A comparative study of root canal preparation with NiTi-TEE and K3 rotary Ni-Ti instruments

To evaluate and compare several parameters of curved root canal preparation using two different Ni-Ti systems: NiTi-TEE (Sjöding Sendoline, Kista, Sweden) and K3 (Sybron Endo, Orange County, CA, USA).

Fifty extracted mandibular molars with mesial root canal curvatures ranging from 20 to 40 degrees were divided into two groups. In one group, 50 root canals were instrumented using NiTi-TEE files to an apical size 30; 0.04 taper (the largest available size at the time of this study). In the other group, 50 root canals were prepared with K3 instruments to an apical size 45; 02 taper. Both systems were used in a crowndown manner, with copious NaOCl (3%) irrigation and a chelating agent (Calcinase Slide, lege artis, Dettenhausen, Germany), employing torque-controlled motors. For assessment of shaping ability, pre- and postinstrumentation radiographs and cross-sectional photographs of canals were taken and changes in canal curvature and root canal diameter documented. Cleaning ability was evaluated by investigating specimens of the apical, medial and coronal third of the root canal wall under a scanning electron microscope using 5-score indices for debris and smear layer. Procedural errors (instrument separations, perforations, apical blockages, loss of working length) and working time were recorded. Nonparametric anova was used to compare straightening of canal curvatures, canal cross-sections and canal wall cleanliness (P < 0.05), whereas working time was analysed using the parametric anova (P < 0.05).

Both Ni-Ti systems maintained curvature well: the mean degree of straightening was 0.2 degrees for NiTi-TEE and 0.4 degrees for K3 with no statistical significance between the groups. Post-instrumentation cross-sections of the root canals revealed an acceptable contour (round or oval) in 50.6% of cases for the NiTi-TEE group and in 65.3% of cases for the K3 group. The difference was not significant. The SEM investigation of canal walls showed equally good debris removal for both systems: NiTi-TEE prepared canal walls in 74.7% of cases with scores I and II; K3 achieved these scores in 78.7% of cases. For smear layer, NiTi-TEE and K3 only received good scores (I and II) in 38.7% and 40% of canal wall specimens, respectively. For both parameters, no significant differences were found between groups. File fractures did not occur, but loss of working length was observed in one case following the preparation with NiTi-TEE and in three cases during K3 instrumentation. Mean working time was significantly shorter for NiTi-TEE (170 s) than for K3 (208 s).

Both systems maintained original canal curvature well and were safe to use. Whilst debridement of canals was considered satisfactory, both systems failed to remove smear layer sufficiently.