An analysis of secular change in the human mandible over the last century.

In light of several recent investigations that have identified notable secular change in cranial size and morphology over the last century, the present study addresses its possible effects in the mandible in U.S. populations. Standard measurements of 407 mandibles from the Terry (Smithsonian) and Hamann-Todd (Cleveland Museum of Natural History) Collections, which are primarily composed of individuals living in the early 20th century, were compared with those of 595 mandibles from the Forensic Anthropology Database (Tennessee), which is primarily composed of individuals living from the later part of the century. The t-tests between the two temporally-different samples by sex and race showed statistically significant decreases in mandibular body width and bigonial breadth as well as significant increases in mandibular body length in nearly all subgroups. White males showed the greatest amount of change, and Black females, the least. Overall, these findings support the conclusion that the mandible is transforming into a longer, narrower, more gracile bone, paralleling many of the morphological shifts seen in the cranium. Factors involved likely include changes in diet, medical care, and dental practices.