The remaining dentin thickness investigation of the attempt to remove broken instrument from mesiobuccal canals of maxillary first molars with virtual simulation technique.

Xuedong Zhou,Ya Shen,Yuan Gao,Qian Yang,Gary Shun-Pan Cheung,Dingming Huang

doi:10.1186/s12903-015-0075-x

Abstract

BackgroundTo 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.MethodsThirty-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.ResultsThere 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°.ConclusionsThe 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°.

Highlights

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 purpose of this study was to evaluate the remaining dentin thickness measurements based on paralleling and parallax radiographic image, versus 3D tomography, after the virtual removal of broken instruments from the mesiobuccal canal of maxillary first molars
For the group with fragment 3 mm below orifice, the minimum RDT value obtained from paralleling radiographic technique (1058 ± 216 μm])was significantly greater than that by the parallax technique (An-RDT) (606 ± 155 μm), as well as the 3D-RDT (581 ± 159 μm) (p < 0.05)

Summary

Introduction

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 remaining dentin thickness (RDT) is probably the most important factor affecting the decision of removing the fragment instrument, as that contributes to the resistance against root fracture [7, 8]. One may attempt to bypass the broken instrument, or to clean/shape and fill the root canal up to the fragment [9]. Earlier studies usually sectioned the tooth to measure the canal wall thickness in cross section [9,10,11] Such method is destructive, and the samples cannot be used for further studies or as their own control. One can measure and calculate the dentin thickness from 3D micro-CT data and the 2D simulated radiographs

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