title: Flute and Shank Dimensions of Reciprocating Instruments before and after Simulated Root Canal shaping.
abstract: OBJECTIVE
  This study analyzed the effect of the dimensions of the flute and shank in the first 4 mm of instrument tips on the deformation and dimensional changes of reciprocating instruments after root canal shaping (RCS).
  
  
  METHODS
  The reciprocating instruments used were Reciproc®R25, R40, and R50; WaveOne®Small, Primary, and Large; and Unicone®#20, #25, and #40. Scanning electron microscopy images of the first 4 mm of the tip were acquired at 30× magnification before and after simulated curved root canals were shaped. Each instrument was used only once. The images were transferred to the AxioVision®software to measure the flute area (μm2), shank area (μm2), flute length (μm), and cross-sectional diameter (μm). Student's t test for paired samples was used to compare differences before and after RCS, and analysis of variance followed by the Tukey test, to compare differences between instruments of similar sizes. The instruments were classified according to deformations after RCS.
  
  
  RESULTS
  Reciproc®instruments had larger flutes and smaller shanks. The Reciproc®R40 had significant differences in cross-sectional diameter at 0.5 mm from the tip. Reciproc®had no plastic deformations. Unicone®#20 instruments had significant differences in cross-sectional diameter at 1.5 and 3.0 mm from the tip, and #25 instruments had differences at 1.5 and 3.0 mm and in length of the second and third flutes. One #20 and three #40 instruments had plastic deformations. The differences in length of the first and fourth flutes of WaveOne®Primary and in cross-sectional diameter at 2.0 mm from the tip of WaveOne®Large were significant. Two of three WaveOne®Large instruments had plastic deformations.
  
  
  CONCLUSIONS
  Reciproc®instruments had greater flute areas and lengths and smaller shanks than Unicone®and WaveOne®instruments of similar sizes. Reciproc®instruments had a greater flute-to-shank ratio. WaveOne®instruments had the lowest flute-to-shank ratio. Unicone®instruments had the most plastic deformations. Instruments with larger flutes and smaller shanks had fewer plastic deformations after curved RCS.
  
  
  CONCLUSIONS
  The knowledge of mechanical behavior before choosing the endodontic instrument may avoid fracture, regardless of the clinical condition, and it is essential to the success of root canal treatment.
authors.affiliation: Department of Endodontics, School of Dentistry, Instituto Tocantinense Presidente Antônio Carlos, Porto Nacional Tocantins, Brazil, e-mail: felipecavalcantisampaio@yahoo.com, drfelipecavalcanti@gmail.com.
authors.forename: Felipe C
authors.initials: FC
authors.lastname: Sampaio
authors.affiliation: Department of Endodontics, School of Dentistry, Instituto Tocantinense Presidente Antônio Carlos, Porto Nacional Tocantins, Brazil.
authors.forename: Ana Pp
authors.initials: AP
authors.lastname: Brito
authors.affiliation: Department of Endodontics, School of Dentistry, Federal University of Paraiba, João Pessoa, Paraiba, Brazil.
authors.forename: Heloisa Hp
authors.initials: HH
authors.lastname: Veloso
authors.affiliation: Department of Stomatological Sciences, School of Dentistry Federal University of Goiás, Goiânia, Goiãs, Brazil.
authors.forename: Ana Hg
authors.initials: AH
authors.lastname: de Alencar
authors.affiliation: Department of Stomatological Sciences, School of Dentistry Federal University of Goiás, Goiânia, Goiãs, Brazil.
authors.forename: Daniel de A
authors.initials: DA
authors.lastname: Decurcio
authors.affiliation: Clinical Department, School of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: José Ap
authors.initials: JA
authors.lastname: de Figueiredo
authors.affiliation: Department of Stomatological Sciences, School of Dentistry Federal University of Goiãs, Goiânia, Goiãs, Brazil.
authors.forename: Carlos
authors.initials: C
authors.lastname: Estrela
mesh_terms: D004868:Equipment Failure; D006801:Humans; D008855:Microscopy, Electron, Scanning; D018915:Root Canal Preparation / Q000295:instrumentation*; D012390:Root Canal Therapy / Q000295:instrumentation
keywords: Endodontic instruments; Flute; Laboratory research; Plastic deformation; Reciprocating instruments Root canal shaping.