title: Intra-canal calcium hydroxide removal by two rotary systems: A comparative study.
abstract: OBJECTIVE
  The presence of calcium hydroxide (Ca(OH)2) in the root canal interferes with the apical root canal sealing and may result in periapical lesions in the long run. The present study was aimed to compare the efficacy of two rotary systems of Race and Mtwo in the removal of Ca (OH)2 aqueous-based from distobuccal canals of human maxillary molars.
  
  
  METHODS
  A total of 44 distobuccal root canals of human maxillary molars were randomly distributed into two groups of 20 canals each and two control groups. Specimens in each group were instrumented with similar master apical rotary (MAR) and flexible files according to the manufacture's guidelines. The Ca (OH)2 paste was placed in canals using # 20 lentulo and radiographs were taken from the two dimensions. The roots were incubated for 1 week at 37°C and 100% humidity and Ca (OH)2 was removed from canals by MAR, afterward. Then, the roots were longitudinally split in halves by diamond disk and chisel without entering the root canals. Photos were taken from the canals' walls by a stereomicroscope with × 10 magnification. Next, according to a defined scoring system, photos were scored by four endodontists, so that scores 1 and 2 (nonvisible remnants or scattered remnants of Ca(OH)2) were considered as acceptable and scores 3 and 4 (distinct mass or densely-packed mass of Ca(OH)2) were regarded as nonacceptable.
  
  
  RESULTS
  The obtained findings indicated that in coronal, middle, and apical portions of the root canal, 45, 60, and 65% of Mtwo specimens and 40, 50, and 55% of specimens prepared by the Race system acquired an acceptable score (1 and 2), respectively. Moreover, the results showed no significant difference between the two groups (P > 0.05).
  
  
  CONCLUSIONS
  Both Mtwo and Race rotary systems with acceptable removal efficiency (score 1 and 2) were similarly able to remove Ca(OH)2.
authors.affiliation: Department of Endodontics, School of Dentistry, Islamic Azad University, Tehran, Iran.
authors.forename: Bahare
authors.initials: B
authors.lastname: Dadresanfar
authors.affiliation: Department of Oral and Maxillofacial Pathology, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Fateme Mashhadi
authors.initials: FM
authors.lastname: Abbas
authors.affiliation: Dentist, Tehran, Iran.
authors.forename: Hamide
authors.initials: H
authors.lastname: Bashbaghi
authors.affiliation: Department of Endodontics, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Shima Sadat
authors.initials: SS
authors.lastname: Miri
authors.affiliation: Dentist, Tehran, Iran.
authors.forename: Farshid
authors.initials: F
authors.lastname: Ghorbani
keywords: Calcium hydroxide; mtwo rotary systems; race; race rotary systems