title: Effectiveness of four electronic apex locators to determine distance from the apical foramen.
abstract: OBJECTIVE
  To evaluate the accuracy of four electronic apex locators (EAL) in the apical region (0-3 mm short of the foramen) and to compare the precision of the readings on the display with the real position of the file in the root canal.
  
  
  METHODS
  Twenty single-rooted extracted teeth with round root canals were used. The canal orifices were preflared, and the length to the major foramen was determined visually under a microscope. Canals were enlarged, so that a size 15 file fitted well inside the canal. Teeth were mounted in acrylic test tubes filled with physiologic saline solution. Electronic length was determined in the region between the major foramen and 3 mm short of it in 0.5 mm steps with the Dentaport ZX, Root ZX mini, Elements Diagnostic Unit and Apex Locator and Raypex 5 using files of size 10 and size 15. The data were analysed using linear regression between true length and EAL reading, Bland-Altman plots and nonparametric tests at a significance level of alpha = 0.05.
  
  
  RESULTS
  The major foramen was detected by all EALs. With a measurement file positioned directly at the major foramen, meter readings were equivalent to a position 0.01-0.38 mm away. For the Dentaport ZX, a better accuracy using the size 15 file for the area 0-1.5 mm short of the apex was found. The differences in measurements between the two files were smaller for the other EALs. In linear regression, a good linearity for Dentaport ZX and Root ZX mini and moderate linearity for Elements Diagnostic Unit and Apex Locator and Raypex 5 were found. The slope of the measurement curve was too low (0.37-0.57) for the Raypex 5 and almost optimal for the Dentaport ZX (1.01-1.05). The Root ZX mini and the Elements Obturation Unit produced lower slope values and especially the Elements Obturation Unit revealed much higher SDs at the different measurement levels.
  
  
  CONCLUSIONS
  Amongst the four EALs, the Dentaport ZX and Root ZX mini had the best agreement between true lengths and meter readings. For the Raypex 5, an interpretation of the colour-coded zones as distance to the foramen cannot be recommended and might lead to erroneous interpretations.
authors.affiliation: Department of Operative Dentistry and Endodontics, Dental School, Philipps University of Marburg, Germany. stoll@mailer.uni-marburg.de
authors.forename: R
authors.initials: R
authors.lastname: Stoll
authors.forename: B
authors.initials: B
authors.lastname: Urban-Klein
authors.forename: M J
authors.initials: MJ
authors.lastname: Roggendorf
authors.forename: A
authors.initials: A
authors.lastname: Jablonski-Momeni
authors.forename: K
authors.initials: K
authors.lastname: Strauch
authors.forename: R
authors.initials: R
authors.lastname: Frankenberger
mesh_terms: D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D055615:Electrical Equipment and Supplies; D004867:Equipment Design; D006801:Humans; D008422:Materials Testing; D008853:Microscopy / Q000295:instrumentation; D009811:Odontometry / Q000295:instrumentation* / Q000706:statistics & numerical data; D018915:Root Canal Preparation / Q000295:instrumentation; D019227:Tooth Apex / Q000033:anatomy & histology*