A Computer-Assisted Approach to Assess the Precision of the Reciprocating Angles and the Rotation Speeds of Endodontic Motors  
[PERSON]  
1 Department of Health, State University of Feira de Santana, Feira de Santana 44036-900, Brazil;  
[EMAIL_ADDRESS] (E.A.R. ); [EMAIL_ADDRESS] (F.J.); [EMAIL_ADDRESS] (L.T.B.L.D.) [PERSON]  
2 INEG, Faculty of Engineering, University of Porto,  
considerable risk of endodontic file fractures, mainly during its use in curved canals [4; 5; 6]. In 2008, a new kinematic for the use of NiTi instruments in an asymmetric oscillatory movement--the so-called reciprocating movement, which was proposed as a potential alternative to the conventional continuous rotation pattern [7], aiming to facilitate the root canal shaping procedure while reducing the instrument fatigue [8; 9]. With movements alternately happening in both directions, in a well-defined forward/backward movement cycle, the performance of the intended endodontic procedures could be significantly improved, while enlarging the average lifetime of the employed files. Originally, reciprocating movement was described with 144\({}^{\circ}\) clockwise (CW) and 72\({}^{\circ}\) counter-clockwise (CCW) rotation angles at a rotational speed of 400 RPM (rotations per minutes), driven by an electric motor [7]; however, new configurations were later defined. Based on the same reciprocating movement concept, two commercial systems were launched in the market: the Reciproc and the WaveOne [10]. Both systems were developed to be used in their specific reciprocating modes, which were RECIPROC ALL (150\({}^{\circ}\) CCW and 30\({}^{\circ}\) CW at 300 RPM) and WAVEONE ALL (170\({}^{\circ}\) CCW and 50\({}^{\circ}\) CW at 350 RPM), driven by a specific contra-angle handpiece attached to an electric motor, such as the Reciproc Silver (VDW) or the X-Smart Plus (Dentsply Sirona). Due to the largely recognized benefits of the reciprocating movement over continuous rotation [5; 8; 11], the open motor concept was fostered to allow the production of different motors by any manufacturer, clearly indicating the ever-increasing popularity of reciprocating movement for endodontic procedures. In this sense, such motors could be configured to operate following different movements patterns by setting clockwise and counter-clockwise angles, torque and speed, since the overall reciprocating movement principle was preserved; however, these configuration parameters have not been clearly disclosed by their manufacturers and there is no evidence that the indicated set up is a reliable choice, because actual kinematic parameters can be different than the assumed operation values. Considering that instrument kinematics have a direct impact on cyclic fatigue resistance of NiTi instruments and root canal shaping outcomes [12; 13; 14], the precision and accuracy of the reciprocating kinematics may be of clinical importance. For that, some mechanisms should be employed to evaluate the movement patterns of the instruments, allowing the assessment of the performed movements according to the information provided by the suppliers. In fact, since a particular file may be fabricated to operate under a certain expected reciprocating movement pattern and speed, knowing the actual operation characteristics of a motor may be relevant when deciding which files to use. Additionally, due to the risk that broken files may have to endodontic procedures, avoiding undesired file fatigue resulted from the adoption of inadequate reciprocating motors is an expected benefit of the proposed assessment approach. Broadly speaking, the movement nature of reciprocating motors makes them hard to be evaluated by the naked eye. In this sense, computer-assisted methods to evaluate \"quality\" parameters, such as movement angles and RPM, could be exploited to allow the desired assessment with a certain level of precision. Among the possibilities for that, image processing presents itself as an affordable and effective approach to provide an account of the movement of the motors over time.