A comparative study of root canal preparation using ProFile .04 and Lightspeed rotary Ni–Ti instruments

Working safety.
High numbers of instrument fractures have been reported for Ni–Ti files in several earlier studies (Barthel et al . 1998, Kavanagh & Lumley 1998, Schäfer & Fritzenschaft 1999, Baumann & Roth 1999), indicating that Ni–Ti instruments may be more susceptible to separation than conventional stainless steel instruments. In the study of Barthel et al . (1998) four fractures occurred during the preparation of 10 root canals with curvatures of more than 35 . Schäfer & Fritzenschaft (1999) had nine fractures in 24 simulated root canals with a 35 curvature. Baumann & Roth (1999) reported that the incidence of fractures of Profile .04 increased with increasing size of the files with most fractures occurring with size 30 and 35 files. Thompson & Dummer (1998a) reported on three fractures and three deformed instruments after preparation of 40 simulated root canals to size 35.
Knowles et al . (1996) could complete enlargement of 20 root canals with Lightspeed to size 50 and Short et al . (1997) completed 15 curved canals to size 40 without fractures. Tharuni et al . (1996) reported on one fracture during preparation of 12 simulated curved canals. In the evaluation of Thompson & Dummer (1997c) Lightspeed proved to be a safe system without any fracture or apical blockage but some cases of loss of working length, which in no case exceeded 1 mm. In a survey amongst Swiss clinicians 76% of the respondents had fractured an instrument at least once. The main reasons for such fractures were non-constant speed of rotation, excessively high rotational speed, overuse of instruments, and too much pressure (Barbakow & Lutz 1997). As advocated by Gambarini (2000), the use of a newly developed low-torque endodontic motor with constant speed for Ni–Ti preparation with individually adjusted torque levels for each file of any Ni–Ti system instead of a hightorque motor might help to reduce the risk of instrument separation. Further studies could show that the frequency of instrument fractures may be related to the operator’s experience with a certain system (Glosson et al . 1995, Pruett et al . 1997, Barbakow & Lutz 1997, Baumann & Roth 1999).
The results of the present study are in general agreement with the results of the studies performed by Thompson & Dummer (1997a,b,c,d) in simulated root canals with different types of curvature. They described a very low incidence of procedural errors such as fractures, apical blockages, elbows, zips, or loss of working length for Lightspeed, as well as for Profile .04.

Working time.
The finding that ProFile instrumentation took significantly less time than Lightspeed preparation, to a large extent, will be due to the fact that the number of instruments for both systems differs (Lightspeed: 20, ProFile: 10). Following the protocol of this study the number of irrigations for ProFile was 10, for Lightspeed 12. Clinically, the difference will be even more evident as time for instrument changes and adjustment of the stopper systems has to be added. On the other hand, the preparation time for each single instrument was shorter for Lightspeed, due to the reduced contact zone between instrument and root canal wall. Conversely, Thompson & Dummer (1997a,b,c,d), in their studies on simulated root canals with different kinds of curvatures, could find nearly equal preparation times for Lightspeed and Profile .04, but when using Profile .04 with ISO-sized tips the working time was shortened substantially (Bryant et al . 1998a). These differences might be explained by the fact that the time an operator keeps the instrument working inside the root canal and the speed for the up and down movement of the files is not clearly defined and will vary individually. The total time for preparation for both systems was clearly shorter in the present investigation than in the studies mentioned above, as time for instrument change, stopper adjustment and irrigation were not included.
Overall, the ability of Ni–Ti systems to shorten preparation time compared to hand instrumentation or to automated root canal preparation using different endodontic handpieces with conventional stainless steel files has been confirmed already in a number of previous studies (Esposito & Cunningham 1995, Glosson et al . 1995, Hülsmann 2000, Hülsmann et al . 2001).