By dr Hira dental materials wrought alloys.

2. WROUGHT ALLOYS
 Cold worked metal that has
been plastically deformed to
alter the shape of the
structure and certain
mechanical properties.
 Wrought---Beaten

3. Applications of wrought Alloys
 Orthodontic wires
 Clasps for partial denture
 Endodontic instruments
 Prefabricated pediatric crowns
 Surgical instruments

4. WROUGHT ALLOYS
Stainless steel
Orthowires,paed
crowns,Endo
instts,surgical instt,clasps
Nickle Titanium
(Ni ti)
Ortho wires
Endo instruments
Cobalt
Chromium
Beta
Titanium
Wrought
commercially
pure Titanium

5. COLD WORKING
 Process in which a metal is hammered, drawn or
bent into shapes at temperature well below the
crystallization temperature of metal(often at
room temperature)
 Cold working increase hardness, strength and
prop.limit
 Decrease corrosion resistance and ductility

6. ANNEALING
 Controlled heating and cooling process designed to
produce the desired properties
 Annealing temperature is half the melting point of a
pure metal or the fusion temperature of an alloy
 Increase softening, plastic deformation potential and
improve machinability

7. Effects of annealing on cold worked metal
Cold working Annealing
 Low ductility
 Distorted grains
 Reverse in 3 stages
 Recovery
 Re crystallization
 Grain growth

8.  Recovery
Recovery of ductility and corrosion resistance
 Recrystallization/Re crystallization Temperature
Usually 1 hour in which the crystalline grain structure
is revived. makes metal soft and ductile(suitable for
clasps)
 Grain growth
 Occurs in a way to minimize grain boundery area with
large grains consuming small grains. Coarse grain
structure is produced

9.  WROUGHT STAINLESS STEEL ALLOYS

10. Stainless Steel
 12-30% chromium added
with iron and carbon makes
STAINLESS STEEL
 TYPES
 Ferrite
 Austenite
 Martensite

12. Composition
Types Chromium Nickle Carbon
Ferrite(bcc) 11.5-27% 0 0.2
Austenite(fcc) 16-26 7-22 0.25
Martensite(bcc) 11.5-17 2.5 0.15-1.2

13. Martensitic stainless steel
 Can be heat treated
 Body centered Cubic- BCC
 High strength and hardness
 Used for surgical and cutting instruments
 Less corrosion resistance than other types

14. Ferritic stainless steel
 Good corrosion resistance provided strength is not
required
 BCC
 Can not be heat treated or readily work hardened

15. Austenitic stainless steel
 Most corrosion resistant of all types(due to high nickle
content and chromium)..also maintain it at this form
at room temperature.
 Highly ductile
 FCC
 Widely used in dentistry
 ortho wires
 endo instruments
 Paedriatic crowns

16. Corossion Resistance
 Chromium forms passivating adherent oxide layer
which prevent corrosion. CHROMIUM OXIDE
 Loss of passivation occurs by
 Sensitization(% age of chromium less than 13% and
more than 27%)
 Poor oral hygiene
 Excessive heat treatment during soldering/welding
 ALSO CALLED WELD DECAY

17. SELF PASSIVATING ALLOYS:
 Chromium
 Titanium
 Aluminium
 Inherent ability to form resistant oxide layer and
maintain polished surface for years

18.  TITANIUM & TITANIUM ALLOYS

19. Properties of titanium
 Corrosion resistance(form most stable oxide layer)
 Low density(light weight of prosthesis)
 Biocompatible
 Low modulus(less brittle)
 High strength as compared to stainless steel

20. Applications of Titanium
COMMERCIALLY PURE TITANIUM
 Implants
 Crowns
 Partial dentures
 Ortho wires
TITANIUM ALLOYS(Ti-6Al-4V)
Ortho wires

21. Titanium Alloys
 Titanium has a and b phase.
 Alloying elements added to stabilize a or b phase
(Ti-6Al-4V)
 a phase is strong but not moldable at room
temperatures (Alumium is a stabilizer, increase
strength)
 b phase is moldable at room temperature
(Vandaium, Palladium or copper are stabilizers to
increase corossion resistance)

22. ORTHODONTIC WIRES

23. Orthodontic Wires
 Apply forces to mal aligned teeth to change their
position and to maintain an ideal dental arch

24. Requirements for orthodontic wires
 Spring back potential
 High stiffness
 Ability to bent without fracture
 Ability to be joined by soldering or welding
 Excellent corrosion resistance
 Ductility to be formed into various shapes
 Low cost

25. ORTHODONTIC FORCES

28. Cross sections of orthodontic wires
 E Circular
 Rounded
 Stiffness of wires depend upon their thickness
 Increasing thickness from 0.6-0.7 mm increase the
stiffness by factor 0f 1.86.

