PURPOSE: The purpose of this study was to evaluate a new technique for localizing impacted mesiodens using its horizontal magnification ratio on panoramic radiographs. MATERIALS AND METHODS: Location-magnification equation of a panoramic equipment was obtained from horizontal magnification ratio of a metal ball which was located variable positions from the center of image layer at interval of 2 mm. Panoramic radiographs were obtained from a skull phantom with a metal ball which was a substitute for impacted mesiodens and was embedded 10mm(Group 1), 15mm(Group 2), and 20mm(Group 3) posterior to the central incisor. Each group obtained 7 panoramic radiographs at variable positions and one periapical radiograph. Three methods were used to estimate the actual width of the incisors and the balls which were used to calculate the magnification ratio. The methods included using the actual incisor width and the calculated ball width (Method 1), using the actual incisor width and the ball widths measured on periapical radiograph (Method 2), and using the incisor and the ball widths measured on periapical radiograph (Method 3). The location of the metal ball was calculated by using the location-magnification equation. RESULTS: The smallest difference between the calculated and the actual distance was 0.1+/-0.7 mm in Group 1/Method 3. The largest difference was -4.2+/-1.6 mm in Group 3/Method 2. In all groups, method 3 was the most accurate. CONCLUSION: Quantitative localization of impacted mesiodens is possible by using panoramic radiograph.