Terminology of Instruments:
AISI:
AISI (American Iron and Steel Institute) employs a numbering system to identify various steel formulations used in surgical instrumentation. Different materials, such as AISI 304, AISI 316L, AISI 410/410X, AISI 420A, AISI 420B, and AISI 440C, are assigned AISI numbers.
ASTM:
ASTM (American Society of Testing and Materials) establishes standards and specifications for a range of materials, both metallic and non-metallic. Some materials are assigned AISI numbers, while others have ASTM numbers.
Austenitic:
Austenitic refers to non-hardenable, non-magnetic Series 300 Stainless Steels. These alloys possess a low carbon content (around 0.08%) and cannot be heat hardened. However, they can be “work hardened” through machining or forming. Their high chromium (18%) and nickel (8%) content makes them highly corrosion resistant and gives them a brilliant shine. This series is often referred to as “18-8 stainless.”
STAINLESS STEEL TYPE AISI 316L:
AISI 316L is a high-purity alloy denoted by ‘L’ for low carbon. Also known as SMO, it’s a favored material for orthopedic implants such as plates, screws, nails, staples, and prostheses. Instruments with prolonged contact with implants also use this material to prevent galvanic corrosion reactions on implants. However, it’s important to note that metal implants may eventually fail, as no metal matches the enduring durability of living bone.
STAINLESS STEEL TYPE AISI 410:
AISI 410 belongs to the Martensitic Series 400 Stainless Steel alloys, which are magnetic and heat hardenable. With higher carbon and lower chromium percentages, they possess specific properties. These alloys are vital when strength and temper are required. Used in most O.R quality instruments, they exhibit high tensile strength, extended edge retention, and corrosion resistance. Proper care is essential to prevent corrosion due to the absence of nickel.
STAINLESS STEEL TYPE AISI 420 & 440:
AISI 420 and 440 are valuable grades for cutting instruments like scissors, knives, bone cutters, drills, and taps. AISI 420 can achieve Rockwell Hardness around C-48 to C-50, while AISI 440, with more carbon, attains C-55 hardness.
TUNGSTEN CARBIDE:
Tungsten Carbide, particularly Grade GC20, is an exceptionally hard material, comparable to diamond. It is used as inserts in high-wearing instruments like needle holders, scissors, and wire cutters. Instruments are often gold-plated for recognition.
INTERNATIONAL STANDARDS:
Standards such as BS 5194, DIN 58298, and ISO 7153-1 provide guidelines for instrument materials.
STERLING SILVER:
Sterling Silver, with 92.5% silver content, is used for specific instruments like trachea tubes and hemostatic clips. It may tarnish, but polishing restores its shine.
GERMAN SILVER:
An alloy of silver and nickel, German Silver serves as a durable and less expensive alternative to Sterling Silver. It retains its color after autoclaving.
ALUMINUM:
Aluminum, with excellent heat dissipation and lightweight properties, is used for sterilization and storage containers. It requires protective hard anodizing.
BRASS AND COPPER:
Free cutting brass and nickel-copper alloys are used for instruments requiring malleability. They are usually plated to enhance surface wear.
NON-METAL MATERIALS:
Materials like Rubber, Plastic, Silicon, and Tufnol find applications in both reusable and disposable instruments due to their diverse characteristics.
PLATING:
Plating protects carbon steel and non-ferrous metal instruments from staining or discoloration. Different plating types are used based on instrument requirements.
NICKLE PLATING:
Nickel adheres well to carbon steel, providing protection against moisture-induced corrosion.
SILVER PLATING:
Copper or brass instruments can be silver plated by electrodeposition. The layer of silver plating is thin and doesn’t crack when instruments are bent.
CHROME PLATING:
Chrome plating on base metals like carbon steel, copper, and brass offers corrosion protection.
BLACK CHROME PLATING:
Black chrome plating enhances visibility under microscopes. It’s achieved by safer methods than before due to toxicity concerns.