Kinematics of a novel reciprocating endodontic handpiece

To analyse the kinematics of the Reciproc Direct^® contra-angle reciprocating device with different motor sources.

Reciproc Direct contra-angle (VDW GmbH, Munich, Germany) was tested with new micro-motor sources. The micro-motor groups were as follows: a brushless electric micro-motor, a brushed electric micro-motor and an air-driven micro-motor. The electric micro-motor sources were also divided into four subgroups as 10 000, 15 000, 20 000 and 25 000 rpm. The maximum air pressure of the air-driven micro-motor was adjusted to 2 and 3 kgf cm^-2 . A custom target object was attached to the Reciproc Direct, and reciprocating motions were recorded with a high-speed camera at 1200 frames per second. The following kinematic parameters were calculated: duration of each reciprocating motion, engaging and disengaging angles, cycle rotational speeds, engaging and disengaging rotational speeds, net cycle angle, total cycle angle and number of cycles to complete full rotation. One-way anova was used where applicable, followed by Tukey's multiple comparison tests, to compare the kinematic values of reciprocating motion for each micro-motor/Reciproc Direct combination. The Kruskal-Wallis test followed by Dunn's multiple comparison test was used for non-normally distributed data. Statistical analysis was performed (α = 0.05).

For the brushless micro-motor, median engaging angle was 186.5 ° at 10 000 rpm and 188.0 ° at 15 000 rpm which were significantly different than median engaging angles at 20 000 (188.5 °) and 25 000 (189.3 °) rpm (P < 0.05). For the brushless micro-motor, median cycle rotational speed was 372.5 rpm at 10 000 and 459.8 rpm at 15 000 rpm which were significantly different than median cycle rotational speed at 20 000 (576.2 rpm) and 25 000 (677.8 rpm) rpm (P < 0.05). For the brushed micro-motor, median cycle rotational speed was 293.5 rpm at 10 000 and 386.3 rpm at 15 000 rpm which were significantly different than median cycle rotational speed at 20 000 (508.9 rpm) and 25 000 (597.6 rpm) rpm (P < 0.05).

Rotational speeds were influenced significantly by motor sources even when the Reciproc Direct was used at speeds recommended by the manufacturer. This could indicate that the kinematics of the Reciproc Direct are dependent on the power of the rotating motor.