Why do we have baby teeth?

Image from iStock Photo

“Baby teeth (also known as deciduous or milk teeth or nipple nashers) are widely found in the animal kingdom.

While fish and reptiles continuously renew their teeth and go through many generations of them in a lifetime, mammals have followed an evolutionary trend toward suppression of tooth replacement since we love our teeth more than fish love theirs.

The reason is not known, but because the cusp pattern on mammalian teeth leads to complex patterns of occlusion (that is, the way the upper and lower teeth fit together = biting), it’s likely that subtle differences in tooth shape that might occur with frequent tooth replacement could lead to malocclusion, a dangerous situation where food couldn’t be chewed properly and you talk funny which would make mammals look more ridiculous than we already are. It could increase cavities as well so it may be that mammals will do just about anything to avoid going to the dentist.

In humans and other mammals, development has been restricted to just two sets of teeth. Young mammals’ skulls are small, and it’s impossible for them to accommodate a full array of adult choppers so juveniles have cute little temporary teeth to fit in their immature, backtalking jaws. Once the bones of the cranium have developed to adult size the Tooth Fairy starts wiggling them at night and they fall out to the great satisfaction of parents and money hungry kids alike.

The process for initiating the formation of permanent teeth in humans is not completely understood. Normally, permanent teeth come in at about age six in humans and this appears to be part of a genetic development program whose temporal trigger is not yet known but may be the teeth jumping ship after being made to chew all sorts of stuff off the floor for the last five years.

There may be a few other factors as well, particularly expression of a protein called Pax-9, which is part of the paired box family of transcription factors. (Pax-9 should not be confused with K-Pax, that movie where Kevin Spacy thinks he’s an alien.)

(Transcription factors are proteins that bind to DNA and activate gene expression. The paired box family is a special class of transcription factors that govern pattern formation during organogenesis. These transcription factors were first discovered in fruit flies (love fruit, not gay). However, paired box genes are strongly conserved throughout evolution. In vertebrates they are implicated in the development of several tissues and organs, including the brain, limb muscles, kidney, eye, nose, and ear.)

Loss of Pax-9 function in humans is an extremely rare genetic disorder—known in just one family in the United States—but it results in the failure to produce adult molars and in the increased incidence of loss of the second premolars. This genetic link tells us that the switch for making adult teeth must involve inducing cells to make Pax-9.

A second genetic cascade, which occurs after Pax-9 expression, leads to the loss of milk teeth. The baby teeth start to get ‘wiggly’ because bone-remodeling cells dissolve the bony root and periodontal ligament by secreting digestive enzymes. It’s not know if these cells need this as food, or just like the taste.

As the enzymes break down the tooth root and surrounding connective tissue, the tooth loosens until it’s time for the old ‘dad and a string ploy’ to provide space for the adult tooth.

You'll need to take care of your teeth whitening on your on.