title: Changes of Root Length and Root-to-Crown Ratio after Apical Surgery: An Analysis by Using Cone-beam Computed Tomography.
abstract: BACKGROUND
  Apical surgery is an important treatment option for teeth with post-treatment periodontitis. Although apical surgery involves root-end resection, no morphometric data are yet available about root-end resection and its impact on the root-to-crown ratio (RCR). The present study assessed the length of apicectomy and calculated the loss of root length and changes of RCR after apical surgery.
  
  
  METHODS
  In a prospective clinical study, cone-beam computed tomography scans were taken preoperatively and postoperatively. From these images, the crown and root lengths of 61 roots (54 teeth in 47 patients) were measured before and after apical surgery. Data were collected relative to the cementoenamel junction (CEJ) as well as to the crestal bone level (CBL). One observer took all measurements twice (to calculate the intraobserver variability), and the means were used for further analysis. The following parameters were assessed for all treated teeth as well as for specific tooth groups: length of root-end resection and percentage change of root length, preoperative and postoperative RCRs, and percentage change of RCR after apical surgery.
  
  
  RESULTS
  The mean length of root-end resection was 3.58 ± 1.43 mm (relative to the CBL). This amounted to a loss of 33.2% of clinical and 26% of anatomic root length. There was an overall significant difference between the tooth groups (P < .05). There was also a statistically significant difference comparing mandibular and maxillary teeth (P < .05), but not for incisors/canines versus premolars/molars (P = .125). The mean preoperative and postoperative RCRs (relative to CEJ) were 1.83 and 1.35, respectively (P < .001). With regard to the CBL reference, the mean preoperative and postoperative RCRs were 1.08 and 0.71 (CBL), respectively (P < .001). The calculated changes of RCR after apical surgery were 24.8% relative to CEJ and 33.3% relative to CBL (P < .001). Across the different tooth groups, the mean RCR was not significantly different (P = .244 for CEJ and 0.114 for CBL).
  
  
  CONCLUSIONS
  This CBCT-based study demonstrated that the RCR is significantly changed after root-end resection in apical surgery irrespective of the clinical (CBL) or anatomic (CEJ) reference levels. The lowest, and thus clinically most critical, postoperative RCR was observed in maxillary incisors. Future clinical studies need to show the impact of resection length and RCR changes on the outcome of apical surgery.
authors.affiliation: Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Bern, Switzerland. Electronic address: thomas.vonarx@zmk.unibe.ch.
authors.forename: Thomas
authors.initials: T
authors.lastname: von Arx
authors.affiliation: Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Bern, Switzerland; Department of Oral and Maxillofacial Surgery, Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Simon S
authors.initials: SS
authors.lastname: Jensen
authors.affiliation: Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Bern, Switzerland; Center for Oral Medicine and Community Dentistry, Department of Ambulatory Care and Community Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Bornstein
mesh_terms: D001047:Apicoectomy; D054893:Cone-Beam Computed Tomography; D006801:Humans; D011446:Prospective Studies; D019237:Tooth Cervix / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D019228:Tooth Crown / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*
keywords: Apical surgery; cone beam computed tomography; root length; root-end resection; root-to-crown ratio