The effect of reciprocating motion on the cyclic fatigue resistance of ProFile and ProTaper

Abstract

1. Objectives Recently, it has been shown that the reciprocating movement (RM), extended the lifespan of an F2 ProTaper instrument in comparison with continuous clockwise rotation (CR), in curved canals. The purpose of this study was to investigate the effect of RM on cyclic flexural stress (fatigue) on NiTi instruments with different cross-sections when they were driven with RM.

2. Methods F2 ProTaper (PT) and #25/.06 taper ProFile (PF) instruments were used. Cyclic flexural fatigue tests simulating clinical use were carried in curved stainless steel tubes. The instruments were used in either CR or RM resulting in 4 experimental groups (n=12). The instruments were driven at 300rpm and with a standardized 4-mm pecking movement until fracture. For the RM groups, the angles were set at 140o and 45o in clockwise and counter-clockwise directions, respectively. The time of fracture and the number of cycles to fracture (NCF) for each instrument were determined. The length of the fractured file tip was measured and the fractured surface was examined with an SEM. Statistical analysis was performed on the data using two-way ANOVA and t-test.

3. Results There were no statistically significant differences in the time to fracture or NCF between RM and CR (p>0.05) for the PF and PT groups, respectively. ProFile instruments had a significantly greater cyclic fatigue resistance compared to ProTaper regardless of the rotational movement used (p<0.05). The length of the fracture segment was not affected by either the type of the rotation (p>0.05). The fractographic analysis showed similar features for both instruments and rotational movements with the presence of crack initiation origin, crack propagation region, and overload (fast fracture) zone.