title: The minimum residual root thickness after using ProTaper, RaCe and Gates-Glidden drills: A cone beam computerized tomography study.
abstract: OBJECTIVE
  The aim of this study was to evaluate the minimum residual root thickness (MRRT) of the danger zone after preflaring of the mesio-buccal (MB) canal of mandibular first molars using ProTaper, RaCe and Gates-Glidden (GG) drills as coronal shapers by cone beam computerized tomography (CBCT).
  
  
  METHODS
  In this experimental study, the initial CBCT scans of 75 MB canals of mandibular first molars were provided within 1, 2, 3 and 4 mm of the furcation level. The samples were divided into three groups. The samples of ProTaper and RaCe groups were prepared up to F2 and #25.04 as the master apical file (MAF), respectively. The coronal preparation of the samples in the GG group was done using GG drills #2, #3 and #4 and canals were prepared till MAF # 25. After obtaining the postinstrumentation images, the MRRT and the amount of removed dentin were analyzed by t-test and ANOVA statistical analyses.
  
  
  RESULTS
  The GG drills removed significantly more dentin than RaCe at all the sections (P < 0.05) and more than ProTaper at 3 mm from the furcation. Statistically there was no significant difference between ProTaper and RaCe groups (P > 0.05). There was no significant difference in MRRT between the groups (P > 0.05). The mean MRRT was not < 0.75 mm at all sections.
  
  
  CONCLUSIONS
  Based on the results of this study, when an appropriate root thickness is initially present, all of the instruments that were investigated may safely be used as coronal shapers in MB canals of mandibular first molars.
authors.affiliation: Department of Endodontics, Dental Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Nahid Mohammadzadeh
authors.initials: NM
authors.lastname: Akhlaghi
authors.affiliation: Private Practice, Tehran, Iran.
authors.forename: Laleh Mohammadian
authors.initials: LM
authors.lastname: Bajgiran
authors.affiliation: Private Practice, Tehran, Iran.
authors.forename: Amirali
authors.initials: A
authors.lastname: Naghdi
authors.affiliation: Private Practice, Tehran, Iran.
authors.forename: Elaheh
authors.initials: E
authors.lastname: Behrooz
authors.affiliation: Department of Endodontics, Dental Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Khalilak
keywords: Dental instruments; dentin; instrumentation; root canal preparation