title: Modification of the working length after rotary instrumentation: a comparative study of four systems.
abstract: OBJECTIVE
  To determine variation in post-instrumentation working length and root area in the following rotary systems: ProTaper, RaCe, Mtwo and K3.
  
  
  METHODS
  A sample of 40 resin blocks with double curvature (at 14 and 16 mm) and a 33 degrees angle was used. Working length was verified with a digital measure using a number 10 K file. The specific sequence for each rotary system was followed. The canal was measured between each file, and the variation noted to determine which file showed the greatest variation within a same system and the different systems were compared. 1.5 X pre and post-instrumentation microscopic photographs were taken and measurements of the area were taken with an image analysis programme.
  
  
  RESULTS
  The area was found to increase by the following amounts: ProTaper: 21.85 mm2; Mtwo: 20.16 mm2; K3: 17.24 mm2 and RaCe: 16.09 mm2. The differences in variation of the working length were: ProTaper: 0.81 mm; Mtwo: 1.07 mm; K3: 0.31 mm and RaCe: 0.81 mm.
  
  
  CONCLUSIONS
  The values for the variation in working length are clinically not very significant. All the rotary systems analysed showed a tendency to straighten the canal and eliminate the apical curvature, and the ProTaper system was found to produce the greatest modification to the canal area and structure.
authors.affiliation: Department of Stomatology, Universidad CEU-Cardenal Herrera, Moncada, Valencia, Spain.
authors.forename: Milagros
authors.initials: M
authors.lastname: Martín-Micó
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Forner-Navarro
authors.forename: Amelia
authors.initials: A
authors.lastname: Almenar-García
mesh_terms: D006801:Humans; D018915:Root Canal Preparation / Q000295:instrumentation*