One of the most common morphologies associated with human upper incisors is that of shovel-shaping. An ordinal framework has been developed to score the expression of shovel-shaping in the central and lateral upper incisors, from absent (0) to extremely shoveled (7). Changes in the distribution of incisor enamel related to shoveling are likely the product of the growth process and is genetically determined. The present study provides a window on this process by examining the morphological correspondence between the incisor crown and the enamel-dentin junction (EDJ). The EDJ will be visualized and analyzed using the non-destructive three-dimensional method of micro-computed tomography (muCT) with the Amira software package. The sample consists of 10 upper incisors (I1 or I2) from 10 individuals in collections housed at Colorado State University. Seven teeth were chosen due to their variation in degree of shoveling, and three teeth chosen due to their variation in degree of non-shoveling and are used as an out group.;Due to the genetics involved with dental initiation and shape patterning, studies on modern human populations concerning shovel-shaped incisors have suggested shoveling as a highly heritable trait likely due to genetic influence. It is not surprising that shoveling is population specific in living humans, more predominantly seen in Asian and Native American populations, and less frequent in European and African populations. Therefore, a connection of external and internal morphology might support a genetically driven morphology that appears early in the development trajectory of the anterior teeth. Shoveling has also been used to assess and diagnose ancient human groups. For example, australopithecines, Asian H.erectus and Neanderthals commonly express shoveling, although of different forms. The present study will help contextualize the use of shoveling as potential autapomorphy in fossil hominins.
展开▼
