Activation and inhibition

Why do they call them wisdom teeth, when in fact what they can really induce is actually pain!?… Beyond the popular belief, a new study shows that these annoying molars are the result of an imbalance in the developmental mechanism that permits them to make their way into the back of the jaw while pressing on the other teeth.

Adult humans possess 12 molars (the rearmost largest teeth, three on each side of the upper and lower jaws), and the last 4 molars are called the wisdom teeth, growing between 16 and 24 of an age. Sometimes, they start to crowd the jaw line, pressing on the nearby teeth, requiring a complex dental procedure: the wisdom-tooth extraction.

But what is really puzzling in humans is the enormous variation in the development of the wisdom teeth: why are they so well developed in some people, while others (luckily for them) may lack them all?

To get an answer, a team at the University of Helsinki in Finland cultivated mice bud teeth, finding that the teeth’s growth is determined by the play between two molecular pathways, activation and inhibition, which tell how many teeth develop from the tooth germ (bud) and their size. When activation and inhibition are in balance, all three molars develop and have equal sizes, but if not, the size of the teeth varies.

If activation dominates, each tooth is increasingly bigger, with the wisdom tooth being the larger and able of causing troubles. In extremely rare cases, even a fourth molar can pop up. But if there is an inhibition domination, the molars grow increasingly tinier or sometimes they may not even develop altogether.

“Most early humans had all their wisdom teeth, with all of them measuring about the same size, so the two forces were likely in balance then,” said co-author Jukka Jernvall.

“But now, our wisdom teeth are usually smaller than the rest of the molars, meaning inhibition might be winning out evolutionarily, though this differs from person to person,” Jernvall told LiveScience.

“Even with wisdom teeth becoming smaller, they can still cause problems because the human jaw has also become smaller with time, which could be because as we learned to cook, our food became softer and required less power to chew,” Jernvall said.

Bad news for the human species, good news for the stomatologists.

[Via Softpedia]