Introduction: The study evaluated the effectiveness of different tube voltages of the cone-beam computed tomography (CBCT) device on the diagnosis of vertical root fractures in teeth with single root canals and posts. Materials and methods: Sixty single-canal and single-rooted extracted human mandibular premolars were selected, all of which were intact and contained no fractures. After disinfection, teeth crowns were sectioned and teeth canals were prepped and obturated by a method similar to the rotary technique. Root fractures were created in half of the teeth by applying controlled buccolingual force. Prefabricated metal posts were subsequently placed in all teeth using AH26 sealer. All teeth, both intact and fractured, were mounted in bovine ribs and X-rayed randomly using a CBCT device (Planmeca Romexis, Helsinki, Finland) with three tube voltages (min = 66 kVp, mid = 80 kVp, and max = 92 kVp). Three experienced maxillofacial radiologists observed and commented on the images. Research data were analyzed using SPSS-25 software. Results: Images taken by kVp min were removed from further statistical analysis due to a lack of diagnostic information. For mid (80) and max kVp (92), the sensitivity values were 86.6% and 60 % (P = 0.04), and the specificity values were 33.3% and 30%, respectively (P = 0.45). Overall, observers’ opinions were more alike concerning images taken with kVp mid than kVp max. Conclusion: Apparently, images taken by a tube voltage of 80 kVp are more efficient in the diagnosis of root fractures.