The current study assessed the accuracy of CBCT with and without using contrast medium to digital periapical radiography (PSP) with and without using contrast medium in the detection and measurement of the length of strip root perforation in 274 mandibular molars, in-vitro. Artificially simulated strip perforations were prepared about 1 to 3 mm below the root canal orifice at the danger zone by Gates Glidden drill No. 3 in the mesio-lingual canal of 137 out of 274 mandibular molars, while the other 137 were allocated in the control group. The teeth of the two groups were positioned in a dry human mandible sockets with wax simulating the periodontal ligaments, the mandible was covered by a 1.5 cm layer of wax to simulate the soft tissues, and imaged with and without contrast medium using CBCT and digital periapical radiography (PSP). The detection of the strip root perforation was based on a scoring system: surface discontinuity, radiolucent defect at the danger zone that communicates the main pulp space to the simulated periodontal ligament space, and extension of the contrast medium beyond the main root canal confines at the danger zone. The results revealed that the sensitivity, specificity and accuracy of CBCT with and without contrast medium as well as the digital periapical radiography with contrast medium were equal and higher than those of digital periapical radiography without contrast medium in the detection of the artificially simulated strip root perforation. The sensitivity of digital periapical radiography has increased with the contrast medium as it enhanced the detection of the strip root perforation.