What are Dental K and H File, Difference between K Files and H Files - A Complete Guide


Endodontic files are used in root canal treatment to remove infected pulp from the root canal and restore the structure and function of the damaged tooth. Every endodontic instrument used has its specific design and function. The same is applicable to K file and H file. Both these files have different function and hence it is clinically important to know the difference between K files and H files.

The different categories of endodontic instruments include diagnostic, extirpating, enlarging, obturating and other miscellaneous instruments.

Enlarging instruments are responsible for cleaning and shaping the pulp. K file and H file come under the category of basic enlarging instruments.

What are endodontics files?

Endodontic files are used to prepare the root canals mechanically. Each file has a specification which significantly impacts the cleaning of root canal. To be more precise, Endodontic files aid in cleaning of the canal and prepare it for obturation.

K files in endodontics:

K files, H files and K reamer are the basic intracanal instruments. These have been standard cutting instruments for years in Dentistry.

As mentioned above, these have a typical function and are manufactured to a specific size and type, which is advised by the ISO (International Standards Organization).

The history of K file is the oldest!

In the early 1900s, a company names “Kerr company”, (Kerr Manufacturing Co. of Romulus, Michigan), first produced K-type file and the K-type reamer. For this reason, these are called K-files.

 Classification of k files in endodontics:

  • As per Grossman classification, according to function, K-file is placed under the category of extirpating instruments.
  • Based on manufacturing, These were manufactured along their long axes, by counterclockwise twisting square or triangular metal blanks. This process produced horizontal cutting blades.

Material of K file:

Speaking historically, root canal instruments were initially manufactured from stainless steel. However, recently these are made up of NiTi. Dentsply manufactures NiTi Flex.

Role of K-files in dentistry:

  • K files can be used by two types of action. It could be either filing action or reaming action.
  • Filing action is the push-pull motion basically. Reaming action involves clockwise for insertion and rotation for withdrawal.
  • The main purpose of K file is to produce a smooth tactile sense during instrumentation inside the canal.
  • K files have purpose of penetration and enlargement of root canals in a reaming motion.

H files in endodontics:

K files and H files, both are the intra canal basic instruments. As previously mentioned, H files are standardised based on size, length, color coding, taper and the tip angle.

Classification of H files:

  • According to method of use, they are Group 1 manually operated instruments.
  • According to manufacturing process, they come under the category of machine grinding.

 H file cross-section:

H file stands for Hedstrom files. H file cross section is tear shaped or coma shaped with one cutting edge. These are used in filing action only.

H file manufacturing:

These files are milled from round, stainless steel blanks.

H file purpose in endodontics:

For translational strokes, H files are considered the most efficient. This is primarily due to the reason that they have positive rake angle and their blade has a cutting angle.

Special caution in H file: Know why it is important to remember these words of caution

H files have chances of fracture when working movements are rotational so such type of movement is strongly discouraged when H files are used.

One of the most important points to remember is the instrument failure and it must be avoided. Since the edges of H file are sharp, so it could bend to string into the canal during rotation so the awareness of threading in forces is vital here so that the instrument failure could be avoided.

H files result in greater stress concentration, so there are chances of crack propagation and fatigue failure.

Transportation refers to loss of excessive dentin from the curved canal's outer wall in the apical segment. H file rotation causes less transportation when compared to the filing motion.

Stainless steel files vs. NiTi files

K file and H file both can be made up of two types of materials, stainless steel and NiTi files. One of the major fact to be indicated here is, stainless steel files are not elastic, so they are not suitable for curved canals, though these have strong cutting force, but there are high chances of breakage as their breaking resistance is low.

Comparatively, NiTi files are very elastic, and they are very good option for use in curved root canals. They are safer. But their cutting force is weak, and their efficiency is somewhat poor compared to stainless steel files.

Difference between K and H file:

The table given below mention some of the important points of difference between K files and H files.

K files

         H files

Clean and enlarge the canal.

Shape the canal.

Meant for rotary motion.

Meant for vertical movement.

Less stress concentration.

Greater stress concentration.

Less sharp edges

More sharp edges

The cross-section is square.

The cross-section is circular.

Has moderate cutting force.

Has strong cutting force.

The angle is 25-40 degree between the cutting groove and the long axis of K file.


The angle is 60-65 degree.

Less efficiency.

More efficiency.

Causes less damage to the root canal

Causes more damage to the root canal.

Takeaway points:

  • A proper knowledge of instrumentation is very important to achieve success in dental treatments.
  • The selection of the file is directly related to the speed and efficiency of the dental treatment.
  • While selecting a file, both working and material characteristics must be considered.
  • Difference between K files and H files is important to choose the best for the procedure.
  • The design of endodontic files is very important because it decides two important questions, “How much debridement could be facilitated?” and “What structural damage did occur to the tooth, while it should be minimum?”

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