Comparison of some physical properties of finger spreaders made of stainless steel or nickel-titanium alloys

The purpose of this study was to evaluate the flexibility, shape, and surface finishing of stainless steel (SS) and nickel-titanium (NiTi) finger spreaders as well as to compare the load required to insert these spreaders along a gutta-percha point adapted to the apical segment of curved or straight artificial canals. Instrument flexibility was investigated by using a universal testing machine in the cantilever-flexibility test. Scanning electron microscopy (SEM) was used to examine the shape and surface finishing of different sizes of SS and NiTi finger spreaders. Penetration load was evaluated only for spreaders size C by using the universal testing machine in a compressive test. As for flexibility, the load needed to bend the SS finger spreader sizes A, B, C, and D was approximately 167%, 146%, 102%, and 64% greater than the respective sizes of NiTi finger spreaders. SEM analysis revealed that the instrument tips were always tapered, but with different vertices. NiTi spreaders showed tips with circumferential grooves; whereas, those from SS spreaders exhibited longitudinal grooves. NiTi finger spreaders required a significantly higher penetration load than SS spreaders. This difference was probably related to the different shapes and surface finishing of the instrument tips. Different characteristics of finger spreaders may result in different clinical performance during the lateral compaction technique.