In this study, we used cone-beam computed tomography (CBCT) images of the mandibular condyle to examine whether bone transformation could be effectively detected by the orthopantomogram (OP), panoramic TMJ projection (TMJ-OP), or lateral roentgen cephalogram (LC), thus improving diagnosis of arthrosis deformans of the TMJ. A total of 377 women presented to our orthodontic clinic to undergo an interview and clinical examinations for temporomandibular disorder (TMD). A total of 126 of these were suspected TMD cases; they underwent an imaging investigation that included CBCT. Twenty-one additional patients developed TMD symptoms during orthodontic treatment in our clinic; they underwent a similar imaging investigation. From these 147 patients who underwent the imaging investigation, we selected 23 women with a retrusive mandible. The average age was 24y 4m (range: 12y 8m-32y 11m). Subjects with a history of facial injury, ankylodactylia, tumor, or generalized arthritis were excluded, as were those with developmental disorders. Two orthodontists conferred to define the CBCT evaluation of bone transformation within the mandibular condyle. The same two orthodontists assessed all other images independently. Using confirmed diagnosis by CBCT image as a source of comparison, diagnostic parameters was determined by the assessments of the two observers on OP and TMJ-OP images and downward and backward rotations of the mandible. Additionally, we compared the success of diagnosis upon combining these methods. 1. CBCT imaging evaluations detected bone transformation in 32 (69.6%) of 46 joints. Erosion, osteophyte, and sclerosis (deformity) were found in 26, 12, and 10 joints, respectively. 2. Among 22 joints in which osteophyte and sclerosis (deformity) were found, 15 joints showed erosion. Therefore, erosion is the primary finding of bone transformation in arthrosis deformans of the TMJ. 3. The diagnostic success rate of the bone transformation of the mandibular condyle was 0.52 and 0.74 for the estimation by OP and TMJ-OP images, respectively. The success rate increased by combining the estimation of OP and TMJ-OP images. 4. By estimating the mandibular rotation, the diagnostic success rate and diagnostic sensitivity were comparatively high (0.87 and 0.95, respectively). This estimation method may be useful for diagnosis by exclusion in a case of arthrosis deformans of the TMJ. Diagnosis of arthrosis deformans of the TMJ is improved using panoramic radiography, as well as division into two temporomandibular joints on the panoramic radiograph and mandibular clockwise rotation decided by lateral roentgen cephalometry.