title: Influence of Surface Roughness on the Fatigue Life of Nickel-Titanium Rotary Endodontic Instruments.
abstract: BACKGROUND
  The goal of the present study was to evaluate the influence of surface grooves (peaks and valleys) resulting from machining during the manufacturing process of polished and unpolished nickel-titanium BR4C endodontic files on the fatigue life of the instruments.
  
  
  METHODS
  Ten electropolished and 10 unpolished endodontic files were provided by the manufacturer. Specimens were from the same batch, but the unpolished instruments were removed from the production line before surface treatment. The instruments were evaluated with a profilometer to quantify the surface roughness on the working part of the instruments. Then the files were subjected to rotating bending fatigue tests.
  
  
  RESULTS
  Analysis with the profilometer showed that surface grooves were deeper on the unpolished instruments compared with their electropolished counterparts. In the rotating bending fatigue test, the mean and standard deviation for the number of cycles until fracture (NCF) were greater for instruments with less pronounced grooves. Student t test revealed significant differences in all tests (P < .05).
  
  
  CONCLUSIONS
  The results from the present study showed that the depth of the surface grooves on the working part affected the NCF of the instruments tested; the smaller the groove depth, the greater the NCF.
authors.affiliation: Department of Endodontics, School of Dentistry, Estácio de Sá University, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Hélio P
authors.initials: HP
authors.lastname: Lopes
authors.affiliation: Materials Science Department, Instituto Militar de Engenharia, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Carlos N
authors.initials: CN
authors.lastname: Elias
authors.affiliation: Advanced Education Program in Endodontics, Funorte, Governador Valadares, Minas Gerais, Brazil. Electronic address: mvieirabrasil@gmail.com.
authors.forename: Márcia V B
authors.initials: MV
authors.lastname: Vieira
authors.affiliation: Department of Endodontics, Grande Rio University, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Victor T L
authors.initials: VT
authors.lastname: Vieira
authors.affiliation: Materials Science Department, Instituto Militar de Engenharia, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Letícia Chaves
authors.initials: LC
authors.lastname: de Souza
authors.affiliation: Department of Endodontics, Grande Rio University, Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Alexander Lopes
authors.initials: AL
authors.lastname: Dos Santos
mesh_terms: D063405:Anatomic Variation; D003722:Dental Alloys / Q000737:chemistry*; D003762:Dental Instruments; D003775:Dental Polishing / Q000379:methods; D003799:Dental Stress Analysis; D055664:Electrochemical Techniques; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013193:Stainless Steel / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D014025:Titanium
keywords: Fatigue; roughness; surface finish