Optimum glide path motion is safer than continuous rotation of files in glide path preparation.

This study evaluated the resistance to flexural fatigue and torsional strength of files for glide path preparation in continuous rotation or Optimum Glide Path motion (OGP). ScoutRace 15.02 and ProGlider 16.02 files were used in a dynamic testing device during preparation of simulating curved root canals (40-degree curvature and 5 mm radius). For the torsional test, a machine was used to test torsion measured maximum torsional strength (N.cm). Two-way anova and Tukey's multiple comparisons test were used for statistical analysis. Files in OGP motion had a statistically better resistance to flexural fatigue (P < 0.05). ProGlider files took longer time to failure than ScoutRace files only when OGP was used (P < 0.05). The torsional test revealed that OGP produced significantly less torsional stress than rotary motions for both types of glide path files (P < 0.05) In conclusion, OGP motion increased substantially the mechanical safety of endodontic glide path files.

Resistência à fadiga cíclica dos instrumentos Reciproc e Mtwo nos movimentos rotatório e reciprocante / Resistance to cyclic fatigue of Reciproc and Mwto files on continuous rotation and reciprocating movements

Objetivo: O objetivo do presente estudo foi avaliar a influência da liga (NiTi convencional e M-Wire) e do movimento (reciprocante e rotação contínua) na resistência à fadiga cíclica. Métodos: Quinze limas Reciproc R25 (VDW GmbH, Munique, Alemanha) foram usadas em movimento reciprocante (MR), enquanto trinta limas Mtwo 25.07 (VDW GmbH, Munique, Alemanha) foram usadas em MR (n=15) ou em rotação contínua (RC) (n=15). Os instrumentos foram submetidos a ensaios dinâmicos movidos por motor elétrico, que permitiram reproduzir o movimento de pecking motion, a 300rpm de velocidade. Os instrumentos simularam a instrumentação de um canal radicular curvo com 40o e 5mm de raio de curvatura. A fratura dos instrumentos foi detectada por um sensor digital, e o tempo e o número de ciclos foram registrados. Os dados foram analisados estatisticamente pelos testes ANOVA e de Tukey (p<0,05). Resultados: Os instrumentos Reciproc R25 movidos por MR alcançaram número significativamente maior (p<0,05) de ciclos antes da fratura (1.777,68±334,2 ciclos), quando comparados aos instrumentos MT 25.07 movidos por MR (610,67±126,3 ciclos) ou RC (432,23±183,2 ciclos). Conclusões: O movimento reciprocante mostrou resistência à fadiga cíclica significativamente maior, e os instrumentos de NiTi M-Wire apresentaram maior resistência à fadiga cíclica do que os instrumentos rotatórios de NiTi convencional (AU).

Objective: The aim of present study was to evaluate the influence of alloy (conventional NiTi and M-Wire NiTi) and movement (reciprocating movement and continuous rotation) on resistance to cyclic fatigue. Methods: Fifteen Reciproc R25 files (VDW GmbH, Munich, Germany) were used in reciprocation motion (RM), while thirty MTwo 25/.07 files (VDW GmbH, Munich, Germany) were used either in RM (n=15) or in continuous rotation (CR) (n=15). The files were submitted to dynamic assays device moved by electric engine that allowed the reproduction of pecking motion under 300 rpm of speed. The files act simulating the instrumentation of a curved root canal with 40º and 5-mm of curvature radius. The fracture was detected by the device sensor and the time and number of cycles were obtained. Data were statistically analyzed by ANOVA and Tukeys tests (p<0.05). Results: The Reciproc R25 instruments moved by RM reached significantly higher number (p<0.05) of cycles before fracture (1777.68 ± 334.2 cycles) when compared with MTwo 25/.07 instruments moved by RM (610.67 ± 126.3 cycles) or CR (432.23 ± 183.2 cycles). Conclusions: The reciprocation motion showed significantly greater cyclic fatigue resistance and the M-Wire NiTi files showed higher cyclic fatigue resistance than conventional NiTi rotary files (AU).

Effect of different torques in cyclic fatigue resistance of K3 rotary instruments

Aim: To assess the effect of different torque values on cyclic fatigue resistance of K3 rotary nickel-titanium (NiTi) files. Methods: Eighty K3 files, size 25 mm, taper 0.04 were divided in 4 groups according to different torques (0.5, 1, 2 and 6 Ncm) and were submitted to a cyclic fatigue test. This test was performed with a device that allowed the file to rotate inside a stainless steel artificial curved canal, simulating the pecking motion. Files rotated until fracture occurred and time to failure was recorded in seconds with a stopwatch. Data were analyzed by ANOVA and Tukey tests (p<0.05). Results: All groups were compared and only the group of 6 N.cm showed statistically significant difference (p=0.0002). Conclusions: For #25.04 K3 files, the evaluated torques up to 2 N.cm had no influence on cyclic fatigue resistance. Using 6 N.cm torque value resulted in lower resistance to cyclic fatigue.

Resistance to flexural fatigue of Reciproc R25 files under continuous rotation and reciprocating movement.

INTRODUCTION: The aim of the present work was to evaluate the resistance to flexural fatigue of Reciproc R25 nickel-titanium files, 25 mm, used in continuous rotation motion or reciprocation motion, in dynamic assays device. METHODS: Thirty-six Reciproc R25 files were divided into 2 groups (n = 18) according to kinematics applied, continuous rotary (group CR) and reciprocation motion (group RM). The files were submitted to dynamic assays device moved by an electric engine with 300 rpm of speed that permitted the reproduction of pecking motion. The files run on a ring's groove of temperate steel, simulating instrumentation of a curved root canal with 40° and 5 mm of curvature radius. The fracture of file was detected by sensor of device, and the time was marked. The data were analyzed statistically by Student's t test, with level of significance of 95%. RESULTS: The instruments moved by reciprocating movement reached significantly higher numbers of cycles before fracture (mean, 1787.78 cycles) when compared with instruments moved by continuous rotary (mean, 816.39 cycles). CONCLUSIONS: The results showed that the reciprocation motion improves flexural fatigue resistance in nickel-titanium instrument Reciproc R25 when compared with continuous rotation movement.