OBJECTIVETo compare the initial penetration depth of nickel-titanium (NiTi) and stainless-steel (SS) spreader during lateral compaction and the quality of the seal in curved canals.

METHODSForty extracted mandibular premolars with a single curved canal were divided into two groups: no more than 20 degrees and more than 20 degrees based on degree of curvature. All canals were instrumented using a rotary instrumentation technique. NiTi and SS spreaders were used to obturate the canals containing a master cone while the penetration depths were measured. Horizontal sections were cut in 2 and 4 mm from the apex and photographed under stereomicroscope. The percentage of gutta-percha-filled are (PGP) of cross-sections was measured using an image analysis program.

RESULTSIn canals of more than 20 degrees, the penetration depths and PGP of 2 mm from the apex of NiTi spreaders were higher than SS spreader. In canals of no more than 20 degrees, there were no significant difference between them (P > 0.05). At 4 mm from the apex, there was no significant difference between two groups.

CONCLUSIONNiTi spreaders has a higher penetrated depth and obturation density than SS spreaders in severed curved canals.