Journal of Prosthetic Dentistry

Cone beam computed tomography analysis of residual dentin thickness after virtual post placement in the palatal roots of maxillary first molars


      Statement of problem

      In endodontically treated maxillary first molars, post space preparations in the palatal roots can compromise the residual dentin thickness (RDT) and increase the risk of perforations or root fractures. This can be attributed to the direction of the buccopalatal curvature that cannot be viewed with conventional 2D imaging.


      The purpose of this clinical study was to investigate the RDT of palatal roots following the placement of digital post analogs of different diameters positioned at various distances from the radiographic apex by using cone beam computed tomography (CBCT).

      Material and methods

      A total of 122 deidentified CBCT data sets containing both maxillary permanent first molars were randomly selected from a private radiology practice. Digital parallel-sided post analogs were superimposed onto the CBCT coronal images at distances of 3 mm, 4 mm, and 5 mm from the radiographic apex and at a depth equal to the height of the anatomic crown (1:1 crown/post ratio). Post analogs of 0.9 mm, 1.0 mm, and 1.14 mm in diameter were matched with safety zone analogs representing 1 mm of circumferential RDT. The minimum RDT for each analog was determined and grouped into 3 categories: RDT≤0 mm, 0 mm<RDT<1 mm, and RDT≥1 mm. The statistical significance between post diameters and post depth was analyzed with the Friedman test and Conover post hoc test (α=.05).


      Significant differences in RDT were found at all tested depths and diameters of post analogs (P<.001). Generally, the amount of RDT increased as the post length was reduced. Most teeth (>50.0%) had inadequate or no RDT. The depth of the post (P<.001) had a greater impact on RDT than the post diameter (P>.017). No similarities were found in the RDT between contralateral molars in 86.9% of the images.


      The risk of insufficient RDT (<1 mm) after the placement of parallel-sided posts in the palatal roots of maxillary first molars is minimized if the post is inserted to a depth equaling the height of the crown compared with 3, 4, and 5 mm from the radiographic apex. The RDT of the palatal root of a maxillary first molar is not a reliable predictor of the contralateral palatal root RDT in the same patient.
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