Impact of smear layer on sealing property of root canal obturation using 3 different techniques and sealers. Part I.

OBJECTIVE: The objective of this study was to determine the influence of smear layer removal on through-and-through fluid movement along root canal fillings obturated using 3 different root canal sealers, namely AH26, Pulp Canal Sealer, and Gutta-Flow, and 3 different obturation techniques. STUDY DESIGN: The fluid transport model was used for detection of through-and-through fluid movement. Root canals of 230 human extracted teeth were mechanically instrumented using the step-back technique. The canals where the smear layer was not removed were irrigated with NaOCl 2.4%, whereas canals where the smear layer was removed were irrigated with EDTA 17% plus NaOCl 2.4%. The teeth were randomly divided into 10 experimental groups (n = 20) and 3 control groups (n = 10) and treated as follows. In group A, where no attempt was made for smear layer removal, the canals were obturated with lateral compaction of gutta-percha and AH26 as a sealer. In group B, the smear layer was removed, and canals were obturated as in group A. In group C (no attempt to remove the smear layer), the canals were obturated with System B plus Obtura II technique and AH26, whereas in group D, the smear layer was removed, and canals were obturated as in group C. The other 4 experimental groups were treated and obturated in the same way as in previous groups, respectively. The sealer that was used in those groups was the Pulp Canal Sealer. Finally, the latter 2 groups were obturated with Gutta-Flow technique. Fluid movement was measured at 24 hours and 30 days and 6 months. RESULTS: In lateral compaction groups (with and without the smear layer), no significant differences were found regarding the ability of the same materials (AH26 and Pulp Canal Sealer) to prevent the fluid movement (P > .05). In warm obturation technique, no significant difference was found between the 2 groups (with and without the smear layer) of AH26 (P > .05). On the contrary, in groups of Pulp Canal sealer, fluid transport values were significantly less when the smear layer was removed (P < .05). Finally, no significant difference was observed between the groups of Gutta-Flow (with and without the smear layer) (P > .05). CONCLUSIONS: Under these in vitro conditions, it seems that smear layer removal improves the ability of the filling materials to prevent the fluid movement, at least after the use of warm obturation techniques. On the contrary, smear layer removal does not seem to improve the same ability after the use of cold lateral compaction technique. Further laboratory and also clinical studies are needed in the future to compose a clear view concerning the improvement of sealing ability following smear layer removal.

A comparative study of the effects of two nickel-titanium preparation techniques on root canal geometry assessed by microcomputed tomography.

The present study was conducted with the aim of evaluating and comparing the effects of a new Hero group (Endoflare, Hero-shaper, and Hero-apical; Micro-Mega, Besancon, France) and Protaper Ni-Ti rotary instruments (Dentsply/Maillefer, Ballaigues, Switzerland) on root canal geometry in extracted human teeth using microcomputed tomography (muCT). Twenty-two mesial root canals of mandibular first molars were randomly divided into two groups. Canals were scanned before and after preparation with both systems. Cross-sectional images of each canal were obtained at 2-mm intervals. Differences in canal roundness, cross-sectional area, perimeter of each canal before and after instrumentation, and the extent of root canal transportation were calculated using image analysis software. There was no difference between the two rotary systems in regards to working time. Both systems create a similar round shape after instrumentation regardless of the initial root canal's shape. The Hero instruments showed a greater cutting efficiency compared with the ProTaper at the levels of 8 mm, 6 mm, and 4 mm but not at the level of 2 mm. On the other hand, the ProTaper seems to have a similar cutting efficiency at all levels. However, the ProTaper showed a tendency toward apical transportation. Under the conditions of the present study, both preparation techniques prepared the canals rapidly with a sufficient round shape. Despite that, it seems that there is a great potential for the improvement of shaping ability of rotary instruments. Hybrid instrumentation techniques should be evaluated by future studies in order to provide better results regarding the shaping ability of rotary instruments.