System comprising a micromotor and a contra angle comprising an endodontic file mounted in said assembly of micromotor and contra angle; - a control unit of the micromotor for causing an alternated movement of an endodontic file in which the file is rotated in a first direction for a certain working angle(δ) and successively in the opposed direction for a certain unloading angle (η) with an alternated movement; - means measuring the torque value originated by the engagement of the file in a root canal being connected to the control unit, the control unit controlling the rotation of the motor such that the working angle in said first direction is decreased when a predetermined torque value, originated by the engagement of said file in a root canal , is reached, wherein 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 in root canal goes under the pre-determined value and characterized in that the reduction of the working angle is carried out stepwise and a counter is provided counting the step of reduction of the working angle (δ) in said first direction, and in that a threshold number of maximum steps of reductions of the said working angle is set in the control unit and in that when the number of said steps of reduction of the angle of rotation in said first direction exceeds the threshold, the control unit is configured to: - reverse the direction of rotation of the motor and the file and the motor and the file being rotated continuously in the said opposed direction or - stop the rotation of the file or of the motor. - a control unit of the micromotor for causing an alternated movement of an endodontic file in which the file is rotated in a first direction for a certain working angle(δ) and successively in the opposed direction for a certain unloading angle (η) with an alternated movement; - means measuring the torque value originated by the engagement of the file in a root canal being connected to the control unit, the control unit controlling the rotation of the motor such that the working angle in said first direction is decreased when a predetermined torque value, originated by the engagement of said file in a root canal , is reached, wherein 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 in root canal goes under the pre-determined value and characterized in that the reduction of the working angle is carried out stepwise and a counter is provided counting the step of reduction of the working angle (δ) in said first direction, and in that a threshold number of maximum steps of reductions of the said working angle is set in the control unit and in that when the number of said steps of reduction of the angle of rotation in said first direction exceeds the threshold, the control unit is configured to: - reverse the direction of rotation of the motor and the file and the motor and the file being rotated continuously in the said opposed direction or - stop the rotation of the file or of the motor. - reverse the direction of rotation of the motor and the file and the motor and the file being rotated continuously in the said opposed direction or - stop the rotation of the file or of the motor. <EOS>