title: A prospective study assessing the effect of coronal tooth structure loss on the outcome of root canal retreatment.
abstract: OBJECTIVE
  To evaluate the outcome of secondary root canal treatment (retreatment) on posterior teeth in relation to the residual volume of coronal tooth structure, measured with an intraoral scanner, using periapical radiography and cone beam computed tomography (CBCT).
  
  
  METHODS
  A total of 137 posterior teeth in 121 patients were assessed clinically and radiographically using periapical radiographs and CBCT scans at baseline and 1 year after root canal retreatment. The increase or decrease in the size of preoperative periapical radiolucencies and development of new radiolucencies were assessed by a consensus panel consisting of two pre-calibrated examiners. A clinical impression was obtained for each tooth after completion of root canal retreatment, before the placement of the temporary restoration and following cast restoration placement to produce two casts. All casts were scanned using an intraoral digital scanner and the three-dimensional volume of remaining tooth structure calculated. Teeth were also classified according to the number of remaining coronal walls before core build-up. χ2test was used to determine the association between the outcome of root canal retreatments and the volume of remaining coronal tooth structure.
  
  
  RESULTS
  At the 1-year recall, teeth retaining less than 30% of their original tooth structure volume had a significantly higher proportion of unfavourable outcomes (χ2, P < 0.05, odds ratio [OR], 2.58; 95% CI, 1.026-6.487).
  
  
  CONCLUSIONS
  The loss of tooth structure volume is an objective parameter that can be used to predict the probability of success of root canal retreatments. At 1-year follow-up, the percentage of unfavourable outcomes of root canal retreated teeth was significantly higher when less than 30% of the original tooth tissue structure was present at baseline.
authors.affiliation: Department of Conservative Dentistry, King's College London Dental Institute, London, UK.|Department of Conservative Dentistry, College of Dentistry, University of Baghdad, Baghdad, Iraq.
authors.forename: N
authors.identifier: http://orcid.org/0000-0002-8748-062X
authors.initials: N
authors.lastname: Al-Nuaimi
authors.affiliation: Department of Conservative Dentistry, King's College London Dental Institute, London, UK.|Specialist Practice, London, UK.
authors.forename: S
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Prosthodontics, King's College London Dental Institute, London, UK.|Division of Tissue Engineering & Biophotonics, King's College London Dental Institute, London, UK.
authors.forename: R S
authors.initials: RS
authors.lastname: Austin
authors.affiliation: Department of Conservative Dentistry, King's College London Dental Institute, London, UK.
authors.forename: F
authors.initials: F
authors.lastname: Mannocci
mesh_terms: D000328:Adult; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D011446:Prospective Studies; D019252:Radiography, Dental, Digital; D019233:Retreatment; D012390:Root Canal Therapy; D014070:Tooth / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D017211:Treatment Failure
keywords: cone beam computed tomography; outcome of root canal retreatment; periapical lesions; remaining coronal tooth structure