This study used micro-CT to compare three obturation techniques with respect to void occurrence in canals filled with bioceramic sealer. Thirty extracted first mandibular premolars were prepared with a ProTaper Universal system and randomly allocated to three groups. Canals were obturated with gutta-percha and bioceramic root canal sealer, using either single-cone, lateral compaction, or Thermafil filling technique. Each tooth was then scanned with micro-CT. Voids in 2D cross-sectional images and void volumes in 3D images of all root thirds were assessed in relation to obturation technique. There was no significant difference between obturation techniques in the proportion of sections with voids (P > 0.05). However, the results of the obturation techniques significantly differed in relation to root region (P < 0.05). In conclusion, no root filling technique resulted in void-free specimens. Void volumes were highest for the single-cone technique and lowest for Thermafil, in all regions (P < 0.05).