title: Apical foramen morphology according to the length of merged canal at the apex.
abstract: OBJECTIVE
  The aim of this study was to investigate the relationship between the apical foramen morphology and the length of merged canal at the apex in type II root canal system.
  
  
  METHODS
  This study included intact extracted maxillary and mandibular human premolars (n = 20) with fully formed roots without any visible signs of external resorption. The root segments were obtained by removing the crown 1 mm beneath the cementum-enamel junction (CEJ) using a rotary diamond disk. The distance between the file tip and merged point of joining two canals was defined as Lj. The roots were carefully sectioned at 1 mm from the apex by a slow-speed water-cooled diamond saw. All cross sections were examined under the microscope at ×50 magnification and photographed to estimate the shape of the apical foramen. The longest and the shortest diameter of apical foramen was measured using ImageJ program (1.44p, National Institutes of Health). Correlation coefficient was calculated to identify the link between Lj and the apical foramen shape by Pearson's correlation.
  
  
  RESULTS
  The average value of Lj was 3.74 mm. The average of proportion (P), estimated by dividing the longest diameter into the shortest diameter of the apical foramen, was 3.64. This study showed a significant negative correlation between P and Lj (p < 0.05).
  
  
  CONCLUSIONS
  As Lj gets longer, the apical foramen becomes more ovally shaped. Likewise, as it gets shorter, the apical foramen becomes more flat shaped.
authors.affiliation: Department of Conservative Dentistry, Chosun University School of Dentistry, Gwangju, Korea.
authors.forename: Hee-Ho
authors.initials: HH
authors.lastname: Kim
authors.forename: Jeong-Bum
authors.initials: JB
authors.lastname: Min
authors.forename: Ho-Keel
authors.initials: HK
authors.lastname: Hwang
keywords: Apical foramen; Type II root canal system