We report a case in which an impacted supernumerary tooth migrated from the mandibular ramus to the mandibular coronoid process. A 19-year-old male underwent a panoramic X-ray for orthodontic treatment at the age of 14 years. An opaque region with a well-defined border was seen at the front edge of the right mandibular ramus. Since the right lower third molar was also present, the opaque region was diagnosed as an impacted supernumerary tooth. Imaging examinations, performed every 2 years, showed that the impacted supernumerary tooth gradually moved from the mandibular ramus to the mandibular coronoid process. Thus, the patient visited our department to undergo detailed examinations and treatment. On panoramic X-ray and CT performed at the patient’s first visit to our department, the impacted supernumerary tooth had a total length (root axis) of about 10 mm, the tooth axis was located at the upper end of the right mandibular coronoid process, and part of the tooth was located outside of the tip of the mandibular coronoid process. Under general anesthesia, the impacted supernumerary tooth was extracted. Since the mandibular coronoid process was thin, it was resected during removal of the supernumerary tooth. There was no trismus or mandibular deviation 1 year after the operation.
