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

Superimposition of photographs of the cross-sections of the pre- and postoperative root canals showed that both systems left uninstrumented canal walls in many cases. Overall, 40 Lightspeed and 30 Profile .04 specimens out of 75 showed no contact between the pre- and postoperative root canal outlines, indicating sufficient circumferential instrumentation of the root canal wall. Following preparation with Lightspeed instruments, all parts of the root canals showed less uninstrumented root canal walls than following preparation with ProFile instruments. Lightspeed instruments enlarged the root canal more uniformly with no specimen showing 50% or more contact between pre- and postoperative diameter (Table 3). The difference was statistically significant for the coronal third of the root canals ( P = 0.032) with the Lightspeed system showing a superior performance. For the apical and the middle third no significant differences occurred.

Root canal cleanliness.
Due to three instrument fractures, the number of specimens for the Profile .04 group was only 66 compared to 75 in the Lightspeed group. The results of the SEM analysis of the root canal walls concerning residual debris and smear layer are detailed in Table 4. Generally, the root canals showed no homogeneous appearance with only few specimens (Lightspeed: 14.7%, Profile .04: 13.6%) with completely clean walls without any remaining debris (score 1) and a high number of scores 2 and 3 for both systems (Lightspeed: 80%, Profile .04 71.2%). Differences between the systems were not significant.
For smear layer Lightspeed preparation resulted in 65.3%, ProFile in 62.1% scored 2 and 3. No statistically significant differences occurred for the apical and middle thirds of the root canals. For the coronal region, Lightspeed cleaned significantly better ( P = 0.029).

Procedural errors.
Lightspeed preparation proved to be a safe technique with no instrument fracture, no perforation, no apical blockage, and no case of loss of working length. With the Profile .04 system three instrument fractures (one fracture with size 40, two fractures with size 35 instruments) occurred, but no perforation, no apical blockage, and no cases with loss of working length.

Working time.
Working time, not including time for instrument changes and irrigation, measured during preparation of the unsectioned roots, resulted in a median of 123.4 s for Lightspeed instrumentation (20 instruments), and 94.3 s for the Profile .04 system (10 instruments). The difference was statistically significant ( P = 0.026). The working time for each single instrument was shorter for Lightspeed than for ProFile. Including time for root canal irrigation, Lightspeed preparation resulted in a working time of 270.9 s (median) and Profile .04 instrumentation in a median working time of 190.1 s.