Objective To investigate the safe frequency of using rotary NITI file in root canal treatment, and to clarify the importance of dental nurses to record the frequency of using NITI file in root canal treatment. Methods PorTaper and FlexMaster were used for root canal preparation of 200 isolated teeth. Results NITI files of both ProIaper and FlexMaster systems broke after at least 14 and at most 20 uses. Different NITI files have a 95% chance of breaking under normal conditions after 15-18 uses. Conclusion Each NITI file should be used no more than 14 times under normal conditions.
A good root canal file needs to be in the hands of a professional dentist to play the best effect. In the dental clinic, dentists are most worried about two problems. The first is the different root canal morphology; The second is root canal files from different manufacturers. It is the existence of these two problems that is most concerned about the separation and fracture of instruments found during root canal treatment. Here we will explain these two problems in detail.

First, root canal morphology
Tooth root canal morphology can be divided into single tooth, double tooth and multiple tooth.
Root canals can be divided into straight canals (root canal curvature ≦15 degrees), curved canals (15 degrees ≦ root canal curvature ≧30 degrees), and complex curved canals (root canal curvature ≧30 degrees).

Second, root canal file
At present, the root canal files used in clinical root canal treatment are divided into stainless steel and NITI, and most of the mechanical root canal files are made of NITI. The rotation mode of the instrument is divided into clockwise rotation and round-trip rotation; The cross section of the instrument is divided into convex triangle, square, triangle, eccentric rectangle, S shape, parallelogram and so on.

NITI root canal files are divided into: natural file, gold reinforced file, heat activated blue file.
Cutting force of file: natural file > Gold reinforced file > Blue heat activated file.
File softness: natural file < Gold reinforced file < Blue heat activated file.
File resistance: natural file < Gold reinforced file < Blue heat activated file.
In summary, the safe number of root canal files during root canal treatment can be roughly divided into:
Natural file: 14 times recommended for simple straight through root canal treatment; It is recommended to use it 8 times for general root canal treatment. It is recommended to be used once for complicated and difficult root canal treatment.
Gold reinforced file: 16-25 times recommended for simple straight-through root canal treatment; Generally, it is recommended to use 8-16 times for curved root canal treatment; It is recommended to be used once for complicated and difficult root canal treatment.
Blue heat activated file: 14-20 times recommended for simple straight-through root canal treatment; Generally, it is recommended to use 8-12 times for curved root canal treatment; It is recommended to be used once for complicated and difficult root canal treatment.

A good tool also requires a standardized operating process, and the following points also play a crucial role in the safe use of root canal files：
1: Before the preparation of the root canal, it is necessary to ensure that a standardized linear channel of the pulp cavity is established to ensure that the root  canal file reaches the root tip or the first bend in a straight line.
2: the tooth crown is fully pre-opened to ensure that the lubricant enters one third of the root tip smoothly with the file and maintains a good feel.
3: Always keep the instrument lubricated, especially at one third of the root tip. EDTA lubricant is recommended.
4: Short lift to ensure that the instrument does not stay too long at a certain point in the root canal.
5: The instrument should not reach the working length at one time, and it should be fully washed once every 4 mm or so.
6: Ensure that each instrument can form a smooth, repeatable access channel when prepared to ensure that subsequent instruments smoothly "glide" forward.
7: Please choose the corresponding speed and torque according to the file of different models.
8: Root canal file deformation and thread separation, please stop using and discard immediately.
9: Please choose a regular qualified manufacturer of root canal filing equipment.

Zogear Dental file recommend for you：

K File : www.zogear.com/product/158.html

H File: https://www.zogear.com/product/552.html

Blue Protaper File: https://www.zogear.com/product/549.html

Gold Protaper File: https://www.zogear.com/product/548.html