Endodontic Instruments Overview

Endodontic Instruments

• Endodontic instruments are categorized by the International Organization for Standardization (ISO) and the American National Standards Institute (ANSI).
• These organizations set standards for terminology, dimensions, physical properties, measuring systems, and quality control for endodontic instruments and materials.
• Instruments are classified as either hand instruments or rotary instruments.

Hand Instruments - General Information

• Hand instruments are grouped by usage according to ISO standards.
• A standard hand file consists of a working area of 16 mm, a handle, a shank, and a rubber stop.
• The handle is numbered and colored according to the file's size.
• The shank is 16mm long with blades.
• The rubber stop is used for length determination.
• Files are used for measuring the length and cleaning, widening, and shaping canals.
• Files create space for root filling materials.
• Hand instruments are made from stainless steel or nickel-titanium.

Types of Hand Instruments

• K-type file: A ground–twisted instrument with a file that is twisted counter-clockwise.
• Hedstroem file: A machined instrument, ground on a lathe.
• Reamer: A ground–twisted instrument with a file that is twisted counter-clockwise.

ISO Standard Instrument Design

• ISO defines the size of a file by its diameter at the tip, measured in one-hundredths of a millimetre.
• ISO standard files have a 2% taper over their working length.
• Example: A #10 file has a tip diameter of 0.10 mm.
• Color Coding:
  • Pink = 06
  • Grey = 08
  • Purple = 10
  • White = 15
  • Yellow = 20
  • Red = 25
  • Blue = 30
  • Green = 35
  • Black = 40

Standardization History

• Standardization of endodontic instruments began in the 1950s due to variations in instruments from different manufacturers.
• Standardization covered the diameter and taper of each instrument, the graduated increase in size from one instrument to the next, and a numbering system based on the diameter of the instrument.

D0 and D16

• D0: The diameter of the projection of the working part at the tip end of the instrument.
• D16: Represents a point 16 mm from D0, where the cutting part of the instrument ends. D16 is 0.32 mm larger than D0.
• The taper for standardized instruments is a constant 0.02 mm per 1mm of cutting flute.
• The length of instruments ranges from 21mm to 31mm, with 25mm being the most commonly used.

Materials for Root Canal Instruments

• Carbon Steel: No longer used due to its tendency to corrode.
• Stainless Steel: More resistant to corrosion but has limited flexibility.
• Nickel Titanium: More flexible, adaptable to canal curves (3 times as flexible as stainless steel), and has a very low modulus of elasticity.

Manufacturing Techniques for Hand Instruments

• Machined Instruments: Created by grinding the instrument on a lathe (e.g., Hedstrom-type files).
• Ground–Twisted Instruments: Made by grinding raw wire and then twisting it counter-clockwise (e.g., K-type files and reamers).

Barbed Broaches

• Barbed broaches are made from soft steel wire.
• Barbs are created by cutting into the metal and forcing the cut portion away from the shaft.
• The tips of the barbs point towards the handle.
• The cuts are made eccentrically around the shaft.