Stainless Steels in Dentistry and Orthodontics

Stainless Steel In Dentistry

Write in brief on stainless steel.
Answer:

Steel is an iron-based alloy that consists of less than 1.2% carbon. When 12 to 25% of chromium is added to steel the alloy is known as stainless steel.

Types of Stainless Steel:

Based on the different crystalloid configurations of structure, stainless steel is of three types, i.e.

1. Ferritic
2. Martensitic
3. Austenitic

1. Ferritic of  Stainless Steel:
   • Pure iron at room temperature has a body-centered cubic (BCC) structure and is referred to as ferrite which is stable up to 912°C.
   • Ferric alloys have good corrosion resistance, but less strength and hardness. So they fid little application in dentistry.
2. Martensitic Stainless Steel
   • When austenite (face-centered cubic structure) is cooled very rapidly (quenched), it will undergo a spontaneous, diffusionless transformation to a body—centered tetragonal (BCT) structure called martensite.
   • This is a highly distorted and strained lattice that results in a very hard and strong but brittle alloy.
   • The corrosion resistance of the martensitic stainless steel is less than that of the other types.
   • Because of their high strength and hardness, martensitic stainless steels are used for surgical and cutting instruments. Bur shanks are also made from this steel.
   • Advantages of  Stainless Steel:
     • Its heat treatment can be done.
     • Due to its high strength and hardness, it is used for making surgical as well as cutting instruments, bur shanks, and orthodontic pliers.
   • Disadvantages of  Stainless Steel:
     • Bitterness is very high owing to distorted and strained lattice structure.
     • It has less corrosion resistance as compared to other types.
3. Austenite  Stainless Steel:
   
   • 18-8 stainless steel was introduced by Dr. WH Hatfield in 1924. At temperatures between 912°C and 1394°C the stable form of iron is a FCC structure called austenite.
   • Austenitic stainless steel alloys are the most corrosion-resistant of stainless steel.
   • This alloy is also called 18-8 stainless steel based on the percentage of nickel and chromium in its composition.
   • Uses: These are used most commonly in orthodontic and pedodontics in the form of bands and wires.

Composition of  Austenite Stainless Steel:

Advantages of Austenite  Stainless Steel:

• It withstands the occlusal forces because of its high stiffness.
• It has high ductility and malleability, so it is easily drawn into wires or hammered into stainless steel sheets.
• Cold working can be done easily with 18-8 stainless steel without the risk of fracture. This increases the strength of the metal.
• The formability of 18-8 stainless steel is good. Due to this many small stainless steel wires are twisted or braided together to form muti stranded arch wires.
• Due to corrosion resistant it is stable in an oral environment.
• It resists distortion so tipping and torquing can easily be done by brackets.
• The presence of smooth surface stainless steel brackets leads to less friction which makes orthodontic treatment faster and more comfortable.
• 18-8 stainless steel is biocompatible
• 18-8 stainless steel is economical.

Disadvantages of  Austenite Stainless Steel:

• It has a low spring back as compared to nickel–titanium alloys which make it a poor initial alignment archwire.
• Due to its high stiffness more frequent activations are required.
• It can lead to discomfort to the patient as it delivers more force compared to the wires made of other alloys of the same diameter.
• In this soldering is needed, if the temperature becomes more than 500°C the corrosion resistance of the alloy is decreased.

Uses of  Austenite Stainless steel:

Various stainless steel alloys are used for manufacturing:

• Bracket and buccal tubes
• Archwires
• Bands
• Ligature wires
• Attchments
• Springs
• Microimplants
• Wires for removable appliances
• For manufacturing orthodontic instruments and pliers.