title: The remaining dentin thickness investigation of the attempt to remove broken instrument from mesiobuccal canals of maxillary first molars with virtual simulation technique.
abstract: BACKGROUND
  To investigate differences in the estimated minimum remaining dentin thickness (RDT) between periapical radiographs using the paralleling and parallax technique, after simulated removal of broken instrument from the mesiobuccal (MB) canal of maxillary first molar in virtual simulation model. The 3D measurement was taken as the standard for comparison.
  
  
  METHODS
  Thirty-six maxillary first molars were scanned by micro-CT and reconstructed as 3-dimensional (3D) model. A virtual fragment of an instrument was created within the MB canal in software. Removal of the broken instrument was simulated in both the 3D and 2D dataset. Then, the models of all specimens were submitted to 2D and 3D measurements for the lowest (RDT) value in each. Differences in the values between the paralleling and parallax radiographic technique and the 3D-RDT value were analyzed with two-way Analysis of Variance. The Intra-class Correlation Coefficient (ICC) was used to assess consistency of the RDT measurements between the two periapical radiographic and techniques and 3D analysis.
  
  
  RESULTS
  There was significant difference between RDT value obtained from the paralleling technique and 3D-RDT. There were no differences between RDT obtained from parallax (angled) technique and 3D-RDT. The ICC of RDT values between paralleling technique and 3D measurement were lower than 0.75. ICC between angled radiographs and 3D technique was close to 0.75. The optimal horizontal angle for the parallax technique was about 21°.
  
  
  CONCLUSIONS
  The virtual simulation technique can provide valuable insight into the benefit/risk analysis before removal of a broken instrument. Parallel radiographs overestimate the actual remain dentin thickness in mesiobuccal canals of maxillary first molars, whereas the parallel technique would give a closer estimate to the actual thickness at a projection angle of about 21°.
authors.affiliation: Department of Operative Dentistry & Endodontics, State Key Laboratory of Oral Diseases, West China College & Hospital of Stomatology, Sichuan University, 14#, 3rd section of RenMin South Road, Chengdu, 610041, China. 495750635@qq.com.
authors.forename: Qian
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Area of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, University of Hong Kong, Hong Kong, China. spcheung@hku.hk.
authors.forename: Gary Shun-Pan
authors.initials: GS
authors.lastname: Cheung
authors.affiliation: Division of Endodontics, Department of Oral Biological & Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada. yashen@ubc.ca.
authors.forename: Ya
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Department of Operative Dentistry & Endodontics, State Key Laboratory of Oral Diseases, West China College & Hospital of Stomatology, Sichuan University, 14#, 3rd section of RenMin South Road, Chengdu, 610041, China. dingminghuang@163.com.
authors.forename: Dingming
authors.initials: D
authors.lastname: Huang
authors.affiliation: Department of Operative Dentistry & Endodontics, State Key Laboratory of Oral Diseases, West China College & Hospital of Stomatology, Sichuan University, 14#, 3rd section of RenMin South Road, Chengdu, 610041, China. zhouxd@scu.edu.cn.
authors.forename: Xuedong
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Department of Operative Dentistry & Endodontics, State Key Laboratory of Oral Diseases, West China College & Hospital of Stomatology, Sichuan University, 14#, 3rd section of RenMin South Road, Chengdu, 610041, China. gaoyuan@scu.edu.cn.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
mesh_terms: D003198:Computer Simulation; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D003804:Dentin / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D004868:Equipment Failure; D005547:Foreign Bodies / Q000000981:diagnostic imaging* / Q000628:therapy; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008437:Maxilla / Q000000981:diagnostic imaging; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D016300:Radiography, Bitewing / Q000379:methods; D018570:Risk Assessment; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D014584:User-Computer Interface; D055114:X-Ray Microtomography / Q000379:methods