Objectives: The aims of the study were to assess diagnostic efficacy in lesion detection, evaluate the effect of cone beam CT on treatment planning and clinician confidence. Methods: Forty digital periapical radiographs alone were compared with the use of both periapical radiographs and cone beam computed tomography. The two modalities were compared by four endodontic residents. The observers were asked to diagnose periapical lesions as well as provide a treatment plan and their confidence in the treatment plan for each case. Results: There was a statistically significant difference between the two modalities for lesion detection (aim 1) and a statistically significant decrease in proposed treatment for the control group (aim 2) with a decrease in clinician confidence (aim 3). Conclusion: The additional information provided by cone beam CT led to an increase in periapical lesion detection and a treatment change in one third of the cases associated with less confidence.