Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 1.

The aim of this study was to determine the shaping ability of Lightspeed nickel-titanium rotary instruments in simulated canals. Forty canals consisting of four different shapes in terms of angle and position of curvature were prepared by Lightspeed instruments using the technique recommended by the manufacturer. This report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length, and three-dimensional canal form. Overall, the mean preparation time for all canals was 8.12 min with canal shape having no significant effect on the speed of preparation. No instruments deformed or separated during the study, and none of the canals became blocked with debris. Seventeen canals retained their original working length, but 16 gained in length and 7 lost length. There was no significant difference between the canal shapes in terms of the mean loss of distance or category of distance change. Apical stops as judged from intracanal impressions were present in 23 of the canals but they were all judged to be of poor quality. The canals were found to be smooth in the apical half of the canal in 36 specimens and in the coronal half of 24 specimens. All the canals had poor taper characteristics, and only 16 specimens showed good flow characteristics. Under the conditions of this study, Lightspeed instruments prepared canals rapidly, with no fractures, canal blockages, and with minimal change in working length. The three dimensional form of the canals was compromised as flow and taper were less than ideal, presumably as a result of an ineffective stepback procedure. The results imply that either the stepback sequence should be modified or another instrument with increased taper should be used to refine the canal walls before obturation.