title: A posteriori registration and subtraction of periapical radiographs for the evaluation of external apical root resorption after orthodontic treatment.
abstract: OBJECTIVE
  This study employed a posteriori registration and subtraction of radiographic images to quantify the apical root resorption in maxillary permanent central incisors after orthodontic treatment, and assessed whether the external apical root resorption (EARR) was related to a range of parameters involved in the treatment.
  
  
  METHODS
  A sample of 79 patients (mean age, 13.5±2.2 years) with no history of trauma or endodontic treatment of the maxillary permanent central incisors was selected. Periapical radiographs taken before and after orthodontic treatment were digitized and imported to the Regeemy software. Based on an analysis of the posttreatment radiographs, the length of the incisors was measured using Image J software. The mean EARR was described in pixels and relative root resorption (%). The patient's age and gender, tooth extraction, use of elastics, and treatment duration were evaluated to identify possible correlations with EARR.
  
  
  RESULTS
  The mean EARR observed was 15.44±12.1 pixels (5.1% resorption). No differences in the mean EARR were observed according to patient characteristics (gender, age) or treatment parameters (use of elastics, treatment duration). The only parameter that influenced the mean EARR of a patient was the need for tooth extraction.
  
  
  CONCLUSIONS
  A posteriori registration and subtraction of periapical radiographs was a suitable method to quantify EARR after orthodontic treatment, and the need for tooth extraction increased the extent of root resorption after orthodontic treatment.
authors.affiliation: Department of Dental Radiology, School of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil.
authors.forename: Eliane Maria
authors.initials: EM
authors.lastname: Kreich
authors.affiliation: Department of Pediatric Dentistry, School of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil.
authors.forename: Ana Cláudia
authors.initials: AC
authors.lastname: Chibinski
authors.affiliation: Department of Orthodontics, School of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil.
authors.forename: Ulisses
authors.initials: U
authors.lastname: Coelho
authors.affiliation: Department of Pediatric Dentistry, School of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil.
authors.forename: Letícia Stadler
authors.initials: LS
authors.lastname: Wambier
authors.affiliation: Department of Dental Radiology, School of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil.
authors.forename: Rosário de Arruda Moura
authors.initials: Rde A
authors.lastname: Zedebski
authors.affiliation: Department of Dental Radiology, School of Dentistry, State University of São Paulo, São José dos Campos, São Paulo, Brazil.
authors.forename: Mari Eli Leonelli
authors.initials: ME
authors.lastname: de Moraes
authors.affiliation: Department of Dental Radiology, School of Dentistry, State University of São Paulo, São José dos Campos, São Paulo, Brazil.
authors.forename: Luiz Cesar
authors.initials: LC
authors.lastname: de Moraes
keywords: Image Processing, Computer-Assisted; Orthodontics; Root Resorption; Subtraction Technique; Tooth Extraction