NYU dental professor discovers biological clock linking tooth growth to other metabolic processes

Why do rats live faster and die younger than humans? A newly discovered biological clock provides tantalizing clues

A 3-D microscopic view of bone from a human femur showing incremental growth lines corresponding to a biological rhythm that repeats itself every eight days. The black hole at the... Click here for more information.

This clock, or biological rhythm, controls many metabolic functions and is based on the circadian rhythm, which is a roughly 24-hour cycle that is important in determining sleeping and feeding patterns, cell regeneration, and other biological processes in mammals.

The newly discovered rhythm, like the circadian rhythm, originates in the hypothalamus, a region of the brain that functions as the main control center for the autonomic nervous system. But unlike the circadian rhythm, this clock varies from one organism to another, operating on shorter time intervals for small mammals, and longer ones for larger animals. For example, rats have a one-day interval, chimpanzees six, and humans eight.

NYU dental professor Dr. Timothy Bromage discovered the rhythm while observing incremental growth lines in tooth enamel, which appear much like the annual rings on a tree. He also observed a related pattern of incremental growth in skeletal bone tissue – the first time such an incremental rhythm has ever been observed in bone.