The aim of this study was to determine the morphologic factors that characterize mandibular edentulous alveolar ridges. The shapes of casts and waxed complete dentures were digitally scanned and the extracted shapes of the ridges were uniformly divided both mesiodistally and buccolingually. Principal component analysis was performed using the coordinates of the points on the grid as variables. Over 82% of the variables could be expressed using seven principal components. However, some of these were not taken into account by the existing criteria. Therefore, the influence of each principal component should be investigated.