This study was performed to simulate various sizes of periapical lesions and condensing osteitis in bone and to clarify that condensing osteitis would give a greater radiographic contrast because of the more radiopacity immediately adjacent to the lesion and what the lamina dura on radiogram is in bone. For this study, two dry and wet human adult mandible and a cadaver were used. Each mandible was sectioned longitudinally to split lingual and buccal cortical plates to gain better access to the apex of tooth. Lesions were gradually enlarged and bordered with tooth ash that burned out at 950℃ for the reproduction of condensing osteitis in sequence. The serial radiograms were taken under the constantly maintained condition and compared with the actual lesions.