In root canal therapy, radiographic imaging of the teeth and surrounding peri-radicular structures is crucial for diagnosis and management. The valuable data necessary to make a diagnosis can be lost because of the complexity of the maxillofacial skeleton, the inaccuracy of 2D radiographic images and the superimposition of surrounding anatomical structures. This case report describes a larger than normal radiolucency that was not visualised on a periapical radiograph (PA), while this was evident on the orthopantogram (OPG) and cone beam computed tomography (CBCT) images. When prescribing a radiograph, it is imperative to maximise the benefit of acquisition of information while maintaining the radiation safety for the patient; adjunct-imaging techniques such as CBCT must be considered if conventional radiographic techniques do not support clinical signs and symptoms. Parole chiave: CBCT, dental radiology, diagnosis, intraoral periapical radiograph, radiolucent lesions