Background and Purpose: The most common type of supernumerary tooth is the mesiodens, which occurs along the palatal midline and can assume a number of shapes and positions relative to the adjacent teeth. Extraction should be performed carefully to prevent damage to the adjacent permanent teeth because it can cause ankylosis and maleruption of these teeth. Therefore, a thorough investigation of the optimal treatment for supernumerary teeth is required. The purpose of this study was to investigate the age-related changes in the shapes and positions of supernumerary teeth using computed tomography （CT）.
Materials and Methods: The study population comprised 266 patients （179 males, 87 females; 4-83 years of age, mean age: 17.4 years） with a total of 337 supernumerary teeth, which were examined using multidetector CT. The subjects were divided into two groups: those aged < 19 years and > 20 years. The distance from the nasal cavity to each supernumerary tooth and the state of the supernumerary tooth roots were evaluated on 3-dimensional CT images. The between-group differences in these parameters were analyzed using a statistical software package （SPSS version 21.0Ⓡ; IBM Japan Inc., Tokyo, Japan）. P < 0.05 was considered to indicate significance.
Results: The mean distance from the nasal cavity to the supernumerary teeth differed significantly between the two age groups
（P < 0.05）. The states of the supernumerary tooth roots also differed significantly between the two age groups （P < 0.05）.
Conclusion: Our study found that changes in the shapes and positions of supernumerary teeth occur with aging. This knowledge may contribute to the diagnosis of supernumerary teeth and avoid errors in their treatment.
