WROGHT DENTAL ALLOYS

Methods of shaping of metals

Dr.Reem Gamal

Wrought metal Cast metal

Fibrous structure Poly crystalline grain Microstructural

low high ductility

high low strength

high low hardness

low high Corrosion resistance

Annealing Need annealing to relief internal stress

Cold work Need homogenization to relief cored structure

Conversion

Applications in Dentistry:

Dr.Reem Gamal

The most commonly alloys used include:

• Stainless steel

• Cobalt chromium

• Nickel chromium

• Nickel Titanium

• Β Titanium

• gold alloys (rarely used economic reasons)

Dr.Reem Gamal

Stainless steel alloys

• Steel = interstitial solid solution of a metal (iron)

and non metal (carbon)

• stainless = chromium (13-28%)

• Stainless steel alloys are sub-classified according to

the concentration of chromium, nickel, carbon and

iron to:

-Ferritic,

-martensitic

-austentic stainless steel.

Dr.Reem Gamal

Ferritic stainless steel (B.C.C)

• Cr=15-25%

• Carbon silicon molybdenum

• Used in narrow limit for Instrument manufacture

Dr.Reem Gamal

Martensitic (B.C.T)

• Cr=12-18%

• Instrument manufacture and Orthodontic appliances with limitation

Dr.Reem Gamal

The austenitic 18/8 (F.C.C) • the most popular for dental appliances

• Carbon(0.08-0.2%) iron72%

• 18% chromium passive layer

• 8 % nickel -strengthening the alloy by

formation of Cr-Ni solid solution

-stabilize the austenitic F.C.C

at room T against martensitic B.C.C

transformation on cooling

• Titanium, tantalum, niobium -stabilizers.

• Silicon, manganese -deoxidizer

-improve the castability

• Molybdenum -improve the strength

Dr.Reem Gamal

Manufacture and supply • Wire formed from casted St-St

• Supplied in 3 grades according to degree of cold

working

soft,

half hard ,

hard

Dr.Reem Gamal

Properties Mechanical properties

• Depend on degree of cold working highest Y.S=1500

Mpa E=134GPa

• lowest value of spring back action( energy stored by

the wire (resilience)) comparing to other type of wire

• highest sprig rate (measure of the wire ability to move

the tooth)

Dr.Reem Gamal

Heat treatment • Wrought wire structure should be annealed

• 450- 500C for 5 to 120s to remove stress

• Usually (450C-60s) prolonged or over heating lead to sensitization

• Above 500C weld decay (sensitization) will occur Cr & C diffuse to grain boundaries forming Chromium carbides lead to

1-brittleness why?

2- reduction of corrosion resistance why?

Desensitization :- incorporation of stabilizing agents as titanium which react with the C maintaining the Cr in its site

Dr.Reem Gamal

• Tarnish and corrosion resistance adequate why?

• Joining by spot welding or low fusion (silver) soldering

why?

Dr.Reem Gamal

Dr.Reem Gamal

THANK YOU