Root dentine thickness in C-shaped lower second molars after instrumentation: A CBCT and micro-CT study.

Stripping perforation is a possible complication in instrumentation of C-shaped canals. This study evaluated the minimum thickness of the root canal wall in C-shaped teeth after instrumentation. Twelve extracted C-shaped mandibular second molars (four teeth of type I, II and III each) were examined by CBCT (voxel size 90 μm) before and after instrumentation with WOG primary file. Micro-CT scans (voxel size 30 μm) were obtained after instrumentation. Percentage of canal wall area touched by the file and minimum thickness of dentine were measured and compared between CBCT and micro-CT. In type I C-shape canals, less than 10% of the canal wall area was touched by the instrument. In ten teeth, the shortest distance to root surface was from the instrumented area; no perforations occurred. CBCT and micro-CT measurements were in good agreement in ten cases; in two teeth, micro-CT revealed considerably shorter distance to root surface. The two shortest distances were 0.27 and 0.41 mm.