title: Evaluation of three different rotary systems during endodontic retreatment - Analysis by scanning electron microscopy.
abstract: BACKGROUND
  Endodontic therapy is considered a series of important and interdependent steps, and failure of any of these steps may compromise the treatment outcome. This study aimed to evaluate the effectiveness of three different rotary systems in removing obturation materials during endodontic retreatment using scanning electron microscopy (SEM) analysis.
  
  
  METHODS
  Thirty-six endodontically treated teeth were selected and divided into 3 groups of 10 and 1 control group with 6 dental elements. The groups were divided according to the rotary system used for removing gutta-percha, as follows: G1: ProTaper system; G2: K3 system; G3: Mtwo system; and G4: Control group. Thereafter, the roots were split and the sections were observed under SEM, for analysis and counting of clear dentinal tubules, creating the variable "degree of dentinal tubule patency" (0: intensely clear; 1: moderately clear; 2: slightly clear; 3: completely blocked). The data were subjected to the Friedman and Kruskal-Wallis statistical tests.
  
  
  RESULTS
  No differences were observed in the "degree of dentinal tubule patency" neither between the root thirds (to each evaluated group) nor between the groups (to each evaluated third). Nevertheless, when the three root thirds were grouped (providing evaluation of all root extension), the "degree of dentinal tubule patency" was lower in G1 than in G3 (p<0.05), but showed no differences neither between G1 and G2 nor G2 and G3.
  
  
  CONCLUSIONS
  No technique was able to completely remove the canal obturation material, despite G1 having shown better results, although without significant difference to G2 KEY WORDS:Scanning electron microscopy, NiTi, retreatment.
authors.affiliation: DDS, MS, Graduate student, Departament of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brasil.
authors.forename: Flávia-Teixeira
authors.initials: FT
authors.lastname: Vidal
authors.affiliation: DDS, MS, PhD, Professor, Departament of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brasil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Nunes
authors.affiliation: DDS, MS, PhD, Professor, Departament of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brasil.
authors.forename: Martinho-Campolina-Rebello
authors.initials: MC
authors.lastname: Horta
authors.affiliation: DDS, MS, Professor, Departament of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brasil.
authors.forename: Maria-Rita-Lopes-da Silva
authors.initials: MR
authors.lastname: Freitas
authors.affiliation: DDS, MS, PhD, Professor, Departament of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brasil.
authors.forename: Frank-Ferreira
authors.initials: FF
authors.lastname: Silveira