Effects of Curvature Location on Cyclic Fatigue of Reciprocating Instruments

Objectives: To evaluate and compare in vitro, the influence of canal curvature position in reciprocating cyclic fatigue fracture of three brands of nickel-titanium reciprocating instruments.
Methods: One hundred and five instruments were selected and divided into three groups (n = 35): Group 1 – Reciproc (VDW), Group 2 – Unicone (MEDIN) and Group 3 - Edge File X1 (EDGE ENDO). The instruments were subject to testing for Vickers microhardness, flexibility and reciprocating cyclic fatigue using two stainless steel artificial canals, differentiated by curvature position. The cyclic fatigue resistance of the instruments was calculated by the time (s) until fracture occurred. Some of the fractured surfaces and the helical shafts of fractured instruments were analyzed by scanning electron microscope. For comparison of microhardness, flexibility and fracture time between groups and in the two types of canals, ANOVA test with Student-Newman-Keuls multiple comparisons test were used. Student's t-test compared the influence of canal curvature location on the time to fracture in each instrument’s group.
Results: EdgeFile X1 instrument showed the lowest hardness (p < 0.05) and the highest flexibility (p < 0.05), while Reciproc obtained the highest hardness and reciprocating cyclic fatigue resistance (p < 0.05). The fracture time of the Unicone and Edge File X1 instruments decreased significantly when the curvature position ranged from apical to cervical.
Conclusions: The curvature location influenced the cyclic fatigue resistance of reciprocating instruments (Unicone and EdgeFile X1), except for Reciproc.