title: Understanding External Cervical Resorption in Vital Teeth.
abstract: BACKGROUND
  The aim of this study was to investigate the 3-dimensional (3D) structure and the cellular and tissue characteristics of external cervical resorption (ECR) in vital teeth and to understand the phenomenon of ECR by combining histomorphological and radiographic findings.
  
  
  METHODS
  Twenty-seven cases of vital permanent teeth displaying ECR were investigated. ECR diagnosis was based on clinical and radiographic examination with cone-beam computed tomographic imaging. The extracted teeth were further analyzed by using nanofocus computed tomographic imaging, hard tissue histology, and scanning electron microscopy.
  
  
  RESULTS
  All examined teeth showed some common characteristics. Based on the clinical and experimental findings, a 3-stage mechanism of ECR was proposed. At the first stage (ie, the initiation stage), ECR was initiated at the cementum below the gingival epithelial attachment. At the second stage (ie, the resorption stage), the resorption invaded the tooth structure 3-dimensionally toward the pulp space. However, it did not penetrate the pulp space because of the presence of a pericanalar resorption-resistant sheet. This layer was observed to consist of predentin, dentin, and occasionally reparative mineralized (bonelike) tissue, having a fluctuating thickness averaging 210 μm. At the last advanced stage (ie, the repair stage), repair took place by an ingrowth and apposition of bonelike tissue into the resorption cavity. During the reparative stage, repair and remodeling phenomena evolve simultaneously, whereas both resorption and reparative stages progress in parallel at different areas of the tooth.
  
  
  CONCLUSIONS
  ECR is a dynamic and complex condition that involves periodontal and endodontic tissues. Using clinical, histologic, radiographic, and scanning microscopic analysis, a better understanding of the evolution of ECR is possible. Based on the experimental findings, a 3-stage mechanism for the initiation and growth of ECR is proposed.
authors: Department of Oral Health Sciences, BIOMAT Research Cluster, KU Leuven and University Hospitals Leuven, Leuven, Belgium; Private Practice, Endo Rotterdam, Rotterdam, The Netherlands. Electronic address: athimavridou@gmail.com.
authors: Athina M
authors: AM
authors: Mavridou
authors: Department of Imaging and Pathology, KU Leuven and University Hospitals Leuven, Leuven, Belgium.
authors: Esther
authors: E
authors: Hauben
authors: Department of Materials Engineering (MTM), KU Leuven, Leuven, Belgium.
authors: Martine
authors: M
authors: Wevers
authors: Department of Oral Health Sciences, BIOMAT Research Cluster, KU Leuven and University Hospitals Leuven, Leuven, Belgium.
authors: Evert
authors: E
authors: Schepers
authors: Department of Oral Health Sciences, BIOMAT Research Cluster, KU Leuven and University Hospitals Leuven, Leuven, Belgium.
authors: Lars
authors: L
authors: Bergmans
authors: Department of Oral Health Sciences, BIOMAT Research Cluster, KU Leuven and University Hospitals Leuven, Leuven, Belgium.
authors: Paul
authors: P
authors: Lambrechts
mesh_terms: D001530:Belgium; D054893:Cone-Beam Computed Tomography / Q000379:methods; D003731:Dental Caries / Q000000981:diagnostic imaging; D003739:Dental Cementum / Q000000981:diagnostic imaging / Q000473:pathology / Q000648:ultrastructure; D003782:Dental Pulp / Q000166:cytology / Q000473:pathology / Q000648:ultrastructure; D003786:Dental Pulp Cavity / Q000000981:diagnostic imaging / Q000648:ultrastructure; D003804:Dentin / Q000000981:diagnostic imaging / Q000473:pathology / Q000648:ultrastructure; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging / Q000473:pathology; D021621:Imaging, Three-Dimensional / Q000379:methods; D008855:Microscopy, Electron, Scanning; D010010:Osteoclasts / Q000648:ultrastructure; D012391:Root Resorption / Q000000981:diagnostic imaging* / Q000473:pathology*; D014057:Tomography, X-Ray Computed / Q000379:methods; D014070:Tooth / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000648:ultrastructure; D019237:Tooth Cervix / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000648:ultrastructure
keywords: Cone-beam computed tomography; external cervical resorption; hypoxia; nanofocus computed tomography; reparative mineralized tissue