Method for controlling an endodontic instrument, wherein an endodontic file (11) mounted on an assembly micromotor (8)-contra angle (9) is rotated in a first direction (working angle, δ) and successively in the opposed direction (unloading angle, η) with an alternated movement.According to the invention the working angle in said first direction gets smaller when a predetermined torque value is reached, originated by the engagement of said file (11) in a root canal (2), and the working angle in the first direction goes back to its original width when the torque value generated by the engagement of said endodontic file (11) in root canal (2) goes under a pre-determined value.System comprising a micromotor (8) and a contra angle (9) and an endodontic file (11) mounted in the said assembly of micromotor and contra angle- a control unit of the micromotor for causing an alternated movement of an endodontic file (11) in which the file (11) is rotated in a first direction (working angle, δ) and successively in the opposed direction (unloading angle, η) with an alternated movement- means measuring the torque value originated by the engagement of the file (11) in a root canal (2) being connected to the control unit, the control unit controlling the rotation of the motor such that the working angle in said first direction gets smaller when a predetermined torque value is reached, originated by the engagement of said file (11) in a root canal (2), while the working angle in the first direction goes back to its original width when the torque value generated by the engagement of said endodontic file (11) in root canal (2) goes under a pre-determined value.
