We’re all familiar with the body’s basic rhythm: the circadian rhythm that governs our 24-hour (more or less) cycle of waking and sleeping. But now researchers think they may have discovered another rhythm that governs the growth of animals and humans. And the key that led to this discovery was the existence of small lines created in the tooth as it grew.
A Cracked Tooth Helped
There aren’t very many times you can sing the praises of a cracked tooth, but this is one of them. Researcher Timothy Bromage was chewing on a lamb chop when he heard a pop. Then he felt a sharp pain and realized he’d cracked a molar .
This is more serious than a simple chipped tooth and Bromage was told he could have the tooth saved with a root canal treatment and other restorative dentistry procedures, or he could have it extracted. Bromage decided to have it extracted, partly so he could have another sample for his research. This research was looking into the way that tooth structures deposited during growth were evidence of a longer biorhythm that could also explain why animals grew to different sizes.
Growth Lines, Growth Rates, and Body Size
The structure that Bromage was looking at is called Retzius lines. Like a tree, our tooth lays down regular growth rings–Retzius lines–that can be used to determine how long the tooth was growing. These Retzius lines are laid down at regular intervals, and in between them there are smaller lines, called cross-striations because they’re nearly perpendicular to the Retzius lines.
The number of cross-striations varies from animal to animal, and, in most cases, they’re directly related to the size of the animal.
In elephants, there are 14 cross-striations between Retzius lines. In humans, there are eight. Squirrel monkeys have three. Bromage has proposed that these different markers are evidence of a new kind of internal clock, one that helps govern growth.
His research has also shown that bones have the same timing for their growth lines, known as lamellae. He says that this is evidence that growth is governed in part by this secondary clock, which, he says, could also govern the overall size of an animal.
Larger animals don’t grow more quickly than smaller animals, they just grow for longer. The new rhythm could account for the longer growth period by expanding the growth cycles. Body size correlates to this rhythm, as do many other aspects of biology, such as life span, lactation length, metabolic rate, length of estrous cycle, and kidney size.
A Controversial Idea with Big Implications
Not everyone accepts Bromage’s evidence. There are many people who disagree with the notion of a multi-day cycle. But if this turns out to be true, it could have many significant potential applications. It could explain manic and depressive cycles in people with bipolar disorder. Or it might be used to sidestep limitations on human lifespan, and it may be instrumental in being able to successfully regrow lost teeth.
We look forward to learning what exciting new dentistry techniques derive from this discovery. And we look forward to applying them in our office, where we strive to remain at the forefront of dental knowledge and practice.