Microcomputer tomography measurement of minimum residual dentin thickness in mandibular first molars after virtual...

In endodontically treated teeth, the residual dentin thickness (RDT) after post space preparation plays a major role in preventing strip perforation and vertical root fracture.

The purpose of this in vitro study was to estimate and identify danger areas in mandibular first molars submitted to post space preparation by virtual fiber post placement and to determine a minimum RDT (mRDT) measurement by microcomputer tomography (μCT) combined with multifunctional software.

A total of 24 human mandibular first molars prepared with ProTaper instruments and commercial fiber posts (#1 to #4) were scanned by using a μCT system. A framework based on MeVisLab was used to simulate clinical post placement in 2 mesial and single distal root canals. The mRDTs were measured on 4 sides (buccal, lingual, mesial, and distal) at positions 1-, 3-, and 5-mm apically from the root canal orifice. The associations between mRDT and different characteristics were examined and analyzed by 4-way ANOVA (α=.05). For each level of each root canal, the least value from the mean mRDTs of 4 sides was selected, and the side related to the least value was identified and recorded. The perforation rate of each level in different root canals was also calculated.

Significant differences were detected among the different posts, root canals, levels, and sides (P<.001). The mean mRDT was higher in distal root canals than in mesiobuccal and mesiolingual root canals (P<.001). mRDTs of each level were mainly found on the mesial sides of distal roots and the distal sides of mesial roots. The perforation rate was higher when using #3 and #4 posts, and perforation mainly occurred at the distal side of mesial roots and at a level 5-mm apically from the canal orifice.

For post placement in endodontically treated mandibular first molars, using a larger-sized post decreased the RDT and increased the perforation rate. Small fiber posts were safer and prevented perforation, with the distal root being the first choice. If more posts are required in a mesiobuccal and mesiolingual canal, the smallest appropriately sized post should be placed less than 3 mm from the root canal orifice. Combining virtual fiber post placement performed using a framework based on MeVisLab with μCT scanning is a convenient and accurate method of evaluating the risk of canal wall perforation.