29. Available materials
 Stainless steel
 Co-Cr-Ni(elgiloy)
 Ni-Ti
 B titanium
 Gold alloys—lacked flexibility and tensile strength,
inappropriate for joining etc. (obsolete)
TYPE IV

30. Stainless steel ortho wires
 18-8 Austenitic stainless steel(18% cr and 8%Ni)
 Processed through rolling and drawing
 Moldable
 High elastic modulus to apply large forces
 Low spring back potential
 Smaller diameter used to apply small forces
 Annealing reheated at450 C for 7-10 min before use
 Soldering gold and silver solders are used

31. Co-Cr-Ni ortho wires (Elgiloy)
 Available as wire and bands
 Composition same as that of casting alloys except low
%age of cobalt and chromium
 Mechanical properties similar to stainless steel
 Processing available in various tempers(color coded)
 Soft, ductile,semiresilient and resilient

32. B-Titanium ortho wires
 B crystallographic form of Ti above 885o
 Vandium,molybdenum and tantalum stabilize B form
at room temperature
 COMPOSITION
 Ti 78%
 Molybdenum 11.5%
 Zirconium 6%
 Tin 4.5%

34. Mechanical properties
 Yield strength and elastic modulus is intermediate
between S.S,Elgiloy and Ni Ti
 Better spring back than stainless steel and elgiloy
 Moldable(structure near to austenitic stainless steel)
 High weldability(only orthowire)
 Excellent corrosion resistance due to Ti Oxide

35. Wrought Nickel Titanium (Ni –Ti) or
Shape Memory Alloy.
 Also known as
Nitinol
 Composition
 Nickel Ni 55%
 Titanium 45%
 Small amounts of
copper cobalt and
chromium

36. Crystallograhic Phases of Niti
 Austenitic Ni Ti phase
 High temperature low stress form
 Complex ordered bcc structure
 Martensitic Ni Ti phase
 Low temperature high stress form
 Distorted monoclinic, triclinic or hexagonal structure.

37. Transformation of phase
 High temperature low stress form
Austenite high stress low ductility
high stress low temperature
Martensite low strength high ductility form

39. Temperature transition range
 Below TTR…………Martensitic form
 Above TTR………..Alloy returns to original shape
 Austenite

40. Shape memory effect
 Lowering the TTR to oral temperature creates shape
memory effect in Niti.
 Co added to reduce TTR
 Orthodontic wires exist as austenite at room
temperature
 Converts to Martensite on transition from TTR-Oral
temp

41. Super Elasticity
 Some amount of permanent deformation remains in
wire.
 Required because very low and nearly constant forces
provided by wires during unloading
 Austenite to Martensite transition induced by stress.

43. MECHANICAL PROPERTIES
 LESS ELASTIC MODULUS
 HIGH SPRING BACK
 HIGH RESILIENCE

44. LIMITATIONS OF NiTi
 Require special bending technique
 Brittle, cannot be soldered or welded
 Rough surface

45. Endodontic instruments
 Types include
Reamers and files
Spreaders
 Materials used
 Stainless steel
 Ni Ti

46. Requirements for Endo Materials
 Super elasticity
 Different values of stiffness and ductility required for
exploring canals and debridement.

47. ALLOY STIFFNESS/MOE SPRINGBACK DUCTILITY EASE OF
SOLDERING/
WELDING
Stainless
Steel
HIGH GOOD ADEQUATE REASONABLE
Gold
Alloy
MEDIUM ADEQUATE ADEQUATE EASY
Co/Cr HIGH ADEQUATE
AFTER HEAT
TREATMENT
VERY
GOOD—in
soft state
DIFFICULT
Ni/Ti LOW EXCELLENT POOR DIFFICULT
B-Ti MEDIUM GOOD ADEQUATE ONLY WELDING