arch wires
whereby they store energy when
deformed elastically, and release energy
when unloaded.
It represents the stored energy available in
the wire to move teeth during
deactivation.

13. Types of wrought alloys used inTypes of wrought alloys used in
dentistrydentistry

14. 1.1. Stainless steel alloyStainless steel alloy
• St.st alloy are iron- carbon-
chromium alloy.
• Chromium ranges from 13-28 %
• Chromium improve corrosion
resistance

15. Mechanism of passivationMechanism of passivation
• The chromium exposed at the surface
of the alloy is readily oxidized to form a
tenacious layer of chromium oxide,
•Resists further attack from
aqueous media
•Prevents corrosion

16. Properties of St-St wiresProperties of St-St wires
• 1. Lower spring-back action and also
store less energy compared to those of
beta-titanium or nickel titanium.
• 2. High stiffness ( modulus of elasticity
180 Mpa). So, they produce high
force applied on tooth during shorter
time periods.
3. High ductility.
4. Good corrosion resistance.

17. Properties of St-St wiresProperties of St-St wires
5. Greater ease of welding and
soldering
6. Low resilience
7. Lowest cost
8. Low friction(advantage) with brackets.

19. Types of St-St alloysTypes of St-St alloys

20. Sensitization of 18-8 st.stSensitization of 18-8 st.st
Definition
•Loss of corrosion resistance if st.st
is heated between 400-900o
C

21. Mechanism and effectMechanism and effect
• Carbon reacts with Cr which precipitates
chromium carbide at the grain
boundaries this occurs very rapidly at
650 o
C and leads to:
a.Brittleness of the alloy
b.Reduction of corrosion

22. Methods of preventing sensitizationMethods of preventing sensitization
a. Avoid heating too high
b. Carbon content in the alloy
c. Severe cold working of the alloy
distribute the carbides evenly
decrease the areas of chromium
deficiency

23. d.d. Stabilization of stainless steel;Stabilization of stainless steel;
• Addition of a stabilizing element as
titanium, niobium or tantalum
• This forms titanium carbide instead
of chromium carbide such that
chromium remains in its place
““stabilized austenitic stainless steel”stabilized austenitic stainless steel”

24. 3. Wrought Nickel- titanium alloyWrought Nickel- titanium alloy
The most commonly used one is; nitinolnitinol
Ni ti n o lNi ti n o l
55% Ni 45% Ti
Naval Ordnance Laboratory

25. Characters of NiTi wiresCharacters of NiTi wires
1. Good spring back action and
flexibility
2. Low stiffness low
force
3. Excellent corrosion resistance
4. Larger stored energy than st-st, so
fewer activation or changes are
required

26. 5. Nitinol is characterized by phasephase
transformationtransformation by changing the
temperaturetemperature
or the stresses;or the stresses;
• At high temperature and low stress
austenitic (BCC, ordered)
• At low temperature and high stress
martensitic ( HCP, disordered)
This transformation is associated withThis transformation is associated with
volumetric changes.volumetric changes.

30. Schematic presentation of lattice structure changes caused by
outer stress in stainless steel or superelastic NiTi alloy

31. According to transformation, Ni-Ti wire has 2According to transformation, Ni-Ti wire has 2
unique propertiesunique properties
1. Shape memory
Definition: It describes the effect of
restoring the original shape of a
plastically deformed sample by heating it.
• This phenomenon results from a
crystalline phase change known as
"thermoelastic martensitic
transformation".
• At temperatures below the
transformation temperature, shape
memory alloys are martensitic.

32. • In this condition. their microstructure is
characterized by "self-accommodating
twins“.
• The manensite is soft and can be
deformed quite easily by de-twinning.
• Heating above the transformation
temperature recovers the original shape
and converts the material to its high
strength austenitic condition.

33. • Shape memory is achieved by first
establishing a shape at temperatures
near 482° C .
• If the appliance wire is then cooled and
formed into a second shape and heated
through a lower transition temperature
range (TTR), the wire will return to its
original shape.
• The cobalt content is used to control
the transition temperature range, which
can be near mouth temperature.

35. m
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Clinical significance
In orthodontic treatment, the wire is
shaped at high temperature into a
ready made arch shape.
After adaptation by clinician into
brackets bonded to the mal-posed
teeth, the wire returns to its original
form which promotes tooth
movement.
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36. 2. Superelasticity (pseudoelastic nitinol)
• It is a stress induced crystalgraphic
transformation from austinitic to
martensitic.
• Within the upper super elastic plateau
region, the markedly increased strain
for a small increase in bending stress
facilitates adaptation of the instrument
along a sharply curved root canal,
thereby minimizing the risk for root
perforations.

37. Super elasticity of nitinol
Pseudo-elasticity

38. minimizing the risk for root
perforation.
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Clinical significance
In orthodontic treatment, it is
desirable clinically because very
low and nearly constant forces or
tooth movement are provided by
wire during deactivation.
In endodontic treatment,
perforation of curved canals is
avoided due to the
increased stress decrease
stiffness.

40. Uses of NitinolUses of Nitinol
1. Good for orthodontic wires when low
force and large working range are
needed.
2. Good for endodontic files in curved
root canalto avoid perforation.

41. Disadvantages of NitinolDisadvantages of Nitinol
1. Limited formability
2. Higher friction than st-st and lower
than ß Titanium
3. Difficulty in soldering
4. Expensive
5. Ni has got some hazardous and
allergic effect

42. No Nickel