Endodontic files and reamers carry a size number, a handle colour and often a taper value such as .02, .04 or .06. These markings follow an international numbering system, mainly set out in ISO 3630-1. This glossary explains what each number and colour means, so any file label can be read the same way.
Where the system comes from
Before the 1950s, root canal instruments were numbered by each manufacturer in its own way. A "number 3" from one company could differ in width, taper and flute length from a "number 3" from another. John Ingle described the need for standardisation in 1955 and presented a standardised system in 1958. In 1976 the American Dental Association approved Specification No. 28 for Type K files and reamers, and its final revision was published in 1981. Today the international reference is ISO 3630-1 (Dentistry — Endodontic instruments — Part 1: General requirements), whose current edition was published in 2019.
Parts of an endodontic instrument
ISO 3630-1 uses a fixed vocabulary for the parts of an instrument:
- Tip: the point of the instrument. Its shape is left to the manufacturer, within a tip angle of 30° to 90°.
- Working part: the section that has a cutting surface (the flutes).
- Shaft: the part between the handle or shank and the working part.
- Handle: the part held by the fingers on a hand instrument.
- Shank: the part of a rotary, oscillating or reciprocating instrument that fits into the chuck of a handpiece.
Size number: the tip diameter
D and dn
The standard uses D for the diameter at the tip and dn for the diameter at n millimetres from the tip. For example, d3 is the diameter 3 mm from the tip and d16 is the diameter 16 mm from the tip. Older textbooks often write these points as D0 and D16.
Reading the size number
The nominal size is the tip diameter in hundredths of a millimetre. A size 25 instrument has a tip diameter of 0.25 mm. A size 10 has a tip of 0.10 mm, and a size 100 has a tip of 1.00 mm.
Size steps
ISO 3630-1 lists standard sizes 6, 8 and 10, then 15 to 60 in steps of 5, then 70 to 140 in steps of 10. Tip sizes outside this list are permitted, but they are not part of the standard table.
Tolerance
Each diameter has a tolerance in the standard table. It is ±0.02 mm for the smaller sizes and ±0.04 mm for the larger sizes. The specified lengths of the working part and the operative part must be within ±0.5 mm.
Taper
What taper means
Taper is how much the diameter grows for each millimetre along the working part, moving away from the tip. It is written in millimetres per millimetre (mm/mm).
The standard .02 taper
A standard instrument in ISO 3630-1 has a uniform taper of 0.02 mm per millimetre. Manufacturers may write this as a two-digit number, "02", or as a percentage, "2%". Over a 16 mm working part, a .02 taper adds 0.32 mm to the diameter. That is why, in the standard table, a size 25 has d16 = 0.57 mm (0.25 + 0.32).
Greater tapers
Instruments with a uniform taper other than .02 are called taper instruments. A label such as 25/.06 means a tip size of 25 (0.25 mm) and a taper of 0.06 mm/mm (6%). Using the same arithmetic, its diameter 16 mm from the tip would be 0.25 + (16 × 0.06) = 1.21 mm.
ISO classification by taper
- Type 1, standard instrument: uniform taper of .02.
- Type 2, taper instrument: uniform taper other than .02.
- Type 3, non-taper instrument: zero taper (cylindrical).
- Type 4, non-uniform taper instrument: more than one taper along the working part.
- Type 5, shape instrument: a contoured working part with a continuously varying profile.
ISO colour codes
For standard (Type 1) instruments, ISO 3630-1 assigns a colour to the handle or shank of each size. Sizes 6, 8 and 10 have their own colours. From size 15 onward, six colours repeat in a fixed order from light to dark: white, yellow, red, blue, green, black.
- Size 6: pink
- Size 8: grey
- Size 10: purple
- White: sizes 15, 45, 90
- Yellow: sizes 20, 50, 100
- Red: sizes 25, 55, 110
- Blue: sizes 30, 60, 120
- Green: sizes 35, 70, 130
- Black: sizes 40, 80, 140
Colours for sizes not in the standard table are at the manufacturer's discretion. The standard also describes the same light-to-dark sequence for brands that colour-code a set of different tapers. Many instruments carry a coloured ring in addition to, or instead of, a coloured handle.
Lengths
The working part of a standard instrument must be at least 16 mm long unless the manufacturer specifies otherwise. Ingle's original system set overall instrument lengths of 21, 25 and 31 mm, and these lengths remain common. The overall and working lengths are stated by the manufacturer.
Key terms
- Nominal size: tip diameter in hundredths of a millimetre.
- D / dn: diameter at the tip / at n mm from the tip.
- Taper: increase in diameter per millimetre of length (mm/mm or %).
- .02 taper: the ISO standard taper, also written 02 or 2%.
- Working part: the fluted, cutting section, at least 16 mm on a standard instrument.
- Shank: the end that fits a handpiece chuck on an engine-driven instrument.
- Colour designation: the ISO handle or shank colour linked to each size.
FAQ
What does "25/.04" mean on a file?
The first number is the tip size: 25 means a tip diameter of 0.25 mm. The second number is the taper: .04 means the diameter increases by 0.04 mm for every millimetre along the working part.
Why do size 15 and size 45 have the same colour?
From size 15 onward, the ISO colour sequence uses six colours (white, yellow, red, blue, green, black) and repeats them. Size 15 starts the first cycle in white, and size 45 starts the second.
Does the colour show the taper?
In the standard table, the colour shows the tip size of a .02 taper instrument. Some brands also colour-code their tapers, using the same light-to-dark order, so always read the printed size and taper on the label.
Is the tip diameter the same as the size number?
Yes, with a change of unit. The size number is the tip diameter multiplied by 100, so a tip of 0.40 mm is size 40.
Sources
- ISO 3630-1:2019. Dentistry — Endodontic instruments — Part 1: General requirements. International Organization for Standardization. iso.org/standard/75260.html
- ANSI/ADA Specification No. 28 (2008). Root Canal Files and Reamers, Type K. American Dental Association.
- Ingle JI. The need for endodontic instrument standardization. Oral Surg Oral Med Oral Pathol. 1955. doi:10.1016/0030-4220(55)90385-6
This article is general educational information about terminology and is not clinical advice.